Spatiotemporal Patterns of Mineral and Organic Matter Deposition Across Two San Francisco Bay-Delta Tidal Marshes

Abstract

Sediment deposition in tidal wetlands is a critical process that determines whether vertical growth will keep pace with sea-level rise. However, more information is needed on how sediment deposition varies spatially and temporally across wetlands, including the effects of elevation, tidal inundation, vegetation, and weather. We investigated variation in sediment deposition due to season, distance from channel, channel size, and vegetation composition at low and high salinity tidal marshes in the San Francisco Bay-Delta Estuary, California using sediment traps deployed monthly between December 2015 and November 2016. Over the course of the year, sediment deposition ranged widely (1.4 – 174.0 kg m−2 yr−1) and averaged 19.5 ± 3.5 kg m−2 yr−1. Deposition increased with flooding duration, decreased with increasing distance from channels, and was highest during the spring and early summer. Higher wind speeds during the spring may have driven re-suspension from mudflats, promoting deposition. Ratios of organic-to-mineral deposition were twice as high at the fresher site and were correlated with differences in vegetation composition between sites. Our results suggest that seasonality, distance from sediment source, salinity regime, and channel size are important sources of spatiotemporal variation in deposition. These results are relevant to accretion sampling and wetland restoration design.