Epilithic diatoms as indicators of stream total N and total P concentration

Patterns of diatom species distribution in relation to total N (TN), total P (TP), and other environmental variables from riffle sites on 2 streams in southern Ontario, Canada, were determined using canonical correspondence analysis (CCA). Relationships with TN and TP were sufficiently strong to develop weighted-averaging (WA) regression-calibration models for inferring stream water concentrations of these nutrients. The models were accurate within ±2.4 μg/L for TP (apparent r2 = 0.52) and ±2 mg/L for TN (apparent r2 = 0.53). An evaluation of the goodness of fit of these models with and without bootstrapping indicated that they performed better (bootstrapped r2 = 0.44 for TP and bootstrapped r2 = 0.42 for TN) than published TN and TP inference models for which similar assessments were made. Based on Organisation for Economic Cooperation and Development eutrophication ratings, the TP model predicted 76% of the mesotrophic and 57% of the eutrophic samples correctly. The model correctly predicted only 20% and 33%, respectively, of oligotrophic and hypereutrophic samples. WA inference models were improved when seasonal variation was removed by using mean summer water quality and diatom data (apparent r2 = 0.76 and bootstrapped r2 = 0.61 for TP; apparent r2 = 0.82 and bootstrapped r2 = 0.70 for TN). Overall, we conclude that epilithic diatoms can be related to TN and TP using these methods, and that WA inference models have utility for indicating eutrophication in southern Ontario lowland streams.