Annualmeeting:2017 CSDMS meeting-091
Spatial gradients in SSC at the interface of an estuary and a salt marsh: Implications for sediment supply to the marsh
[[Image:|300px|right|link=File:]]Salt marsh provides critical estuarine habitat and shoreline protection, and is highly vulnerable to sea-level rise. Models of marsh accretion and resilience to sea-level rise rely on estimates of sediment supply, yet the factors governing sediment supply to marshes and its temporal variation are poorly understood. This presentation focuses on temporal variability in suspended-sediment concentration (SSC) and spatial gradients in SSC at the marsh edge, with two goals: 1) to identify processes important to sediment supply, and 2) to inform the choice of SSC values to use as input to marsh accretion models. We present data collected as part of an investigation of the influence of tides and wind waves on sediment supply to an estuarine salt marsh in China Camp State Park, adjacent to San Pablo Bay, in northern San Francisco Bay (tide range approximately 2 m). The long-term sediment accretion rate in the lower China Camp marsh is 3 mm/year. The marsh vegetation is predominately Salicornia pacifica, with Spartina foliosa occupying the lower elevations adjacent to the mudflat. The marsh is bordered by wide intertidal mudflats and extensive subtidal shallows. In the winter of 2014/2015 and the summer of 2016 we collected time series of SSC, tidal stage and currents, and wave heights and periods in the bay shallows, in a tidal creek, and (except for currents) on the marsh plain. On the mudflats, SSC depends strongly on wave energy, and also varies inversely with water depth, increasing toward the marsh edge and with decreasing tidal stage. Within the marsh, SSC is lower in the Salicornia-dominated marsh plain than at the marsh edge, as expected, but in the Spartina zone SSC is greater than at the marsh edge. This effect is greater in summer, when Spartina is significantly taller and denser, than in winter. SSC over the marsh was typically greater during flood than ebb tides in both seasons, indicating net deposition over the tidal cycle. However, median flood-tide SSC over the marsh, and the inferred deposition, were greater in summer than winter. We attribute the increased SSC and deposition in summer to greater sediment trapping in Spartina, followed by mobilization and transport of sediment onto the marsh during subsequent high tides.