| Throughout Chesapeake Bay, fluvial sediments have been rapidly building river-mouth deltas. Previous research demonstrated that accumulating sediments derive from European deforestation, agriculture, and urbanization. Tributaries of upper Chesapeake Bay contain fresh water, so river-mouth deltas form tidal freshwater wetlands. These wetlands serve as critical buffers protecting the estuary against sediments, nutrients, and toxics. Through a combination of field monitoring and computer modeling this study sought to determine the ecological factors and hydrometeorological processes responsible for the dynamics of tidal freshwater delta evolution over multiple time scales.; Mapping and monitoring of vegetation, substrates, sedimentation rates, delta geomorphology and hydrology, wind vectors, watershed runoff, and rainfall were carried out April 1995 to November 1997 in the Otter Point Creek tidal freshwater delta at the head of Bush River on Chesapeake Bay. Bi-weekly sedimentation rates showed significant spatial and temporal variability ({dollar}-{dollar}2.84 to 5.57 {dollar}rm g{lcub}cdot{rcub}cmsp2).{dollar} When the rates were stratified by habitat, seasonal cycles in deposition and organic content were found, with deposition decreasing exponentially and organic content increasing exponentially among habitats. Spatial variability in summer sedimentation, organic content, and grain size distributions were explained by an index representing plant association, elevation, distance to nearest channel, and distance to the subtidal front.; Spectral analyses of wind, water level, and watershed runoff time series showed that each has cycles at multiple frequencies. The diurnal tide along with cycles in South to North wind were responsible for changing water level on daily to weekly time scales. Modeling of wave conditions and sediment entrainment demonstrated that sediment is resuspended from subtidal areas daily, with the most resuspended in spring and autumn, and transported upslope to intertidal marshes the majority of time. Field monitoring of sedimentation independently confirms model findings.; A diffusion model of long term delta progradation at Otter Point Creek was calibrated with a paleoecologically reconstructed sedimentation history. The model showed two intervals of growth, one of significant erosion, and one of sediment redistribution among delta zones. The model compared favorably with field observed sedimentation and the known history of delta growth behind a reservoir in the adjacent watershed. |
