Some Indices of Lake Productivity

In an attempt to evaluate lake-survey procedures some of the chemical, physical, and biological measurements that have been considered possible indices of lake productivity have been examined in the light of 11 years of lake surveys and 6 years of pond rearing of yellow pikeperch. In Minnesota waters total alkalinity and total phosphorus appear to be the most valuable indices. Nitrogen is usually present in excess; sulphates are of most value in considering waterfowl areas; and chlorides, pH, and dissolved carbon dioxide are of little value in comparing waters and judging potential productivity. Potassium, manganese, and iron concentrations also are discussed. Quantitative plankton and bottom-fauna samples have been found unsatisfactory as productivity indices for ordinary lake surveys, and the distribution and abundance of larger aquatic plants are of greatest value when related to waterfowl management. In estimating the potential productivity and formulating fish-management plans for lakes the structure of the fish population and the nature of the lake basin should be considered.