Sediments as a source of nutrients to hypereutrophic marshes of Point Pelee, Ontario, Canada

Elevated concentrations of nutrients, resulting in prolific algal growth, w ere reported in some open-water ponds in one of the finest surviving wetlan ds on the Lower Great Lakes, Point Pelee National Park. Ontario, Canada. A study was undertaken to identify the sources of nutrients to the most impac ted pond in the complex, Sanctuary Pond. Sediment chemistry and chemistry o f interstitial water were examined to determine thr role of benthic sedimen ts in nutrient dynamics. The results indicate high concentrations of dissol ved nutrients (about 4 mg/l of P and over 20 mg/l of N) in sediment porewat er, a consequence of organic matter decomposition. No spatial differences w ere observed between porewater profiles, nor in the levels of dissolved con stituents. Likewise, sediment P concentrations were similar at both investi gated sites. Thermodynamic calculations, carried out to determine mineral e quilibria of phosphate minerals potentially controlling the concentrations of dissolved P in sediment porewater, suggest that P generated from organic matter decomposition should he reacting with Fz, Ca and Al to form authige nic mineral phases vivianite, hydroxyapatite and variscite. The high levels of nutrients in porewater, the lack of spatial differences in sediment and porewater nutrient concentrations and the absence of known external nutrie nts sources suggest that at the Sanctuary Pond internal regeneration of nut rients from sediments is responsible for the hypereutrophic conditions in t he pond. (C) 1999 Elsevier Science Ltd. All rights reserved.