Abstract |
After more than 60 years of cultural eutrophication Lake Sallie supports dense growths of phytoplankton and rooted vegetation. Its major water mass has the chemical character imparted by photosynthesis at all seasons, and chemical effects of decomposition are rather localized. Phytoplankton dominance alternates among diatoms, blue-green, and green algae, in that order of abundance. Prior to operation of a weed harvester, attached plants grew densely over 34% of the bottom area. The bulk of nitrogen and phosphorus is usually contained in the water mass, with noticeably smaller amounts in upper bottom sediments and biota. The fish population, less than one half the mass of weeds, contained considerable more N and P than weeds in 1971. Harvest in 1970 evidently reduced weed density in 1971, and increased the cost per unit of nutrients removed. Nitrogen and phosphorus removed in weeds were insignificant when compared with annual wastewater effluent contributions to the lake. (Modified author abstract) |