The ecophysiology of epilithic diatom communities of acid lakes in Galloway, southwest Scotland

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Abstract
Lake-water chemistry in Galloway, southwest Scotland is characterized by strong correlations between low calcium and high aluminium concentrations and low pH. Nitrate and silicate levels were sufficient for diatom growth but phosphate was limiting. N:P and Si:P ratios indicated severe phosphate limitation according to the Redfield ratio. Chlorophyll- a specific epilithic phosphatase activity expressed as a ratio of acid to alkaline phosphatase activity showed a clear relation to pH with acid phosphatase predominating at pH 5.5 and below. Acid phosphatase activity in epilithon from low pH lakes was inducible as phosphate levels decreased, and inhibited by the addition of phosphate. Inducible acid phosphatase activity clearly confers a selective advantage to epilithic diatom communities growing in oligotrophic lakes of low pH.