A HISTORY OF MERCURY DEPOSITION IN THE OSSIPEE PINE BARRENS AS INDICATED BY SEDIMENT CORES FROM COOKS POND, MADISON, NEW HAMPSHIRE

Increased atmospheric deposition of mercury (Hg) from anthropogenic sources such as coal burning and gold mining is affecting high trophic level organisms far from the sources of pollution. In New Hampshire, large piscivorous fish and birds have been found to have dangerously high levels of Hg.

Lake sediments hold a detailed record of environmental change and can be used to document the history of Hg deposition. Two cores were collected at locations separated by a partially submerged esker within Cook’s Pond located at the north end of the Ossipee Pine Barrens. Both 60cm cores were collected at similar water depths (6m) using a Uwitec gravity corer with secondary hammer action. Samples were removed from the core in the field at 1 cm intervals. Each sample was air­dried, homogenized using a coffee grinder, and analyzed for total Hg by Cold Vapor Atomic Adsorption using a Teledyne Leeman Labs Hydra IIC Mercury Analyzer.

Both cores show a significant increase in Hg concentration toward the upper part of the core beginning at 20cm below the sediment water interface. This increase is interpreted to be due to atmospheric deposition of Hg associated with coal burning during the industrial revolution. Although both show similar trends, their ranges vary with one core having higher preindustrial Hg levels while the other contains higher postindustrial levels. Below 20cm both cores show a decrease in Hg concentrations from 170­260ng/g to 20­25ng/g. Loss on ignition (LOI) was determined by comparing sample weights before and after analysis in the Hydra IIC, to be representative of the relative concentration of organic matter in the core. There appears to be a consistent relationship between LOI and Hg with higher LOI’s generally being associated with lower Hg concentrations.

Mining at the Madison Lead Mine, active 1910­-18 could explain an anomalous decrease in Hg observed at a depth of 7­8cm in both cores. The unvegetated beach at the south shore of the pond is the result of mine tailings from an ore crushing operation. The influx of sediment into the pond may have diluted atmospheric Hg. In the early 1800s an increase in settlement in the area could explain the decrease in LOI at the top of the core due to erosion associated with land clearance for agriculture. Subsequent reforestation could also explain slight increases in LOI beginning at 10cm.