Evaluating the use of periphyton as an indicator of nutrient over-enrichment in North Carolina wadeable streams

Abstract

The North Carolina Department of Environmental Quality (NCDEQ) is currently working to define statewide nutrient criteria for its waterbodies. As a subset of this nutrient criteria development project, approaches to identify where high concentrations of nitrogen and phosphorus are occurring in streams were evaluated. The primary focus was to evaluate if biomass and taxonomic identification of periphyton can effectively detect nutrient impacts in wadeable streams. Land use and other water quality parameters were also evaluated as potential tools to predict nutrient concentrations. The goals were to identify preliminary measures that indicate nutrient impairment, to assess if further development of a periphyton monitoring program is feasible, and to make recommendations about the direction of future studies. Results show that high proportions of developed land can be used to identify potential downstream nutrient problem areas. Additionally, high proportions of vegetated land can be used to identify reference stream reaches. Specific conductance is a measurable parameter in the field that can adequately predict elevated concentrations of nitrogen (N) and phosphorus (P). Several results suggested that watershed land-use influences stream periphyton cover and taxonomic composition. Elevated periphyton cover was found downgradient of agricultural land and wastewater treatment plants and an increase in motile species richness was found in periphyton in streams draining watersheds with greater developed land. More research is needed to adequately determine if patterns exist between periphyton biomass, taxonomic composition, and nutrient concentrations.