Phosphorus cycling in a managed lake ecosystem: Seasonal and longer-term trends

Abstract

► P cycling in an oxygenated lake. ► Internal P loading during summer thermal stratification. ► Release of P from oxyhydroxide phases during periods of low dissolved oxygen. Irondequoit Bay, adjacent to Rochester, New York, is one of the larger embayments along the southern coast of Lake Ontario. Since the 1980s, management activities have been focused on improving water quality and the trophic status of the bay, including a program of hypolimnetic oxygenation. During the summers of 2003, 2004 and 2009, a program of basic water quality parameter profiles and sediment sampling completed. Results of these surveys show an increase in hypolimnetic P throughout each summer season. The increase in P is concordant with decreasing dissolved O 2 concentrations. Although the dissolved O 2 levels are persistent in the suboxic range for most of the summer season, the oxygenation program prevents anoxic conditions, limiting the release of P to that associated with Mn oxyhydroxides. Longer-term trends show an upward linear trend in metalimnetic P which is associated with the trophic status of the bay. This upward trend may be linked to cycling and enrichment of the near surface sediment in P.