Predicting internal phosphorus loading in stratified lakes

The ability to predict internal phosphorus loading in stratified lakes has been given new urgency by the realization that traditional best management practices to control external loading have limited effectiveness. We tested the hypothesis that lake sediments with molar Al:Fe ratios greater than 3 would release very little P (Kopáček et al., Environ Sci Technol 39:8784–8789, 2005). We fractionated operationally-defined species of phosphorus, aluminum, and iron in the profundal sediments from a diverse collection of lakes, and sought predictive relationships with previously determined phosphorus release rates from these same sediments. Our results suggest that sediments with Al:Fe molar ratios greater than 3 release negligible amounts P, and that in sediments with Al:Fe ratios less than 3, P release is significantly correlated with the concentrations of reductant-extractible P and the contribution (%) of NaOH-extractible P. We constructed a decision tree model to enable lake managers to anticipate the magnitude of internal P loads in lakes undergoing increased watershed development or changes in thermal stratification and subsequent anoxia due to climate change.