BIOGEOCHEMISTRY OF A EUTROPHIC LAKE, WEST-CENTRAL OHIO

Crystal Lake, located in Medway, Clark County, in west-central Ohio, is the southern-most kettle lake created by the retreat of the Wisconsin ice sheet in Ohio. The surface area of this lake is about 0.044 Km2, and the maximum depth about 12.2 meters. The surface drainage basin is only about 5 Km2. Crystal Lake is connected with two upstream natural ponds in series by a shallow channel. A small stream flows from the lake to the regional Mad River drainage network. The lake is moderately eutrophic and typically dimictic. The goal of this investigation is to establish a biogeochemical baseline for future studies.

Samples were collected from April to December, 1998. Since the lake is situated within a carbonate terrain, the water is Ca-Mg-HCO3- type. Seasonal trends show that thermo-stratification was a major control on the biogeochemical characteristics of this lake. Photosynthesis in epilimnion and metalimnion, and respiration in the hypolimnion were the driving processes that generated the observed biogeochemical characteristics. As a result, lower concentrations of dissolved carbon dioxide and total dissolved solid and oxygen maximum existed in the metalimnion, and high concentration of respiration products existed in the hypolimnion. A maximum in the ƒÔ13C profile at the same position as the oxygen maximum was caused by assimilation of 12C-enriched DIC by photosynthetic organisms. Decay or organic matter in the hypolimnoium also produced high concentrations of ammonium, sulfide, phosphate, silica, and carbon dioxide.

Based on the oxygen and hydrogen isotope composition of water in the lake and the surrounding ground water system, the interaction between the lake and the surrounding ground water seemed limited to the immediate boundary. All lake waters showed a clear isotopic signature of evaporation and were much heavier than ground waters.