Classification of the Productivity of Lakes

The factors influencing the productivity of lakes are well known. Correlations between phosphorus loadings, chlorophyll a, water clarity (Secchi depth), and hypolimnetic oxygen depletion have been established. A measure of one gives a reliable estimate of any other. This simplifies field work and reduces the sampling costs of lake trophic monitoring. A trophic (productivity) classification of lakes based on these criteria is probably the most important tool resource managers have that indicate a lakes ecological well being.

For example a value of <10 micro g/L of total phosphorus concentration at spring overturn designates an oligotrophic lake. The range of 5-15 micro g/L total phosphorus is generally accepted as best for salmonid species. Values >10 micro g/L result in oxygen depletion in the hypolimnion. This effect is modified in lakes with high renewal rates and/or with large hypolimnia to epilimnia ratios. However, these conditions are generally not characteristic of reservation lakes. Increased phosphorus values at spring overturn also cause increased hydrogen sulfide, soluble iron and manganese, and organic compounds. Knowledge of a lake's phosphorus levels can be powerful predictors of a lake's trophic condition.