Writing in today's (June 13) online edition of the Proceedings of the National Academy of Sciences (PNAS), University of Wisconsin-Madison limnologist Stephen R. Carpenter reported results of a study that showed that the buildup of phosphorus in soils in lake watersheds is likely to be the source of serious chronic environmental problems for hundreds of years.
"If these results are correct, and I suspect that they are, things could get considerably worse," says Carpenter, a UW-Madison professor of zoology and one of the world's leading authorities on freshwater lakes. "The buildup of phosphorus in watersheds is very threatening. Sooner or later it is going to hit the lakes and it is going to pose problems."
Eutrophication occurs when nutrient-rich soil washes into lakes and streams. It stimulates the growth of algae and has transformed many of the world's lakes from clear freshwater reservoirs to soupy, weed-choked pools. It contributes to oxygen depletion, which leads to fish kills, and can stimulate the growth of toxic algae.
According to the study, industrial agriculture, with its reliance on phosphorus-rich fertilizers, is the primary source of much of the excess nutrients responsible for fouling lakes. In rich farming areas, like southern Wisconsin, the routine application of chemical fertilizers and phosphorus-laden manure, has resulted in the gradual accumulation of phosphorus in the soil, which, ultimately, has nowhere to go but into the streams, lakes and rivers of the watershed where it is applied.
"There's a huge amount of phosphorus in the watershed that hasn't washed into the lake yet," says Carpenter, meaning the problem is likely to persist for centuries.