A simulation of saltmarsh water column dynamics

Abstract

This deterministic model of water column dynamics in saltmarsh tidal creeks focuses mainly on mechanisms of carbon and nitrogen cycling within the water. The model includes biotic interactions among phytoplankton, zooplankton, dissolved inorganic nitrogen, detritus and dissolved organics. In addition, the model examines the effects of tidal exchange with the nearshore coastal ocean. In simulation experiments, the model isolates the water column submodel from simulated vegetated marsh surface, oyster reefs, and subtidal benthos. By comparing simulation results with field data from the North Inlet saltmarsh (Georgetown County, SC) we examined the relative importance of water column processes in controlling seasonal changes observed in the tidal creeks. Results suggest that for the components with rapid biotic turnover rates (phytoplankton and dissolved inorganic nitrogen) much of the observed seasonal pattern is controlled by internal cycling within the water column (planktonic productivity, nutrient uptake and remineralization). For components with slower turnover rates (zooplankton, detritus, and dissolved organic matter) tidal exchange with the coastal ocean plays a larger role in controlling seasonal variability. The model accounts for less of the observed variability in detritus and dissolved organic matter, suggesting the seasonal importance of upland runoff and exchanges with other marsh subsystems in controlling concentrations in tidal creek.