Abstract |
Density of planktonic algae, rates of photosynthesis, nutrient concentrations, and other limnological characteristics were recorded during 1968-1970 in different parts of Lake Minnetonka, Minn. In the course of the past 30 years, the density of algae increased 2 or 3 times, and the dominance of diatoms was replaced by that of blue-green algae. A linear relationship was disclosed between the algae density and the content of total phosphorus within the range of 50 to 200 mg/cu m. A decrease of phosphorus below 45 mg/cu m promises a rapid improvement of the lake quality. The nutrient enrichment of the lake is largely due to the land runoff and storm drainage, rather than the discharge of sewage. A mathematical model of the photosynthetic system was based on the relation between the intensity of illumination and the biomass of algae. The report includes a detailed record of taxa and densities of algae during different months of 1968 and 1969. (WRSIC abstract) |