LIMITING NUTRIENT DETERMINATION IN LOTIC ECOSYSTEMS USING A QUANTITATIVE NUTRIENT ENRICHMENT PERIPHYTOMETER

The decline of water quality in United States' lotic ecosystems (strea ms and rivers) has been linked to nonpoint source nutrient loading (U. S. EPA, 1990). Determining limiting nutrients in streams is difficult due to the variable nature of lotic ecosystems. We developed a quantit ative passive diffusion periphyton nutrient enrichment system, called the Matlock Periphytometer, to measure the response of attached algae (periphyton) to nutrient enrichment. The system is simple to build and provides quantitative nutrient enrichment of a surface for periphytic growth. The periphyton grow on a glass fiber filter, which allows com plete recovery of periphyton for chlorophyll a analysis. A 14-kilodalt on dialysis membrane was used as a biofilter to prevent bacterial and algal contamination of the nutrient solution. We determined the rates of diffusion of nitrogen and phosphorus ions across the Matlock Periph ytometer's dialysis membrane and glass fiber filter over a 21-day peri od (42 and 22 mu g/cm(2)/hr, respectively). We used the Matlock Periph ytometer to determine the limiting nutrient in a woodland stream. Six replicates each of a control, nitrogen, and phosphorus treatment were placed in the stream for 14 days. The results indicated that phosphoru s was the limiting nutrient in the stream for the period and location sampled.