Effects of Temperature and Other Factors on Summer Phosphorus in the Inner Bay of Quinte, Lake Ontario: Implications for Climate Warming

Summer total phosphorus (TP) concentrations in the inner Bay of Quinte (northeastern Lake Ontario), averaging about five times higher than winter concentrations, were strongly influenced by positive reflux of sediment TP. Several factors potentially influencing the magnitude of the summer peak (1 July to 30 September mean), including seasonal point-source and non-point-source TP loading, seasonal flushing rates, and water temperature, were explored in a multiple regression analysis. Three variables contributed significantly to explanation of the variance in the overall regression (adjusted R2 = 0.876): June to September water temperature, total daily TP loading rate from three local point-sources (sewage treatment plants) and flow-weighted averaged July to September TP concentrations in the lower Trent and Moira rivers. The strong influence of temperature on summer TP concentrations in the inner Bay of Quinte (where water and air temperatures are nearly 1:1) has important implications for climate change. Summer average water temperature increases of 3 to 4°C are within the range of those predicted by several general circulation models (GCMs with 2x CO2 end points). The multiple regression model suggests that summer TP concentrations could about double with a water temperature rise of 3 to 4°C above the 1990 to 1994 mean. This would effectively “undo” many benefits achieved to date in point-source TP loading control.