ORCID Profile
0000-0002-0950-2942
Current Organisations
Luxembourg Institute of Science and Technology
,
École Nationale Vétérinaire d'Alfort
,
Université de Tours
,
University of the Sunshine Coast
,
University of New South Wales
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Other Biological Sciences | Climatology (excl. Climate Change Processes) | Global Change Biology
Sparseland, Permanent Grassland and Arid Zone Land and Water Management | Effects of Climate Change and Variability on Australia (excl. Social Impacts) |
Publisher: Wiley
Date: 23-12-2022
DOI: 10.1111/GCB.16012
Abstract: Despite their size and contribution to the global carbon cycle, we have limited understanding of tropical savannas and their current trajectory with climate change and anthropogenic pressures. Here we examined interannual variability and externally forced long‐term changes in carbon and water exchange from a high rainfall savanna site in the seasonal tropics of north Australia. We used an 18‐year flux data time series (2001–2019) to detect trends and drivers of fluxes of carbon and water. Significant positive trends in gross primary productivity (GPP, 15.4 g C m 2 year −2 ), ecosystem respiration ( R eco , 8.0 g C m 2 year −2 ), net ecosystem productivity (NEE, 7.4 g C m 2 year −2 ) and ecosystem water use efficiency (WUE, 0.0077 g C kg H 2 O −1 year −1 ) were computed. There was a weaker, non‐significant trend in latent energy exchange (LE, 0.34 W m −2 year −1 ). Rainfall from a nearby site increased statistically over a 45‐year period during the observation period. To examine the dominant drivers of changes in GPP and WUE, we used a random forest approach and a terrestrial biosphere model to conduct an attribution experiment. Radiant energy was the dominant driver of wet season fluxes, whereas soil water content dominated dry season fluxes. The model attribution suggested that [CO 2 ], precipitation and T air accounting for 90% of the modelled trend in GPP and WUE. Positive trends in fluxes were largest in the dry season implying tree components were a larger contributor than the grassy understorey. Fluxes and environmental drivers were not significant during the wet season, the period when grasses are active. The site is potentially still recovering from a cyclone 45 years ago and regrowth from this event may also be contributing to the observed trends in sequestration, highlighting the need to understand fluxes and their drivers from sub‐diurnal to decadal scales.
Publisher: Wiley
Date: 03-05-2019
Publisher: American Geophysical Union (AGU)
Date: 16-01-2014
DOI: 10.1002/2013GL058533
Publisher: Copernicus GmbH
Date: 28-01-2022
DOI: 10.5194/BG-2021-311
Abstract: Abstract. Forest transpiration is controlled by the atmospheric water demand, potentially constrained by soil moisture availability, and regulated by plant physiological properties. During summer periods, soil moisture availability at sites with thin soils can be limited, forcing the plants to access moisture stored in the weathered bedrock. Land surface models (LSMs) have considerably evolved in the description of the physical processes related to vegetation water use but the effects of bedrock position and water uptake from fractured bedrock has not received much attention. In this study, the Community Land Model version 5.0 (CLM 5) is implemented at four forested sites with relatively shallow bedrock and located across an environmental gradient in Europe. Three different bedrock configurations (i.e., default, deeper, and fractured) are applied to evaluate if the omission of water uptake from weathered bedrock could explain some model deficiencies with respect to the simulation of seasonal transpiration patterns. Sap flow measurements are used to benchmark the response of these three bedrock configurations. It was found that the simulated transpiration response of the default model configuration is strongly limited by soil moisture availability at sites with extended dry seasons. Under these climate conditions, the implementation of an alternative (i.e., deeper and fractured) bedrock configuration resulted in a better agreement between modeled and measured transpiration. At the site with a continental climate, the default model configuration accurately reproduced the magnitude and temporal patterns of the measured transpiration. The implementation of the alternative bedrock configurations at this site provided more realistic water potentials in plant tissues but negatively affects the modeled transpiration during the summer period. Finally, all three bedrock configurations did not show differences in terms of water potentials, fluxes, and performances on the more northern and colder site exhibiting a transition between oceanic and continental climate. Model performances at this site are low, with a clear overestimation of transpiration compared to sap flow data. The results of this study call for increased efforts into better representing lithological controls on plant water uptake in LSMs.
Publisher: Copernicus GmbH
Date: 02-09-2011
Abstract: Abstract. Hydrological processes are irreversible and produce entropy. Hence, the framework of non-equilibrium thermodynamics is used here to describe them mathematically. This means flows of water are written as functions of gradients in the gravitational and chemical potential of water between two parts of the hydrological system. Such a framework facilitates a consistent thermodynamic representation of the hydrological processes in the model. Furthermore, it allows for the calculation of the entropy production associated with a flow of water, which is proportional to the product of gradient and flow. Thus, an entropy budget of the hydrological cycle at the land surface is quantified, illustrating the contribution of different processes to the overall entropy production. Moreover, the proposed Principle of Maximum Entropy Production (MEP) can be applied to the model. This means, unknown parameters can be determined by setting them to values which lead to a maximisation of the entropy production in the model. The model used in this study is parametrised according to MEP and evaluated by means of several observational datasets describing terrestrial fluxes of water and carbon. The model reproduces the data with good accuracy which is a promising result with regard to the application of MEP to hydrological processes at the land surface.
Publisher: Copernicus GmbH
Date: 02-2022
Abstract: Abstract. The Vegetation Optimality Model (VOM, Schymanski et al., 2009, 2015) is an optimality-based, coupled water–vegetation model that predicts vegetation properties and behaviour based on optimality theory rather than calibrating vegetation properties or prescribing them based on observations, as most conventional models do. Several updates to previous applications of the VOM have been made for the study in the accompanying paper of Nijzink et al. (2022), where we assess whether optimality theory can alleviate common shortcomings of conventional models, as identified in a previous model inter-comparison study along the North Australian Tropical Transect (NATT, Whitley et al., 2016). Therefore, we assess in this technical paper how the updates to the model and input data would have affected the original results of Schymanski et al. (2015), and we implemented these changes one at a time. The model updates included extended input data, the use of variable atmospheric CO2 levels, modified soil properties, implementation of free drainage conditions, and the addition of grass rooting depths to the optimized vegetation properties. A systematic assessment of these changes was carried out by adding each in idual modification to the original version of the VOM at the flux tower site of Howard Springs, Australia. The analysis revealed that the implemented changes affected the simulation of mean annual evapotranspiration (ET) and gross primary productivity (GPP) by no more than 20 %, with the largest effects caused by the newly imposed free drainage conditions and modified soil texture. Free drainage conditions led to an underestimation of ET and GPP in comparison with the results of Schymanski et al. (2015), whereas more fine-grained soil textures increased the water storage in the soil and resulted in increased GPP. Although part of the effect of free drainage was compensated for by the updated soil texture, when combining all changes, the resulting effect on the simulated fluxes was still dominated by the effect of implementing free drainage conditions. Eventually, the relative error for the mean annual ET, in comparison with flux tower observations, changed from an 8.4 % overestimation to an 10.2 % underestimation, whereas the relative errors for the mean annual GPP remained similar, with an overestimation that slightly reduced from 17.8 % to 14.7 %. The sensitivity to free drainage conditions suggests that a realistic representation of groundwater dynamics is very important for predicting ET and GPP at a tropical open-forest savanna site as investigated here. The modest changes in model outputs highlighted the robustness of the optimization approach that is central to the VOM architecture.
Publisher: Wiley
Date: 30-01-2013
DOI: 10.1111/JBI.12075
Publisher: Wiley
Date: 12-09-2022
DOI: 10.1111/MEC.16676
Abstract: The koala, one of the most iconic Australian wildlife species, is facing several concomitant threats that are driving population declines. Some threats are well known and have clear methods of prevention (e.g., habitat loss can be reduced with stronger land‐clearing control), whereas others are less easily addressed. One of the major current threats to koalas is chlamydial disease, which can have major impacts on in idual survival and reproduction rates and can translate into population declines. Effective management strategies for the disease in the wild are currently lacking, and, to date, we know little about the determinants of in idual susceptibility to disease. Here, we investigated the genetic basis of variation in susceptibility to chlamydia using one of the most intensively studied wild koala populations. We combined data from veterinary examinations, chlamydia testing, genetic s ling and movement monitoring. Out of our s le of 342 wild koalas, 60 were found to have chlamydia. Using genotype information on 5007 SNPs to investigate the role of genetic variation in determining disease status, we found no evidence of inbreeding depression, but a heritability of 0.11 (95% CI: 0.06–0.23) for the probability that koalas had chlamydia. Heritability of susceptibility to chlamydia could be relevant for future disease management, as it suggests adaptive potential for the population.
Publisher: Copernicus GmbH
Date: 04-05-2017
Publisher: Copernicus GmbH
Date: 31-03-2017
Publisher: Zenodo
Date: 2019
Publisher: Copernicus GmbH
Date: 11-06-2021
Publisher: Copernicus GmbH
Date: 25-05-2016
DOI: 10.5194/HESS-20-2063-2016
Abstract: Abstract. We combine ecohydrological observations of sap flow and soil moisture with thermodynamically constrained estimates of atmospheric evaporative demand to infer the dominant controls of forest transpiration in complex terrain. We hypothesize that daily variations in transpiration are dominated by variations in atmospheric demand, while site-specific controls, including limiting soil moisture, act on longer timescales. We test these hypotheses with data of a measurement setup consisting of five sites along a valley cross section in Luxembourg. Both hillslopes are covered by forest dominated by European beech (Fagus sylvatica L.). Two independent measurements are used to estimate stand transpiration: (i) sap flow and (ii) diurnal variations in soil moisture, which were used to estimate the daily root water uptake. Atmospheric evaporative demand is estimated through thermodynamically constrained evaporation, which only requires absorbed solar radiation and temperature as input data without any empirical parameters. Both transpiration estimates are strongly correlated to atmospheric demand at the daily timescale. We find that neither vapor pressure deficit nor wind speed add to the explained variance, supporting the idea that they are dependent variables on land–atmosphere exchange and the surface energy budget. Estimated stand transpiration was in a similar range at the north-facing and the south-facing hillslopes despite the different aspect and the largely different stand composition. We identified an inverse relationship between sap flux density and the site-average sapwood area per tree as estimated by the site forest inventories. This suggests that tree hydraulic adaptation can compensate for heterogeneous conditions. However, during dry summer periods differences in topographic factors and stand structure can cause spatially variable transpiration rates. We conclude that absorption of solar radiation at the surface forms a dominant control for turbulent heat and mass exchange and that vegetation across the hillslope adjusts to this constraint at the tree and stand level. These findings should help to improve the description of land-surface–atmosphere exchange at regional scales.
Publisher: American Geophysical Union (AGU)
Date: 03-2016
DOI: 10.1002/2015WR017910
Abstract: In this Commentary, we argue that it is possible to improve the physical realism of hydrologic models by making better use of existing hydrologic theory. We address the following questions: (1) what are some key elements of current hydrologic theory (2) how can those elements best be incorporated where they may be missing in current models and (3) how can we evaluate competing hydrologic theories across scales and locations? We propose that hydrologic science would benefit from a model‐based community synthesis effort to reframe, integrate, and evaluate different explanations of hydrologic behavior, and provide a controlled avenue to find where understanding falls short.
Publisher: Copernicus GmbH
Date: 02-07-2013
DOI: 10.5194/HESSD-10-8581-2013
Abstract: Abstract. Throughout its historical development, hydrology as an engineering discipline and earth science has relied strongly on the assumption of long-term stationary boundary conditions and system configurations, which allowed for simplified and sectoral descriptions of the dynamics of hydrological systems. However, in the face of rapid and extensive global changes (of climate, land use etc.) which affect all parts of the hydrological cycle, the general validity of this assumption appears doubtful. Likewise, so does the application of hydrological concepts based on stationarity to questions of hydrological change. The reason is that transient system behaviours often develop through feedbacks between the system constituents, and with the environment, generating effects that could often be neglected under stationary conditions. In this context, the aim of this paper is to present and discuss paradigms and theories potentially helpful to advancing hydrology towards the goal of understanding and predicting hydrological systems under change. For the sake of brevity we focus on catchment hydrology. We begin with a discussion of the general nature of explanation in hydrology and briefly review the history of catchment hydrology. We then propose and discuss several perspectives on catchments: as complex dynamical systems, self-organizing systems, co-evolving systems and open dissipative thermodynamic systems. We discuss the benefits of comparative hydrology and of taking an information-theoretic view of catchments, including the flow of information from data to models to predictions. In summary, we suggest that the combination of these closely related perspectives can serve as a paradigm for the further development of catchment hydrology to address predictions under change.
Publisher: Springer Science and Business Media LLC
Date: 21-05-2022
DOI: 10.1038/S41598-022-12304-3
Abstract: Land surface temperature (LST) is a preeminent state variable that controls the energy and water exchange between the Earth’s surface and the atmosphere. At the landscape-scale, LST is derived from thermal infrared radiance measured using space-borne radiometers. In contrast, plot-scale LST estimation at flux tower sites is commonly based on the inversion of upwelling longwave radiation captured by tower-mounted radiometers, whereas the role of the downwelling longwave radiation component is often ignored. We found that neglecting the reflected downwelling longwave radiation leads not only to substantial bias in plot-scale LST estimation, but also have important implications for the estimation of surface emissivity on which LST is co-dependent. The present study proposes a novel method for simultaneous estimation of LST and emissivity at the plot-scale and addresses in detail the consequences of omitting down-welling longwave radiation as frequently done in the literature. Our analysis uses ten eddy covariance sites with different land cover types and found that the LST values obtained using both upwelling and downwelling longwave radiation components are 0.5–1.5 K lower than estimates using only upwelling longwave radiation. Furthermore, the proposed method helps identify inconsistencies between plot-scale radiometric and aerodynamic measurements, likely due to footprint mismatch between measurement approaches. We also found that such inconsistencies can be removed by slight corrections to the upwelling longwave component and subsequent energy balance closure, resulting in realistic estimates of surface emissivity and consistent relationships between energy fluxes and surface-air temperature differences. The correspondence between plot-scale LST and landscape-scale LST depends on site-specific characteristics, such as canopy density, sensor locations and viewing angles. Here we also quantify the uncertainty in plot-scale LST estimates due to uncertainty in tower-based measurements using the different methods. The results of this work have significant implications for the combined use of aerodynamic and radiometric measurements to understand the interactions and feedbacks between LST and surface-atmosphere exchange processes.
Publisher: Wiley
Date: 04-10-2007
DOI: 10.1111/J.1365-3040.2007.01740.X
Abstract: Common empirical models of stomatal conductivity often incorporate a sensitivity of stomata to the rate of leaf photosynthesis. Such a sensitivity has been predicted on theoretical terms by Cowan and Farquhar, who postulated that stomata should adjust dynamically to maximize photosynthesis for a given water loss. In this study, we implemented the Cowan and Farquhar hypothesis of optimal stomatal conductivity into a canopy gas exchange model, and predicted the diurnal and daily variability of transpiration for a savanna site in the wet-dry tropics of northern Australia. The predicted transpiration dynamics were then compared with observations at the site using the eddy covariance technique. The observations were also used to evaluate two alternative approaches: constant conductivity and a tuned empirical model. The model based on the optimal water-use hypothesis performed better than the one based on constant stomatal conductivity, and at least as well as the tuned empirical model. This suggests that the optimal water-use hypothesis is useful for modelling canopy gas exchange, and that it can reduce the need for model parameterization.
Publisher: Zenodo
Date: 2019
Publisher: Wiley
Date: 11-10-2014
DOI: 10.1111/NPH.12552
Publisher: Wiley
Date: 24-07-2019
DOI: 10.1111/ACV.12528
Publisher: Copernicus GmbH
Date: 24-02-2011
Abstract: Abstract. Most hydrological models are valid at most only in a few places and cannot be reasonably transferred to other places or to far distant time periods. Transfer in space is difficult because the models are conditioned on past observations at particular places to define parameter values and unobservable processes that are needed to fully characterize the structure and functioning of the landscape. Transfer in time has to deal with the likely temporal changes to both parameters and processes under future changed conditions. This remains an important obstacle to addressing some of the most urgent prediction questions in hydrology, such as prediction in ungauged basins and prediction under global change. In this paper, we propose a new approach to catchment hydrological modeling, based on universal principles that do not change in time and that remain valid across many places. The key to this framework, which we call behavioral modeling, is to assume that there are universal and time-invariant organizing principles that can be used to identify the most appropriate model structure (including parameter values) and responses for a given ecosystem at a given moment in time. These organizing principles may be derived from fundamental physical or biological laws, or from empirical laws that have been demonstrated to be time-invariant and to hold at many places and scales. Much fundamental research remains to be undertaken to help discover these organizing principles on the basis of exploration of observed patterns of landscape structure and hydrological behavior and their interpretation as legacy effects of past co-evolution of climate, soils, topography, vegetation and humans. Our hope is that the new behavioral modeling framework will be a step forward towards a new vision for hydrology where models are capable of more confidently predicting the behavior of catchments beyond what has been observed or experienced before.
Publisher: Springer Science and Business Media LLC
Date: 11-05-2020
Publisher: American Geophysical Union (AGU)
Date: 06-2012
DOI: 10.1029/2011WR011586
Publisher: Wiley
Date: 28-01-2020
DOI: 10.1002/HYP.13693
Publisher: Public Library of Science (PLoS)
Date: 18-06-2015
Publisher: Copernicus GmbH
Date: 20-04-2022
Abstract: Abstract. The widely used Budyko framework defines the water- and energy-limits of catchments. Generally, catchments plot close to these physical limits and Budyko (1974) developed a curve that predicted the positions of catchments in this framework. The original formulation of the curve had no parameters, but later a more general, parameterized form was adopted. Originally, Budyko defined the independent variable as an aridity index with the potential evaporation ided by the precipitation (Ep / P) and used this to predict the ratio of actual evaporation over precipitation (Ea / P). However, the framework can be formulated in different ways and others defined the framework with the potential evaporation as the common denominator for the dependent and independent variables, i.e. P / Ep and Ea / Ep. It is possible to mathematically convert between these formulations, but if the parameterized Budyko curves are fit to data, the different formulations could lead to differences in the resulting parameter values. Here, we tested this for 357 catchments across the contiguous United States. This was done by fitting a parameterized form of the curve for the two different formulations. In this way, we found that differences in n-values due to the used projection could be +/- 0.2. If robust fitting algorithms were used, instead of a linear least squares algorithm, the differences in n-values reduced, but were nonetheless still present. The distances to the curve, often used as a metric in Budyko-type analyses, systematically dependended on the projection, with larger differences for the side of the framework with Ep / P 1 for a projection with a dryness index and P / Ep 1 for a projection with a wetness index (i.e. the non-contracted sides od the framework). When using the two projections for predicting Ea, we found that uncertainties due to the used projections could exceed 1.5 %. An important reason for the differences in n-values, curves and resulting estimates of Ea could be found in datapoints that clearly appear as outliers in one projection, but less so in the other projection. We argue here that the non-contracted side of the framework in the two projections should always be assessed, especially for datapoints that appear as outliers. At least, one should consider the additional uncertainty of the projection and assess the robustness of the results in both projections.
Publisher: Copernicus GmbH
Date: 27-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-5306
Abstract: & & Plant water uptake is often a limiting factor for above-ground productivity and therefore models of soil-vegetation-atmosphere transfer strongly rely on a precise characterization of the spatial organization of root systems. However, roots display plasticity in morphology and physiology under environmental fluctuations. Plants, in fact, can adjust their root length distribution to soil moisture. The phenomenon of hydropatterning consists of preferential lateral root development in water-rich soil areas and suppression of lateral root growth in dry soil areas. The preferential root growth in wet soil areas was previously observed in large portions of root systems exposed to wet soil patches, including erse types of roots and both pre-existing and newly grown roots. Here we refer to this phenomenon as & #8220 global hydropatterning& #8221 . However, the capacity of the root systems to adapt to fluctuating soil water availability at daily time scales, for ex le after a rainfall event, are less clear.& & & & We conducted an experiment with the aim to answer the following research questions: (a) can we detect global hydropatterning in response to a water pulse in a hydraulically isolated soil layer, (b) how fast does global hydropatterning occur and (c) does the phenomenon get interrupted in the previously wetted layer and promoted in another layer when a second pulse is applied there?& & & & We grew maize in 45 cm long cylindrical soil columns organized in four hydraulically isolated soil layers separated by vaseline barriers. After six days of water depletion by the plant, water pulses to reach 15% VWC were injected specifically into selected layers while the remaining layers remained unwatered.& & & & For quantifying dynamic responses of the root systems to the water pulses, we measured root distribution repeatedly and non-destructively every 48 hours using a Magnetic Resonance Imaging (MRI) for four weeks. Vertical soil moisture distribution was quantified using the Soil Water Pro& #64257 ler (SWaP) [1].& & & & A preliminary analysis indicates that roots grew preferentially in layers where water pulses had been applied and that allocation to root growth changed dynamically in response to water pulses. Our non-invasive measurements suggest that the global hydropatterning appears in less than 48 hours, and that plants adjust root growth to highly dynamic soil moisture conditions.& & & & A more detailed analysis of root growth rates in response to water pulses in different soil layers will be presented and will provide insights into the response time of maize root systems to changing soil moisture conditions and in how far allocation of carbon to different portions of the root system is an absolute response to soil moisture or a relative response to soil moisture distribution.& & & & & & & & & [1] van Dusschoten, D., Kochs, J., Kuppe, C., Sydoruk, V.A., Couvreur, V., P& #64258 ugfelder, D., Postma, J.A., 2020. Spatially resolved root water uptake determination using a precise soil water sensor. Plant Physiol. 0.1104 p.20.00488& &
Publisher: Copernicus GmbH
Date: 09-02-2022
Abstract: Abstract. Open, accessible, reusable, and reproducible hydrologic research can have a significant positive impact on the scientific community and broader society. While more in iduals and organizations within the hydrology community are embracing open science practices, technical (e.g., limited coding experience), resource (e.g., open access fees), and social (e.g., fear of weaknesses being exposed or ideas being scooped) challenges remain. Furthermore, there are a growing number of constantly evolving open science tools, resources, and initiatives that can be overwhelming. These challenges and the ever-evolving nature of the open science landscape may seem insurmountable for hydrologists interested in pursuing open science. Therefore, we propose the general “Open Hydrology Principles” to guide in idual and community progress toward open science for research and education and the “Open Hydrology Practical Guide” to improve the accessibility of currently available tools and approaches. We aim to inform and empower hydrologists as they transition to open, accessible, reusable, and reproducible research. We discuss the benefits as well as common open science challenges and how hydrologists can overcome them. The Open Hydrology Principles and Open Hydrology Practical Guide reflect our knowledge of the current state of open hydrology we recognize that recommendations and suggestions will evolve and expand with emerging open science infrastructures, workflows, and research experiences. Therefore, we encourage hydrologists all over the globe to join in and help advance open science by contributing to the living version of this document and by sharing open hydrology resources in the community-supported repository (open-hydrology.github.io, last access: 1 February 2022).
Publisher: Copernicus GmbH
Date: 20-04-2022
Publisher: Wiley
Date: 05-05-2019
Abstract: Wildlife diseases are a recognized driver of global bio ersity loss, have substantial economic impacts, and are increasingly becoming a threat to human health. Disease surveillance is critical but remains difficult in the wild due to the substantial costs and potential biases associated with most disease detection methods. Noninvasive scat surveys have been proposed as a health monitoring methodology to overcome some of these limitations. Here, we use the known threat of Chlamydia disease to the iconic, yet vulnerable, koala Phascolarctos cinereus to compare three methods for Chlamydia detection in scats: multiplex quantitative PCR, next generation sequencing, and a detection dog specifically trained on scats from Chlamydia-infected koalas. All three methods demonstrated 100% specificity, while sensitivity was variable. Of particular interest is the variable sensitivity of these diagnostic tests to detect sick in iduals (i.e., not only infection as confirmed by Chlamydia-positive swabs, but with observable clinical signs of the disease) for koalas with urogenital tract disease signs, sensitivity was 78% with quantitative PCR, 50% with next generation genotyping and 100% with the detection dog method. This may be due to molecular methods having to rely on high-quality DNA whereas the dog most likely detects volatile organic compounds. The most appropriate diagnostic test will vary with disease prevalence and the specific aims of disease surveillance. Acknowledging that detection dogs might not be easily accessible to all, the future development of affordable and portable "artificial noses" to detect diseases from scats in the field might enable cost-effective, rapid and large-scale disease surveillance.
Publisher: American Geophysical Union (AGU)
Date: 28-11-2014
DOI: 10.1002/2014GL061668
Publisher: Springer Netherlands
Date: 2008
Publisher: Zenodo
Date: 2017
Publisher: Copernicus GmbH
Date: 21-03-2022
Publisher: The Royal Society
Date: 12-05-2010
Abstract: Feedbacks between water use, biomass and infiltration capacity in semiarid ecosystems have been shown to lead to the spontaneous formation of vegetation patterns in a simple model. The formation of patterns permits the maintenance of larger overall biomass at low rainfall rates compared with homogeneous vegetation. This results in a bias of models run at larger scales neglecting subgrid-scale variability. In the present study, we investigate the question whether subgrid-scale heterogeneity can be parameterized as the outcome of optimal partitioning between bare soil and vegetated area. We find that a two-box model reproduces the time-averaged biomass of the patterns emerging in a 100 × 100 grid model if the vegetated fraction is optimized for maximum entropy production (MEP). This suggests that the proposed optimality-based representation of subgrid-scale heterogeneity may be generally applicable to different systems and at different scales. The implications for our understanding of self-organized behaviour and its modelling are discussed.
Publisher: Copernicus GmbH
Date: 11-05-2016
DOI: 10.5194/BG-2016-190
Abstract: Abstract. The savanna complex is a highly erse global biome that occurs within the seasonally dry tropical to sub-tropical equatorial latitudes. Savannas are open-canopy environments that encompass a broad demographic continuum, often characterised by a dynamically changing dominance between C3-tree and C4-grass vegetation, where frequent environmental disturbances such as fire modulates the balance between ephemeral and perennial life forms. Climate change is projected to result in significant changes to the savanna floristic structure, with increases to woody biomass expected through CO2 fertilisation in mesic savannas and increased tree mortality expected through increased rainfall interannual variability in xeric savannas. The complex interaction between vegetation and climate that occurs in savannas has traditionally challenged current-generation terrestrial biosphere models (TBMs), which aim to simulate the interaction between the atmosphere and the land-surface to predict responses of vegetation to changing in environmental forcing. In this review, we examine whether TBMs are able to adequately represent savanna dynamics and what implications potential deficiencies may have for climate change projection scenarios that rely on these models. We start by highlighting the defining characteristic traits and behaviours of savanna, how these differ across continents, and how this information is (or is not) represented in the structural framework of many TBMs. We highlight three dynamic processes that we believe directly affect the water-use and productivity of the savanna system, namely: phenology root-water access and fire dynamics. Following this, we discuss how these processes are represented in many current generation TBMs and whether they are suitable for simulating savanna dynamics. Finally, we give an overview of how eddy-covariance observations in combination with other data sources, can be used in model benchmarking and inter-comparison frameworks to diagnose the performance of TBMs in this environment and formulate roadmaps for future development. Our investigation reveals that many TBMs systematically misrepresent phenology, effects of fire and root-water access (if they are considered at all) and that these should be critical areas for future development. Furthermore, such processes must not be static (i.e. prescribed behaviour), but be capable of responding to the changing environmental conditions in order to emulate the dynamic behaviour of savannas. Without such developments, however, TBMs will have limited predictive capability in making the critical projections needed to understand how savannas will respond to future global change.
Publisher: Copernicus GmbH
Date: 18-01-2016
Abstract: Abstract. We combine ecohydrological observations of sapflow and soil moisture with thermodynamically constrained estimates of atmospheric evaporative demand to infer the dominant controls of forest transpiration in complex terrain. We hypothesize that daily variations in transpiration are dominated by variations in atmospheric demand, while site-specific controls, including limiting soil moisture, act on longer time scales. We test these hypotheses with data of a measurement setup consisting of 5 sites along a valley cross-section in Luxembourg. Both hillslopes are covered by forest dominated by European beech (Fagus sylvatica L.). Two independent measurements are used to estimate stand transpiration: (i) sapflow and (ii) diurnal variations in soil moisture, which were used to estimate the daily root water uptake. Atmospheric evaporative demand is estimated through thermodynamically-constrained evaporation which only requires absorbed solar radiation and temperature as input data without any empirical parameters. Both transpiration estimates are strongly correlated to atmospheric demand at the daily timescale. We find that neither vapor pressure deficit nor wind speed add to the explained variance, supporting the idea that they are dependent variables on land-atmosphere exchange and the surface energy budget. Estimated stand transpiration was rather similar between the north- and the south-facing hillslopes despite the different aspect and the largely different stand composition. We identified an inverse relationship between sap flux density and the site-average sapwood area per tree as estimated by the site forest inventories. This suggests that tree hydraulic adaptation can compensate for heterogeneous conditions. However, during dry summer periods differences in topographic factors and stand structure can cause spatially variable transpiration rates.
Publisher: California Digital Library (CDL)
Date: 22-04-2021
DOI: 10.31223/X58P62
Publisher: Copernicus GmbH
Date: 20-07-2022
Abstract: Abstract. Forest transpiration is controlled by the atmospheric water demand, potentially constrained by soil moisture availability, and regulated by plant physiological properties. During summer periods, soil moisture availability at sites with thin soils can be limited, forcing the plants to access moisture stored in the weathered bedrock. Land surface models (LSMs) have considerably evolved in the description of the physical processes related to vegetation water use, but the effects of bedrock position and water uptake from fractured bedrock have not received much attention. In this study, the Community Land Model version 5.0 (CLM 5) is implemented at four forested sites with relatively shallow bedrock and located across an environmental gradient in Europe. Three different bedrock configurations (i.e., default, deeper, and fractured) are applied to evaluate if the omission of water uptake from weathered bedrock could explain some model deficiencies with respect to the simulation of seasonal transpiration patterns. Sap flow measurements are used to benchmark the response of these three bedrock configurations. It was found that the simulated transpiration response of the default model configuration is strongly limited by soil moisture availability at sites with extended dry seasons. Under these climate conditions, the implementation of an alternative (i.e., deeper and fractured) bedrock configuration resulted in a better agreement between modeled and measured transpiration. At the site with a continental climate, the default model configuration accurately reproduced the magnitude and temporal patterns of the measured transpiration. The implementation of the alternative bedrock configurations at this site provided more realistic water potentials in plant tissues but negatively affected the modeled transpiration during the summer period. Finally, all three bedrock configurations did not show differences in terms of water potentials, fluxes, and performances on the more northern and colder site exhibiting a transition between oceanic and continental climate. Model performances at this site are low, with a clear overestimation of transpiration compared to sap flow data. The results of this study call for increased efforts into better representing lithological controls on plant water uptake in LSMs.
Publisher: Informa UK Limited
Date: 05-07-2013
Publisher: Copernicus GmbH
Date: 18-01-2016
Publisher: Copernicus GmbH
Date: 28-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-8901
Abstract: & & The universe of Open Science is expanding with many scientific disciplines, organizations and policymakers committing to openness, accessibility, transparency and reproducibility. The paper & #8220 & em& A Hydrologist& #8217 s Guide to Open Science& #8221 & /em& (Hall et al., 2022) introduces four & em& Open Hydrology Principles& /em& and provides a practical guide to empower hydrologists across the globe as they transition to open, accessible, reusable, and reproducible research in their academic work and beyond. In this poster, we will focus on the fourth principle of Hall et al. (2022), & em& Open Publishing& /em& , which should build on the other three principles (1. & em& Open Research Process and Approach& /em& , 2. & em& Open Data& /em& , 3. & em& Open Software Development and Use& /em& ). We will present current Open Science policies of major hydrology journals based on the following five criteria: a) open-access model, b) publication finance policy, c) preprint policy, d) release requirements for data, code and software, and e) peer-review procedure.& This overview can serve as a guideline for researchers that are in search of journals aligning with their Open Science perspectives. Additionally, we hope to kick off a broader discussion about the hydrologic publishing landscape and how it can evolve to foster Open Science.& & & & Reference& & & & Hall, C.A., Saia, S.M., Popp, A.L., Dogulu, N., Schymanski, S., Drost, N., van Emmerik T. Hut, R., A Hydrologist& #8217 s Guide to Open Science. Hydrology and Earth System Sciences, 0.5194/hess-2021-392 (in print)& &
Publisher: Copernicus GmbH
Date: 27-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-4268
Abstract: & & The concept of canopy-scale resistances was developed to investigate and evaluate the transfer of momentum, heat and mass from the leaf surface to the canopy air space and to the atmosphere. Therefore, reliable estimates of resistances are of fundamental importance for studying the ecosystem scale fluxes and land-atmosphere interaction. The canopy-scale resistance has two components: the leaf boundary layer resistance and canopy-air-to-atmosphere resistance. In big-leaf conceptualizations, canopy-scale resistances are represented in a single term called aerodynamic resistance, which refers to the resistance between an idealized & #8216 big-leaf& #8217 and the atmosphere for the transfer of momentum, heat and mass. A decent amount of literature exists on the estimation of aerodynamic resistances for various ecosystems based on the roughness length parametrizations and atmospheric stability correction. Most of these parametrizations do not include the leaf boundary layer explicitly and therefore rely on a conceptual 'aerodynamic temperature' at some distance above the leaf surface. This gap h ers reliable modelling of canopy gas exchange (transpiration and CO2 assimilation) as these processes happen directly at the leaf surface and strongly rely on accurately capturing the leaf surface temperature. To bridge this gap, an additional resistance based on a & #8216 kB& sup& -1& /sup& ' parametrization is commonly added to the classical aerodynamic resistance.& & & & & & & & & The objective of the present study is to estimate the total resistance to heat transfer from the heat exchanging surfaces to the measurement height and to find the most appropriate mathematical formulation for this resistance. We used radiometric and eddy covariance (EC) measurements from a wide range of land cover types and estimated the total resistance to heat transport using measured fluxes and radiometric surface temperatures by inverting the flux-profile equation. We also performed a comprehensive comparison of total resistance estimates with commonly used stability and roughness-based resistance formulations, including & #8216 KB& sup& -1& /sup& ' parametrizations and the momentum flux resistance inverted from EC measurements. We found that total resistances were consistently greater than the roughness length-based resistance parametrizations at most of the study sites. We further found that the difference between the total and aerodynamic resistance can be largely explained by dominant leaf sizes at the in idual sites.& & & & & & & & & Based on these results, we propose a consistent canopy resistance formulation by explicitly considering leaf sizes and leaf boundary layer resistances in combination with an adequate representation of aerodynamic canopy-atmosphere resistance. This approach will enable a consistent coupling of the aerodynamic process with physiological leaf-scale processes such as photosynthesis and stomatal control, which depend on and interact with leaf temperature, and aerodynamic stability.& & & & & & &
Publisher: Copernicus GmbH
Date: 27-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-5357
Abstract: & & Commonly, xylem hydraulic conductance is measured by applying a positive pressure (above atmospheric) to push water through a twig. To imitate flow in twig s les under natural conditions, we developed a method that applies a controlled flow rate using suction, similar to transpiration-driven flow in plants.& & & & The setup consists of a syringe pump to control water flow, where a twig is inserted in the flow path and hydraulic conductivity is calculated from measurements using pressure sensors and a flow meter. The syringe pump can be used to generate controlled flow rates in both directions and a series of bypasses can be used to self-calibrate the sensors and reverse flow directions through the twig while the syringe pump is either pushing or pulling. In this way, we were able to compare our suction method with the more conventional pushing method and assess the effect of flow direction on hydraulic conductance measurements. We found a reproducible pattern in measured conductivity values, where measurements using suction resulted in a 50% lower conductivity than when flow was induced by pushing. The direction of flow (root-shoot vs. shoot-root) also had a strong influence, with suction in root-shoot direction resulting in the lowest conductivity measurements, but repeated reversals of flow revealed an intricate pattern of loss and partial restoration of conductivity, implicating the existence of particles that move with the flow and accumulate at the vessel ends.& & & & Here we present the intriguing results and propose an explanation capable of explaining the reproducible patterns in observed conductivity dynamics during the experiments. The explanation involves nanobubbles that shrink and swell depending on the liquid pressure and surface tension, move with the flow and reduce conductivity as they accumulate at vessel ends.& &
Publisher: Copernicus GmbH
Date: 21-03-2014
DOI: 10.5194/HESSD-11-3249-2014
Abstract: Abstract. This opinion paper proposes a novel framework for exploring how spatial organization alongside with spatial heterogeneity controls functioning of intermediate scale catchments of organized complexity. Key idea is that spatial organization in landscapes implies that functioning of intermediate scale catchments is controlled by a hierarchy of functional units: hillslope scale lead topologies and embedded elementary functional units (EFUs). We argue that similar soils and vegetation communities and thus also soil structures "co-developed" within EFUs in an adaptive, self-organizing manner as they have been exposed to similar flows of energy, water and nutrients from the past to the present. Class members of the same EFU (class) are thus deemed to belong to the same ensemble with respect to controls of the energy balance and related vertical flows of capillary bounded soil water and heat. Class members of superordinate lead topologies are characterized by the same spatially organized arrangement of EFUs along the gradient driving lateral flows of free water as well as a similar surface and bedrock topography. We hence postulate that they belong to the same ensemble with respect to controls on rainfall runoff transformation and related vertical and lateral fluxes of free water. We expect class members of these functional units to have a distinct way how their architecture controls the interplay of state dynamics and integral flows, which is typical for all members of one class but dissimilar among the classes. This implies that we might infer on the typical dynamic behavior of the most important classes of EFU and lead topologies in a catchment, by thoroughly characterizing a few members of each class. A major asset of the proposed framework, which steps beyond the concept of hydrological response units, is that it can be tested experimentally. In this respect, we reflect on suitable strategies based on stratified observations drawing from process hydrology, soil physics, geophysics, ecology and remote sensing which are currently conducted in replicates of candidate functional units in the Attert basin (Luxembourg), to search for typical and similar functional and structural characteristics. A second asset of this framework is that it blueprints a way towards a structurally more adequate model concept for water and energy cycles in intermediate scale catchments, which balances necessary complexity with falsifiability. This is because EFU and lead topologies are deemed to mark a hierarchy of "scale breaks" where simplicity with respect to the energy balance and stream flow generation emerges from spatially organized process-structure interactions. This offers the opportunity for simplified descriptions of these processes that are nevertheless physically and thermodynamically consistent. In this respect we reflect on a candidate model structure that (a) may accommodate distributed observations of states and especially terrestrial controls on driving gradients to constrain the space of feasible model structures and (b) allows testing the possible added value of organizing principles to understand the role of spatial organization from an optimality perspective.
Publisher: Copernicus GmbH
Date: 27-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-2886
Abstract: & & Leaf area dynamics are often prescribed in terrestrial biosphere models (TBMs) or based on predefined carbon allocation rules and plant functional types. However, reliance on observational data h ers predictions under future scenarios, as leaf area dynamics and allocation patterns may change due to feedbacks with soil and atmosphere. Therefore, dynamical modelling of leaf area in TBMs based on fundamental principles could greatly improve our ability to better understand and predict vegetation response to environmental change.& & & & The Vegetation Optimality Model (VOM, Schymanski et al., 2009) uses an optimality principle based on the maximization of the Net Carbon Profit (NCP) to predict vegetation properties such as root distributions, photosynthetic capacity and vegetation cover at the daily time scale, as well as water and CO& sub& & /sub& exchange at the hourly scale. The NCP is defined as the difference between the total CO& sub& & /sub& assimilated by photosynthesis and the carbon costs for construction and maintenance of the light and water harvesting plant organs. In a previous study (Nijzink et al. 2021), we found that the VOM systematically overestimated wet season light absorption and CO& sub& & /sub& uptake along the North Australian Tropical Transect (NATT), suggesting that the original big-leaf approach may be missing self-shading effects at high leaf area index (LAI) values. Therefore, we extended the VOM to explicitly consider light absorption as a function of the LAI, and dynamically optimize LAI while considering the carbon costs and benefits of maintaining leaf area. The model was extended step-wise while its predictions were compared to measurements at five flux tower sites along the NATT, with a strong precipitation gradient from north to south.& & & & Here we present the insights gained from this process, including the importance of considering sunlit and shaded leaf area fractions, and separate optimization of photosynthetic capacity for each. In a first step, dynamical leaf area was introduced in the VOM without considering shading, which led to a relatively high CO& sub& & /sub& -assimilation. Nevertheless, including shaded and sunlit leaf fractions in the big leaf approach of the VOM was not sufficient, as in nature, shaded leaves in the lower canopy have lower photosynthetic capacities than the mostly sunlit upper canopy leaves. For this reason, a separate optimization of photosynthetic capacities, in order to maximize the NCP, was included for shaded and sunlit leaves. Eventually, we will compare the modelled leaf area dynamics and fluxes with remotely sensed LAI and locally measured fluxes at the different flux tower sites along the NATT.& & & & & & & & & & strong& References& /strong& & & & & Nijzink, R. C., Beringer, J., Hutley, L. B., and Schymanski, S. J.:, 2021. Does maximization of net carbon profit enable the prediction of vegetation behaviour in savanna sites along a precipitation gradient?, Hydrol. Earth Syst. Sci. Discuss. [preprint], 0.5194/hess-2021-265, accepted& & & & Schymanski, S.J., Sivapalan, M., Roderick, M.L., Hutley, L.B., Beringer, J., 2009. An optimality& #8208 based model of the dynamic feedbacks between natural vegetation and the water balance. Water Resources Research 45. 0.1029/2008WR006841& &
Publisher: American Geophysical Union (AGU)
Date: 10-2008
DOI: 10.1029/2008GL035393
Publisher: Zenodo
Date: 2020
Publisher: American Geophysical Union (AGU)
Date: 2009
DOI: 10.1029/2008WR006841
Publisher: Copernicus GmbH
Date: 15-05-2023
DOI: 10.5194/EGUSPHERE-EGU23-11630
Abstract: Plant leaves absorb solar radiation and carbon dioxide (CO2) from the atmosphere while releasing water vapour, oxygen and heat to the atmosphere. The leaf-atmosphere interface is hence the primary determinant of water-carbon interactions, where stomata control transpiration according to soil water availability, but at the cost of reducing carbon uptake by photosynthesis. It has been proposed that stomata not only respond to water stress, but function in a way to maximise a plant's long-term carbon gain by dynamically economising plant available water according to varying environmental conditions (Cowan and Farquhar, 1977). While the search for the relevant costs of stomatal opening focuses more and more on the costs of the infrastructure needed to supply water to the leaves, the consequences of opening stomata in the presence of leaf-atmosphere feedbacks, potentially resulting in a cooling and humidification of the air at the diurnal scale, hence reducing evaporative demand (Cowan, 1978), and/or depletion of atmospheric CO2, hence reducing CO2 uptake, have so far not been considered in stomatal optimality modelling. It has been shown that optimal response of vegetation to even small long-term variations in atmospheric CO2 can lead to substantial changes in land-atmosphere exchange (Schymanski et al., 2015), while the effect of trends in atmospheric vapour pressure concentration and temperature has also been documented widely. However, little research has been conducted on the optimal behaviour of plants in the presence of land-atmosphere feedbacks.Here we present a theoretical analysis and preliminary experimental results of (optimal) stomatal control in the presence of leaf-atmosphere coupling. The coupling strength is represented theoretically by adding an additional control volume representing the leaf boundary layer or canopy air space, and experimentally by varying the flow rate of dry and CO2-rich air into a leaf cuvette. We discuss the positive and negative effects of a de-coupled canopy air space for leaf gas and energy exchange, and present experimental and mathematical methods to put them into relation to each other.Literature:Cowan, I. R.: Water use in higher plants, in: Water: planets, plants and people, edited by: McIntyre, A. K., Australian Academy of Science, Canberra, 71& #8211 , 1978.Cowan, I. R. and Farquhar, G. D.: Stomatal Function in Relation to Leaf Metabolism and Environment, in: Integration of activity in the higher plant, edited by: Jennings, D. H., Cambridge University Press, Cambridge, 471& #8211 , 1977.Schymanski, S. J., Roderick, M. L., and Sivapalan, M.: Using an optimality model to understand medium and long-term responses of vegetation water use to elevated atmospheric CO2 concentrations, AoB Plants, 7, plv060, 0.1093/aobpla lv060, 2015.
Publisher: Copernicus GmbH
Date: 02-2022
Abstract: Abstract. Most terrestrial biosphere models (TBMs) rely on more or less detailed information about the properties of the local vegetation. In contrast, optimality-based models require much less information about the local vegetation as they are designed to predict vegetation properties based on general principles related to natural selection and physiological limits. Although such models are not expected to reproduce current vegetation behaviour as closely as models that use local information, they promise to predict the behaviour of natural vegetation under future conditions, including the effects of physiological plasticity and shifts of species composition, which are difficult to capture by extrapolation of past observations. A previous model intercomparison using conventional TBMs revealed a range of deficiencies in reproducing water and carbon fluxes for savanna sites along a precipitation gradient of the North Australian Tropical Transect (Whitley et al., 2016). Here, we examine the ability of an optimality-based model (the Vegetation Optimality Model, VOM) to predict vegetation behaviour for the same savanna sites. The VOM optimizes key vegetation properties such as foliage cover, rooting depth and water use parameters in order to maximize the net carbon profit (NCP), defined as the difference between total carbon taken up by photosynthesis minus the carbon invested in construction and maintenance of plant organs. Despite a reduced need for input data, the VOM performed similarly to or better than the conventional TBMs in terms of reproducing the seasonal litude and mean annual fluxes recorded by flux towers at the different sites. It had a relative error of 0.08 for the seasonal litude in ET and was among the three best models tested with the smallest relative error in the seasonal litude of gross primary productivity (GPP). Nevertheless, the VOM displayed some persistent deviations from observations, especially for GPP, namely an underestimation of dry season evapotranspiration at the wettest site, suggesting that the hydrological assumptions (free drainage) have a strong influence on the results. Furthermore, our study exposes a persistent overprediction of vegetation cover and carbon uptake during the wet seasons by the VOM. Our analysis revealed several areas for improvement in the VOM and the applied optimality theory, including a better representation of the hydrological settings as well as the costs and benefits related to plant water transport and light capture by the canopy. The results of this study imply that vegetation optimality is a promising approach to explain vegetation dynamics and the resulting fluxes. It provides a way to derive vegetation properties independently of observations and allows for a more insightful evaluation of model shortcomings as no calibration or site-specific information is required.
Publisher: Copernicus GmbH
Date: 15-05-2023
DOI: 10.5194/EGUSPHERE-EGU23-2910
Abstract: Hydrologists often need to choose between competing hypotheses or weight the predictions of different models when averaging models. Several criteria for choosing and weighting models have been developed, which balance model complexity and goodness of fit by penalising the number of model parameters. The penalty is explicit for information theory approaches or implicit for Bayesian model selection based on marginal likelihood and, by extension, the Bayes factor. The Bayes factor is the ratio of the marginal likelihoods of two competing models. Also, the Bayes factor can be used for non-nested models in contrast to information-theoretic approaches. However, marginal likelihood estimation is computationally intensive and slow for dynamic models with multiple modes. This study uses Replica Exchange Hamiltonian Monte Carlo and thermodynamic integration for fast, simultaneous calculation of marginal likelihood and parameter identification of dynamic rainfall-runoff models. Using synthetic data, the method selected the true model in our numerical experiments. The technique was also applied to real data from Magela Creek in Australia. The selected model was not the model with the highest or lowest number of parameters for real data. The method is implemented using the differentiable programming software ''TensorFlow Probability". This implementation can be applied to other types of models for fast simultaneous parameter estimation and model comparison.
Publisher: Copernicus GmbH
Date: 03-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-4188
Abstract: & & Ecohydrological systems are a result of long-term co-evolution of soils, biota and atmospheric conditions, and often respond to perturbations in non-intuitive ways. Their short-term responses can be explained and sometimes predicted if we understand the underlying dynamic processes and if we can observe the initial state precisely enough. However, how do they co-evolve in the long-term after a change in the boundary conditions? In 1922, Alfred Lotka hypothesised that the natural selection governing the evolution of biota and composition of ecosystems may be obeying some thermodynamic principles related to maximising energy flow through these systems. Similar thoughts have been formulated for various components of the Earth system and in idual processes, such as heat transport in the atmosphere and oceans, erosion and sediment transport in river systems and estuaries, the formation of vegetation patterns, and many others. Different thermodynamic optimality principles have been applied to predict or explain a given system property or behaviour, of which the maximum entropy production and the maximum power principles are most widespread. However, the different studies did not use a common systematic approach for the formulation of the relevant system boundaries, state variables and exchange fluxes, resulting in considerable ambiguity about the application of thermodynamic optimality principles in the scientific community. Such a systematic framework has been developed recently and can be tested online at:& & & & & span& & span& renkulab.io rojects/stanislaus.schymanski/thermodynamic_optimality_blueprint& /span& & /span& & & & & In the present study, we illustrate how such a common framework can be used to classify and compare different applications of thermodynamic optimality principles in the literature, and discuss the insights gained and key criteria for a more rigorous testing of such principles.& &
Publisher: Wiley
Date: 04-2017
Publisher: Oxford University Press (OUP)
Date: 2019
DOI: 10.1093/JUE/JUZ005
Abstract: Urban environments present some of the greatest challenges to species survival. This is particularly true for species that exhibit thermally sensitive traits, such as temperature-dependent sex determination (TSD). This is because urban environments not only present species with entirely novel ecosystems, but species will also experience increased temperatures. These temperature increases may result not only in offspring mortality, but also skewed population sex ratios. To persist in cities, urban dwellers with TSD will therefore need to adjust the temperature of the nesting environment, either through phenotypic plasticity or rapid evolution through natural selection. Here, we investigate the nesting ecology of a long-lived, urban dwelling reptile, the eastern water dragon (Intellagama lesueurii), to understand how a TSD species may respond to urban environments. Based on data collected from 72 nests over 2 nesting seasons, we show that city dragons not only dug significantly deeper nests than previously observed across their natural riparian habitat, but also nested in novel substrates. Furthermore, we observed a behaviour not previously described in this species, where mothers travel outside of their core home range to nest. This excursion behaviour potentially represents a greater maternal investment and is linked to the selection of specific microhabitats.
Publisher: Public Library of Science (PLoS)
Date: 24-01-2013
Publisher: Zenodo
Date: 2020
Publisher: Wiley
Date: 23-03-2022
DOI: 10.1111/AEC.13162
Publisher: Wiley
Date: 12-02-2013
Publisher: Wiley
Date: 28-01-2019
DOI: 10.1111/NPH.15652
Abstract: Leaves with stomata on both upper and lower surfaces, termed histomatous, are relatively rare compared with hypostomatous leaves with stomata only on the lower surface. Amphistomaty occurs predominantly in fast-growing herbaceous annuals and in slow-growing perennial shrubs and trees. In this paper, we present the current understanding and hypotheses on the costs and benefits of histomaty related to water and CO
Publisher: Research Square Platform LLC
Date: 15-12-2021
DOI: 10.21203/RS.3.RS-1169624/V1
Abstract: Land surface temperature (LST) is a preeminent state variable that controls the energy and water exchange between the Earth’s surface and the atmosphere. At the landscape-scale, LST is derived from thermal infrared radiance measured using space-borne radiometers. At the plot-scale, the flux tower recorded longwave radiation components are inverted to retrieve LST. Since the down-welling longwave component was not measured routinely until recently, usually only the up-welling longwave component is used for the plot-scale LST retrieval. However, we found that ignoring reflected down-welling longwave radiation for plot-scale LST estimations can lead to substantial error. This also has important implications for estimating the correct surface emissivity using flux tower measurements, which is needed for plot-scale LST retrievals. The present study proposes a new method for plot-scale emissivity and LST estimation and addresses in detail the consequences of omitting down-welling longwave radiation as frequently done in the literature. Our analysis uses ten eddy covariance sites with different land cover types and found that the LST values obtained using both up-welling and down-welling longwave radiation components are 0.5 to 1.5 K lower than estimates using only up-welling longwave radiation. Furthermore, the proposed method helps identify inconsistencies between plot-scale radiometric and aerodynamic measurements, likely due to footprint mismatch between measurement approaches. We also found that such inconsistencies can be removed by slight corrections to the up-welling longwave component and subsequent energy balance closure, resulting in realistic estimates of surface emissivity and consistent relationships between energy fluxes and surface-air temperature differences. Landscape-scale daytime LST obtained from satellite data (MODIS TERRA) was strongly correlated with our plot-scale estimates for most of the sites, but higher by several Kelvin at two sites. We also quantified the uncertainty in estimated LST and surface emissivity using the different methods and found that the proposed method does not result in increased uncertainty. The results of this work have significant implications for the combined use of aerodynamic and radiometric measurements to understand the interactions and feedbacks between LST and surface-atmosphere exchange processes.
Publisher: Hindawi Limited
Date: 2012
DOI: 10.1155/2012/631856
Abstract: Establishing species distribution and population trends are basic requirements in conservation biology, yet acquiring this fundamental information is often difficult. Indirect survey methods that rely on fecal pellets (scats) can overcome some difficulties but present their own challenges. In particular, variation in scat detectability and decay rate can introduce biases. We studied how vegetation communities affect the detectability and decay rate of scats as exemplified by koalas Phascolarctos cinereus : scat detectability was highly and consistently dependent on ground layer complexity (introducing up to 16% non-detection bias) scat decay rates were highly heterogeneous within vegetation communities exposure of scats to surface water and rain strongly accelerated scat decay rate and finally, invertebrates were found to accelerate scat decay rate markedly, but unpredictably. This last phenomenon may explain the high variability of scat decay rate within a single vegetation community. Methods to decrease biases should be evaluated when planning scat surveys, as the most appropriate method(s) will vary depending on species, scale of survey and landscape characteristics. Detectability and decay biases are both stronger in certain vegetation communities, thus their combined effect is likely to introduce substantial errors in scat surveys and this could result in inappropriate and counterproductive management decisions.
Publisher: Copernicus GmbH
Date: 14-09-2022
DOI: 10.5194/HESS-26-4575-2022
Abstract: Abstract. The widely used Budyko framework defines the water and energy limits of catchments. Generally, catchments plot close to these physical limits, and Budyko (1974) developed a curve that predicted the positions of catchments in this framework. Often, the independent variable is defined as an aridity index, which is used to predict the ratio of actual evaporation over precipitation (Ea/P). However, the framework can be formulated with the potential evaporation as the common denominator for the dependent and independent variables, i.e., P/Ep and Ea/Ep. It is possible to mathematically convert between these formulations, but if the parameterized Budyko curves are fit to data, the different formulations could lead to differences in the resulting parameter values. Here, we tested this for 357 catchments across the contiguous United States. In this way, we found that differences in n values due to the projection used could be ± 0.2. If robust fitting algorithms were used, the differences in n values reduced but were nonetheless still present. The distances to the curve, often used as a metric in Budyko-type analyses, systematically depended on the projection, with larger differences for the non-contracted sides of the framework (i.e., Ep/P or P/Ep ). When using the two projections for predicting Ea, we found that uncertainties due to the projections used could exceed 1.5 %. An important reason for the differences in n values, curves and resulting estimates of Ea could be found in data points that clearly appear as outliers in one projection but less so in the other projection. We argue here that the non-contracted side of the framework in the two projections should always be assessed, especially for data points that appear as outliers. At least, one should consider the additional uncertainty of the projection and assess the robustness of the results in both projections.
Publisher: Copernicus GmbH
Date: 20-06-2011
Abstract: Abstract. As a system is moved away from a state of thermodynamic equilibrium, spatial and temporal heterogeneity is induced. A possible methodology to assess these impacts is to examine the thermodynamic entropy budget and assess the role of entropy production and transfer between the surface and the atmosphere. Here, we adopted this thermodynamic framework to examine the implications of changing vegetation fractional cover on land surface energy exchange processes using the NOAH land surface model and eddy covariance observations. Simulations that varied the relative fraction of vegetation were used to calculate the resultant entropy budget as a function of fraction of vegetation. Results showed that increasing vegetation fraction increases entropy production by the land surface while decreasing the overall entropy budget (the rate of change in entropy at the surface). This is accomplished largely via simultaneous increase in the entropy production associated with the absorption of solar radiation and a decline in the Bowen ratio (ratio of sensible to latent heat flux), which leads to increasing the entropy export associated with the latent heat flux during the daylight hours and dominated by entropy transfer associated with sensible heat and soil heat fluxes during the nighttime hours. Eddy covariance observations also show that the entropy production has a consistent sensitivity to land cover, while the overall entropy budget appears most related to the net radiation at the surface, however with a large variance. This implies that quantifying the thermodynamic entropy budget and entropy production is a useful metric for assessing biosphere-atmosphere-hydrosphere system interactions.
Publisher: Zenodo
Date: 2020
Publisher: Wiley
Date: 13-01-2012
Publisher: Copernicus GmbH
Date: 12-06-2015
DOI: 10.5194/PIAHS-371-99-2015
Abstract: Abstract. Transpiration is commonly conceptualised as a fraction of some potential rate, driven by so-called "atmospheric evaporative demand". Therefore, atmospheric evaporative demand or "potential evaporation" is generally used alongside with precipitation and soil moisture to characterise the environmental conditions that affect plant water use. Consequently, an increase in potential evaporation (e.g. due to climate change) is believed to cause increased transpiration and/or vegetation water stress. In the present study, we investigated the question whether potential evaporation constitutes a meaningful reference for transpiration and compared sensitivity of potential evaporation and leaf transpiration to atmospheric forcing. A physically-based leaf energy balance model was used, considering the dependence of feedbacks between leaf temperature and exchange rates of radiative, sensible and latent heat on stomatal resistance. Based on modelling results and supporting experimental evidence, we conclude that stomatal resistance cannot be parameterised as a factor relating transpiration to potential evaporation, as the ratio between transpiration and potential evaporation not only varies with stomatal resistance, but also with wind speed, air temperature, irradiance and relative humidity. Furthermore, the effect of wind speed in particular implies increase in potential evaporation, which is commonly interpreted as increased "water stress", but at the same time can reduce leaf transpiration, implying a decrease in water demand at leaf scale.
Publisher: Springer Science and Business Media LLC
Date: 12-2020
DOI: 10.1038/S41598-020-77865-7
Abstract: Members of the genus Nannizziopsis are emerging fungal pathogens of reptiles that have been documented as the cause of fatal mycoses in a wide range of reptiles in captivity. Cases of severe, proliferative dermatitis, debility and death have been detected in multiple free-living lizard species from locations across Australia, including a substantial outbreak among Eastern water dragons ( Intellagama lesueurii ) in Brisbane, Queensland. We investigated this disease in a subset of severely affected lizards and identified a clinically consistent syndrome characterized by hyperkeratosis, epidermal hyperplasia, dermal inflammation, necrosis, ulceration, and emaciation. Using a novel fungal isolation method, histopathology, and molecular techniques, we identified the etiologic agent as Nannizziopsis barbatae , a species reported only once previously from captive lizards in Australia. Here we report severe dermatomycosis caused by N. barbatae in five species of Australian lizard, representing the first cases of Nannizziopsis infection among free-living reptiles, globally. Further, we evaluate key pathogen and host characteristics that indicate N. barbatae -associated dermatomycosis may pose a concerning threat to Australian lizards.
Publisher: Copernicus GmbH
Date: 15-02-2019
DOI: 10.5194/ESD-2019-6
Abstract: Abstract. Thermodynamic optimality principles have been often used in Earth sciences to estimate model parameters or fluxes. Applications range from optimizing atmospheric meridional heat fluxes to sediment transport and from optimizing spatial flow patterns to dispersion coefficients for fresh and salt water mixing. However, it is not always clear what has to be optimized and how. In this paper we aimed to clarify terminology used in the literature and to infer how these principles have been used and when they give proper predictions of observed fluxes and states. We distinguish roughly four classes of applications: predictions using a flux-gradient feedback, predictions using a constant thermodynamic potential boundary conditions, predictions based on information theoretical approaches and comparative studies quantifying entropy production rates from observations at different sites. Here we mainly focus on the flux-gradient feedback, since it results in clear physical limits of energy conversion rates occurring in the Earth system and its subsystems. We show that within the flux-gradient feedback application, maximum entropy production is in many cases equivalent to maximum power and maximum energy dissipation. We advocate the maximum power principle above the more widely used maximum entropy production principle because entropy can be produced by all kinds of fluxes, but only optimized fluxes performing work coincided with observations. Furthermore, the maximum power principle links to the maximum amount of free energy that can be converted into another form of energy. This clearly separates the well defined physical conversion limit from the hypothesis that a system evolves to that limit of maximum power. Although attempts have been made to fundamentally explain why a system would evolve to such a maximum in power, there is still no consensus. Nevertheless, we think that when the maximum power approach is correctly and consistently used, the positive (or negative) results will speak for themselves. We end this review with some open research questions that may guide further research in this area.
Publisher: Copernicus GmbH
Date: 28-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-7199
Abstract: & & The drought resilience of forest ecosystems depends on the water use strategies and the degree of vulnerability to hydraulic failure of in idual tree species. The coordination between hydraulic and allocation traits along with stomatal control determines the tree water-use strategy, ranging from acquisitive to conservative tree species. This work explores the role of different plant hydraulic traits (& #936 & sub& P50& /sub& , & em& c& /em& & sub& k& /sub& , and & em& k& /em& & sub& max& /sub& in the Community Land Model 5.0) on the simulated plant water use dynamics. We selected two broadleaved tree species (& em& Quercus ilex& /em& L. and & em& Fagus sylvatica& /em& L.) at four SAPFLUXNET experimental sites having contrasting climate conditions. From the range of plant hydraulic traits reported for each species in the Xylem Functional Traits (XFT) database and other literature, the most vulnerable and most resistant parameter combination was chosen as extreme cases. Four sets of experiments were carried out that include modification of the shape of the plant vulnerability curve changing only & #936 & sub& P50& /sub& and & em& c& /em& & sub& k& /sub& (CS-experiment), changing only & em& k& /em& & sub& max& /sub& (k-experiment), changing the three parameters of the vulnerability equation (FC-experiment), and changing gradually & em& k& /em& & sub& max& /sub& (KS-experiment) to test the model sensitivity to & em& k& /em& & sub& max& /sub& . The stand transpiration obtained from SAPFLUXNET was used as a benchmark for the model comparisons. The CS-experiment revealed that a vulnerable configuration increases the modeled transpiration during conditions with le water supply, and causes severe water stress and reduced transpiration during dry periods as compared to a resistant configuration. This indicates that transpiration is hydraulically limited even at le water supply in the model so that the more negative & #936 & sub& P50& /sub& enables increased transpiration. Although a more negative & #936 & sub& P50& /sub& allows the vegetation to access more soil water than would be the case for vulnerable configurations, the difference in actual plant available water is small at this dry end of the water retention curve, and hence the dry period water stress is mainly determined by early-season transpiration. The K- and KS- experiments illustrate the role of & em& k& /em& & sub& max& /sub& to effectively scale up/down the transpiration response. Finally, the FC-experiments revealed the potential of plant hydraulic traits to mimic either conservative or acquisitive water-use strategies, allowing the vegetation to manage more efficiently the soil water resources. This work underlines the importance of selecting a suitable plant hydraulic parametrization contemplating the ersity of plant water use strategies.& &
Publisher: Copernicus GmbH
Date: 28-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-8841
Abstract: & & Vegetation responds to environmental change in many ways and at various time scales. For ex le, increasing atmospheric CO& sub& & /sub& concentrations can reduce stomatal conductance and, hence, transpiration at an hourly scale, whereas adjustments in leaf area, photosynthetic capacity and root distributions follow at the daily to seasonal scale. Evidence for root growth plasticity and adaptation to soil moisture conditions can be found in field and experimental data. However, the time scales at which roots respond to a sudden change in soil moisture are not well documented, and the dynamics of root allocation in response to soil moisture changes at daily time scales is not well understood. In addition, when looking at even longer time scales, shifts in tree density and species composition may happen over decades or centuries only. These responses give rise to feedbacks with soil water resources and atmospheric conditions, affecting the entire soil-vegetation-atmosphere system on a large range of spatio-temporal scales.& & & & Reliable projections of long-term ecosystem response to environmental change require adequate understanding and quantitative representation of the physical processes and biological trade-offs related to vegetation-environment interactions. This includes answering the following questions:& & & & ) What is the trade-off between canopy CO& sub& & /sub& uptake and water loss under given atmospheric conditions?& & & & ) How much carbon do the plants need to invest into their root system, as well as water transport and storage tissues in order to achieve a certain water and nutrient supply for the canopy?& & & & ) How quickly can root systems respond to changing conditions?& & & & ) What are the trade-offs between carbon investments into foliage, stems and roots and returns in terms of carbon uptake by photosynthesis?& & & & ) Do plants adapt to the environment in an optimal way in order to maximise their net carbon profit, i.e. the carbon uptake minus carbon invested into tissues needed for its uptake?& & & & ) And finally, can vegetation behaviour be predicted by assuming a community-scale optimal adaptation for maximum net carbon profit?& & & & Here we present promising results related to Question 6) based on the Vegetation Optimality Model (VOM), which was recently applied and tested along a precipitation gradient in Australia. We also explain the benefits of quantitative answers to Questions 1-4 and point to targeted experiments needed to address these questions, some of which will be presented separately.& &
Publisher: Copernicus GmbH
Date: 07-07-2017
DOI: 10.5194/HESS-21-3377-2017
Abstract: Abstract. Leaf transpiration and energy exchange are coupled processes that operate at small scales yet exert a significant influence on the terrestrial hydrological cycle and climate. Surprisingly, experimental capabilities required to quantify the energy–transpiration coupling at the leaf scale are lacking, challenging our ability to test basic questions of importance for resolving large-scale processes. The present study describes an experimental set-up for the simultaneous observation of transpiration rates and all leaf energy balance components under controlled conditions, using an insulated closed loop miniature wind tunnel and artificial leaves with pre-defined and constant diffusive conductance for water vapour. A range of tests documents the above capabilities of the experimental set-up and points to potential improvements. The tests reveal a conceptual flaw in the assumption that leaf temperature can be characterized by a single value, suggesting that even for thin, planar leaves, a temperature gradient between the irradiated and shaded or transpiring and non-transpiring leaf side can lead to bias when using observed leaf temperatures and fluxes to deduce effective conductances to sensible heat or water vapour transfer. However, comparison of experimental results with an explicit leaf energy balance model revealed only minor effects on simulated leaf energy exchange rates by the neglect of cross-sectional leaf temperature gradients, lending experimental support to our current understanding of leaf gas and energy exchange processes.
Publisher: Wiley
Date: 21-08-2012
Publisher: Copernicus GmbH
Date: 26-07-2016
Abstract: Abstract. The Penman-Monteith (PM) equation is commonly considered the most advanced physically based approach to computing transpiration rates from plants considering stomatal conductance and atmospheric drivers. It has been widely evaluated at the canopy scale, where aerodynamic and canopy resistance to water vapour are difficult to estimate directly, leading to various empirical corrections when scaling from leaf to canopy. Here we evaluated the PM equation directly at the leaf scale, using a detailed leaf energy balance model and direct measurements in a controlled, insulated wind tunnel using artificial leaves with fixed and pre-defined "stomatal" conductance. Experimental results were consistent with a detailed leaf energy balance model however, the results revealed systematic deviations from PM-predicted fluxes, which pointed to fundamental problems with the PM equation. Detailed analysis of the derivation by Monteith (1965) and later amendments revealed two errors in considering the effect of stomata and the two-sided exchange of sensible heat. A corrected set of analytical solutions for leaf temperature as well as latent and sensible heat flux is presented and comparison with the original PM equation indicates a major improvement in reproducing experimental results at the leaf scale. The errors in the original PM equation and its failure to reproduce experimental results at the leaf scale (for which it was originally derived) propagate into inaccurate sensitivities of transpiration and sensible heat fluxes to changes in atmospheric conditions, such as those associated with climate change (even with reasonable present day performance after calibration). The new formulation presented here rectifies some of the shortcomings of the PM equation and could provide a more robust starting point for canopy representation and climate change studies.
Publisher: Copernicus GmbH
Date: 13-01-2017
Abstract: Abstract. Leaf transpiration and energy exchange are coupled processes that operate at small scales yet exert a significant influence on terrestrial hydrological cycle and climate. Surprisingly, experimental capabilities required for quantifying the energy-transpiration coupling at the leaf scale are lacking, challenging our ability to test basic questions of importance for resolving large scale processes. The present study describes an experimental setup for the simultaneous observation of transpiration rates and all leaf energy balance components under controlled conditions, using an insulated closed-loop miniature wind tunnel and artificial leaves with pre-defined and constant diffusive conductance for water vapour. A range of tests documents the above capabilities of the experimental setup and points to potential improvements. The tests reveal a conceptual flaw in the assumption that leaf temperature can be characterised by a single value, suggesting that even for thin, planar leaves, a temperature gradient between the irradiated and shaded or transpiring and non-transpiring leaf side can lead to bias when using observed leaf temperatures and fluxes to deduce effective conductances to sensible heat or water vapour transfer. However, comparison of experimental results with an explicit leaf energy balance model revealed only minor effect on simulated leaf energy exchange rates by the neglect of cross-sectional leaf temperature gradients, lending experimental support to our current understanding of leaf gas and energy exchange processes.
Publisher: Zenodo
Date: 2019
Publisher: Wiley
Date: 09-2008
Publisher: Wiley
Date: 13-03-2023
DOI: 10.1111/MEC.16877
Abstract: The genetic consequences of the sub ision of populations are regarded as significant to long‐term evolution, and research has shown that the scale and speed at which this is now occurring is critically reducing the adaptive potential of most species which inhabit human‐impacted landscapes. Here, we provide a rare and, to our knowledge, the first analysis of this process while it is happening and demonstrate a method of evaluating the effect of mitigation measures such as fauna crossings. We did this by using an extensive genetic data set collected from a koala population which was intensely monitored during the construction of linear transport infrastructure which resulted in the sub ision of their population. First, we found that both allelic richness and effective population size decreased through the process of population sub ision. Second, we predicted the extent to which genetic drift could impact genetic ersity over time and showed that after only 10 generations the resulting two sub ided populations could experience between 12% and 69% loss in genetic ersity. Lastly, using forward simulations we estimated that a minimum of eight koalas would need to disperse from each side of the sub ision per generation to maintain genetic connectivity close to zero but that 16 koalas would ensure that both genetic connectivity and ersity remained unchanged. These results have important consequences for the genetic management of species in human‐impacted landscapes by showing which genetic metrics are best to identify immediate loss in genetic ersity and how to evaluate the effectiveness of any mitigation measures.
Publisher: Copernicus GmbH
Date: 11-06-2021
Abstract: Abstract. Most terrestrial biosphere models (TBMs) rely on more or less detailed information about the properties of the local vegetation. In contrast, optimality-based models require much less information about the local vegetation as they are designed to predict vegetation properties based on general principles related to natural selection and physiological limits. Although such models are not expected to reproduce current vegetation behaviour as closely as models that use local information, they promise to predict the behaviour of natural vegetation under future conditions, including the effects of physiological plasticity and shifts of species composition, which are difficult to capture by extrapolation of past observations. A previous model intercomparison using conventional terrestrial biosphere models (TBMs) revealed a range of deficiencies in reproducing water and carbon fluxes for savanna sites along a strong precipitation gradient of the North Australian Tropical Transect (Whitley et al., 2016). Here we examine the ability of an optimality-based model (the Vegetation Optimality Model, VOM) predict vegetation behaviour for the same savanna sites. The VOM optimizes key vegetation properties such as foliage cover, rooting depth and water use parameters in order to maximize the Net Carbon Profit (NCP), defined here as the difference between total carbon taken up by photosynthesis minus the carbon invested in construction and maintenance of plant organs. Despite a reduced need for input data, the VOM performed similarly or better than the conventional TBMs in terms of reproducing the seasonal litude and mean annual fluxes recorded by flux towers at the different sites. It had a relative error of 0.08 for the seasonal litude in ET, and was among the best three models tested with the smallest relative error in the seasonal litude of gross primary productivity (GPP). Nevertheless, the VOM displayed some persistent deviations from observations, especially for GPP, namely an underestimation of dry season evapo-transpiration at the wettest site, suggesting that the hydrological assumptions (free drainage) have a strong influence on the results. Furthermore, our study exposes a persistent overprediction of vegetation cover and carbon uptake during the wet seasons by the VOM. Our analysis revealed several areas for improvement in the VOM, including a better representation of the hydrological settings, as well as the costs and benefits related to plant water transport and light capture by the canopy. The results of this study imply that vegetation optimality is a promising approach to explain vegetation dynamics and the resulting fluxes. It provides a way to derive vegetation properties independently from observations, and allows for a more insightful evaluation of model shortcomings as no calibration or site-specific information is required.
Publisher: Springer Science and Business Media LLC
Date: 12-2008
Publisher: Springer Science and Business Media LLC
Date: 19-01-2023
Publisher: Copernicus GmbH
Date: 18-06-2021
Publisher: Royal Zoological Society of New South Wales
Date: 2020
DOI: 10.7882/AZ.2019.030
Abstract: In conservation, consistent and extensive under-funding has necessitated creative thinking to address conservation issues on a low budget, and innovations are burgeoning as a result. One ex le is the use of dogs that, thanks to their heightened olfactory abilities and bond with humans, are trained to detect odours of interest to conservationists. Conservation dogs have proven to repeatedly outperform alternative survey methods in terms of accuracy, efficiency and/or cost. They have now been used for the detection of endangered and invasive species, fauna and flora, direct and indirect (e.g. scat) targets, on land and at sea, across every continent and most taxa from fire ants to whales. Here, we emphasise the versatility of detection dogs through their multiple uses applied to one species, the koala Phascolarctos cinereus . We selected, trained, tested and deployed five dogs two for koala habitat (koala scats), one for genetic s ling (fresh scats only), one for the koala itself and one for koala disease ( Chlamydia spp. ) detection. Dogs enabled both large-scale and fine-scale survey design, with 2370 surveys performed, and 1479 genetic s les collected to date. Detection dogs are subject to similar (although sometimes much lower) limitations in terms of survey biases (e.g. in idual or environmental conditions) and, importantly, detection dog/handler teams need to be tested regularly for accuracy. Nonetheless, detection dogs can, and are, helping researchers and land managers to collect more robust datasets and better inform conservation decisions. Alliances with unexpected partners in conservation (such as with police forces), citizen science, and timeshare use of dogs might improve the democratisation of their use and enable conservation detection dogs to fulfil their astonishing potential.
Publisher: Zenodo
Date: 2020
Publisher: Wiley
Date: 05-02-2016
DOI: 10.1111/PCE.12700
Abstract: A widespread perception is that, with increasing wind speed, transpiration from plant leaves increases. However, evidence suggests that increasing wind speed enhances carbon dioxide (CO 2 ) uptake while reducing transpiration because of more efficient convective cooling (under high solar radiation loads). We provide theoretical and experimental evidence that leaf water use efficiency (WUE, carbon uptake per water transpired) commonly increases with increasing wind speed, thus improving plants' ability to conserve water during photosynthesis. Our leaf‐scale analysis suggests that the observed global decrease in near‐surface wind speeds could have reduced WUE at a magnitude similar to the increase in WUE attributed to global rise in atmospheric CO 2 concentrations. However, there is indication that the effect of long‐term trends in wind speed on leaf gas exchange may be compensated for by the concurrent reduction in mean leaf sizes. These unintuitive feedbacks between wind, leaf size and water use efficiency call for re‐evaluation of the role of wind in plant water relations and potential re‐interpretation of temporal and geographic trends in leaf sizes.
Publisher: Public Library of Science (PLoS)
Date: 25-11-2013
Publisher: Copernicus GmbH
Date: 28-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-8851
Abstract: & & The goals of open science include easy reproducibility of research results, transparency of research methods and re-usability of artefacts, e.g. data, code, and graphics. Consequently, open science is expected to foster scientific collaboration and sustainability of research, as it enables building on each others' methods and results for many years and decades to come.& & & & Here we report about our collective attempts in the last 4-10 years of taking open science to the extreme by using exclusively open formats, open-source software, sharing all stages of our work online and recording workflows and provenance of code and data. Most of our analyses are carried out in Jupyter Notebooks, which are all shared online through gitlab. In these notebooks and our python-analyses, we integrate the python package essm for transparent and easily reproducible mathematical derivations. For more complex analyses, including large model runs, we use the tool Renku of the Swiss Data Science Center in order to record workflows and provenance of code and data.& & & & Find out where we succeeded, where we failed, what we gained and what we lost in pursuing open science to the extreme. Hear about the views and experiences with open science at the undergraduate, postgraduate, postdoc, engineer and senior researcher level. Eventually, we will also report about what we are still missing for entirely reproducible, verifiable, and reusable open science. We hope we can foster a debate about good open science practices, and how we can remove obstacles that are still in our way.& &
Publisher: Wiley
Date: 24-05-2021
DOI: 10.1002/SAJ2.20240
Abstract: Soil compaction by farm machinery may persist for decades, h ering soil productivity and functioning. Assessing compaction costs and guiding recovery strategies are hindered by paucity of data on soil structure recovery rates. A long‐term Soil Structure Observatory was established on a loamy soil in Switzerland to monitor soil structure recovery after prescribed compaction, and to better assess the roles of natural processes (vegetation, macrofauna, and shrink–swell cycles) on recovery patterns. The aim of this study was to quantify short‐term soil structure recovery under natural conditions in the presence and absence of plant cover (ley and bare soil). We measured soil porosity and gas and water transport capabilities at 0.1 and 0.3 m depth. Two years after the compaction event, soil physical properties have not recovered to precompaction levels, even within the topsoil. Surprisingly, no differences were observed in the recovery patterns of ley and bare soil treatments. Measurements show that recovery rates differ among soil properties with the most severely affected properties by compaction (permeability) exhibiting highest recovery rates. Total soil porosity shows no recovery trend, suggesting lack of soil decompaction. Improved soil functions and decompaction are distinct aspects of soil structure recovery, with the latter requiring net upward transport of soil mass. We suggest that soil structure recovery proceeds at two fronts: from the soil surface downward, and expanding around local biologically‐active pockets (marked by biopores) into the compacted soil volumes. This concept could be tested with additional data of longer time series at our site as well as in other soils and climates.
Publisher: Copernicus GmbH
Date: 26-11-2014
DOI: 10.5194/HESS-18-4635-2014
Abstract: Abstract. According to Dooge (1986) intermediate-scale catchments are systems of organized complexity, being too organized and yet too small to be characterized on a statistical/conceptual basis, but too large and too heterogeneous to be characterized in a deterministic manner. A key requirement for building structurally adequate models precisely for this intermediate scale is a better understanding of how different forms of spatial organization affect storage and release of water and energy. Here, we propose that a combination of the concept of hydrological response units (HRUs) and thermodynamics offers several helpful and partly novel perspectives for gaining this improved understanding. Our key idea is to define functional similarity based on similarity of the terrestrial controls of gradients and resistance terms controlling the land surface energy balance, rainfall runoff transformation, and groundwater storage and release. This might imply that functional similarity with respect to these specific forms of water release emerges at different scales, namely the small field scale, the hillslope, and the catchment scale. We thus propose three different types of "functional units" – specialized HRUs, so to speak – which behave similarly with respect to one specific form of water release and with a characteristic extent equal to one of those three scale levels. We furthermore discuss an experimental strategy based on exemplary learning and replicate experiments to identify and delineate these functional units, and as a promising strategy for characterizing the interplay and organization of water and energy fluxes across scales. We believe the thermodynamic perspective to be well suited to unmask equifinality as inherent in the equations governing water, momentum, and energy fluxes: this is because several combinations of gradients and resistance terms yield the same mass or energy flux and the terrestrial controls of gradients and resistance terms are largely independent. We propose that structurally adequate models at this scale should consequently disentangle driving gradients and resistance terms, because this optionally allows equifinality to be partly reduced by including available observations, e.g., on driving gradients. Most importantly, the thermodynamic perspective yields an energy-centered perspective on rainfall-runoff transformation and evapotranspiration, including fundamental limits for energy fluxes associated with these processes. This might additionally reduce equifinality and opens up opportunities for testing thermodynamic optimality principles within independent predictions of rainfall-runoff or land surface energy exchange. This is pivotal to finding out whether or not spatial organization in catchments is in accordance with a fundamental organizing principle.
Publisher: Zenodo
Date: 2017
Publisher: Copernicus GmbH
Date: 23-03-2020
DOI: 10.5194/EGUSPHERE-EGU2020-10740
Abstract: & & Vegetation properties such as rooting depths and vegetation cover play a key role in coupling ecological and hydrological processes. These properties are however highly variable in space and/or time and their parametrization generally poses challenges for terrestrial biosphere models (Whitley et al., 2016). Models often use static values for dynamic vegetation properties or prescribe values based on observations, such as remotely sensed leaf area index. Here, vegetation optimality provides a way forward in order to predict such vegetation properties and their response to environmental change (Schymanski et al., 2015).& & & & In this study, we explore the utility of a combined water-vegetation model, the Vegetation Optimality Model (VOM, Schymanski et al., 2009), to predict vegetation properties such as rooting depths, foliage cover, photosynthetic capacity and water use strategies. The VOM schematizes perennial trees and seasonal grasses each as a single big leaf with an associated root system and optimizes leaf and root system properties in order to maximize the Net Carbon Profit, i.e. the difference between the total carbon taken up by photosynthesis and all the carbon costs related to the construction and maintenance of the plant organs involved. The VOM was applied along the North-Australian Tropical Transect, which consists of six savanna sites equipped with flux towers along a strong rainfall gradient between 500 and 1700 mm per year. The multi-annual half-hourly measurements of evaporation and CO& sub& & /sub& -assimilation at the different sites were used here to evaluate the model.& & & & The VOM produced similar or better results than more traditional models even though it requires much less information about site-specific vegetation properties. However, we found a persistent bias in the predicted vegetation cover. More detailed numerical experiments revealed a likely misrepresentation of the foliage costs in the model, which are based on a linear relation between leaf area and fractional vegetation cover. This finding, and the already favourable comparison with traditional models, implies that optimization of vegetation properties for Net Carbon Profit is a very promising approach for predicting the soil-vegetation-atmosphere exchange of water and carbon in complex ecosystems such as savannas.& & & & & strong& References& br& & /strong& Schymanski, S.J., Roderick, M.L., Sivapalan, M., 2015. Using an optimality model to understand medium and long-term responses of vegetation water use to elevated atmospheric CO2 concentrations. AoB PLANTS 7, plv060. 0.1093/aobpla lv060& & & & Schymanski, S.J., Sivapalan, M., Roderick, M.L., Hutley, L.B., Beringer, J., 2009. An optimality& #8208 based model of the dynamic feedbacks between natural vegetation and the water balance. Water Resources Research 45. 0.1029/2008WR006841& & & & Whitley, R., Beringer, J., Hutley, L.B., Abramowitz, G., De Kauwe, M.G., Duursma, R., Evans, B., Haverd, V., Li, L., Ryu, Y., Smith, B., Wang, Y.-P., Williams, M., Yu, Q., 2016. A model inter-comparison study to examine limiting factors in modelling Australian tropical savannas. Biogeosciences 13, 3245& #8211 . 0.5194/bg-13-3245-2016& &
Publisher: Copernicus GmbH
Date: 14-12-2022
DOI: 10.5194/HESS-26-6289-2022
Abstract: Abstract. The Budyko framework puts the long-term mean annual evapotranspiration (ET) of a catchment in relation to its maximum possible value determined by the conservation of mass (ET cannot exceed mean annual precipitation) and energy (ET can not exceed mean annual net radiation) in the absence of significant storage contributions. Most catchments plot relatively close to this physical limit, which allowed the development of an empirical equation (often referred to as the Budyko curve) for estimating mean annual evaporation and runoff from observed net radiation and precipitation. Parametric forms of the curve often use a shape parameter, n, that is seen as a catchment characteristic. However, a satisfying explanation for the convergence and self-organization of catchments around such an empirical curve is still lacking. In this study, we explore if vegetation optimality can explain the convergence of catchments along a Budyko curve and in how far can n be seen as a catchment characteristic. The Vegetation Optimality Model (VOM) optimizes vegetation properties and behavior (e.g., rooting depths, vegetation cover, stomatal control) to maximize the difference between the total carbon taken up from the atmosphere and the carbon used for maintenance of plant tissues involved in its uptake, i.e., the long-term net carbon profit (NCP). This optimization is entirely independent of observed ET and hence the VOM does not require calibration for predicting ET. In a first step, the VOM was fully optimized for the observed atmospheric forcing at five flux tower sites along the North Australian Tropical Transect, as well as 36 additional locations near the transect and six Australian catchments. In addition, the VOM was run without vegetation for all sites, meaning that all precipitation was partitioned into soil evaporation and runoff. For comparison, three conceptual hydrological models (TUWmodel, GR4J, and FLEX) were calibrated for the Australian catchments using the observed precipitation and runoff. Subsequently, we emulated step changes in climate by multiplying precipitation (P) by factors ranging between 0.2 and 2 before running the VOM and hydrological models without changing the vegetation properties or model parameters, emulating invariant catchment characteristics under a changed climate. In a last step, the VOM was re-optimized for the different P amounts, allowing vegetation to adapt to the new situation. Eventually, Budyko curves were fit by adapting the parameter n to the model results. This was carried out for both multiple sites simultaneously and for each in idual study site, thereby assuming that n is a site-specific characteristic. The optimized VOM runs tracked relatively close to a Budyko curve with a realistic n value and close to observations, whereas the runs without vegetation led to significantly lower evaporative fractions and unrealistically low n values compared with literature. When fitting n to in idual catchments, changes in P led to changes in n (increasing n for decreasing P) in all model runs (including the three conceptual models) except if the VOM was re-optimized for each change in P, which brought the value of n back close to its value for the unperturbed P in each catchment. For the re-optimized VOM runs, the variation in n between catchments was greater than within each catchment in response to multiplications of P with a factor 0.2 to 2. These findings suggest that optimality may explain the self-organization of catchments in Budyko space, and that the accompanying parameter n does not remain constant for constant catchment and vegetation conditions as hypothesized in the literature, but in fact emerges through the adaptation of vegetation to climatic conditions in a given hydrological setting. Moreover, the results suggest that n might initially increase in response to suddenly reduced P, and only slowly returns to its original, catchment-specific value, as vegetation re-adjusts to the new climate over decades and centuries. This may constitute a new basis for the evaluation and prediction of catchment responses to climatic shifts.
Publisher: Copernicus GmbH
Date: 17-06-2008
Abstract: Abstract. The main processes determining soil moisture dynamics are infiltration, percolation, evaporation and root water uptake. Modelling soil moisture dynamics therefore requires an interdisciplinary approach that links hydrological, atmospheric and biological processes. Previous approaches treat either root water uptake rates or root distributions and transpiration rates as given, and calculate the soil moisture dynamics based on the theory of flow in unsaturated media. The present study introduces a different approach to linking soil water and vegetation dynamics, based on vegetation optimality. Assuming that plants have evolved mechanisms that minimise costs related to the maintenance of the root system while meeting their demand for water, we develop a model that dynamically adjusts the vertical root distribution in the soil profile to meet this objective. The model was used to compute the soil moisture dynamics, root water uptake and fine root respiration in a tropical savanna over 12 months, and the results were compared with observations at the site and with a model based on a fixed root distribution. The optimality-based model reproduced the main features of the observations such as a shift of roots from the shallow soil in the wet season to the deeper soil in the dry season and substantial root water uptake during the dry season. At the same time, simulated fine root respiration rates never exceeded the upper envelope determined by the observed soil respiration. The model based on a fixed root distribution, in contrast, failed to explain the magnitude of water use during parts of the dry season and largely over-estimated root respiration rates. The observed surface soil moisture dynamics were also better reproduced by the optimality-based model than the model based on a prescribed root distribution. The optimality-based approach has the potential to reduce the number of unknowns in a model (e.g. the vertical root distribution), which makes it a valuable alternative to more empirically-based approaches, especially for simulating possible responses to environmental change.
Publisher: Wiley
Date: 13-10-2019
DOI: 10.1111/ACV.12455
Publisher: Copernicus GmbH
Date: 23-09-2016
Publisher: Copernicus GmbH
Date: 26-10-2016
Publisher: Zenodo
Date: 2017
Publisher: Wiley
Date: 02-11-2022
Publisher: Copernicus GmbH
Date: 02-02-2017
Abstract: Abstract. The Penman–Monteith (PM) equation is commonly considered the most advanced physically based approach to computing transpiration rates from plants considering stomatal conductance and atmospheric drivers. It has been widely evaluated at the canopy scale, where aerodynamic and canopy resistance to water vapour are difficult to estimate directly, leading to various empirical corrections when scaling from leaf to canopy. Here, we evaluated the PM equation directly at the leaf scale, using a detailed leaf energy balance model and direct measurements in a controlled, insulated wind tunnel using artificial leaves with fixed and predefined stomatal conductance. Experimental results were consistent with a detailed leaf energy balance model however, the results revealed systematic deviations from PM-predicted fluxes, which pointed to fundamental problems with the PM equation. Detailed analysis of the derivation by Monteith(1965) and subsequent amendments revealed two errors: one in neglecting two-sided exchange of sensible heat by a planar leaf, and the other related to the representation of hypostomatous leaves, which are very common in temperate climates. The omission of two-sided sensible heat flux led to bias in simulated latent heat flux by the PM equation, which was as high as 50 % of the observed flux in some experiments. Furthermore, we found that the neglect of feedbacks between leaf temperature and radiative energy exchange can lead to additional bias in both latent and sensible heat fluxes. A corrected set of analytical solutions for leaf temperature as well as latent and sensible heat flux is presented, and comparison with the original PM equation indicates a major improvement in reproducing experimental results at the leaf scale. The errors in the original PM equation and its failure to reproduce experimental results at the leaf scale (for which it was originally derived) propagate into inaccurate sensitivities of transpiration and sensible heat fluxes to changes in atmospheric conditions, such as those associated with climate change (even with reasonable present-day performance after calibration). The new formulation presented here rectifies some of the shortcomings of the PM equation and could provide a more robust starting point for canopy representation and climate change studies.
Publisher: Copernicus GmbH
Date: 23-03-2020
DOI: 10.5194/EGUSPHERE-EGU2020-4969
Abstract: & & Land surface temperature (LST) is an important variable that controls the energy and water exchange between the Earth& #8217 s surface and the atmosphere. It is widely used to estimate evapo-transpiration and vegetation water stress through surface energy balance models. On a large scale, LST is obtained from space-borne instruments (remote sensing) consisting of radiometers measuring the thermal radiance from the underlying surface& !-- Radiometers don't assume emissivity, it is only used to convert radiometer data to Ts. --& . On the other hand, at plot scale, flux towers record longwave radiation, which can be used to estimate LST locally. The up-welling and down-welling longwave radiation measured by radiometers mounted on the eddy covariance towers can be inverted to deduce LST using the Stefan-Boltzmann law and longwave balance (Eq.1):& & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & L& #8593 = & #949 & #963 T& sub& s& /sub& & sup& & /sup& + (1& #8722 & #949 )L& #8595 (1)& & & & where L& #8593 = upwelling longwave radiation (Wm& sup& & #8722 & /sup& ), L& #8595 = downwelling longwave radiation (Wm& sup& & #8722 & /sup& ), & #949 = surface emissivity, T& sub& s& /sub& = surface temperature (K) and & #963 = Stefan Boltzmann constant (Wm& sup& -2& /sup& K& sup& -4& /sup& ).& & & & Since down-welling longwave radiation was not measured routinely for a long time, the second term in Eq. 1 is commonly omitted, arguing that emissivity is close to unity and therefore Eq. 1 can be approximated by Eq. 2:& & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & & L& #8593 = & #949 & #963 T& sub& s& /sub& & sup& & /sup& (2)& & & & Even with the availability of down-welling longwave measurements it is very common to use Eq. 2. This gives rise to the query if the simplified equation is adequate to estimate LST from flux tower measurements. Another question associated with this method is how to obtain the correct surface emissivity (SE) values needed for LST retrievals.& & & & The present work addresses these two important issues by using FLUXNET data for different land cover types (mulga, tropical savanna, and eucalyptus forest). SE was estimated by comparing measured sensible heat flux (H) with estimated radiometric surface-air temperature difference (& #916 T) and assuming that & #916 T=0 if H=0 (Holmes et al., 2009). Our FLUXNET-based estimate of LST and SE was compared with space-borne measurements (MODIS). We found that LST values obtained using Eq. 1 were more strongly correlated with MODIS (MOD11) estimates, compared to Eq. 2. However, the SE derived using Eq. 1 was much lower than the MODIS emissivities, whereas surface emissivity based on Eq. 2 was very close to the MODIS values. Generally, we found that, even at the high emissivity values taken from MODIS, the estimated LST values differed significantly (2 K or more) between the two equations for all ecosystems.& & & & Considering that Eq. 1 physically correct equation, whereas Eq. 2 is an approximation, our analysis suggests that results based on Eq. 2 are likely biased and should be considered with caution. It further questions the implication of large scale SE at plot scale.& & & & & & & & & & br& & br& & & & & References:& & & & & & Holmes, T. R. H., Jeu, R. A. M. D., Owe, M., & Dolman, A. J. (2009). Land surface temperature from Ka band (37 GHz) passive microwave observations. & em& Journal of Geophysical Research: Atmospheres& /em& , & em& & /em& (D4). 0.1029/2008JD010257& & & / & & & & br& & br& & & & & & br& & br& & & & & & br& & br& & & & & & br& & br& & &
Publisher: Wiley
Date: 29-06-2020
DOI: 10.1111/MEC.15488
Publisher: Oxford University Press (OUP)
Date: 2015
Publisher: Copernicus GmbH
Date: 23-03-2020
DOI: 10.5194/EGUSPHERE-EGU2020-8084
Abstract: & & Thermodynamic optimality principles, such as maximum entropy production or maximum power extraction, hold a great promise to help explain self-organisation of various compartments of planet Earth, including the climate system, catchments and ecosystems. There is a growing number of ex les for more or less successful use of these principles in earth system science, but a common systematic approach to the formulation of the relevant system boundaries, state variables and exchange fluxes has not yet emerged. Here we present a blueprint for the thermodynamically consistent formulation of box models and rigorous testing of optimality principles, in particular the maximum entropy production (MEP) and the maximum power (MP) principle. We investigate under what conditions these principles can be used to predict energy transfer coefficients across internal system boundaries and demonstrate that, contrary to common perception, these principles do not lead to similar predictions if energy and entropy balances are explicitly considered for the whole system and the defined sub-systems. We further highlight various pitfalls that may result in thermodynamically inconsistent models and potentially wrong conclusions about the implications of thermodynamic optimality principles.& & br& The analysis is performed in an open source mathematical framework, using the notebook interface Jupyter, the programming language Python, Sympy and a newly developed package for Python, & quot Environmental Science using Symbolic Math& quot (ESSM, nvironmentalscience/essm). This ensures easy verifiability of the results and enables users to re-use and modify variable definitions, equations and mathematical solutions to suit their own thermodynamic problems.& & &
Publisher: Wiley
Date: 17-09-2007
DOI: 10.1111/J.1365-3040.2007.01728.X
Abstract: Photosynthesis provides plants with their main building material, carbohydrates, and with the energy necessary to thrive and prosper in their environment. We expect, therefore, that natural vegetation would evolve optimally to maximize its net carbon profit (NCP), the difference between carbon acquired by photosynthesis and carbon spent on maintenance of the organs involved in its uptake. We modelled N(CP) for an optimal vegetation for a site in the wet-dry tropics of north Australia based on this hypothesis and on an ecophysiological gas exchange and photosynthesis model, and compared the modelled CO2 fluxes and canopy properties with observations from the site. The comparison gives insights into theoretical and real controls on gas exchange and canopy structure, and supports the optimality approach for the modelling of gas exchange of natural vegetation. The main advantage of the optimality approach we adopt is that no assumptions about the particular vegetation of a site are required, making it a very powerful tool for predicting vegetation response to long-term climate or land use change.
Publisher: Copernicus GmbH
Date: 23-09-2022
DOI: 10.5194/IAHS2022-609
Abstract: & & Open science is high on the agenda of academic, national, and intergovernmental organizations because of its commitment to transparency and reproducibility. Transparent and inclusive research practices facilitate reproducibility and collaboration while improving research accessibility, attribution, governance, and community-driven support for marginalized researchers and stakeholders not usually included or credited in research. Hydrology is an inter- and multi-disciplinary science that integrates qualitative and quantitative data (field, lab, models, etc.) to address human life and natural ecosystems issues. Research progress in hydrology depends on accessibility of research output, like data, code, and publications. This necessitates openness & #8211 documentation and sharing of one& #8217 s research process, including definitions, motivations, justifications and assumptions, practices, and methods.& & & & One fundamental step toward a more inclusive and erse research community is to create equal access to knowledge for all hydrologists across the globe. Open science can facilitate equitable advancement and innovation to solve challenges and work towards the United Nations Sustainable Development Goals. To address barriers to starting or advancing one& #8217 s open science practices, we introduced the & em& Open Hydrology Principles& /em& (Hall et al., 2021, HESS) and practical guide for hydrology researchers. We discuss the benefits and share tips to engaging in open science by focusing on four principal themes related to (1) & em& Open Research Process and Approach& /em& , (2) & em& Open Data& /em& , (3) & em& Open Software Development and Use& /em& , and (4) & em& Open Publishing& /em& . We hope that this guide enriched with practical advice (tips, tools, and resources) will help strengthen inclusivity and ersity in hydrology and globally inspire more hydrologists to pursue open science. We encourage everyone to contribute to the community-supported repository of open hydrology resources at open-hydrology.github.io/. & & & &
Publisher: Copernicus GmbH
Date: 18-06-2021
DOI: 10.5194/GMD-2021-151
Abstract: Abstract. The Vegetation Optimality Model (VOM, Schymanski et al., 2009, 2015) is an optimality-based, coupled water-vegetation model that predicts vegetation properties and behaviour based on optimality theory, rather than calibrating vegetation properties or prescribing them based on observations, as most conventional models do. In order to determine wheter optimality theory can alleviate common shortcomings of conventional models, as identified in a previous model inter-comparison study along the North Australian Tropical Transect (NATT) (Whitley et al., 2016), a range of updates to previous applications of the VOM have been made for increased generality and improved comparability with conventional models. To assess in how far the updates to the model and input data would have affected the original results, we implemented them one-by-one while reproducing the analysis of Schymanski et al. (2015). The model updates included extended input data, the use of variable atmospheric CO2-levels, modified soil properties, implementation of free drainage conditions, and the addition of grass rooting depths to the optimized vegetation properties. A systematic assessment of these changes was carried out by adding each in idual modification to the original version of the VOM at the flux tower site of Howard Springs, Australia. The analysis revealed that the implemented changes affected the simulation of mean annual evapo-transpiration (ET) and gross primary productivity (GPP) by no more than 20 %, with the largest effects caused by the newly imposed free drainage conditions and modified soil texture. Free drainage conditions led to an underestimation of ET and GPP, whereas more fine-grained soil textures increased the water storage in the soil and resulted in increased GPP. Although part of the effect of free drainage was compensated for by the updated soil texture, when combining all changes, the resulting effect on the simulated fluxes was still dominated by the effect of implementing free drainage conditions. Eventually, the relative error for the mean annual ET, in comparison with flux tower observations, changed from an 8.4 % overestimation to an 10.2 % underestimation, whereas the relative errors for the mean annual GPP stayed similar with a change from 17.8 % to 14.7 %. The sensitivity to free drainage conditions suggests that a realistic representation of groundwater dynamics is very important for predicting ET and GPP at a tropical open-forest savanna site as investigated here. The modest changes in model outputs highlighted the robustness of the optimization approach that is central to the VOM architecture.
Publisher: Copernicus GmbH
Date: 27-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-5798
Abstract: & & A large part of photosynthetically fixed carbon is translocated below-ground in order to construct and maintain the roots needed to supply the shoot with adequate water and nutrients. However, the amount of carbon translocated below-ground is not easily quantified, as an unknown part is lost as root respiration, which is not easily distinguished from microbial soil respiration.& & & & Here we present a novel plant growth chamber enabling continuous and separate monitoring of above-ground and below-ground gas exchange. The above-ground compartment is separated from the soil compartment by an impermeable fat layer, and a custom-developed carbon-free soil substrate is used to eliminate CO& sub& & /sub& release due to microbial decomposition of pre-existing soil carbon. Each compartment of the growth chamber is connected to an infrared gas analyzer, enabling simultaneous monitoring of above-ground and below-ground fluxes. A novel experimental approach using chemical agents was employed to test if CO& sub& & /sub& uptake and release was adequately quantified in each compartment over several days.& & & & In a pilot experiment performed to identify a suitable carbon-free soil, maize plants grown at a 20% volumetric water content, 1.3g/cm& sup& & /sup& bulk density and a 14h/10h day/night regime showed a correlation between evapo-transpiration and root length but not with root biomass, suggesting that the cost/benefit ratio of root allocation may be more related to root respiration and mechanical energy expenditure than accumulated root biomass. In fact, our preliminary results suggest that cumulative root respiration over 2 weeks was of a similar order of magnitude as the carbon stored in the root system at the end of the experiment, and that root respiration rates were relatively similar to nocturnal shoot respiration rates. A detailed analysis is underway and will be presented during the conference.& &
Publisher: Wiley
Date: 03-2016
Publisher: Copernicus GmbH
Date: 23-03-2020
DOI: 10.5194/EGUSPHERE-EGU2020-9177
Abstract: & & Scientific theory is commonly formulated in the form of mathematical equations and new theory is often derived from a set of pre-existing equations. Most of us have experienced difficulty in following mathematical derivations in scientific publications and even more so their transfer into numerical algorithms that eventually result in quantitative tests and data plots. The Python package Environmental Science using Symbolic Math (ESSM, nvironmentalscience/essm) offers an open and transparent way to (a) verify derivations in the literature, (b) ensure dimensional consistency of the equations, (c) perform symbolic derivations, and (d) transfer mathematical equations into numerical code, perform computations and (e) generate plots.& & & & Here we present an ex le workflow using jupyter notebooks illustrating the capabilities of the package from (a) to (e), including recently added advanced features.& &
Publisher: Copernicus GmbH
Date: 03-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-1300
Abstract: & & The Budyko-framework is widely used to assess the water balance of catchments, with large catchments worldwide converging to a constrained set of empirical curves. Ongoing research focuses on explaining deviations of catchments from the Budyko-curve, implying that local characteristics, such as hydrological settings and land use, determine an in idual curve for each catchment, along which the catchment travels in response to climatic variability. Here we use vegetation optimality to explain convergence on the Budyko-curve and assess if the Vegetation Optimality Model (VOM, Schymanski et al., 2009) and three conceptual hydrological models support the assumption that catchments follow in idual Budyko-curves as climate varies.& & & & The VOM optimizes vegetation properties, such as rooting depths and vegetation cover, for maximum Net Carbon Profit (NCP), i.e. the difference between the total amount of CO& sub& & /sub& assimilated from the atmosphere and the carbon costs for maintenance and respiration of plants. In this sense, the VOM represents vegetation water use as the result of ecological adaptation, while the conceptual hydrological models lump water use into a set of calibration parameters. The following research questions were investigated:& & & & - Does vegetation optimality lead to convergence of catchments on the Budyko-curve?& & & & - Does modelled catchment response to changing precipitation follow a catchment-specific Budyko-curve?& & & & The VOM was applied at five flux tower sites, as well as 36 additional points, along the North Australian Tropical Transect, following a strong precipitation gradient from north to south, and six other catchments in Australia. Beside the VOM, three conceptual hydrological models were applied to the Australian catchments for comparison. In a final step, these hydrological models were run for a selection of catchments in the contiguous United States to generalize the results from Australia.& & & & For each site, the vegetation parameters of the VOM were optimized for maximum NCP, while the conceptual models were calibrated to reproduce observed streamflow. The simulated water balances were used to generate in idual Budyko-curves for each site and model run. Subsequently, rainfall was stepwise increased or decreased and the models were re-run to test if each site would stay on its curve. In a second step, the vegetation was re-optimized in the VOM to simulate vegetation response to the new precipitation and the resulting water balance was again plotted on the Budyko-curve.& & & & The in idual Budyko-curves were consistently different for the different precipitation amounts, indicating that modelled responses do not follow a catchment-specific curve. Conversely, if vegetation was re-optimized in the VOM for each rainfall scenario, the different scenarios converged to a single curve for each study site. In other words, adjusting the vegetation to maximize the NCP made the study sites converge back to the initial Budyko-curve. This indicates that convergence onto a Budyko-curve and tracking along a catchment-specific Budyko-curve may not be due to physical constraints, as commonly assumed, but the result of biological adaptation to the environment.& & & & & strong& References& /strong& & & & & Schymanski, S.J., Sivapalan, M., Roderick, M.L., Hutley, L.B., Beringer, J., 2009. An optimality& #8208 based model of the dynamic feedbacks between natural vegetation and the water balance. Water Resources Research 45. 0.1029/2008WR006841& &
Publisher: Springer Science and Business Media LLC
Date: 10-02-2015
DOI: 10.1038/SREP08349
Abstract: Accurate data on presence/absence and spatial distribution for fauna species is key to their conservation. Collecting such data, however, can be time consuming, laborious and costly, in particular for fauna species characterised by low densities, large home ranges, cryptic or elusive behaviour. For such species, including koalas ( Phascolarctos cinereus ), indicators of species presence can be a useful shortcut: faecal pellets (scats), for instance, are widely used. Scat surveys are not without their difficulties and often contain a high false negative rate. We used experimental and field-based trials to investigate the accuracy and efficiency of the first dog specifically trained for koala scats. The detection dog consistently out-performed human-only teams. Off-leash, the dog detection rate was 100%. The dog was also 19 times more efficient than current scat survey methods and 153% more accurate (the dog found koala scats where the human-only team did not). This clearly demonstrates that the use of detection dogs decreases false negatives and survey time, thus allowing for a significant improvement in the quality and quantity of data collection. Given these unequivocal results, we argue that to improve koala conservation, detection dog surveys for koala scats could in the future replace human-only teams.
Publisher: Oxford University Press (OUP)
Date: 09-05-2022
Abstract: Resource competition among conspecifics is central to social evolution, as it serves as one of the primary selective pressures of group living. This is because the degree of competition for resources impacts the costs and benefits of social interactions. Despite this, how heterogeneity in resource competition drives variation in the type and quantity of long-term social relationships in iduals foster has been overlooked. By measuring male mating competition and female foraging competition in a highly social, long-lived mammal, we demonstrate that in idual variation in long-term intrasexual social relationships covaries with preferred habitat and experienced resource competition, and this effect differs based on the sex of the in idual. Specifically, greater resource competition resulted in fewer social preferences, but the magnitude of the effect varied by both habitat and sex, whereas for social avoidances, both the directionality and magnitude of the effect of resource competition varied by habitat and sex. Together our work shows how fine-scale variation in in idual socioecological niches (i.e., unique physical and social environments) can drive extensive variation in in idual social behavior (here long-term relationships) within a population, thereby broadening current theories of social evolution.
Publisher: Copernicus GmbH
Date: 15-05-2023
DOI: 10.5194/EGUSPHERE-EGU23-12489
Abstract: Open science is commonly associated with open access publications, and FAIR (findable, accessible, interoperable and reusable) data. Open source code is progressively being considered an essential component of open science, too. However, even if all these ingredients are available and openly accessible, it is often impossible to reproduce the graphs in a paper from the data and code provided. Which script was used on what part of the data to generate a given plot? Which version of a cited database was used, and what query to extract the presented data points? Moreover, even the basic steps of a scientific analysis, i.e. the derivation of mathematical equations, are often not traceable. Ever came across the famous & #8220 it follows that& #8221 , where, what follows, contains variables that were not present in the preceding equations?Here I present part of a hydrology course based on a framework designed to address many of the above challenges. It is based on the open-source RENKU platform and deployed in a Jupyterhub instance at renkulab.io. RENKU enables the tracking of datasets and their versions, and records executions of code with their respective input and output files, producing a knowledge graph of the entire project and enabling the user to easily re-do all necessary steps to update relevant results whenever a data or code file is updated. RENKULAB uses the docker system to help reproduce the computational environment needed to re-execute the analysis. This greatly facilitates collaborative research and learning, as it removes the need for collaborators and students to recreate the computational environment in their local systems. Integration of GITLAB in RENKULAB facilitates student feedback and collaborative problem solving through issue tracking, where students can gain points by submitting meaningful issues and helping others.The course also uses an open source package for mathematical derivations (ESSM, essm.readthedocs.org), which is based on the Python package Sympy, and facilitates clear definitions of variables including their dimensions and units, and dimensionally consistent fundamental equations. These can then be used to deduce derived equations by automatic solving of systems of equations for unknown variables, derivatives, integrations, and many other mathematical operations contained in Sympy. The package combines graphical depiction of equations, as seen in papers, with computational reproducibility of derivations and transparent re-use of equations in numerical code.By employing Open Science approaches from the start, students become naturally accustomed to reproducible research and can use the skills they learn in any professional environments, as they are not bound to proprietary software that their future employers and collaborators may or may not have purchased licenses for.
Publisher: Wiley
Date: 21-10-2009
DOI: 10.1002/0470848944.HSA319
Abstract: Hydrological systems are governed by an incredible wealth of interactive processes, ranging from small‐scale processes within the soil domain such as unsaturated flow, bioturbation, and root water uptake to large‐scale feedbacks between the water balance and the global atmospheric circulation. Optimality approaches aim toward a simpler and more general representation of hydrological systems. As the hydrology of land is strongly affected by the presence of vegetation, these optimality approaches generally need to be explored in the context of how purely hydrological processes are linked to ecological processes. This article summarizes the different optimality assumptions that have been used to describe ecohydrological processes and how these are related to each other. Most approaches can be classified as either physical or ecological optimality. A range of ex les are given for applying optimality approaches at various temporal and spatial scales, ranging from the scale of in idual leaves and how they control water loss in relation to carbon uptake to the larger scale attributes of vegetation types, ecosystem properties, and river basin networks. The article concludes with a discussion of the usefulness of optimality approaches and their advantages as well as their disadvantages and the need for improvement.
Publisher: Copernicus GmbH
Date: 23-08-2016
Publisher: Copernicus GmbH
Date: 03-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-3962
Abstract: & & The surface energy balance (SEB) is defined as the balance between incoming energy from the sun and outgoing energy from the Earth& #8217 s surface. All components of the SEB depend on land surface temperature (LST). Therefore, LST is an important state variable that controls the energy and water exchange between the Earth& #8217 s surface and the atmosphere. LST can be estimated radiometrically, based on the infrared radiance emanating from the surface. At the landscape scale, LST is derived from thermal radiation measured using& satellites.& At the plot scale, eddy covariance flux towers commonly record downwelling and upwelling longwave radiation, which can be inverted to retrieve LST& using the grey body equation :& br& & & & & & & & & & & & & R& sub& lup& /sub& = & #949 & #963 T& sub& s& /sub& & sup& & /sup& + (1 & #8722 & #949 ) R& sub& ldw& & & & & & & & & /sub& (1)& br& where R& sub& lup& /sub& is the upwelling longwave radiation, R& sub& ldw& /sub& is the downwelling longwave radiation, & #949 is the surface emissivity, & em& T& sub& s& /sub& & & /em& is the surface temperature and & #963 & is the Stefan-Boltzmann constant. The first term is the temperature-dependent part, while the second represents reflected longwave radiation. Since in the past downwelling longwave radiation was not measured routinely using flux towers, it is an established practice to only use upwelling longwave radiation for the retrieval of plot-scale LST, essentially neglecting the reflected part and shortening Eq. 1 to:& br& & & & & & & & & & & & & & & R& sub& lup& /sub& = & #949 & #963 T& sub& s& /sub& & sup& & /sup& & & & & & & & & & & & & (2)& br& Despite& widespread availability of downwelling longwave radiation measurements, it is still common to use the short equation (Eq. 2) for in-situ LST retrieval. This prompts the question if ignoring the downwelling longwave radiation introduces a bias in LST estimations from tower measurements. Another associated question is how to obtain the correct & #949 needed for in-situ LST retrievals using tower-based measurements.& br& The current work addresses these two important science questions using observed fluxes at eddy covariance towers for different land cover types. Additionally, uncertainty in retrieved LST and emissivity due to uncertainty in input fluxes was quantified using SOBOL-based uncertainty analysis (SALib). Using landscape-scale emissivity obtained from satellite data (MODIS), we found that the LST& obtained using the complete equation (Eq. 1) is 0.5 to 1.5 K lower than the short equation (Eq. 2). Also, plot-scale emissivity was estimated using observed sensible heat flux and surface-air temperature differences. Plot-scale emissivity obtained using the complete equation was generally between 0.8 to 0.98 while the short equation gave values between 0.9 to 0.98, for all land cover types. Despite additional input data for the complete equation, the uncertainty in plot-scale LST was not greater than if the short equation was used. Landscape-scale daytime LST obtained from satellite data (MODIS TERRA) were strongly correlated with our plot-scale estimates, but on average higher by 0.5 to 9 K, regardless of the equation used. However, for most sites, the correspondence between MODIS TERRA LST and retrieved plot-scale LST estimates increased significantly if plot-scale emissivity was used instead of the landscape-scale emissivity obtained from satellite data.& &
Publisher: Copernicus GmbH
Date: 23-03-2020
DOI: 10.5194/EGUSPHERE-EGU2020-2675
Abstract: & & Usually hydraulic conductance and vulnerability are measured under extreme conditions never experienced by living plants (e. g. centrifugation, bench dehydration, and large pressure gradients). A common factor that is known to inhibit the water transport in plants is cavitation, which is believed to occur either by air entry through the pit valves on the walls of the xylem, or by ex-solution of dissolved gases, or vaporization of water at very low pressures. Various physical characteristics of the xylem influence the efficiency of transport and the vulnerability to cavitation.& & & & Here we explore possibilities to measure hydraulic conductance and induce cavitation under close to natural conditions. We designed a very simple & #8220 artificial plant& #8221 consisting of a root and a transpiring membrane, equipped with pressure and flow meters, where a twig can be inserted in the flow path to measure its hydraulic conductance. Attempts to induce cavitation resulted in surprising results, provoking new questions on the role of xylem structural traits and their relevance for water transport in plants.& &
Publisher: Elsevier BV
Date: 05-2012
Publisher: Copernicus GmbH
Date: 03-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-605
Abstract: & & To have lasting impact on the scientific community and broader society, hydrologic research must be open, accessible, reusable, and reproducible. With so many different perspectives on and constant evolution of open science approaches and technologies, it can be overwhelming for hydrologists to start down the path towards or grow one& #8217 s own push for open research. Open hydrology practices are becoming more widely embraced by members of the community and key organizations, yet, technical (e.g., limited coding experience), resource (e.g., open access fees), and social barriers (e.g., fear of being scooped) still exist. These barriers may seem insurmountable without practical suggestions on how to proceed. Here, we propose the Open Hydrology Principles to guide in idual and community progress toward open science. To increase accessibility and make the Open Hydrology Principles more tangible and actionable, we also present the Open Hydrology Practical Guidelines. Our aim is to help hydrologists transition from closed, inaccessible, not reusable, and not reproducible ways of conducting scientific work to open hydrology and empower researchers by providing information and resources to equitably grow the openness of hydrological sciences. We provide the first version of a practical open hydrology resource that may evolve with open science infrastructures, workflows, and research experiences. We discuss some of the benefits of open science and common reservations to open science, and how hydrologists can pursue an appropriate level of openness in the presence of barriers. Further, we highlight how the practice of open hydrology can be expanded. The Open Hydrology Principles, Practical Guide, and additional resources reflect our knowledge of the current state of open hydrology and we recognize that recommendations and suggestions will evolve. Therefore, we encourage hydrologists all over the globe to join the open science conversation by contributing to the living version of this document and sharing open hydrology resources at the community-supported repository at open-hydrology.github.io.& &
Publisher: Copernicus GmbH
Date: 23-03-2020
DOI: 10.5194/EGUSPHERE-EGU2020-9228
Abstract: & & Numerical experiments become more and more complex, resulting in workflows that are hard to repeat or reproduce. Even though many journals and funding agencies now require open access to data and model code, the linkages between these elements are often still poorly documented or even completely missing. The software platform Renku (renkulab.io/), developed by the Swiss Data Science Center, aims at improving reproducibility and repeatability of the entire scientific workflow. Data, scripts and code are stored in an online repository, and Renku records explicitly all the steps from data import to the generation of final plots, in the form of a knowledge graph. In this way, all output files have a history attached, including linkages to scripts and input files used generate them. Renku can visualize the knowledge graph, to show all scientific links between inputs, outputs, scripts and models. It enables easy re-use and reproduction of the entire workflow or parts thereof.& & & & In the test case presented here, the Vegetation Optimality Model (VOM, Schymanski et al., 2009) is applied along six study sites of the North-Australian Tropical Transect to simulate observed canopy-atmosphere exchange of water and carbon dioxide. The VOM optimizes vegetation properties, such as rooting depths and canopy properties, in order to maximize the Net Carbon Profit, i.e. the total carbon taken up by photosynthesis minus all the carbon costs of the plant organs involved. The vegetation is schematized as one big leaf for trees and one leaf for seasonal grasses, and is combined with a water balance model. Flux tower measurements of evaporation and CO2-assimilation, and remotely sensed vegetation cover are used for model evaluation, in addition to meteorological data as input for the model. A numerical optimization, the Shuffled Complex Evolution, is used to optimize the vegetation properties for each in idual site by repeatedly running the model with different parametrizations and computing the net carbon profit over 20 years. The optimization was repeated several times for each site to analyze the sensitivity of the results to a range of different input parameters.& & & & This case demonstrates an ex le of a complex numerical experiment with all its associated challenges concerning documenting model choices, large datasets and a variety of pre- and post- processing steps. Renku assured the repeatability and reproducibility of this experiment, by documenting this in a proper and systematic way. We demonstrate how Renku helped us to repeat analyses and update results, and we will present the knowledge graph of this experiment.& & & & & & & strong& References& br& & /strong& Schymanski, S.J., Sivapalan, M., Roderick, M.L., Hutley, L.B., Beringer, J., 2009. An optimality& #8208 based model of the dynamic feedbacks between natural vegetation and the water balance. Water Resources Research 45. 0.1029/2008WR006841& & & / &
Publisher: Authorea, Inc.
Date: 25-07-2022
DOI: 10.22541/AU.165874643.34577990/V1
Abstract: The koala, one of the most iconic Australian wildlife species, is facing several concomitant threats that are driving population declines. Some threats are well known and have clear methods of prevention (e.g. habitat loss can be reduced with stronger land-clearing control), whereas others are less easily addressed. One of the major current threats to koalas is chlamydial disease, which can have major impacts on in idual survival and reproduction rates, and can translate into population declines. Effective management strategies for the disease in the wild are currently lacking, and to date we know little about the determinants of in idual susceptibility to disease. Here we used a rare opportunity to investigate the genetic basis of variation in susceptibility to chlamydia using one of the most intensively studied wild koala populations. We combine data from veterinary examinations, chlamydia testing, genetic s ling and movement monitoring. Out of our s le of 342 wild koalas, 60 were found to have chlamydia. Using genotype information on 8649 SNPs to investigate the role of genetic characteristics in determining disease status, we found no evidence of inbreeding depression, but a heritability of 0.14 (95%CI: 0.06 – 0.23) for the probability that koalas had chlamydia. Heritability of susceptibility to chlamydia could be relevant for future disease management in koalas, as it suggests the potential to select for disease resilience through assisted breeding.
Publisher: Zenodo
Date: 2020
Publisher: Copernicus GmbH
Date: 21-03-2022
DOI: 10.5194/HESS-2022-97
Abstract: Abstract. The Budyko framework puts the long-term mean annual evapo-transpiration (ET) of a catchment in relation to its maximum possible value determined by the conservation of mass (ET can not exceed mean annual precipitation) and energy (ET can not exceed mean annual net radiation) in the absence of significant storage contributions. Most catchments plot relatively close to this physical limit, which allowed to develop an empirical equation (often referred to as the Budyko curve) for estimating mean annual evaporation and runoff from observed net radiation and precipitation. Parametric forms of the curve often use a shape parameter (n), that is seen as a catchment characteristic. However, a satisfying explanation for the convergence and self-organization of catchments around such an empirical curve is still lacking. In this study, we explore if vegetation optimality can explain the convergence of catchments along a Budyko curve and in how far n can be seen as a catchment characteristic. The Vegetation Optimality Model (VOM) optimizes vegetation properties and behaviour (e.g. rooting depths, vegetation cover, stomatal control), to maximize the difference between the total carbon taken up from the atmosphere and the carbon used for maintenance of plant tissues involved in its uptake, i.e. the long-term net carbon profit (NCP). This optimization is entirely independent of observed ET and hence the VOM does not require calibration for predicting ET. In a first step, the VOM was fully optimized for the observed atmospheric forcing at five flux tower sites along the North Australian Tropical Transect, as well as 36 additional locations near the transect and six Australian catchments. In addition, the VOM was run without vegetation for all sites, meaning that all precipitation was partitioned into soil evaporation and runoff. For comparison, three conceptual hydrological models (TUWmodel, GR4J and FLEX) were calibrated for the Australian catchments using the observed precipitation and runoff. Subsequently, we emulated step changes in climate by multiplying precipitation (P) by factors ranging between 0.2 and 2, before running the VOM and hydrological models without changing the vegetation properties or model parameters, emulating invariant catchment characteristics under a changed climate. In a last step, the VOM was re-optimized for the different P amounts, allowing vegetation to adapt to the new situation. Eventually, Budyko curves were fit by adapting the parameter n to the model results. This was carried out for both multiple sites simultaneously and for each in idual study site, thereby assuming that n is a site specific characteristic. The optimized VOM runs tracked relatively close to a Budyko curve with a realistic n value and close to observations, whereas the runs without vegetation led to significantly lower evaporative fractions and unrealistically low n values compared with literature. When fitting n to in idual catchments, changes in P led to changes in n (increasing n for decreasing P) in all model runs (including the three conceptual models) except if the VOM was re-optimized for each change in P, which brought the value of n back close to its value for the unperturbed P in each catchment. For the re-optimized VOM runs, the variation in n between catchments was greater than within each catchment in response to multiplications of P with a factor 0.2 to 2. These findings suggest that optimality may explain the self-organization of catchments in Budyko space, and that the accompanying parameter n does not remain constant for constant catchment and vegetation conditions as hypothesized in the literature, but in fact emerges through the adaptation of vegetation to climatic conditions in a given hydrological setting. Moreover, the results suggest that n might initially increase in response to suddenly reduced P, and only slowly returns to its original, catchment-specific value, as vegetation re-adjusts to the new climate over decades and centuries. This may constitute a new basis for the evaluation and prediction of catchment responses to climatic shifts.
Publisher: Copernicus GmbH
Date: 24-10-2017
Abstract: Abstract. The savanna complex is a highly erse global biome that occurs within the seasonally dry tropical to sub-tropical equatorial latitudes and are structurally and functionally distinct from grasslands and forests. Savannas are open-canopy environments that encompass a broad demographic continuum, often characterised by a changing dominance between C3-tree and C4-grass vegetation, where frequent environmental disturbances such as fire modulates the balance between ephemeral and perennial life forms. Climate change is projected to result in significant changes to the savanna floristic structure, with increases to woody biomass expected through CO2 fertilisation in mesic savannas and increased tree mortality expected through increased rainfall interannual variability in xeric savannas. The complex interaction between vegetation and climate that occurs in savannas has traditionally challenged terrestrial biosphere models (TBMs), which aim to simulate the interaction between the atmosphere and the land surface to predict responses of vegetation to changing in environmental forcing. In this review, we examine whether TBMs are able to adequately represent savanna fluxes and what implications potential deficiencies may have for climate change projection scenarios that rely on these models. We start by highlighting the defining characteristic traits and behaviours of savannas, how these differ across continents and how this information is (or is not) represented in the structural framework of many TBMs. We highlight three dynamic processes that we believe directly affect the water use and productivity of the savanna system: phenology, root-water access and fire dynamics. Following this, we discuss how these processes are represented in many current-generation TBMs and whether they are suitable for simulating savanna fluxes.Finally, we give an overview of how eddy-covariance observations in combination with other data sources can be used in model benchmarking and intercomparison frameworks to diagnose the performance of TBMs in this environment and formulate road maps for future development. Our investigation reveals that many TBMs systematically misrepresent phenology, the effects of fire and root-water access (if they are considered at all) and that these should be critical areas for future development. Furthermore, such processes must not be static (i.e. prescribed behaviour) but be capable of responding to the changing environmental conditions in order to emulate the dynamic behaviour of savannas. Without such developments, however, TBMs will have limited predictive capability in making the critical projections needed to understand how savannas will respond to future global change.
Publisher: Copernicus GmbH
Date: 02-08-2021
Abstract: Abstract. Open, accessible, reusable, and reproducible hydrologic research can have a significant impact on the scientific community and broader society. While more in iduals and organizations within the hydrology community are embracing open science practices, technical (e.g., limited coding experience), resource (e.g., open access fees), and social (e.g., fear of being scooped) challenges remain. Furthermore, there are a growing number of constantly evolving open science tools, resources, and initiatives that can seem overwhelming. These challenges and the ever-evolving nature of the open science landscape may seem insurmountable for hydrologists interested in pursuing open science. Therefore, we propose general Open Hydrology Principles to guide in idual and community progress toward open science for research and education and the Open Hydrology Practical Guide to improve the accessibility of currently available tools and approaches. We aim to inform and empower hydrologists as they transition to open, accessible, reusable, and reproducible research. We discuss the benefits as well as common open science challenges and how hydrologists can overcome them. The Open Hydrology Principles and Open Hydrology Practical Guide reflect our knowledge of the current state of open hydrology we recognize that recommendations and suggestions will evolve and expand with emerging open science infrastructures, workflows, and research experiences. Therefore, we encourage hydrologists all over the globe to join in and help advance open science by contributing to the living version of this document and by sharing open hydrology resources in the community-supported repository (open-hydrology.github.io).
Publisher: Copernicus GmbH
Date: 19-02-2014
Abstract: Abstract. Throughout its historical development, hydrology as an earth science, but especially as a problem-centred engineering discipline has largely relied (quite successfully) on the assumption of stationarity. This includes assuming time invariance of boundary conditions such as climate, system configurations such as land use, topography and morphology, and dynamics such as flow regimes and flood recurrence at different spatio-temporal aggregation scales. The justification for this assumption was often that when compared with the temporal, spatial, or topical extent of the questions posed to hydrology, such conditions could indeed be considered stationary, and therefore the neglect of certain long-term non-stationarities or feedback effects (even if they were known) would not introduce a large error.
Publisher: Copernicus GmbH
Date: 03-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-2887
Abstract: & & Usually hydraulic conductance and vulnerability are measured under extreme conditions never experienced by living plants (e. g. centrifugation, bench dehydration, and large pressure gradients). A common factor that is known to inhibit the water transport in plants is embolism, which is believed to occur either by air entry through the pit valves on the walls of the xylem, or by ex-solution of dissolved gases, or vaporization of water at very low pressures.& & & & Here we explore possibilities to measure hydraulic conductance and induce embolism under close to natural conditions. The setup consists of a syringe pump to control water flow, where a twig is inserted in the flow path to measure its hydraulic conductivity using pressure and flow meters. This setup has enabled us to imitate natural conditions where transpiration rate induces a pressure difference between the sink (leaf) and source (root) along the flow path. It has also allowed us to induce flow in both directions through the twig without having to rotate or change out the s le. Using our setup, we found that the conductivity of the same twig was 50% lower when pulling compared to pushing. This can be explained by the emptying and filling of cut end vessels and the pressure gradient along the twig, which is induced by the flow rate and flow direction. Our findings are discussed in the context that currently employed methods for measuring wood hydraulic conductance employ either centrifugation, where water is pulled on both ends, or pushing of water by applying positive pressure on one end.& &
Publisher: Wiley
Date: 08-2017
Publisher: Copernicus GmbH
Date: 04-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-7655
Abstract: & & Good scientific practice requires good documentation and traceability of every research step in order to ensure reproducibility and repeatability of our research. However, with increasing data availability and ability to record big data, experiments and data analysis become more complex. This complexity often requires many pre- and post-processing steps that all need to be documented for reproducibility of final results. This poses very different challenges for numerical experiments, laboratory work and field-data analysis. The platform Renku (renkulab.io/), developed by the Swiss Data Science Center, aims at facilitating reproducibility and repeatability of all these scientific workflows. Renku stores all data, code and scripts in an online repository, and records in their history how these files are generated, interlinked and modified. The linkages between files (inputs, code and outputs) lead to the so-called & span& knowledge graph, used to record the provenance of results and connecting those with all other relevant entities in the project.& /span& & & & & We will discuss here several use ex les, including mathematical analysis, laboratory experiments, data analysis and numerical experiments, all related to scientific projects presented separately. Reproducibility of mathematical analysis is facilitated by clear variable definitions and a computer algebra package that enables reproducible symbolic derivations. We will present the use of the Python package ESSM (essm.readthedocs.io) for this purpose, and how it can be integrated into a Renku workflow. Reproducibility of laboratory results is facilitated by tracking of experimental conditions for each data record and instrument re-calibration activities, mainly through Jupyter notebooks. Data analysis based on different data sources requires the preservation of links to external datasets and snapshots of the dataset versions imported into the project, that is facilitated by Renku. Renku also takes care of clear links between input, code and output of large numerical experiments, our last use ex le, and enables systematic updating if any of the input or code files are changed.& & & & These different ex les demonstrate how Renku can assist in documenting the scientific process from input to output and the final paper. All code and data are directly available online, and the recording of the workflows ensures reproducibility and repeatability.& &
Publisher: Wiley
Date: 27-12-2022
DOI: 10.1002/ECE3.8459
Abstract: Effective conservation requires accurate data on population genetic ersity, inbreeding, and genetic structure. Increasingly, scientists are adopting genetic non‐invasive s ling (gNIS) as a cost‐effective population‐wide genetic monitoring approach. gNIS has, however, known limitations which may impact the accuracy of downstream genetic analyses. Here, using high‐quality single nucleotide polymorphism (SNP) data from blood/tissue s ling of a free‐ranging koala population ( n = 430), we investigated how the reduced SNP panel size and call rate typical of genetic non‐invasive s les (derived from experimental and field trials) impacts the accuracy of genetic measures, and also the effect of s ling intensity on these measures. We found that gNIS at small s le sizes (14% of population) can provide accurate population ersity measures, but slightly underestimated population inbreeding coefficients. Accurate measures of internal relatedness required at least 33% of the population to be s led. Accurate geographic and genetic spatial autocorrelation analysis requires between 28% and 51% of the population to be s led. We show that gNIS at low s le sizes can provide a powerful tool to aid conservation decision‐making and provide recommendations for researchers looking to apply these techniques to free‐ranging systems.
Location: Germany
Start Date: 2013
End Date: 2016
Funder: Swiss National Science Foundation
View Funded ActivityStart Date: 2023
End Date: 2027
Funder: Swiss National Science Foundation
View Funded ActivityStart Date: 2013
End Date: 2015
Funder: Australian Research Council
View Funded ActivityStart Date: 2020
End Date: 2023
Funder: Fonds National de la Recherche Luxembourg
View Funded ActivityStart Date: 2011
End Date: 2014
Funder: Deutsche Forschungsgemeinschaft
View Funded ActivityStart Date: 2017
End Date: 2022
Funder: Fonds National de la Recherche
View Funded ActivityStart Date: 2013
End Date: 06-2016
Amount: $527,500.00
Funder: Australian Research Council
View Funded Activity