RESPONSE OF TIDAL FRESHWATER MARSHES IN CHESAPEAKE BAY TRIBUTARIES TO SHORT-TERM VARIABILITY IN SEA LEVEL AND SUSPENDED SEDIMENT CONCENTRATIONS

Tidal marshes are among the world’s most important ecosystems and are essential to the sustainability of coastal societies in temperate latitudes. Their capacity to store sediment, carbon, and nutrients will be a key component of many watershed management plans in the coming decades. However, the future sustainability of tidal marshes is threatened by environmental changes, such as increasing rates of sea-level rise (SLR) and declines in fluvial suspended-sediment concentrations (SSC). This presentation evaluates the response of tidal freshwater marshes to these environmental changes, focusing on 3 systems within the Chesapeake Bay watershed - Dyke Marsh Preserve, a degrading marsh in the Potomac River; Jug Bay Wetlands Sanctuary, a relatively pristine marsh in the Patuxent River; and Kenilworth Aquatic Gardens, a restored marsh in the Anacostia River. We assess the short-term (over 1 year) response to fluctuations in sea level and sediment supply at these marshes, using concurrent measurements of the vegetation community (species type and cover) and the sedimentary environment (coarse and organic content; bimonthly and seasonal sedimentation rates from ceramic tiles and ⁷Be (half-life 53.3 d) geochronology). This approach provides insight into the spatial and temporal variability of potential factors influencing marsh response to that be compared to insights from decadal-scale observations of the sedimentary record (using ²¹⁰Pb (half-life 22.3 y) geochronology) and long-term measurements of sea level and SSC. We find that sedimentation rates generally scale with sediment supply to individual marshes and that synergies exist between sediment and vegetation parameters that the role of physical drivers and plant contributions vary among marshes and with elevation. Understanding these synergies between the vegetation community and sediment dynamics will be key to developing “early warning systems” for marsh vulnerability to environmental change.