ORCID Profile
0000-0001-6819-6167
Current Organisations
Southern Cross University
,
Universität Hamburg
Does something not look right? The information on this page has been harvested from data sources that may not be up to date. We continue to work with information providers to improve coverage and quality. To report an issue, use the Feedback Form.
Publisher: Copernicus GmbH
Date: 27-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-3300
Abstract: & & Tree stem methane emissions are gaining rapid research momentum, with about one-third of all literature in this field published in 2021 alone. Long term and seasonal studies are currently rare, limiting our ability to constrain spatial and seasonal emissions variability, and to resolve the tree stem contribution to the total wetland methane flux i.e. soil, water and trees. Here we present preliminary methane flux data from a lowland & em& Melaleuca quinquenervia& /em& forest. We measured emissions & em& in situ& /em& along a ~3 m litude topo-gradient, encompassing forest in lower, transitional and upper elevation zones. Eight (ongoing) field c aigns at monthly intervals, captured flooded to dry to re-flooded site conditions. We measured the stem fluxes from 30 trees at four stem heights, along with 30 adjacent soil and water CH& sub& & /sub& fluxes. Ancillary parameters such as pore water (CH& sub& & /sub& , DO%, pH, temp, redox, EC), water table depth, and soil moisture (VWC %) were also measured. Tree stem fluxes ranged several orders of magnitude between hydrological seasons and topo-gradient zones (ranging from negligible to 17, 426 mmol ha& sup& -1& /sup& d& sup& -1& /sup& ). Soil fluxes were similar in litude and shifted from maximal CH& sub& & /sub& emissions during the wet conditions, to CH& sub& & /sub& uptake in dry locations. The importance of tree stem flux to the net ecosystem flux (NEF) differed between c aigns and hydrological zones, but were most substantial during flooded conditions and ranged from 36-75% of the NEF in the lower and transitional zones during peak emissions respectively. In the upper zone, the tree stem emissions offset the soil sink capacity by ~50% when the water table was closest to the soil surface. This study shows the importance of quantifying lowland tree stem CH& sub& & /sub& emissions to the total wetland flux. This data provides important baseline readings for southern hemisphere and Australian wetland forests, that generally experience dynamic rainfall and soil redox oscillations between flooding and droughts.& &
Publisher: Authorea, Inc.
Date: 13-09-2023
Publisher: Wiley
Date: 21-08-2023
DOI: 10.1002/LOM3.10570
Abstract: Accurate measurements of seawater carbonate chemistry are crucial for marine carbon cycle research. Certified reference materials (CRMs) are typically analyzed alongside s les to correct measurements for calibration drift. However, the COVID‐19 pandemic led to a limited access to CRMs. In response to this shortage, we prepared and monitored in‐house reference materials (IHRMs) for total alkalinity (TA) and dissolved inorganic carbon (DIC), over 12 and 15 months, respectively. Overall, TA was stable, but a slight increase in DIC of about 2 μ mol kg −1 occurred over 15 months. The increase could potentially be attributed to bacterial growth, despite mercuric chloride fixation and repeated UV exposure. It is noted that this small increase was most likely within our instrument and measurements uncertainties. Our repeated measurements also identified a few bottles that had TA or DIC concentrations 4–5 μ mol kg −1 higher than the rest, indicating issues during cleaning, fixation, or storage of in idual bottles. This study emphasizes the importance of careful and continuous monitoring if self‐prepared IHRMs are used. Given that the amount of work required is very high, IHRM preparation is only recommended when CRMs are not available.
Publisher: Copernicus GmbH
Date: 08-2022
Abstract: Abstract. Ocean alkalinity enhancement (OAE) is a method that can remove carbon dioxide (CO2) from the atmosphere and counteract ocean acidification through the dissolution of alkaline minerals. Currently, critical knowledge gaps exist regarding the dissolution of different minerals suitable for OAE in natural seawater. Of particular importance is to understand how much alkaline mineral can be dissolved before secondary precipitation of calcium carbonate (CaCO3) occurs, since secondary CaCO3 precipitation reduces the atmospheric CO2 uptake potential of OAE. Using two types of mineral proposed for OAE, quick lime (CaO) and hydrated lime (Ca(OH)2), we show that both ( µm of diameter) dissolved in seawater within a few hours. No CaCO3 precipitation occurred at a saturation state (ΩA) of ∼5, but CaCO3 precipitation in the form of aragonite occurred above an ΩA value of 7. This limit is lower than expected for typical pseudo-homogeneous precipitation, i.e. in the presence of colloids and organic matter. Secondary precipitation at low ΩA (∼ 7) was the result of heterogeneous precipitation onto mineral surfaces, most likely onto the added CaO and Ca(OH)2 particles. Most importantly, runaway CaCO3 precipitation was observed, a condition where significantly more total alkalinity (TA) was removed than initially added. Such runaway precipitation could reduce the OAE CO2 uptake efficiency from ∼ 0.8 mol of CO2 per mole of added TA down to 0.1 mol of CO2 per mole of TA. Runaway precipitation appears to be avoidable by dilution below the critical ΩA threshold of 5, ideally within hours of the mineral additions to minimise initial CaCO3 precipitation. Finally, OAE simulations suggest that for the same ΩA threshold, the amount of TA that can be added to seawater would be more than 3 times higher at 5 ∘C than at 30 ∘C. The maximum TA addition could also be increased by equilibrating the seawater to atmospheric CO2 levels (i.e. to a pCO2 of ∼ 416 µatm) during addition. This would allow for more TA to be added in seawater without inducing CaCO3 precipitation, using OAE at its CO2 removal potential.
Publisher: Springer Science and Business Media LLC
Date: 03-11-2018
Publisher: Copernicus GmbH
Date: 10-12-2021
DOI: 10.5194/BG-2021-330
Abstract: Abstract. Ocean Alkalinity Enhancement (OAE) has been proposed as a method to remove carbon dioxide (CO2) from the atmosphere and to counteract ocean acidification. It involves the dissolution of alkaline minerals such as quick lime, CaO, and hydrated lime, Ca(OH)2. However, a critical knowledge gap exists regarding their dissolution in natural seawater. Particularly, how much can be dissolved before secondary precipitation of calcium carbonate (CaCO3) occurs is yet to be established. Secondary precipitation should be avoided as it reduces the atmospheric CO2 uptake potential of OAE. Here we show that both CaO and Ca(OH)2 powders ( 63 µm of diameter) dissolved in seawater within a few hours. However, CaCO3 precipitation, in the form of aragonite, occurred at a saturation (ΩAr) threshold of about 5. This limit is much lower than what would be expected for typical pseudo-homogeneous precipitation in the presence of colloids and organic materials. Secondary precipitation at unexpectedly low ΩAr was the result of so-called heterogeneous precipitation onto mineral phases, most likely onto CaO and Ca(OH)2 prior to full dissolution. Most importantly, this led to runaway CaCO3 precipitation by which significantly more alkalinity (TA) was removed than initially added, until ΩAr reached levels below 2. Such runaway precipitation would reduce the CO2 uptake efficiency from about 0.8 moles of CO2 per mole of TA down to only 0.1 mole of CO2 per mole of TA. Runaway precipitation appears to be avoidable by dilution below the critical ΩAr threshold of 5, ideally within hours of the addition to minimise initial CaCO3 precipitation. Finally, model considerations suggest that for the same ΩAr threshold, the amount of TA that can be added to seawater would be more than three times higher at 5 °C than at 30 °C, and that equilibration to atmospheric CO2 levels during mineral dissolution would further increase it by a factor of ~6 and ~3 respectively.
Publisher: Copernicus GmbH
Date: 15-05-2023
DOI: 10.5194/EGUSPHERE-EGU23-330
Abstract: Ocean Alkalinity Enhancement (OAE) is a carbon dioxide (CO2) removal technology with one of the largest potentials, which simultaneously decreases the pressure of ocean acidification. Most of the current understanding of OAE stems from numerical models. However, two recent studies have shown that secondary calcium carbonate (CaCO3) precipitation can occur at unexpectedly low saturation state, when using particle based OAE feedstocks. This is undesirable as it reduces OAE efficiency and can lead to & #8220 runaway CaCO3 precipitation& #8221 .Both mineral dissolution kinetics and secondary CaCO3 precipitation are influenced by the physical and environmental properties of mineral feedstock and seawater. For ex le, the surface area of particles in suspension is an important factor for dissolution kinetics of minerals, as well as secondary CaCO3 precipitation kinetics. Furthermore, CaCO3 precipitation depends directly on the concentrations of calcium (Ca2+) and carbonate ions (CO32-) in seawater. The higher their concentrations, the more likely CaCO3 will precipitate. Since Ca2+ concentration have a positive correlation with salinity in the open ocean, variations in seawater salinity could be an important modifier.Here, we present experimental data on the effects of grain size and salinity on the kinetics of brucite (magnesium hydroxide) dissolution and secondary CaCO3 precipitation. Preliminary results on the effect of grain size suggest that CaCO3 precipitation for medium sized particles (63-180 & #181 m) is slower. At larger grain size, the slower dissolution rate, as of the smaller surface area, leads to more quickly measurable CaCO3 precipitation. At smaller grain size, it is the greater surface area that seems to increase the CaCO3 precipitation rate.For salinity, first results suggest that dissolution rates increase towards lower salinities, while CaCO3 precipitates quicker. The former finding is most likely related to higher brucite dissolution at lower ambient magnesium concentrations, due to lower salinity. The quicker CaCO3 precipitation is also likely due to the lower magnesium concentration in lower salinity seawater. Magnesium ions are known to inhibit CaCO3 precipitation, hence CaCO3 precipitation is less likely inhibited at lower rather than higher salinities. Therefore, both feedstock grain size and seawater salinity are two key parameters for real-world OAE applications.
Publisher: Elsevier BV
Date: 2023
Location: France
No related grants have been discovered for Charly Andre Moras.