SEDIMENT MERCURY LEVELS AND MERCURY ACCUMULATION RATES IN EIGHT KETTLE LAKES IN NORTHWESTERN PENNSYLVANIA

Mercury contamination in lakes in northwestern Pennsylvania has resulted in high number of fish consumption advisories. The area is located in the airshed of the industrial heartland of the United States, resulting in high concentrations of atmospheric mercury and other pollutants accumulating in lentic systems. In addition, point sources of pollution in the area, such as open-pit coal mines, gravel pits, and asphalt may also be sources of mercury. Sediment cores from eight kettle lakes in northwestern Pennsylvania were analyzed for mercury, carbon, nitrogen, and sulfur. The Hg concentrations ranged from 61 to 252 ppb. An accumulation rate was estimated for seven of the lakes using a dated core from Lake Pleasant and the mercury horizon for each of the lakes. The mercury horizon is a sharp increase in mercury concentrations due to the start of the Industrial Revolution in the early 1800’s and was estimated visually on the graphs. The mercury accumulation rates of the eight lakes range from 9.08 to 16.18 ugHg/cm²/year. In addition, all cores except that from Sugar Lake show a significant correlation between mercury and sulfur, a pollutant known to be emitted from coal combustion, suggesting that much of the mercury in this region is atmospheric in origin. Supporting this theory, the estimated mercury accumulation rates were found to be correlated to the watershed:lake area ratios (r² = 0.50). There was an evident peak in mercury accumulation rates in the dated Pleasant and Edinboro cores around the mid 1950s; this could possibly be attributed to the surge in industry after the end of World War II. Lakes Sandy and Pleasant were suspected of having point source inputs of mercury into their watersheds, but Sandy was the only lake that had higher than normal estimated mercury accumulation rates. Further studies on these lakes should focus on determining the actual mercury accumulation rates by the use of lead-210 dating in order to more accurately demonstrate its correlation with watershed:lake area.