A COMPARISON OF MERCURY IN THE AVERY BROOK WATERSHED, WEST WHATELY MASSACHUSETTS WITH THE OSSIPEE PINE BARRENS, NEW HAMPSHIRE

Atmospheric deposition of Hg from anthropogenic sources has led to high levels of Hg in terrestrial and aquatic systems in many areas far from the industrial sources. Mercury accumulates in forest soils and is transferred from the terrestrial system to surface waters via shallow subsurface runoff through organic soil horizons during precipitation and snowmelt events. Methylation of Hg by sulfur reducing bacteria enables bioaccumulation in aquatic systems.

Water samples from both sites were collected from July to October 2014 and analyzed for pH, alkalinity, major cations and anions as well as for Total Hg (THg), Dissolved Organic Carbon (DOC), and Ultra Violet adsorption at 254 nm (UV 254). Sample aliquots were filtered and acidified in the field. Samples for THg analysis were collected using clean hands/dirty hands procedures and analyzed by Cold Vapor Atomic Fluorescence using a Teledyne Leeman Labs Hydra AF Gold ercury analyzer.

Other studies examining THg concentrations in soils have found higher concentrations in the Avery Brook watershed as compared to the Ossipee Pine Barrens. Studies have also shown higher THg concentrations in similar size fish from Avery Brook. In this study we found higher THg and DOC in the surface waters of Avery Brook as compared to the Pine Barrens. These differences can be explained, in part, by the surficial geology that helps control the flow path of water through these two watersheds. Avery Brook lies within a till dominated watershed that promotes surface runoff while the Pine Barrens is underlain by thick deposits of highly permeable stratified drift that enables infiltration into the groundwater system. Analysis of stream water samples collected during hydrologic events at Avery Brook show a positive correlation between DOC and stream discharge. This is caused by shallow subsurface runoff picking up DOC as it moves through organic soil horizons. A strong correlation (r² = 0.92) was also found between DOC and THg. This suggests that shallow subsurface runoff also collects Hg. This relationship was used to estimate the maximum THg concentration (15ng/L) in Avery Brook during Tropical Storm Irene.