Periphyton nutrient composition as a robust measure of nutrient status in streams
Jeffrey A. Back and Ryan S. King. Biology, Baylor University, One Bear Place #97388, Waco, TX 76798
Periphyton exhibit tremendous plasticity in nutrient content depending largely upon nutrient availability. Because periphyton integrate nutrient conditions over time, they may better reflect nutrient conditions in streams than water chemistry. We collected epilithic periphyton from 26 stream sites in central Texas spanning a wide range of nutrient enrichment based on water chemistry. We collected periphyton on 3 occasions over a 7-month period. We used colloidal silica centrifugation to separate bulk periphyton into predominately sediment and organic fractions for comparisons of elemental content with bulk periphyton. The percent phosphorus, nitrogen, and carbon content were considerably higher in the periphyton (organic) fraction than the sediment fraction. Nutrient content in the organic fraction varied by several fold across the 26 sites and consistently separated sites with either low or high surface-water nutrients. However, periphyton nutrients, particularly phosphorus, did a better job of separating sites with apparently similar but relatively low surface-water nutrients. Moreover, periphyton P was an excellent predictor of diatom species composition across sites. Even sites with high nutrient concentrations but low algal biomass reflected enrichment via elevated nutrient content of the periphyton. Bulk periphyton was less useful as an indicator. Periphyton elemental composition may be a robust measure of nutrient status.