Spatial Gradient Analyses Of Nutrients And Chlorophyll A Biomass In An Urbanized Lagoonal Estuary: A Comparison Between Wet And Dry Periods

The effects of stochastic events on estuarine water quality parameters are often difficult to quantify spatially due to R S the inherent variability in these systems. The use of geographic information systems to identify spatial patterns and trends can improve such efforts. This work describes the use of geographic information systems and the Mantel Test to determine the existence of trends and the persistence of spatial patterns in the relationships between nutrients and chlorophyll a in an urbanized lagoonal estuarine system, Murrells Inlet, South Carolina. Relatively dry and wet periods were compared, the latter following several substantial precipitation events related to tropical hurricane activity in the summer of 1999. Dissolved inorganic nitrogen concentrations were elevated following the passage of Hurricane Irene, and chlorophyll a did not increase concomitantly. Orthophosphate was found to have persistently higher concentrations in the more urbanized regions of Murrells Inlet that were consistent spatially during the two sampling periods. Strong spatial and temporal correlations between chlorophyll a and dissolved silicate: dissolved inorganic nitrogen suggest a relationship between the latter ratio and the phytoplankton growth. However, there appeared to be only a tenuous relationship between chlorophyll a and dissolved inorganic nitrogen and phosphorus, both spatially and temporally, suggesting that nutrient requirements for phytoplankton growth were met by internal estuarine processes, during this time period.