Marsh Sedimentation Controls Delta Top Morphology, Slope, and Mass Balance

Abstract

River deltas and their marsh platforms host diverse ecosystems threatened by anthropogenic impacts to coastal areas, such as rising sea levels, subsidence, and leveeing of channels (Ericson et al., 2006). Organic material production, a critical form of sediment accumulation in many river deltas, is the primary driver of marsh platform growth (Nyman et al., 2006), whereas clastic sedimentation via rivers drives deltaic lobe growth (Edmonds et al., 2009). To successfully predict the long-term fate of these ecosystems, the interaction controlling delta and marsh growth must be understood (Paola et al., 2011). While much is known about surface processes in channelized portions of river deltas (

Sediment Compaction in Experimental Deltas: Toward a Meso‐Scale Understanding of Coastal Subsidence Patterns

“…These deltas are constructed by flows that have a higher sediment to water ratio than field-scale systems, resulting in higher delta slopes and significantly altered morphodynamics (Sanks et al, 2023). Delta topset slopes tend to be multiple orders of magnitude lower than those observed in the control experiment, with similar slopes only widespread on the subaqueous foreset (Edmonds et al, 2011;Sanks et al, 2022a). While creep has been observed in coastal environments, we know of no field data that shows such tight elevation-control of subsidence rates.…”

“…Each experiment was allowed to prograde for 120 hr before hour zero of run time. The treatment experiment differed only in that a proxy for marsh sedimentation was applied to regions near sea level (−9 to 5 mm relative to sea level, hereafter RSL), resulting in about 8% of the final deposit mass and 15% of the final deposit volume (Sanks et al., 2022a). Therefore, significant statistical differences in subsidence rates can be attributed to the impact of the marsh proxy deposits.…”

“…This study is part of a larger project (including Sanks et al. (2022a)) which aims to assess the impact of marshes on a wide range of deltaic processes, from delta‐top kinematics to stratigraphic patterns. No studies have previously described autogenic subsidence due to sediment compaction (hereafter, just subsidence) in a delta experiment.…”

Modeling the Dynamic Response of River Deltas to Sea‐Level Rise Acceleration

“…However, we do not believe that all of these additional forcings would significantly change the results found here; Van De Lageweg and Slangen (2017) simulated delta evolution over centennial timescales with different forcing and SLR conditions, and found river, tidal, and wave‐dominated deltas all responded similarly to SLR. Conversely, studies examining the role of subsidence and faulting (e.g., A. J. Moodie & Passalacqua, 2021; Liang, Kim, & Passalacqua, 2016), vegetation and marsh growth (e.g., Lauzon & Murray, 2018; Sanks et al., 2022), and ice and permafrost (e.g., Lauzon et al., 2019; Piliouras et al., 2021) have shown that these processes can influence delta morphology and channel mobility. Therefore, future studies should endeavor to explore a different parameter space, using results from this work to limit the SLR scenarios considered, and aim to understand how additional processes or coupled changes to forcings, such as rising sea levels and a flashier input hydrograph, may alter deltaic evolution.…”

“…Conversely, studies examining the role of subsidence and faulting (e.g., A. J. Liang, Kim, & Passalacqua, 2016), vegetation and marsh growth (e.g., Lauzon & Murray, 2018;Sanks et al, 2022), and ice and permafrost (e.g., Lauzon et al, 2019;Piliouras et al, 2021) have shown that these processes can influence delta morphology and channel mobility. Therefore, future studies should endeavor to explore a different parameter space, using results from this work to limit the SLR scenarios considered, and aim to understand how additional processes or coupled changes to forcings, such as rising sea levels and a flashier input hydrograph, may alter deltaic evolution.…”