Nutrient limitation of periphyton growth in the Truckee River, California-Nevada

Nutrient resource limitation of periphyton growth in the Truckee River was determined using nitrogen to phosphorus ratios (N:P) in water and periphyton, nutrient diffusing substrate bioassays (NDS), and measurements of ectoenzymatic alkaline phosphatase and leucine aminopeptidase activity. TN:TP ratios in the Truckee River from 1990 to 2000 suggested that nutrient limitation of periphyton changes longitudinally from phosphorus-limited growth to nitrogen-limited growth. However, this trend was not easily apparent during the summer of 2001. Nitrogen concentrations in the river, aufwuchs phosphorus contents, and aufwuchs N:P ratios suggested that the Truckee River was anomalous with respect to nitrogen and phosphorus balance during 2001. Potential reasons for the imbalance included drought conditions throughout the catchment, two fires in the upper catchment, and a nitrogen pulse to the lower river from a wastewater treatment facility. Even with anomalous nitrogen dynamics during 2001, ectoenzyme activities, soluble reactive phosphorus concentrations and water N:P ratios suggested a trend from phosphorus to nitrogen limitation.