Phytoplankton Summer Standing Crop and Annual Productivity as Functions of Phosphorus Loading and Various Physical Factors

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Abstract
Relations of phytoplankton summer standing crop and annual productivity to morphometric properties and edaphic factors, especially phosphorus loading, have been examined for a large, diverse, globally distributed group of lakes. Standing crop was highly correlated with dissolved phosphorus loading when mixing of the water column was taken into account. A regression applicable to lakes of all depths is given as a log-log function with predictive confidence intervals for summer mean values. Boundary conditions for the exclusion of certain lakes have been roughly determined. For lakes of mean depth > 25 m areal loading accounted for 97% of the variance in summer phytoplankton standing crop. Phosphorus inputs to shallower systems were adjusted to give a simple approximation of the influence of mixing processes and the ratio of bottom area to overlying water volume. Annual primary productivity seems to be a more complex and variable function of phosphorus loading than is summer standing crop. The former correlated fairly well with the morphoedaphic index. Productivity and standing crop showed well-defined trends in relation to other variables, but point scatter was so great that more exact definition of these functions was not justified. Key words: phytoplankton, phosphorus, eutrophication, lakes, morphoedaphic index