River Organic Carbon Fluxes Modulated by Hydrodynamic Sorting of Particulate Organic Matter

Repasch, Marisa; Scheingross, Joel S.; Hovius, Niels; Vieth‐Hillebrand, Andrea; Mueller, Carsten W.; Höschen, Carmen; Szupiany, R. N.; Sachse, Dirk

doi:10.1029/2021gl096343

Cited by 18 publications

(14 citation statements)

References 64 publications

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“…The occurrence of wood‐laden currents has previously been described in the Madre de Dios River where particulate lignin accumulated in the lower water column (Feng et al., 2016 ; Repasch et al., 2022 ). However, we find that the transport of coarse organic matter in the Mackenzie River basin is not limited to woody (lignin‐rich) debris.…”

Section: Discussionmentioning

confidence: 90%

“…Particulate organic matter entrained and carried in rivers can be heterogeneous in its source, chemical composition, and size, and subjected to hydrodynamic processes that affect its dispersal, reactivity, and age (Bianchi et al., 2018 ; Freymond, Kündig et al., 2018 ; Repasch et al., 2022 ; Ward et al., 2017 ; Yu et al., 2019 ). River depth profiles typically show variations in suspended sediment concentration and grain size as a function of depth (Bouchez, Gaillardet et al., 2011 ; Bouchez, Métivier et al., 2011 ; Galy, France‐Lanord, & Lartiges, 2008 ).…”

Section: Introductionmentioning

confidence: 99%

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Vegetal Undercurrents—Obscured Riverine Dynamics of Plant Debris

et al. 2022

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Much attention has been focused on fine‐grained sediments carried as suspended load in rivers due to their potential to transport, disperse, and preserve organic carbon (OC), while the transfer and fate of OC associated with coarser‐grained sediments in fluvial systems have been less extensively studied. Here, sedimentological, geochemical, and biomolecular characteristics of sediments from river depth profiles reveal distinct hydrodynamic behavior for different pools of OC within the Mackenzie River system. Higher radiocarbon (14C) contents, low N/OC ratios, and elevated plant‐derived biomarker loadings suggest a systematic transport of submerged vascular plant debris above the active riverbed in large channels both upstream of and within the delta. Subzero temperatures hinder OC degradation promoting the accumulation and waterlogging of plant detritus within the watershed. Once entrained into a channel, sustained flow strength and buoyancy prevent plant debris from settling and keep it suspended in the water column above the riverbed. Helical flow motions within meandering river segments concentrate lithogenic and organic debris near the inner river bends forming a sediment‐laden plume. Moving offshore, we observe a lack of discrete, particulate OC in continental shelf sediments, suggesting preferential trapping of coarse debris within deltaic and neritic environments. The delivery of waterlogged plant detritus transport and high sediment loads during the spring flood may reduce oxygen exposure times and microbial decomposition, leading to enhanced sequestration of biospheric OC. Undercurrents enriched in coarse, relatively fresh plant fragments appear to be reoccurring features, highlighting a poorly understood yet significant mechanism operating within the terrestrial carbon cycle.

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Section: Discussionmentioning

confidence: 90%

Section: Introductionmentioning

confidence: 99%

Vegetal Undercurrents—Obscured Riverine Dynamics of Plant Debris

et al. 2022

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“…For rivers in the loess area more than 80% of the total suspended sediment can be ascribed to bank erosion and collapse (Simon et al., 2000). In addition, the transit of bank‐derived sediment from a given catchment to the ocean contributes to the global carbon cycle (Galy et al., 2015; Golombek et al., 2021; Repasch et al., 2022). For instance, lateral erosion of rivers cutting through floodplains releases additional organic carbon fluxes to downstream depositional sinks (e.g., tidal flats and deltas).…”

Section: Feedbacks Between Bank Retreat and Morphodynamicsmentioning

confidence: 99%

A Review on Bank Retreat: Mechanisms, Observations, and Modeling

Zhao

Coco

Gong

et al. 2022

Reviews of Geophysics

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Bank retreat plays a fundamental role in fluvial and estuarine dynamics. It affects the cross‐sectional evolution of channels, provides a source of sediment, and modulates the diversity of habitats. Understanding and predicting the geomorphological response of fluvial/tidal channels to external driving forces underpins the robust management of water courses and the protection of wetlands. Here, we review bank retreat with respect to mechanisms, observations, and modeling, covering both rivers and (previously neglected) tidal channels. Our review encompasses both experimental and in situ observations of failure mechanisms and bank retreat rates, modeling approaches and numerical methods to simulate bank erosion. We identify that external forces, despite their distinct characteristics, may have similar effects on bank stability in both river and tidal channels, leading to the same failure mode. We review existing data and empirical functions for bank retreat rate across a range of spatial and temporal scales, and highlight the necessity to account for both hydraulic and geotechnical controls. Based on time scale considerations, we propose a new hierarchy of modeling styles that accounts for bank retreat, leading to clear recommendations for enhancing existing modeling approaches. Finally, we discuss systematically the feedbacks between bank retreat and morphodynamics, and suggest that to move this agenda forward will require a better understanding of multifactor‐driven bank retreat across a range of temporal scales, with particular attention to the differences (and similarities) between riverine and estuarine environments, and the role of feedbacks exerted by the collapsed bank soil.

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“…In addition to these core building blocks for deltaic deposits, many other fluvially transported materials of scientific interest make their way through river deltas. Some of these materials may affect deltaic morphology, such as ice (Forbes & Taylor, 1994; Lauzon et al., 2019; Piliouras et al., 2021) or nutrients (Hiatt et al., 2018; Knights et al., 2020), but many others are of interest for reasons relating to contaminant fate and transport (Atwood et al., 2019; Lebreton et al., 2017), ecology (Glenn et al., 2001), or carbon budgeting (Repasch et al., 2022; Shields et al., 2017; Torres et al., 2020).…”

Section: Introductionmentioning

confidence: 99%

“…The relevant idea to underscore here is that vertical segregation of material in the water column, when combined with topographic steering, can subsequently influence horizontal transport (Chambert & James, 2009; Repasch et al., 2022; Slingerland, 1984). Particulates concentrated near the top or bottom of the water column have a different relative likelihood to make the jump over obstacles in the flow path, such as submerged levees or vegetation (Figure 2), resulting in different patterns of connectivity.…”

Section: Introductionmentioning

confidence: 99%

From Grains to Plastics: Modeling Nourishment Patterns and Hydraulic Sorting of Fluvially Transported Materials in Deltas

et al. 2022

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Understanding the way fluvially transported materials are partitioned in river deltas is essential for predicting their morphological change and the fate of environmental constituents and contaminants. Translating water‐based partitioning estimates into fluxes of nonwater materials is often difficult to constrain because most materials are not uniformly distributed in the water column and may have characteristic transport pathways that differ from the mean flow. Here, we present a novel reduced‐complexity modeling approach for simulating the patterns of transport of a diverse range of suspended fluvial inputs influenced by vertical stratification and topographic steering. We utilize a mixed Eulerian‐Lagrangian modeling approach to estimate the patterns of nourishment and connectivity in the Wax Lake and Atchafalaya Deltas in coastal Louisiana. Using the reduced‐complexity particle routing model dorado, in conjunction with a calibrated ANUGA hydrodynamic model, we quantify how transport patterns in each system change as a function of a material's Rouse number and environmental conditions. We find that even small changes to local topographic steering lead to emergent system‐scale changes in patterns of fluvial nourishment, with greater channel‐island connectivity for positively buoyant materials than negatively buoyant materials, hydraulically sorting different materials in space. We also find that the nourishment patterns of some materials are more sensitive than others to changes in discharge, tidal conditions, and anthropogenic dredging. Our results have important implications for understanding the eco‐geomorphic evolution of deltas, and our modeling framework could have interdisciplinary implications for studying the transport of materials in other systems, including sediments, nutrients, wood, plastics, and biotic materials.

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River Organic Carbon Fluxes Modulated by Hydrodynamic Sorting of Particulate Organic Matter

Cited by 18 publications

References 64 publications

Vegetal Undercurrents—Obscured Riverine Dynamics of Plant Debris

Vegetal Undercurrents—Obscured Riverine Dynamics of Plant Debris

A Review on Bank Retreat: Mechanisms, Observations, and Modeling

From Grains to Plastics: Modeling Nourishment Patterns and Hydraulic Sorting of Fluvially Transported Materials in Deltas

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