Date of Completion

11-30-2018

Embargo Period

11-29-2020

Keywords

Mercury, Methylmercury, Estuary, Multi-Estuary Analysis, Sediment Resuspension, Methylmercury Speciation

Major Advisor

Robert Mason

Associate Advisor

Penny Vlahos

Associate Advisor

Pieter Visscher

Associate Advisor

Celia Chen

Field of Study

Oceanography

Degree

Doctor of Philosophy

Open Access

Campus Access

Abstract

The goal of this dissertation research was to better understand the sources of methylmercury (MeHg) to estuarine water columns and its bioavailability to phytoplankton. This was achieved through large and fine-scale field and laboratory studies including a multi-estuary statistical analysis, sediment resuspension experiments, and lab-based Hg transformation and speciation reactions. It was found through principal component analyses and partial least squares regression models on the overall dataset that sources of MeHg to typical, temperate estuarine ecosystems in the northeast USA appear to be internally driven but linked to external inputs of inorganic Hg, dissolved organic carbon, and the composition of suspended particulate matter. However, at highly Hg impacted sites, coastal sediments remain a continual source of inorganic Hg and MeHg to overlying waters and downstream environments. Sedimentary sources of particulate Hg in low-impact environments are present in turbid estuarine regions, especially under high shear stress events, but resuspension chambers suggest that under typical tidal shear stress conditions resuspension aids more in Hg and MeHg recycling at the sediment-water interface rather than providing a new source of MeHg to the water column. Even though the statistical analysis and resuspension study point toward in situ sources of MeHg, quantifying this source is challenging. I found that both Hg methylation and MeHg demethylation are linked to photosynthetically driven heterotrophic bacterial activity which changes by location and sampling season. To understand MeHg bioavailability, MeHg binding with dissolved organic matter (DOM) was evaluated. The composition of DOM was assessed based on total C/N/S and S speciation while binding was determined using competitive ligand exchange reactions. Overall, marine derived DOM had a more oxidized S signal, less binding ligands, and faster ligand exchange reactions than terrestrial OM suggesting that MeHg bound to marine DOM is potentially more bioavailable. The results of this dissertation emphasize the importance of non-sedimentary sources of MeHg to temperate estuarine water columns. Specifically, watershed land use is important to consider for its influence on Hg, carbon, and nutrient loading to coastal waters, all of which impact water column MeHg and its incorporation into the coastal food web.

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