Nutrient limitation of periphyton in moderately nutrient enriched agricultural streams of west-central Wisconsin

Periphyton is an important component of the biological community in stream ecosystems and can be sensitive to changes in nutrient concentrations, primarily those of nitrogen (N) and/or phosphorus (P).  The majority of studies examining the effects of nutrient availability on periphyton have been conducted in relatively low-nutrient systems.  Less is known how changes in nutrient availability will alter periphyton communities in higher nutrient streams, like those associated with agricultural systems.  The objective of this research was to determine the effects of additional nutrient enrichment on nutrient limitation of periphyton in six moderately enriched agricultural streams of west-central Wisconsin.  Nutrient limitation was assessed using nutrient diffusing substrates (NDS) filled with an agar/nutrient mixture of either control (no amendment), +N, +P, or +N+P.  Twelve replicates of each treatment were incubated in streams for 21 days during the winter 2009 base flow period.  After the incubation period pheophytin-corrected chlorophyll a concentration and phophatase activity were determined spectrophotometrically.  Preliminary results suggest co-limitation of N and P in several of the study streams.  The results of this study may provide addition insights in forecasting the biological and chemical changes that may occur in agricultural streams that continue to receive elevated levels of nutrients.