Vegetation‐Driven Seasonal Sediment Dynamics in a Freshwater Marsh of the Mississippi River Delta

Abstract

Deltaic wetlands are uniquely vulnerable to sea level rise due to their coastal setting, low elevation gradient, and the high rate of subsidence in recently deposited sediments (Blum & Roberts, 2009;Giosan et al., 2014;Hoitink et al., 2020;Törnqvist et al., 2020). Many deltas host dense human populations that rely on vast expanses of wetlands for critical ecosystem services including protection from storms (e.g., Edmonds et al., 2020). Despite the vulnerability that is inherent in a delta setting, deltaic ecosystems are also uniquely able to adapt to sea level rise by making use of the riverine sediment transport system to locally increase elevation. A delta's distributary channels provide both the source of sediment and the means for delivering sediment to the locations where it can be most useful for land building. In many deltas the connections between distributary channels and the delta plain have been restricted (e.g., Esposito et al., 2020), and land use managers are working to plan diversions of water and sediment that will leverage delta sediment transport processes to deliver sediment to vulnerable or valuable wetlands (

Effects of Seasonal Variations in Seagrass Density and Storms on Sediment Retention and Connectivity Between Subtidal Flats and Intertidal Marsh

“…The timing of storms relative to the SAV growth cycle is another factor that affects sediment connectivity between SAV beds and salt marshes (Beltrán-Burgos et al, 2023). Because high-density seagrass meadows can effectively inhibit sediment resuspension from the seabed even under strong storm conditions (Zhu et al, 2021), storm events during growing seasons had little effect on increasing marsh sediment flux (Figure 3b).…”

“…This impact may be ameliorated in environments where SAV meadows exhibit strong seasonal density variations during growth and senescence cycles and where storms that drive sediment flux to marshes occur during periods of senescence, leading to seasonal cycles of sediment storage and release in SAV beds (Hansen & Reidenbach, 2013;. Field-based studies investigating seasonal sediment exchange between freshwater marshes and feeder channels occupied by SAV found that sediment delivery to the marshes varied with SAV growth cycles and channel flow conditions (Beltrán-Burgos et al, 2023;Lacy et al, 2021).…”