Cooperator: North Dakota State Department of Health, U.S. Fish and Wildlife Service, U.S. Environmental Protection Agency
Project Chief: David P. Krabbenhoft
Location: Lostwood National Wildlife Refuge, Northwestern North Dakota
Project Number: ARN00
Period of Project: July 2003–September 30, 2004
Problem
The Lostwood National Wildlife Refuge (LNWR) is a 26,904-acre rolling prairie/wetland ecosystem in northwestern North Dakota, and is a critically important aquatic ecosystem for resident migratory wildlife. Recently, however, the U.S. Fish and Wildlife Service and the State of North Dakota have become concerned that the proximal location of a large coal combustion facility immediately upwind of the LNWR may be impacting the ecosystem through the deposition of atmospherically transported mercury. In the past 15 years, scientists have revealed that wetlands and their landscapes have a pronounced ability to expose resident wildlife to mercury loads; however, no known mercury assessments have ever been conducted on pothole wetlands in this region or anywhere else. Recent surveys have revealed that certain ecosystem types (for example, wetland ecosystems, newly flooded reservoirs, or seasonal impoundments) are particularly sensitive to mercury inputs and can result in high concentrations of mercury in fish or other aquatic biota. The pothole wetlands at the LNWR have most or all of these environmental characteristics, and in addition, the annual or semiannual wetting and drying cycles that are characteristic of the pothole wetlands likely exacerbate the methylmercury production cycle. However, previous to this study, there were no available data to test whether high mercury exposure levels to the food web occurred in pothole wetlands like the LNWR.
Objective
The overall goal of this project is to assess the mercury contamination level of pothole wetland environments, and to determine whether these ecosystems are “naturally prone” to be high in mercury exposure to indigenous wildlife. The goal of decreasing wildlife and human exposure to mercury presents major challenges to environmental managers and scientists alike. However, the first steps are to provide a better definition of the environments that are most prone to producing methylmercury, and then to establish what the limiting factors are for mercury exposure for each ecosystem type such that the most effective decision can be made. Currently, there is no known information on mercury cycling, fate, and biological exposure in prairie pothole wetlands. Many tens of thousands of these wetlands exist across the northern high plains, and they serve as a critical aquatic ecosystem for native and migratory wildlife in North America. This assessment study would provide sorely needed information on the level of methylmercury exposure in pothole wetlands, the controls on the levels of methylmercury produced across a range of physical, hydrological, and chemical characteristics represented at the LNWR, and whether or not local mercury source contributions play a role in potentially elevated levels of exposure.
Approach
This assessment project will have three integrated work elements, including: (1) a widespread synoptic sampling effort, (2) an atmospheric mercury monitoring effort to assess whether any nearby emissions sources can be “sensed” at LNWR, and (3) a historical determination of mercury deposition using dated sediment cores. The first element will be accomplished by sampling approximately 30 prairie pothole wetlands on the LNWR that span a wide range of geomorphic, hydrologic, and chemical conditions. The primary land-management method currently used by the Fish and Wildlife Service at LNWR is planned prairie burns. Recent studies have revealed that burning generally serves to stimulate mercury methylation by oxidizing sulfur to sulfate, and produces more reactive carbon substrate for bacteria to utilize when the soils are re-flooded. We will include sites that have been recently burned in the synoptic sampling to test whether this practice is possibly exacerbating methylmercury exposure at LNWR. Atmospheric mercury monitoring can be used to ascribe source-receptor relationships for areas of concern. Recently, the USGS has constructed a mobile mercury lab that has the capability of providing real-time atmospheric mercury measurements, that when coupled with supporting information, can help ascertain the relative importance of local versus global mercury pools. Lastly, a carefully collected set of sediment cores will be used to determine whether the establishment of several nearby coal combustion facilities in northwestern North Dakota and southern Saskatchewan, Canada has any local impacts on mercury deposition rates to the LNWR. The cores will be dated with radio-isotope markers (210Pb and 137Cs) and combined with mercury profiles to determine if local mercury deposition conditions were altered in response to startup operations of these facilities.
Progress (July 2003–June 2004)
During this time period, two field trips were conducted to sample about 30 pothole wetlands on the LNWR. Sediment and water samples were collected and shipped to the Wisconsin District Mercury Research Laboratory for analysis. In addition, the mobile mercury lab was deployed to LNWR for five weeks in the spring of 2004. Presently, sample analyses of the dated cores are underway, and are expected to be completed by October 2004.
Plans (July 2004–June 2005)
Future plans on this project call for synthesis of all the data collected at LNWR, and the formulation of a USGS report. If data gaps are identified during the reporting process, a proposal will be developed to follow up the present studies. |
