Resources
Mancos Shale landscapes: Science and management of black-shale terrains
Black shale (organic-rich, generally dark-colored, fine-grained, sedimentary rock deposited in very low oxygen conditions) can be a source of mineral wealth and a cause for environmental concern. Oil and gas are the most obvious of the resources that originate in black shale, and some of the world’s largest mineral deposits (syngenetic and epigenetic) are hosted by black shale. Black shale is the probable source of metals found in some mineral deposits. A variety of industrial minerals, such as clay and phosphate, also are derived from black shale. In some environments, black shale-derived soil provides necessary nutrients for specific crops and plant populations.
In addition to their economic and ecologic value, some black shale sequences have potential for negative impacts. Many black shale sequences are non-point sources for potentially toxic elements, such as arsenic, selenium, chromium, and mercury. Additionally, some black shale-hosted ore deposits and associated waste rock can be point sources for a variety of toxicants. Slope stability and a variety of other engineering issues further contribute to the list of problems encountered in black shale landscapes.
Mancos Shale landscapes, especially in the Upper Colorado River Basin, have become a focal point for the need for science information supporting sound land-use policies. This need has risen in prominence primarily because of: (1) increased and changing demands for land use (2) issues related to the bioavailability of selenium and the salinity of surface and ground water.
Selenium Warning Sign at Sweitzer Lake State Park near Delta, Colorado.
USFWS interest in the Mancos Shale is related to the effects of selenium on endangered fish. This issue is written into the Recovery Goals of the Upper Colorado River Endangered Fish Recovery Program (CRFP). "Selenium is hypothesized as contributing to the decline of endangered fishes of the Colorado River Basin (U.S. Fish and Wildlife memorandum, December 22, 1998). It is a water-quality factor that may inhibit recovery by adversely affecting reproduction and recruitment (Stephens et al., 1992; Hamilton and Waddell 1994; Hamilton et al. 1996;Stephens and Waddell, 1998; Osmundson et al. 2000a).
Selenium concentrations in certain areas of the basin (e.g., Green River near Jensen, Utah; Gunnison River downstream from the confluence of the Uncompahgre River; and the upper Colorado River downstream from Palisade, Colorado) exceed those shown to impact fish and wildlife elsewhere, and, although results are inconclusive as to exposure thresholds that cause specific effects, some studies suggest deleterious effects on razorback sucker and Colorado pikeminnow."
In addition, the Recovery Goals state that the CRFP will, "Minimize adverse effects of selenium contamination on razorback sucker reproductive success and survival of young and reduce deleterious levels of selenium contamination...."
Sweitzer Lake State Park near Delta, CO: The inflow to the lake is from an irrigation canal that carries return water from fields developed on the Mancos Shale.
USGS Mancos Shale landscapes research is providing further definition of the selenium issue as it relates to the weathering and transport of selenium from undisturbed and disturbed landscapes. In addition, efforts to model the selenium cycle in Sweitzer Lake near Delta, Colorado will provide USFWS with information on selenium bioaccumulation in aquatic flora and fauna, which will compliment work done by the DOI National Irrigation Water Quality Program. This information will be useful in determining which actions will be effective in reaching the CRFP Recovery Goals for Endangered Fish. Results from the USGS Mancos landscapes research will provide new insights for USFWS regarding processes that control the occurrence of selenium in aquatic environments. This information will help USFWS administer their responsibilities under the Clean Water Act, Endangered Species Act, and the Migratory Bird Treaty Act.
References cited:
Hamilton, S.J., Buhl, K.J., Bullard, F.A., and McDonald, S.F., 1996,
Evaluation of toxicity to larval razorback sucker of selenium-laden
food organisms from Ouray NWR on the Green River, Utah: Denver Colorado
River Recovery Implementation Program report, 79 p.
Hamilton, S.J. and Waddell, Bruce, 1994, Selenium in eggs and milt of razorback sucker (xyrauchen texanus) in the middle Green River: Archives of Environmental Contaminants and Toxicology, v. 27, p. 195-201.
Osmundson, B.C., May, T.W., and Osmundson, D.B., 2000, Selenium concentrations in the Colorado Pike Minnow (ptychocheilus lucius): relationship with flows in the upper Colorado River: Archives of Environmental Contaminants and Toxicology, v. 38, p. 479-485.
Stephens, D.W. and Waddell, Bruce, 1998, Field screening of water quality, bottom sediment, and biota associated with irrigation on the Uintah and Ouray Indian Reservation, eastern Utah, 1995, Water-Resources Investigations - U. S. Geological Survey, Report: WRI 98-4161, 45 pp.
Stephens, D.W., Waddell, B., Peltz, L.A., and Miller, J.B., 1992, Detailed study of selenium and selected elements in water, bottom sediment, and biota associated with irrigation drainage in the middle Green River basin, Utah, 1988-90: Water-Resources Investigations - U. S. Geological Survey, Report: WRI 92-4084, 164 pp., 1992.
