Phosphorus flow in a watershed-lake ecosystem

Cultural eutrophication of lakes caused by excess phosphorus (P) loading fr om agricultural areas is a persistent and serious environmental problem. We quantified P flows in a watershed-lake ecosystem using a simple mathematic al model that coupled in-lake and upland processes to assess and compare th e long-term impacts of various management strategies. Our model compares ab atement by in-lake strategies (such as increasing the flux of P from algae to consumers and alum application) with riparian management to decrease P f low and with balancing P budgets at the watershed scale. All of these strat egies are effective to some extent. However, only reducing the amount of fe rtilizer P imported to the watershed will decrease the total P in the syste m at steady state. Soil P-a large reservoir with slow turnover rate-governs long-term nux to the lake and must be decreased in size to maintain long-t erm control of eutrophication.