Spatial and temporal analyses of water quality and phytoplankton community structure in two lagoonal estuarine systems on the South Carolina coast: A comparative analysis of an urban and pristine system

Nutrient availability and primary productivity in shallow well-mixed estuarine systems vary over time and space. However, temporal studies are usually the primary focus, and information on spatial variability within these systems is generally insufficient. The robust growth of coastal communities in the southeast is putting unique pressures on estuarine resources. Urbanization of estuarine systems may alter ecosystem function, and thus affect the spatial scale and magnitude of nutrient concentrations and primary production in both a temporal and spatial manner. We examine the spatial and temporal patterns of nutrients and primary productivity and phytoplankton community composition in two well-mixed estuarine systems, (1) a developed estuary, Murrells Inlet (MI), SC, and (2) a relatively pristine estuary, North Inlet (NI), SC. Results indicate that the urbanized estuary had higher chlorophyll a biomass during the summer maximum when compared to NI. Nitrogen (N) and phosphorous (P) were also found to be greater following stochastic storm events in MI. Diatoms were dominated community structure in the fall, winter, and spring with a distinct shift to a community dominated by pico- and nanoplankton in the summer including diatoms, flagellates and cyanobacteria. Minor differences were observed in phytoplankton community structure between MI and NI, but longer-term studies are needed.; Spatio-temporal models in MI indicated the influence of a stochastic storm event in forcing spatial gradients in nutrient concentrations. Chlorophyll a and the Si:DIN were spatially and temporally correlated and found to be spatially unrelated to overall nutrient concentrations. Orthophosphate exhibited a distinct and stable spatial pattern over a wet and dry period. Spatial gradients indicated the presence of three regions in MI (1) an urbanized area that receives greater inputs of inorganic nitrogen and orthophosphate, (2) a southern region that is less affected by anthropogenic inputs likely due to the forested state park in that region and (3) an oceanic region near the inlet characterized by minimum concentrations on a system-wide scale.