Date of Award

December 2019

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Civil and Environmental Engineering

Advisor(s)

Charles T. Driscoll

Keywords

fish, invertebrates, mercury, methylmercury, New York State, water

Subject Categories

Engineering

Abstract

Mercury is a known neurotoxin which can bioaccumulate and biomagnify as methylmercury, causing significant human and ecological impacts. New York State and the surrounding region is impacted by mercury in complex ways as some areas are recovering from the effects of acidic deposition while the entire region is increasingly influenced by climate change. In order to better understand the drivers and trends of mercury dynamics in New York State, my research was conducted in three phases: 1) the impact of lime (calcium carbonate) additions on mercury cycling in small acid-sensitive headwater streams of the Adirondack State Park; 2) applied advanced analytical techniques to improve our understanding of the complex relationship between mercury and dissolved organic matter; and 3) examined spatial and temporal trends of fish mercury concentrations across New York State

Given interest in the relationship between acidification and fish mercury concentrations, in phase one I examined the use of lime as an acidification remediation strategy and its impact on mercury cycling. Lime has been shown to effectively mitigate the effects of acidic deposition in northern Europe as well as northeastern North America, however the impact of this management strategy on mercury cycling has not been examined. Previous work at Honnedaga Lake has shown a watershed scale application of lime alters mercury transport and cycling and is highly correlated with dissolved organic matter in headwater streams. Extending the period of record demonstrates that elevated mercury and dissolved organic matter in streamwater draining a limed watershed continued for the three years of my study. This pattern contrasts with streams that received direct channel applications which resulted in much more limited increases lasting only 72 - 96 hours. In these small headwater streams, mercury was mobilized from treated areas but was not methylated before being exported from the study site. Critically, there was no evidence of increased bioaccumulation in stream macroinvertebrates following treatment, however my study period was too short to examine the long-term impacts and potential community changes resulting from continued calcium amendments.

In phase two, I explored the relationship between mercury and dissolved organic carbon (DOC). Following the watershed addition at Honnedaga Lake, a shift in the specific ultraviolet absorbance of DOC was observed. This shift suggests an increased molecular weight and aromaticity of DOC entering the limed tributary. Several studies have shown that the quality of dissolved organic matter can have important effects on the bioavailability of mercury and methylmercury. Using advanced analytical techniques and methods developed from laboratory experiments, I analyzed aquatic samples collected from the watershed treatment and reference streams. Preliminary analysis of surface waters by Fourier Transform Ion Cyclotron Resonance Mass Spectroscopy (FTICR-MS) reveals an increase in the proportion of thiol functional groups and aromaticity in the first four weeks following treatment, but no significant difference between study sites in later samples. This information could help inform watershed management decisions and serve as a proxy for natural recovery of aquatic ecosystems from acidic deposition.

Phase three built upon a previous state-wide survey of lake fish conducted from 2003-2005. This survey found significant biological mercury hotspots in the Adirondack and Catskill State parks, and significant correlations of fish mercury concentrations with factors related to acidification and wetland area. The latest survey, conducted from 2013-2015, I found somewhat different results. Fish Hg in the Adirondack and Catskill regions remained elevated relative to the rest of NYS, however, the landscape and chemistry drivers from the earlier survey no longer applied across the whole state. Long-term changes in fish mercury concentrations were not evident in the recent survey. This lack of a change may suggest the major driver of fish mercury for inland waters is shifting away from regional Hg emissions towards the effects of legacy Hg and acid inputs or changes in nutrient status, invasive species, climate change and/or increasing global Hg emissions.

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