Date of Completion
Allison Mackay; Timothy Vadas
Field of Study
Master of Science
Dissolved organic matter (DOM) is ubiquitous in aquatic ecosystems, interacting with and controlling the bioavailability and transport of mercury (Hg) and other trace metals through complexation. The complexation of ionic Hg (Hg2+) with DOM can either limit methyl mercury (MeHg) bioavailability or increase MeHg production by stimulating microbial growth. While substantial investigations have examined Hg-DOM interactions in forested ecosystems, little research has been conducted on the Hg-DOM relationship within an urbanized river setting subjected to various anthropogenic sources. The various runoff and pollutant sources vary in DOM quality and character. Three sources of organic matter from the North Branch Park River (NBPR watershed in Hartford, CT (forest, FOR; impervious surface runoff, SWR; and an urban stream, USS) as well as the influent (InfOM) and effluent (EfOM) from the Hartford Water Pollution Control Facility were collected and isolated using Amberlite DAX-8 and XAD-4 resins into operationally defined hydrophobic and hydrophilic acid fractions. Each fraction was characterized for chemical and spectral properties prior to an assessment of Hg-DOM fraction binding by measuring conditional stability constants (KDOM’) using an equilibrium dialysis ligand exchange (EDLE) method. Molecular weights ranged from 668 Da (forest) to 209 Da (influent), SUVA254 ranged from 3.17 (forest) to 0.02 (influent) L mg-1 m-1, and FI ranged from 1.2 (forest) to 1.8 (effluent). Spectral properties of the forest site represented those for a terrestrial source while those for the wastewater constituted a microbial end member. The SWR and USS sources were indicative of urban stream organic matter origin. KDOM’ values were affected by Hg/DOM ratios and ranged from 1023- 1024 L kg-1, comparable to Hg-DOM binding coefficients from previous studies. NMR and chemical analysis suggest that binding is controlled by a small number of strong thiol as well as weaker carboxyl functional groups and likely is connected to the low molecular weights. Hg-DOM binding varied over an order of magnitude with source, demonstrating the need for future research to examine the potential implications of shifting DOM contributions in urban ecosystems.
Mendes, Mykel, "Dissolved Organic Matter Characterization and Impact on Mercury Binding in an Urbanizing Watershed" (2011). Master's Theses. 169.