Seasonal variations in sedimentation and organic content in five plant associations on a Chesapeake Bay tidal freshwater delta

Research on sedimentation processes in tidal freshwater marshes is lagging far behind that for salt marshes despite the importance of tidal freshwater systems for understanding impacts of watershed land use on estuarine habitats and water quality. From September 1996 to November 1997, biweekly sedimentation rates were monitored at 30 sites spanning 5 distinct habitat types across the intertidal zone of the tidal freshwater delta at the head of the Bush River tributary to upper Chesapeake Bay. These data were used to determine the spatio-temporal dynamics of sedimentation and erosion in the delta as well as the role of vegetation in seasonal to interannual physical processes. The observed mean net sedimentation rate was 1.00 g cm(-2) yr(-1), with a range of -74.15 to 145.2 g cm(-2) yr(-1). No relations between delta sedimentation rate and total precipitation, peak precipitation intensity, or watershed discharge were found over time. Instead, three distinct temporal regimes in the data predominantly reflected seasonal patterns in vegetation life cycle. With regard to spatial patterns, nonparametric statistical tests demonstrated that each habitat had a unique cycle of sedimentation and erosion. When sedimentation rates were multiplied by habitat area, the floating leaf habitat was found to have sequestered 6370 t yr(-1). In contrast, the high marsh lost 624 t yr(-1). These data indicate that the greater diversity of plant species in tidal freshwater marshes generates a wider variation in geomorphic processes than is possible for salt marshes. (C) 2001 Academic Press.