The Influence of Canal Water Releases on the Distribution of Methylmercury in Everglades National Park: Implications for Ecosystem Restoration
Abstract
Elevated levels of mercury (Hg) in the food web of the Florida Everglades have been well recognized for about two decades. Researchers have revealed the vexing complexity of ecosystem-scale factors that control Hg bioaccumulation across the Everglades, including: land use, elevated levels of atmospheric Hg deposition, water use and management, and disturbances (e.g., fire and droughts). Many of these factors directly interface with the Everglades Restoration Program; a fifteen year effort to return this unique ecosystem to a condition more closely resembling the historical uninterrupted flow way from Lake Okeechobee to Florida Bay. However, some activities of the Everglades restoration plan may result in exacerbated methylmercury (MeHg) production due to chemical and hydrologic effects on methylation. Specifically, planned increasing amounts of canal water releases, rich in sulfate and dissolved organic carbon (DOC), to the southern most part of the Everglades (Everglades National Park, ENP). In addition, with a more “natural” flow regime, regions of the ENP may also experience more frequent wetting and drying cycles, a phenomenon known to stimulate MeHg production in the Everglades and elsewhere. In the past two years, the U.S. Geological Survey and the National Park Service have been undertaking annual surveys of surface water and forage fish from about 70 sites across the ENP. The project is designed to assess the distribution and occurrence of MeHg across the ENP, and relate it to the major factors that affect Hg methylation discussed above. Results from the analysis of fish and water samples clearly show that canal water travels through ENP along the Shark River Slough, the historical center of flow through the Everglades. Several chemical makers of the canal water are evident, including sulfate, chloride and fluoride. Also evident in the data is a significant increase in the abundance of MeHg along the Shark River Slough, and direct result of sulfate stimulation of methylation. Total Hg concentrations show remarkably uniform concentrations in surface waters of the ENP, supporting the hypothesis of this research team that uniform deposition of atmospheric Hg has varying impacts to the ecosystem depending on the presence or absence canal water throughout the ENP. In many areas of the Park where there is no evidence of canal water impact to surface water chemistry, MeHg levels in water and fish are at or below reporting levels. This observation gives credence to the idea that historical MeHg levels in the Everglades (before man related releases of sulfate were present) were likely very low.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.B13G..08K
- Keywords:
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- 0409 BIOGEOSCIENCES / Bioavailability: chemical speciation and complexati;
- 0414 BIOGEOSCIENCES / Biogeochemical cycles;
- processes;
- and modeling;
- 0426 BIOGEOSCIENCES / Biosphere/atmosphere interactions;
- 0432 BIOGEOSCIENCES / Contaminant and organic biogeochemistry