Chemical and Isotopic Balances for a Meromictic Lake1

A chemical and isotopic study of the waters and sediments of Fayetteville, New York, Green Lake has allowed the cause of its meromixis to be defined. Stagnation is clearly the result of two different water types entering the lake. Water entering below the chemocline is almost twice as saline as that entering the surface layer. This conclusion is based on hydrologic, isotopic, and chemical balances. For carbon and its isotopes, the contributions of CaCO3 precipitation, of the photosynthetic cycle, of gas exchange with the atmosphere, and of hydrologic transport are considered. Our results indicate a mean residence time of two years for surface water and of 4–30 years for deep water. The water entering the deep reservoir must be richer in Na+ + K+ + Cl− relative to Mg2+ + Ca2+ + HCO3− + SO42− than that entering the surface reservoir. Its carbon must also be more deficient in 13C and 14C and its degree of supersaturation with respect to calcite lower than surface water. Although both reservoirs are supersaturated with calcite, the carbon isotope data clearly indicate that precipitation takes place largely from the surface water.