Tributary phosphorus loading to Lake Ontario

Tributary phosphorus (P) loading was estimated for 145 Canadian and American streams entering Lake Ontario and was compared with historical P loads of the Niagara River. The 145 Lake Ontario tributaries contributed 2606 mT/year of P. with the U.S. tributaries contributing 1411 mT/year and the Canadian tributaries contributing 1195 mT/year. In New York, the largest tributary sources of total phosphorus (TP) were from the Genesee River (417 mT/year), followed by the Oswego River (336 mT/year) and the Black River (135 mT/year). In Ontario, the largest tributary sources of TP were from the Trent River (200 mT/year), the Humber River (93.0 mT/year), and the Welland Canal (80.8 mT/year). Phosphorus loading from both Canadian and American wastewater treatment plants was 781 mT in 2008. The total P load of tributaries (2606 mT/year) to Lake Ontario was 234% higher than that of wastewater treatment plants and was 67.5% of the 1982 Niagara River P load and 50.3 to 70.6% of the 1999 and 2004 Niagara River P loads. While the P load from the Niagara River connecting channel is important to the overall trophic status of the offshore of Lake Ontario, the impact of tributaries on water chemistry and ecology of the nearshore and embayments of Lake Ontario is potentially great and is being increasingly recognized as a driver of nearshore conditions. (C) 2012 International Association for Great Lakes Research. Published by Elsevier B.V. All rights reserved.