Influence of Water Temperature and Nitrogen to Phosphorus Ratios on the Dominance of Blue-Green Algae in Lake St. George, Ontario

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Abstract
Data collected at Lake St. George, Ontario, over five summers spanning a period of 13 yr showed that there was no correlation between percent blue-green algal composition and the ratio of total nitrogen (TN) to total phosphorus (TP), However, percent blue-green algae was positively correlated with temperature and negatively correlated with nitrate nitrogen (NO3-N), total inorganic nitrogen (TIN), and the ratio of NO3-N:TP. Multiple correlations involving percent blue-green algae (dependent variable) with respect to temperature, in combination with one of NO3-N, TIN, NO3-N:TP, or TIN:TP, were also significant. In all cases, temperature effects accounted for most of the explained variation. The strongest correlation was found for the multiple regression involving percent blue-green algae versus temperature and the NO3-N: TP ratio. The pattern that emerged from the Lake St. George data set was that when temperature exceeded 21 °C and the ratio of NO3-N:TP was below 5:1, the likelihood of a blue-green algal bloom was high. When temperature was below 21 °C and NO3-N:TP exceeded 5:1, blue-green blooms never occurred.