Abstract
Mercury (Hg) and lead (Pb) are naturally occurring heavy metals and considered toxic to many living organisms. The atmospheric emission of these elements from human induced activities such as coal combustion and industrial processes has rendered them environmentally ubiquitous. Within the past 40 years various environmental regulations have been enacted at the national and international levels to reduce the emissions of Hg and Pb. Atmospheric deposition can be a primary source of these heavy metals to ecosystems, especially in remote regions. Event based wet deposition samples (i.e. rain, snow) were collected at the Thompson Farm AIRMAP site in Durham, New Hampshire from June 2006 to September 2009. Samples were analyzed for total aqueous Hg, total Pb, and dissolved organic carbon (DOC) concentrations. This multi-year dataset allows for seasonal comparisons between the analytes. Volume weighted mean (VWM) concentrations of Hg were greatest during the summer, while the VWM of Pb was greatest during the winter. Hg and Pb concentrations are positively correlated (tau =0.2252, p<0.001) over the entire dataset, however this correlation does not persist among all seasons. Spring and summer have statistically significant positive correlations between Pb and Hg, whereas correlations in winter and fall are not statistically significant. DOC concentrations were also examined due to the common correlation between Hg and DOC in fresh water ecosystems. This relationship remains relatively unexamined in wet deposition studies. A positive correlation exists between DOC and Hg concentrations over the entire dataset (tau =0.3722, p<0.001) at this site. Winter is the only season when this correlation is not statistically significant. These seasonal differences between Pb and Hg correlations, and Hg and DOC correlations may reflect different seasonal atmospheric sources and/or seasonal differences in atmospheric chemical reactions. Additionally, seasonal variations in wet deposition concentrations may influence the bioavailability of these heavy metals in ecosystems.