Phosphorus Uptake and Release by Lake Ontario Sediments

Sediment cores were obtained from 15 lake stations representing the three major basins and the Inshore Zone of Lake Ontario. Cores were sectioned for characterization of the surface sediments according to inorganic P chemical mobility. Physical mobility was characterized by measurement of P release from intact cores incubated under controlled laboratory conditions. The proportions of potentially chemically mobile inorganic P were usually high (30 to 60%) in the central basin sediments and low (2 to 8%) for the inshore zone sediments. Although the amounts of inorganic P desorbed after three successive equilibrations (in .lM NaC1) of Lake Ontario sediments represented only 3 to 17% of the potentially mobile inorganic P, sufficient inorganic P was desorbed to restore a large part of the original interstitial inorganic P concentrations. Interstitial inorganic P (mobile P) concentrations ranged from 14 to 1280 Ng/l and were higher than dissolved inorganic P concentrations in the overlying water. Diffusion rates estimated from the range of observed interstitial inorganic P values ranged from about 0.05 to 0.6 mg m-‘ day-’ and were in agreement with the range of 0.03 to 0.8 mg m-2 day-’ estimated from P release from intact cores incubated under controlled laboratory conditions. Based on an inorganic P flux of 0.2 mg estimated annual contribution of inorganic P to Lake Ontario water is equal to about 10% of the external P loading.Enviromental Protection Agenc