Effects of Concentrations of Ca²⁺, Mg²⁺, Na⁺, K⁺, Total Phosphorus and Orthophosphate on Growth of Phytoplankton in the Water of Lake Biwa

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We studied the effects of concentrations of Ca²⁺, Mg²⁺, Na⁺, K⁺, total phosphorus and orthophosphate on growth of phytoplankton in the water of Lake Biwa. Water samples were taken from the southern part of the lake 15 times from June 1986 to May 1987. The metal ion concentrations in the samples were determined by an atomic absorption spectrophotometric method after diluting with 0.01 N-HNO₃, while the concentrations of total phosphorus and orthophosphate were determined by an atomic absorption spectrophotometric method with or without oxidation by potassium peroxodisulfate. The number of phytoplankton cells was counted under a microscope. No significant correlation was observed between the number of phytoplankton and concentrations of Ca²⁺, Mg²⁺, Na⁺, or K⁺. In contrast, the numbers were highly significantly correlated with the concentrations of total phosphorus.