Phosphate Exchange Between Littoral Sediments and Overlying Water in an Oligotrophy North-Temperate Lake

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Abstract
The soluble phosphate equilibrium between aerobic sediment and overlying water was examined in intact cores of marginal sediment and water from Lake Memphremagog. Radiotracer experiments demonstrated a dynamic phosphate exchange between sediments and water under steady-state conditions. Perturbations of this equilibrium in batch and continuous-flow systems show that aerobic sediment can act as a phosphate source or sink, depending on the phosphate concentration of the overlying water. The existence of an oxidized microzone on the sediment surface does not preclude phosphate release when concentrations in the overlying water drop below the equilibrium concentration. Under natural conditions, soluble reactive phosphorus concentrations in the surface waters of Lake Memphremagog are always lower than the equilibrium concentrations measured in this study. This suggests that aerobic marginal sediments may serve as a phosphate source in lakes where algal demand maintains low levels of soluble phosphate in the water.