Master of Science in Environmental Science, Cleveland State University, 2024, College of Arts and Sciences

Despite the critical role of organic matter (OM) oxidation in depleting oxygen in the hypolimnetic waters of Lake Erie, uncertainties regarding the sources, quantity, and fate of OM continue to challenge our understanding and management of hypoxia in the lake. This study evaluates the effects of OM oxidation through the analysis of stable carbon isotopes (δ13C) of dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) in the central and eastern basins of Lake Erie. We disclose DIC contributions from OM oxidation and provide insight into the origins of OM in the hypolimnion. Our results reveal significant declines in δ13CDIC in hypolimnetic waters compared to surface waters, indicative of OM oxidation in the deepest portions of the lake. To further examine this process, we employed the Keeling plot method to estimate the composite isotopic signature of OM respiration (δ13CR). The good agreement between the respired source (-24.4‰) and the signature of the organic material (-24.6‰) support the idea that autochthonous material (internally produced OM) fuels OM oxidation in the central and eastern basins. Additionally, a binary mixing model was utilized to quantify the amount of DIC produced and the respective amount of oxygen required by OM oxidation. We estimate that 11.8 ± 1.6 % of DIC was produced in the central basin and 5.6 ± 1.2% in the eastern basin, which accounts, on average, for 89.3 ± 7.1 % of hypolimnetic oxygen depletion in the central basin and 99.2 ± 17.7 % in the eastern basin. This suggests OM oxidation accounts for most of the hypolimnetic oxygen depletion in the lake, however instances of hypoxia in the central basin may promote other mechanisms of oxygen depletion such as oxidation of CH4, Fe2+, and Mn2+. This study reveals a strong coupling between carbon cycling and oxygen depletion in Lake Erie. Our results underscore the applicability of δ13CDIC as a meaningful tracer to quantify the amount of oxygen-consuming OM in hypolimn (open full item for complete abstract)

Committee: Fasong Yuan (Advisor); Brice Grunert (Committee Member); Julie Wolin (Committee Member) Subjects: Biogeochemistry; Environmental Science; Limnology

Master of Science, The Ohio State University, 2016, Evolution, Ecology and Organismal Biology

Terrestrial land use is intimately connected to the amounts and characteristics of organic and inorganic carbon (C) exported to aquatic ecosystems. However, the effect of land use on the contributions of various potential C sources to headwater streams is poorly established quantitatively. In this study we examined the fluxes and δ13C and Δ14C signatures of dissolved inorganic C (DIC), dissolved organic C (DOC), and particulate organic C (POC) exported from headwater streams of six watersheds of differing land use in a long-term experimental watershed. We employed Bayesian modeling (MixSIR) to determine relative contributions of potential C sources to DIC, DOC, and POC. Agricultural activity (i.e., tilled and non-tilled corn planting) increased watershed C export fluxes by 50-400% due to a 4-9-fold greater export of terrestrial plant-derived biomass C and a 5-15-fold greater export of soil C, compared to all other land uses (i.e., pasture, mixed land use, and forested). In addition, the sources of C contributing to exports from the forested watershed differed from watersheds with both agricultural land uses and those with pasture or mixed land uses. By scaling our results to the Mississippi River Basin watershed, we estimate that historic conversion of land to tilled agricultural practices may have increased the terrestrial-aquatic C flux by 11.4 ± 0.5 Tg•C•yr-1 (nearly six-fold). If non-tilled practices were implemented across all agricultural land in the Mississippi watershed, we estimate that C exports to inland waters and subsequent CO2 release to the atmosphere could be reduced by as much as 60%.

Committee: James Bauer (Advisor); Andréa Grottoli (Advisor); Peter Curtis (Committee Member); Kathleen Knight (Committee Member) Subjects: Biogeochemistry; Environmental Science; Freshwater Ecology

PhD, University of Cincinnati, 2014, Engineering and Applied Science: Chemical Engineering

A primary objective of this study is to investigate the feasibility of using sodium bicarbonate (NaHCO&sub3;) as a buffer to increase dissolved inorganic carbon (DIC) concentrations in a culture medium for the growth of microalgae and the effects of DIC concentrations, pH and light on growth and lipid accumulation in microalgae. Another objective is to investigate the feasibility of removing residual nutrients such as nitrogen and phosphorus from wastewater using microalgae. C. vulgaris was used to remove residual NH&sub3;/NH&sub4;&sup+; and PO&sub4;³-; from secondary wastewater effluent. C. vulgaris could effectively remove nitrogen and phosphorus under autotrophic growth, and the removal rate could be promoted by a high initial biomass concentration (e.g. ~350 mg/L). A Monod model was used to express the growth kinetics with a limiting substrate.

Committee: Joo Youp Lee Ph.D. (Committee Chair); Carole Dabney-Smith Ph.D. (Committee Member); Junhang Dong Ph.D. (Committee Member); Timothy Keener Ph.D. (Committee Member); Soon Jai Khang Ph.D. (Committee Member) Subjects: Chemical Engineering

Master of Science, Miami University, 2003, Geology and Environmental Earth Science

Dissolved inorganic carbon in the freshwater lens of an aquifer contains a record of processes affecting the carbon budget; in particular, limestone diagenesis, rain/soil inputs, and in-situ microbial activity. Water samples were taken from North Andros Island, Bahamas, from multi-level wells from three sampling periods (June 2001, January 2002, and June 2001) and were analyzed for pH, alkalinity, major cations and anions. These data were used to evaluate the carbon budget equation proposed for the North Andros Aquifer: ODIC = C(rain and soil input)+C(CaCO3 dissolution)+C(microbial respiration)- C(CaCO3 precipitation) Based on this equation, the expected DIC (sources - sinks) should equal the measured DIC. Dissolution of carbonate minerals account for 92% of the DIC contributed to the system. The remaining 8% is equally contributed by plant root and soil respiration (4%) and in-situ microbial activity (4%). There must be another source of inorganic carbon to the aquifer. Contrary to the original hypothesis that the DIC reservoir would be affected by seasonal variability, there are slight differences between contributions of sources to the DIC reservoir in June and January. Statistical analyses on major cations and anions showed no seasonality. In each well, cations and anions increased with depth, suggesting possible upward diffusion of ions from the marine waters below.

Committee: Mark Boardman (Advisor) Subjects: Geology