The Impact of Nutrient Availability and Algal Community on Carbon Isotope Fractionation in Crystal Lake, Clark County, Ohio

Crystal Lake is a glacial lake located in southwestern Ohio. Several studies have looked at separate geochemical and isotopic information at this location. However, no one has thoroughly studied the relationship between the algal community, geochemistry, and carbon isotope fractionation within Crystal Lake. Fractionation is affected by the process of photosynthesis; photosynthesis rates are affected by the amount of algae in the aquatic community; the amount of algae is affected by the available nutrients. Therefore, there should be a correlation between the nutrients, the amount of algae, and the extent of carbon isotope fractionation. If such a correlation is found, it could be used as a proxy for paleonutrient availability.

Water samples were collected every 1.5 meters at approximately the deepest location in Crystal Lake. Several important indicators of photosynthesis, such as dissolved oxygen and pH, were measured in situ. Samples were analyzed for nutrient and chlorophyll content, and sent out for carbon isotope analysis.

The measured values of ä¹³C in Crystal Lake are highest in areas of photosynthesis, and decrease in the hypolimnion where decomposition occurs. There are trends between carbon isotope fractionation, photosynthetic indicators, and several nutrient concentrations. Samples with ä¹³C values less than -10 ‰ V-PDB have pH values below 8 and little dissolved oxygen. Samples with ä¹³C values between -9 and -6 ‰ V-PDB have pH values greater than 8, dissolved oxygen levels between 5-20 mg/L, silica concentrations below 3.25 mg/L, magnesium below 27 ppm, and calcium above 60 mg/L. Samples with ä¹³C values above -6 ‰ V-PDB have a pH between 8-9, dissolved oxygen levels between 10-30 mg/L, silica above 3.25 mg/L, magnesium above 27 ppm, and calcium below 60 mg/L. More research is needed to corroborate these trends and expand our understanding of the affect of nutrient concentrations on carbon isotope fractionation.