A SEDIMENTARY RECORD OF MERCURY FROM A SMALL URBAN WATERSHED

Mercury (Hg) is delivered to the environment from a variety of anthropogenic sources such as coal combustion and waste incineration, as well as many other sources. This Hg is transported through the environment and can accumulate in the bottom sediments of rivers and lakes. For this study we measured Hg concentrations in surface sediment and sediment cores from Summit Lake, within the city of Akron, Ohio. Sediment samples include intervals from before the industrial revolution (1860s) up to the present. From sediment depths of 223 to 404 cm, which is presumably from prior to the industrial revolution, the average Hg concentration is 0.2 ± 0.1 µg /g (n=22). At a depth of 224 cm an increase in Hg concentration occurs, which is estimated to be the year 1863. From 224 to 100 cm Hg concentrations were elevated and range from 0.8 ± 0.1 µg/g to 9.3 ± 0.1 µg/g. Previous work showed that other anthropogenic metals from this same core indicates that the industrialization within the Akron watershed contributed to a sudden increase of metals during this period (Haney, 2004). Hg concentrations decline from 83 cm to the core top and average 0.5 ± 0.1 µg/g (n=12). Surface samples collected in 2003 have an average Hg concentration of 0.4 ± 0.2 µg/g (n=19), whereas more recent surface samples have an average value of 0.3 ± 0.2 µg/g (n=20) of Hg. For both 2003 and 2015, the highest Hg concentrations occur in the southeastern portion of the lake. In 2003 the concentration was 1.1 ± 0.2 µg/g, and in 2015 it was 0.6 ± 0.1 µg/g. These high concentrations are adjacent to human-filled land along the shoreline. Despite these elevated concentrations, there appears to be an overall declining trend in Hg concentrations within the surface sediments over the past decade and this pattern is consistent with the broader decline since the peak concentrations observed in the sediment core. Haney, Stephanie, 2004, The sediment record of anthropogenic impact on the Summit Lake ecosystem, MS Thesis, The University of Akron, Akron, Ohio.