Phosphorus release from sediments in hardwater eutrophic lakes: the effects of redox-sensitive and -insensitive chemical treatments

1. Phosphorus (P) release from bottom sediments is an important source of n utrient enrichment in many lakes in sedimentary basins, such as those in we stern Canada. On the Boreal Plain, sediment P release is particularly stron g during periods of seasonal anoxia. 2. In this study, the effects of reduction-oxidation (redox)-sensitive and -insensitive chemicals on P release were examined in sediment cores collect ed from three eutrophic lakes. 3. Contrary to expectations, redox-sensitive treatments were no more effect ive at lowering total phosphorus (TP) in sediment cores than some redox-ins ensitive treatments. Redox-sensitive treatments with FeCl3 and FeCl3 + O-2 reduced TP to 8 and 6%, respectively, of reference concentrations, whereas redox-insensitive treatments with alum or lime + alum reduced TP to 14% of reference concentrations. Lime and O-2 treatments reduced TP concentrations to 35 and 52% of reference concentrations, respectively. 4. The fraction of P that adsorbed and co-precipitated with iron and alumin ium in the sediment cores was low (non-apatite phosphorus fractions < 5%), suggesting that P release was controlled by apatite solubility and bacteria l metabolism.