Modeling studies of three-dimensional tide- and buoyancy-induced flow, sediment resuspension, and water quality in the Satilla River estuary, Georgia.

摘要

This study developed an interdisciplinary estuarine model that includes complex physical, biological, and chemical processes and their nonlinear interactions in the Satilla River estuary, Georgia. The model helps us to identify and qualify how the physical, biological, and chemical processes and their interactions control the spatial and temporal distribution of water quality parameters.; A three-dimensional coupled hydrodynamic, suspended sediment, and water quality model was developed and applied to the Satilla River estuary. The hydrodynamic model is a modified ECOM-si with inclusion of the flooding/drying process over the intertidal zone. The suspended sediment model consists of a simple passive tracer equation with inclusion of sinking, resuspension, and sedimentation processes. The water quality model is a modified WASP5 with inclusion of benthic nutrient fluxes and heterotrophic bacterial respiration.; The hydrodynamic model successfully simulated the spatial and temporal distributions of tidal elevation and current, spring and neap tidal variation, and water exchange between the channel and the intertidal zone. The flooding/drying process over the intertidal zone plays a key role in tidal current and thus water transport simulation. Tidal-induced residual flow is characterized by multiple eddy-like convergences and divergences. Tidal asymmetry is controlled by frictional interaction between tidal currents and bottom topography, estuarine geometry, amount of water storage in intertidal zone, and spring-neap tidal variation.; The spatially non-uniform distribution of suspended sediment concentration is controlled by horizontal and cross-estuary convergent and divergent residual flows, non-uniform along-estuary distribution of bottom stress, and inertial effects of a curved estuarine shoreline. The temporal variation of vertical resuspension is caused by asymmetrical tidal mixing during flood and ebb tides.; Low dissolved oxygen in the Satilla River estuary results from large sediment oxygen demand in the salt marsh and the large ratio of salt marsh to channel area, which suggests that low dissolved oxygen is a natural condition, rather than due to anthropogenic activity.; Benthic nutrient flux and nitrification are two important processes controlling nutrient concentrations in the Satilla River estuary. Groundwater input does not have a significant effect on estuarine circulation and salinity, but possibly contributes to nutrient, especially nitrate concentration when the residence time is longer.