CLIMATE CHANGE EFFECTS ON THE MECHANISMS OF INTERNAL PHOSPHORUS LOADING AND ALGAL ECOLOGY IN ALKALINE EUTROPHIC LAKES

Recent and rapid eutrophication of two alkaline lakes followed the onset of anomalous atmospheric temperatures in central Alberta. Historical changes in sediment C, N, P content from two hypereutrophic lakes correlated with molar S:Fe and Fe:Mn ratios, and a reorganization of algal assemblages. Pore-water samples retrieved from cores collected in seven Central Alberta alkaline lakes suggested that P retention in sediments was regulated by Fe rather than Ca. Simultaneous release of alkalinity generating ions and P occurred in Fe deficient pore-water regardless of saturation with respect to hydroxyapatite. Higher temperatures, lower redox potentials and accelerated internal P-loading established positive feedbacks that lead to diminished sediment P-binding capacity of sediments via sequestration of un-reactive Fe by S and a modification of algal assemblages. As many lakes subject to internal P-loading are becoming more productive in the absence of catchment development, sediment Fe-S-P dynamics may inform efforts towards mitigating climate impacts on the water quality, the aesthetics, and the growth of harmful algal blooms in alkaline eutrophic lakes.