Publication Date


Document Type


Committee Members

Abinash Agrawal (Committee Member), Songlin Cheng (Committee Chair), Rebecca Teed (Committee Member)

Degree Name

Master of Science (MS)


Photosynthesis, respiration, and decay of organic matter all involve the transfer of carbon among the carbon-bearing species in the systems. These biogeochemical processes also fractionate the carbon isotope composition, which results in changes to the carbon isotope composition of the dissolved inorganic carbon (DIC) pool. This thesis presents two separate, but related studies regarding the influence of biogeochemical processes on carbon isotopes in local lakes. Crystal Lake is a small but deep glacial lake (12.5 acres, 11.9 meters). The study shows that during thermal stratification, the heaviest carbon can be found in the epilimnion near the surface, where photosynthesis dominates the biogeochemical processes. At greater depths, the DIC carbon becomes lighter as 12C-enriched organic matter decomposes. In the hypolimnion, methane production in the late summer could be the process that resulted in slight increase in 13C of DIC. The second study investigated the relationship between the carbon isotope composition of DIC and the trophic status of three lakes in Southwestern Ohio; Indian Lake, Grand Lake St. Marys and Kiser Lake. All three lakes are shallow, man-made reservoirs, but each has unique biogeochemical characteristics. Among these three lakes, Grand Lake St. Marys had the heaviest carbon isotope composition in DIC, the highest phosphorus (P) concentration, and the lowest nitrate (N) concentration. It is the only lake among the three that has suffered severe toxin-producing blue-green algae (cyanobacteria) blooms in recent years. The P and N concentrations indicated nitrate was the limiting nutrient. This study shows that carbon isotope composition can be used as a proxy for trophic status in large, shallow lakes, like Indian Lake and Grand Lake St. Marys. It is concluded that carbon isotope composition of DIC is closely related to the biogeochemical processes in lakes and can provide important insight into those processes. However, a quantification of the impact of biogeochemical processes on carbon isotope composition of DIC would require precise knowledge of fractionation factors associated with algal species and other biological and physicochemical factors, such as pH, temperature, and cell growth rate.

Page Count


Department or Program

Department of Earth and Environmental Sciences

Year Degree Awarded