Effects of Manipulations of Aluminum Concentrations and pH on Phosphate Uptake and Photosynthesis of Planktonic Communities in Two Precambrian Shield Lakes

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Abstract
From June 1982 to October 1983 we studied the physiological responses of phytoplankton to aluminum perturbations in a circumneutral lake (St. Nora Lake) and an acid-stressed lake (Plastic Lake) on the Precambrian Shield in Ontario. In both lakes, addition of aluminum to water samples decreased microbial phosphate uptake and photosynthesis; significant decreases occurred at 50 μg Al∙L−1. Both processes were affected more at pH 5.2–6.9 than at pH 4.5, phosphate uptake was depressed relatively more than photosynthesis, and depression of both processes was larger in Plastic Lake than in St. Nora Lake. Precipitation of phosphate as particles > 0.45 μm upon addition of aluminum, as well as direct toxicity of aluminum, appear to be responsible for the observed detrimental effects of aluminum.