MERCURY DEPOSITION IN LAKE FORT SMITH

Mercury is a ubiquitous pollutant in the environment with severe implications for human health. Lake Fort Smith is one of over 20 water bodies in the State of Arkansas with Hg-level fish consumption advisories. In 1994, the Arkansas Department of Health issued a mercury advisory for Lake Shepherd Springs. In 2006, Lake Shepherd Springs and Lake Fort Smith were combined into a single, dammed reservoir to meet future water supply demand for the city of Fort Smith, Arkansas. The mercury advisory carried over to the new Lake Fort Smith without additional analysis. Mercury Deposition Network data were collected from a station upwind of Lake Fort Smith in Gregg, Texas. Precipitation data for Lake Fort Smith was collected from the Global Historical Climate Network data set for the period 1948 – 2014. Lake sediment cores were collected March 7, 2012. Cores and samples were analyzed for organic matter, bulk-density, metals, redox-sensitive species (iron, manganese, and sulfur), carbon and nitrogen concentrations and isotopic composition, total mercury, methylmercury, and mercury isotopes. An age model for the longest core was created using ²¹⁰Pb, ²⁰⁶Ra and ¹³⁷Cs. Anoxic deep-water sampling was conducted August 29, 2012 at three sites. Water and sediment samples were from five shallow, near-shore locations in August of 2012 and 2013. Samples were collected after littoral zones had been exposed and resubmerged several weeks. Mercury species were analyzed and methylation efficiency was calculated for water and sediment samples. In lake sediment, total mercury concentrations were between 42.3 – 74.6 ug/kg. Mercury in lake sediments was derived from wet and dry atmospheric deposition, and had undergone many of the same biological (e.g. methylation), physical (e.g. adsorption), and chemical (e.g. photodegradation) processes, as observed analysis of mercury in water samples. In littoral waters, mercury concentrations ranged from 0.52 – 1.08 ng/L, below EPA drinking water and ambient water goals. Mercury deposition data collected upwind of the lake were not directly correlated with total mercury in lake sediment cores. Mercury concentrations in lake sediments were positively correlated with energy production from coal fired power plants in the western United States through the 1960s and negatively correlated with precipitation.