Trace metal applications in atmospheric and watershed dynamics: Case studies of mercury deposition in New England and bedrock groundwater-surface water mixing

The studies presented in this dissertation focus on the environmental chemistry of two trace metals, mercury (Hg) and strontium (Sr). Both are naturally occurring and exist in the environment at trace levels. Chapters II-IV of this dissertation focus on understanding the atmospheric chemistry of Hg and the wet and dry deposition of this toxic element. Chapter II presents results from Hg wet deposition measurements and ambient reactive gaseous Hg (RGM) measurements collected at Thompson Farm located in Durham, NH over a 3 year time period. The duration of this study allowed for seasonal and inter-annual comparisons. Seasonally, Hg wet deposition was greatest in the summer and spring and lowest in the winter and fall. Evidence of ineffective scavenging of RGM is provided due to the less frequent depletion of RGM during winter precipitation events in comparison with other seasons. RGM dry deposition estimates based on real time concentration measurements are greatest during the winter and spring. Ratios of the seasonal Hg wet deposition to RGM dry deposition vary greatly from 1.6 to 80. A comparison between Hg wet deposition at Thompson Farm and a marine site, Appledore Island, is included in Chapter III. There were no significant differences in event concentration or deposition between the two sites, however, the sample collection efficiency varied greatly between the sites and may effect the results. Additionally, major ion concentrations were measured at the Appledore Island site and compared to the Hg concentrations. The analytical results coupled with air mass back trajectories suggest that the greatest amount of Hg wet deposition occurs when polluted continental air mixes with marine air. A new filter extraction method for determining the environmentally mobile Hg concentration in bulk aerosol filters is presented in Chapter IV. This method is applied during a 2 week intensive sampling campaign at Appledore Island during summer 2009. Chapter V explores the use of Sr isotope ratios to determine groundwater inputs to the Lamprey River. The groundwater and surface waters in the watershed exhibit large differences in 87Sr/86Sr indicating this geochemical indicator could be a useful tool in hydrogeologic studies of the watershed