Biogeochemistry of a mesotrophic lake and it's carbon isotope geochemistry

Crystal Lake, located in west-central Ohio, is the main lake of a series of 4 interconnected lakes. The location and orientation indicate that they are most likely moulin-induced glacial lakes. Crystal Lake is about 5 hectares (12.5 acres). The maximum depth and mean depth are about 11.9 meters and 3.8 meters, respectively. As a result of this high depth-to-surface area ratio, it creates a strong thermal stratification during warm season. The lake was classified as eutrophic lake. However, the water quality has improved in the past decades. The chlorophyll in the epillimnion and upper metalimlion is about 4 μg/l and the Secchi disk depth is about 3.0 meters (10 feet). It is therefore reclassified as mesotrophic lake. Dissolved oxygen maximum (15.6 ppm) and pH peak (8.6) existed at 4.1 meter on August 16, 2010. At around 7.3 meter, where redox potential reading shows a sudden change from oxidizing to reducing , a ~half meter layer of dense purple sulfur bacteria coincides with turbidity, chlorophyll, and sulfate maxima. The chemical depth profiles are a result of thermal stratification, oxygenic photosynthesis by algae, non-oxygenic photosynthesis by purple sulfur bacteria, and respiration in the hypolimnion. Precipitation of calcium carbonate in the epilimnion and metalimnion is coupled by it’s dissolution in the hypolimnion. The purpose of the current project is to present extensive background study to form the framework for quantifying the carbon isotope evolution with multiple reaction pathways. Carbon isotope composition of dissolved inorganic carbon is being analyzed. Wigley-Plummer-Pearson mass transfer model will be used for the quantification of carbon isotope reaction pathways.