The Carbonate Chemistry of Green Lake, Jamesville, NY^a

ABSTRACT

The temporal and vertical distributions of inorganic carbon and related forms were assessed for the mixolimmion of Green Lake, Jamesville, NY, based on a biweekly monitoring program conducted for a 14 month period. The daily time structure of the distributions was delineated for a single diurnal cycle. Attendant [H₂CO₃*] ([H₂CO₃] + [CO₂(aq)]) and calcite equilibrium conditions were determined through solution of equilibrium equations, adjusted for temperature and ionic-strength. Inorganic carbon equilibrium conditions within the ion-rich chemocline/monimollmnion were evaluated with the aid of a computer model, which incorporated ion-pair interactions, utilizing data obtained from a single sampling.

A seasonal cycle was demonstrated for the inorganic carbon species within the lake's mixolimnion which was temporally consistent with the system's thermal and productivity transformations. Dramatic differences in carbonate chemistry developed between the epilmnion and hypolimnion during summer stratification. The epilimnion was highly supersaturated with respect to calcite throughout summer stratification. Minimum H₂CO₃* saturation was observed for the same period. These seasonal variations in equilibrium conditions, as well as diurnal variations, were mediated largely through temporal changes in pH. Factoral analysis of the temporal trends with respect to the influencing factors of temperature, ionic strength, and CO₂ metabolism, indicates they were largely a result of photosynthetic consumption of CO₂. Precipitation of calcite within the upper 5 m during summer was implied by the continuing decrease in [Ca⁺²] during the calcite supersaturation period. Seventy-five percent of the calcite formed is estimated to reach either the mixolimnic sediments or the monimolimnion. Most of the calcite entering the monimolimnion would probably reach the sediments, since the layer is nearly saturated or supersaturated with the mineral.