Accelerated water quality improvement during oligotrophication in peri-alpine lakes.

Monitoring of four eutrophic Swiss lakes undergoing oligotrophication during more than 25 years (i.e., gradually decreasing nutrient loading, productivity, and associated symptoms of eutrophication) revealed that phosphorus (P) net sedimentation rates (the fraction of a lake's total P content that is buried within its sediments each year) and P export rates (the fraction of the lakes' total P content that is exported via the outlet each year) increased as the lakes' P contents decreased. These findings are of scientific as well as practical interest because they imply that, contrary to the hitherto prevailing view, the P concentration of eutrophic lakes will decrease more than proportional to the reduction of their external P load, and faster than predicted by the linear (eutrophic state-based) models.