Lake Simcoe water quality update, with emphasis on phosphorus trends
Lake Simcoe is a valuable natural resource, easily accessible to more than one-half of the Ontario population and generating approximately $160 Million in the local economies through recreational activities alone (LSEMS, 1995). The goal of the Lake Simcoe Environmental Management Strategy (LSEMS) Implementation program is to restore water quality and fish habitat to conditions that support self-reproducing populations of lake whitefish and lake trout (species that are presently maintained in the lake through stocking programs). A major objective of the LSEMS program is to reduce phosphorus loading to the lake by about 25% in an attempt to increase end-of-summer deepwater dissolved oxygen concentrations (volume-weighted through the depth interval 18-42 metres) from present levels of about 3 mg L1, to 5 mg L-1 (Nicholls, 1995, 1997). Phosphorus concentrations, when measured regularly at several locations, provide an indication of the trophic (or nutrient enrichment") status of the lake and when continued over long term can reveal progress (or lack of progress) towards the phosphorus loading objective. Several other lake processes can influence phosphorus concentrations in Lake Simcoe besides phosphorus loading (biotic interactions invading species effects and year-to-year weather differences); long periods of monitoring are often necessary to gain some understanding of these impacts on lake function. This report updates phosphorus trend information summarized from several regularly sampled locations on Lake Simcoe. Some ancillary water quality data deemed important for their indicator value (e.g. chloride dissolved oxygen) are briefly updated as well.