Empirical Insights into Lake Response to Nutrient Loadings, with Application to Models of Phosphorus in Lakes

Data from 128 phosphorus limited lakes are used to determine the significance of various limnological parameters in models that allow the prediction of lake trophic state for given phophorus loadings. A basic parameter used in the study is the steady-state concentration of a conservative substance in lakes (the average inflow concentration). By isolating this expression for phosphorus, the ability of various morphological parameters (hydraulic residence time, mean depth, surface area) to account for the nonconservative behavior of this nutrient is investigated. The data are first plotted on the phosphorus loading diagrams of Vollenweider and Dillon and then subjected to stepwise discriminant analysis. In each approach the residence time alone is statistically significant in describing the nonconservative behavior of phosphorus. The ability of residence time to replace Dillon's retention coefficient in predictive trophic state models and the advantages thereof are argued. Possible explanations for the significance of residence time are discussed.