Determination of limiting nutrient for periphyton growth in Piedmont streams

Nonpoint-source pollution from agricultural and urban sources is a major cause of N and P over-enrichment of aquatic ecosystems. Nutrient enrichment can lead to anthropogenic eutrophication of surface waters, decreasing their ecological, economic, and recreational value. Attached algal communities (periphyton) can be an indicator of stream trophic status. Limitation of periphyton growth by N and P or both was determined using both nutrient-diffusing bottles and nutrient-diffusing agar vials at eight stream sites in two Georgia Piedmont watersheds. Using the nutrient-diffusing bottles, only one site out of seven was limited by N in spring 2005, and no sites were limited by P. The NO3-N concentration in the N-limited stream was 2.9 mg L. In contrast, no N limitation was found and P-limitation was indicated for four sites out of seven in spring 2005 when using nutrient-diffusing agar vials. Stream concentrations at P-limited sites were below 0.03 mg PO4-P L.