PHYTOPLANTKON RESPONSES TO NITROGEN AND PHOSPHORUS AS INDICATORS OF LAND USE PATTERNS IN COASTAL SOUTH CAROLINA

Human population growth and associated development are among the greatest stressors for aquatic systems due to impacts on hydrography, habitat, nutrient loading, and others. For example, the South Carolina (SC) coastal zone is undergoing some of the most rapid population growth and urbanization in the United States, and this will presumably affect nitrogen (N), phosphorus (P), and dissolved organic carbon (DOC) delivery to receiving estuaries and affiliated plankton and microbial communities. We have been examining how N, P, and DOC influence phytoplankton and microbial assemblages in several SC systems spanning a wide range of land uses (forested tidal creeks to stormwater detention ponds). Nutrient (N and P) addition bioassays were conducted in situ seasonally over 48 h each site. Phytoplankton biomass and assemblage responses to various forms of N, with and without P, were assessed using diagnostic pigments and microscopy, whereas microbial assemblages were evaluated using flow cytometry. Results thus far suggest that extent of development is positively associated with phytoplankton responses to N-form, and development is generally negatively correlated with DOC inputs from the land to the coastal zone. Current work is examining the role of hydrology on N and P delivery on phytoplankton assemblages and biological responses. This has important management implications because numeric criteria for N and P have not been established for coastal SC, but thresholds are being considered. Since biological (phytoplankton) responses are indicators of overall estuarine health, these results will be critically important for both understanding how land use shapes planktonic communities and informing management decisions.