Mercury Concentrations and Mercury Methylation Along the Freshwater to Marine Continuum

• Main Author: Starr, Lindsay D.
• Format: Text
• Language: unknown
• Published: CORE Scholar 2022
• Subjects: Department of Earth and Environmental Sciences; Environmental Science; mercury; methylmercury; marine food webs; freshwater Hg; marine Hg; Hg water column distribution; speciation; methylation; nitrification; Lake Erie; Tropical North Atlantic Ocean; Central Pacific Ocean; Environmental Sciences; Physical Sciences and Mathematics; Detroit; Pacific; Western Basin; Western Lake; North Atlantic
• Online Access: https://corescholar.libraries.wright.edu/etd_all/2603; https://corescholar.libraries.wright.edu/cgi/viewcontent.cgi?article=3744&context=etd_all

Mercury (Hg) is a neurotoxin that can have detrimental impacts on the human nervous system and on brain development in infants. Methylmercury (MeHg) is the most toxic form of Hg and can concentrate to potentially harmful levels in higher levels of marine food webs. Production of MeHg in oxic water columns is poorly understood due to lack of knowledge of the mechanisms of formation and distribution. Recent work has reported widespread, putative Hg methylation genes in nitrite oxidizers, but any relationship with nitrifiers is unknown. This work focuses on Hg water column distribution, speciation, and methylation. The aims of this dissertation are to quantify: (1) rates and distribution of HgT and MeHg in the western basin of Lake Erie; (2) Hg methylation and nitrification rates in the Tropical North Atlantic Ocean; and (3) Hg species distribution in the Central Pacific Ocean. In Lake Erie, a Laurentian Great Lake, the mean fraction of total Hg as MeHg in water column measurements from lake areas near three Lake Erie river inputs (summers of 2018, 2019, and 2021) were comparable (~5%), suggesting similar biogeochemical cycling for rivers feeding Lake Erie. Estimated river fluxes of MeHg were an order of magnitude greater than in situ production, and greater from the Detroit River (9.5 kg yr–1) than from either the Maumee River (0.78 kg yr–1) or Sandusky iii Bay (0.03 kg yr–1), as expected since the Detroit River accounts for about 95% of total water discharge into Lake Erie. These results suggest that the Detroit River is a major source of MeHg from the upper Great Lakes basin to western Lake Erie. Overall, Hg concentrations and fluxes observed in this study were up to orders of magnitude less than those reported in previous decades, which may be a positive result of the Ohio Clean Air and Water Act of 2004. In a marine system, potential Hg methylation and nitrification rates were measured in Western Tropical North Atlantic Ocean surface waters (June and July 2019), within and near the Amazon River plume. The Hg ...