MERCURY ACCUMULATION IN BEAVER POND SEDIMENTS WITHIN THE AVERY BROOK WATERSHED, WEST WHATELY, MASSACHUSETTS

Beaver ponds are biogeochemical “hot spots” for mercury accumulation and transformation. In this study we examine the accumulation of total Hg in sediments collected at the inlets and outlets of 5 beaver ponds within the Avery Brook Watershed, a small forested catchment located in western Massachusetts. The beaver ponds sampled in this study are all located in the upper part of the watershed, on small headwater tributaries. Sedimentation in the ponds is characterized by mainly organic material generated from the areas immediately surrounding the ponds. Hammer cores were taken with a 5 cm diameter plastic tube and sampled every 2cm. Cores were extruded in the field, returned to the lab, dried at 105¢ªC and analyzed for total mercury (THg) using a Teledyne Leeman Labs Hydra IIC Mercury Analyzer.

Results from cores near the pond outlets show THg increasing from 60 ng/g at the bottom of the core (50 – 60 cm depth) increasing to at least 160 ng/g 10 – 20 cm below the sediment water interface then decreasing to 110 – 120 ng/g at the sediment water interface. This trend is consistent with results reported from many other lake studies in the area and is believed to represent the history of anthropogenic mercury deposition since the industrial revolution. The presence of this signal in these ponds suggests that the ponds have been present in the area at least since a time just before the industrial revolution began around 1800.

Results from the pond inlets are consistently different from the outlets in that there is no decrease in THg concentrations near the sediment water interface. This is most likely due to erosion of the bottom sediments near the inlets. Tropical Storm Irene in August of 2011 produced very high flows in the Avery Brook Watershed and it is likely that these flows eroded pond bottom sediments as they entered these shallow beaver ponds.

Mercury concentrations in one beaver pond were significantly higher than the others. This pond is located upstream of the other ponds and likely trapped more THg bearing sediment coming from the headwater regions.