Contributors
Emilia DiBiasio
Fasong Yuan
Abstract
Dissolved oxygen (DO) is a critical water quality indicator. Despite decades of nutrient abatement efforts, hypoxia persists in Lake Erie, particularly in the central basin, due to oxygen consumption in the water column and sediments. This study measures δ13C of dissolved inorganic carbon (δ13CDIC) and applies a binary mixing model to estimate CO2 production and respective oxygen consumption in Lake Erie’s central and eastern basins during the 2023 field season. Water samples were collected during April and August cruises aboard the R/V Lake Guardian from USEPA offshore stations, measuring temperature, DO, pH, alkalinity, chloride, DIC, dissolved organic carbon (DOC), δ18OH2O, δ13CDIC, and δ13CDOC. In April, both basins were well-mixed with high DO (∼13.5 mg/L). By August, the central basin hypolimnion exhibited pronounced oxygen depletion (2.5 mg/L) and a substantial decrease in δ13CDIC (−3.7‰), whereas the eastern basin remained oxic (8.7 mg/L, −2.6‰). The binary mixing model indicated that bacterial oxidation of organic matter contributed 11.7% of DIC in the central basin and 5.5% in the eastern basin, accounting for 89.6% and 96.5% of apparent oxygen utilization, respectively. On average, sediment oxygen demand accounted for ∼31% of hypolimnetic oxygen depletion in the central basin. Hypolimnion thickness emerged as a key regulating factor, with thinner hypolimnion in the central basin (∼6 m) intensifying oxygen loss relative to the eastern basin (∼24 m). Despite uncertainties related to turbulent diffusion and variable respiratory quotients, this study demonstrates the applicability of δ13CDIC for constraining carbon dynamics, oxygen depletion, and the sources of oxygen-consuming materials.