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MERCURY RISK MANAGEMENT IN LIVESTOCK PONDS ON THE CHEYENNE RIVER SIOUX RESERVATION
Citation:
Johnston, J M., D. Hoff, R. Hoogerheide, R. Edgar, D. Wall, AND C. Ducheneaux. MERCURY RISK MANAGEMENT IN LIVESTOCK PONDS ON THE CHEYENNE RIVER SIOUX RESERVATION. Presented at Science Forum 2003, Washington, DC, May 5-7, 2003.
Impact/Purpose:
To improve the scientific understanding of the linkage between fish methylmercury and ambient mercury in the environment.
To complete a model for transformation and bioaccumulation of mercury than can be linked with models for atmospheric deposition and hydrology to yield a multimedia integrated modeling system capable of quantifying regional exposure to mercury.
To apply state of the art watershed and water body modeling to assess exposures to mercury for impacted aquatic ecosystems.
Description:
In a prior collaborative 3 year study with the Cheyenne River Sioux Tribe Department of Environmental Protection (CRST DEP), and the Agencies' Environmental Response Team, RegionVIII investigated Hg levels in fish tissues from the Cheyenne River and Lake Oahe in South Dakota. In 2000, the CRST released a fish advisory recommending less consumption of fish, especially for sensitive individuals within their population (pregnant and elderly). One mitigating risk management recommendation from the CRST to its constituents was to consume fish from livestock ponds, which, having no influence from mining related activities and at the time, presumably would have lower concentrations of mercury in fish tissue. However, fish from livestock ponds with seemingly similar outward appearances had significant differences in accumulation in both the same species or within species of the same trophic position.
The goals of the ongoing RARE project involving the Ecosystems Research Division (ORD/NERL) are twofold: 1) Determine the source and dominant pathways of methyl mercury bioaccumulation in fish tissue (presumably due to aerial deposition and/or naturally occurring sources), and 2) Make risk management recommendations to tribal members to reduce mercury exposures. The goal here is to use the results from the first objective to make future fish stocking recommendations in ponds with the least potential for bioaccumulation of methyl mercury. Sampling of biotic and environmental media during the characterization phase will be used to support the application of the USEPA Watershed Characterization System (WCS) and Mercury Cycling Model (MCM) models.
USEPA and Tribal personnel completed an initial comprehensive sampling effort in the Summer of 2002. Mercury was detected in soil samples across the region, and high levels of methyl mercury were found in aquatic invertebrates, e.g., caddisflies (110 ppb), copepods (810ppb). Region VIII personnel have developed and installed a low-budget atmospheric deposition sampler on site to characterize the source term of loadings to the ponds and surrounding watersheds. Initial results confirm high levels of methyl mercury in aquatic food webs, with communities dominated by predatory zooplankton to be much more contaminated than ponds dominated by herbivorous plankton (Cladocerans). Smaller ponds appear to be at greater risk for greater methyl mercury bioaccumulation. Sample collection is ongoing in support of model development to fully characterize the fate and transport of mercury and its biomagnification in these managed aquatic ecosystems of the Sioux Tribe.