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Seasonal variation in sediment delivery across the bay-marsh interface of an estuarine salt marsh

November 8, 2019

Sediment transport across bay–marsh interfaces depends on wave energy, vegetation, and marsh-edge morphology, and varies over a range of timescales. We investigated these dynamics in a tidal salt marsh with a gently-sloped, vegetated edge adjacent to northern San Francisco Bay. Spartina foliosa (cordgrass) inhabits the lower marsh and Salicornia pacifica (pickleweed) predominates on the marsh plain. We measured suspended-sediment concentration (SSC) and hydrodynamics in bay shallows and along a 100-m cross-shore transect in the marsh, during winter and summer. Four-year averaged accretion measured with marker-horizon plots was twice as great along the marsh transect as adjacent to a tidal creek, 50 m from the bay. We estimated deposition and trapping efficiency from the time-series data to assess its variation with season and wave energy. At high tide the transition zone (between cordgrass and pickleweed) was usually erosional, the pickleweed zone was depositional, and both erosion and deposition increased with wave energy, as did the landward position of maximum deposition. Erosion from the transition zone accounted for approximately one-third of the sediment flux into the pickleweed. In the pickleweed zone, SSC, the difference between flood- and ebb-tide SSC and trapping efficiency were greater in summer than winter for comparable wave conditions, which we attribute to increased sediment trapping by dense summer cordgrass. Moderate waves in summer (46%) accounted for more annual accretion in the pickleweed zone than larger waves in winter (28%), although the contribution of winter storms was diminished by the dry winter during the study.

Publication Year 2020
Title Seasonal variation in sediment delivery across the bay-marsh interface of an estuarine salt marsh
DOI 10.1029/2019JC015268
Authors Jessica R. Lacy, Madeline R. Foster-Martinez, Rachel (Contractor) Allen, Matthew C. Ferner, John C. Callaway
Publication Type Article
Publication Subtype Journal Article
Series Title Journal of Geophysical Research C: Oceans
Index ID 70208112
Record Source USGS Publications Warehouse
USGS Organization Pacific Coastal and Marine Science Center