ORCID Profile
0000-0003-2636-9896
Current Organisations
University of Colorado at Boulder
,
University of New Mexico
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Publications
The fate of fluvially-deposited organic carbon during transient floodplain storage
Publisher: Elsevier BV
Date: 05-2021
Preservation of organic carbon during active fluvial transport and particle abrasion
Publisher: Geological Society of America
Date: 30-08-2019
DOI: 10.1130/G46442.1
Abstract: Oxidation of particulate organic carbon (POC) during fluvial transit releases CO2 to the atmosphere and can influence global climate. Field data show large POC oxidation fluxes in lowland rivers however, it is unclear if POC losses occur predominantly during in-river transport, where POC is in continual motion within an aerated environment, or during transient storage in floodplains, which may be anoxic. Determination of the locus of POC oxidation in lowland rivers is needed to develop process-based models to predict POC losses, constrain carbon budgets, and unravel links between climate and erosion. However, sediment exchange between rivers and floodplains makes differentiating POC oxidation during in-river transport from oxidation during floodplain storage difficult. Here, we isolated in-river POC oxidation using flume experiments transporting petrogenic and biospheric POC without floodplain storage. Our experiments showed solid phase POC losses of 0%–10% over ∼103 km of fluvial transport, compared to ∼7% to % losses observed in rivers over similar distances. The production of dissolved organic carbon (DOC) and dissolved rhenium (a proxy for petrogenic POC oxidation) was consistent with small POC losses, and replicate experiments in static water tanks gave similar results. Our results show that fluvial sediment transport, particle abrasion, and turbulent mixing have a minimal role on POC oxidation, and they suggest that POC losses may accrue primarily in floodplain storage.
Fluvial organic carbon cycling regulated by sediment transit time and mineral protection
Publisher: Springer Science and Business Media LLC
Date: 28-10-2021
DOI: 10.1038/S41561-021-00845-7
Abstract: Rivers transfer terrestrial organic carbon (OC) from mountains to ocean basins, playing a key role in the global carbon cycle. During fluvial transit, OC may be oxidized and emitted to the atmosphere as CO 2 or preserved and transported to downstream depositional sinks. The balance between oxidation and preservation determines the amount of particulate OC (POC) that can be buried long term, but the factors regulating this balance are poorly constrained. Here, we quantify the effects of fluvial transit on POC fluxes along an ~1,300 km lowland channel with no tributaries. We show that sediment transit time and mineral protection regulate the magnitude and rate of POC oxidation, respectively. Using a simple turnover model, we estimate that annual POC oxidation is a small percentage of the POC delivered to the river. Modelling shows that lateral erosion into POC-rich floodplains can increase POC fluxes to downstream basins, thereby offsetting POC oxidation. Consequently, rivers with high channel mobility can enhance CO 2 drawdown while management practices that stabilize river channels may reduce the potential for CO 2 drawdown.
Fluvial Organic Carbon Composition Regulated by Seasonal Variability in Lowland River Migration and Water Discharge
Publisher: American Geophysical Union (AGU)
Date: 22-12-2021
DOI: 10.1029/2021GL093416
Abstract: Identifying drivers of seasonal variations in fluvial particulate organic carbon (POC) composition can aid sediment provenance and biogeochemical cycling studies. We evaluate seasonal changes in POC composition in the Río Bermejo, Argentina, a lowland river running ∼1,270 km without tributaries. Weekly POC concentration and isotopic composition from 2016 to 2018 show that during the wet season, increased lateral channel migration generates an influx of 13 C‐enriched and 14 C‐enriched floodplain‐sourced material, overprinting the 13 C‐depleted and 14 C‐depleted headwater signature that is observed during the dry season. These findings demonstrate how channel morphodynamics can drive variability of POC composition in lowland rivers, and may modulate the composition of POC preserved in sedimentary archives.
Related Organisations
Lawrence Livermore National Laboratory
Location: United States of America
Related Funding Activities
No related grants have been discovered for Marisa Repasch.