Phosphate Ion Interactions at the Sediment–Water Interface in Lake Ontario: Relationship to Sediment Adsorption Capacities

Abstract

The chemical forms of iron and phosphorus in surficial sediments of the Niagara Basin of Lake Ontario were determined by Mossbauer spectral and chemical extraction methods. The core locations lie on a transect across a boundary separating sediments displaying a crusty iron- and phosphorus-rich red layer a few centimetres beneath the sediment–water interface from sediments displaying no such layer. Concentrations of nonapatite inorganic phosphorus are relatively low at the surfaces of the layered cores whereas the iron forms are quantitatively similar. It is proposed that the red layers prevent upward diffusion of pore-water ferrous and phosphate ions to the surface. The degree of phosphorus recycling within the top few centimetres of sediment can then be estimated. Approximately 0.035% nonapatite inorganic phosphorus is carried into the anoxic zone. The data, combined with loadings of fine-grained sediment, indicate that Lake Ontario sediments have a net annual binding capacity of ~3500 metric tons of phosphorus, which compares with current loadings of ~8900 metric tons. This binding capacity supports current recommended phosphorus loadings to Lake Ontario.