Interstitial inorganic phosphorus concentrations in lakes Mendota and Wingra

Interstitial P levels in Lake Mendota and Lake Wingra were evaluated as a function of season and water column and sediment depth. Interstitial water was obtained by the centrifugation-filtration method. Temporal variations were observed over the entire 15 cm sediment depth interval examined in all four locations evaluated. Interstitial reactive P (IRP) levels in Lake Mendota ranged from 0.014–1.67 mg l^?1 at the 5–6 m water column depth and from 1.20–5.75 mg l^?1 at the 18–19.5 m depth. IRP levels in Lake Wingra ranged from 0.029–2.15 mg l^?1 at 3.5 m and from 0.191–3.96 mg l^?1 at 2 m. Variations in interstitial P were attributed to variations in oxidation state of Fe as influenced by oxygen transport and reduction rates.