Linking Selenium Sources to Ecosystems:
Local and Global Perspectives
A predictive global map of latent risk for environmental Se loading indicates that ancient organic-rich depositional marine basins, unrestricted by age, are linked to the contemporary global distribution of Se source rocks. Given the geographic patterns, Se emerges as a contaminant within specific regions of the globe that may limit phosphate mining, oil refining, and drainage of agricultural lands because of potential ecological risks to vulnerable food webs. Selenium also may serve as a geochemical exploration tool that signals an ancient productive biological environment.
The sources and biogeochemistry of selenium (Se) combine to produce a widespread potential for ecological risk (Figure 1). Documented environmental effects across scientifically investigated sites include deformities in birds and fish, degraded fish communities, and exclusion of habitats for bird use (see Modeling and Irrigation pages).
The large geologic extent of Se sources is connected by human activities that include power generation, oil refining, irrigation drainage, and coal, phosphate, copper, and uranium mining (Figure 2). Study areas from the 1) San Joaquin Valley and San Francisco Bay-Delta Estuary, California, 2) watersheds of the Colorado River and other arid basins of the western US; 3) upper Blackfoot River watershed, Idaho; 4) upper Mud River watershed and other Appalachian basins, West Virginia; and 5) coal ash receiving basins such as Belews Lake in North Carolina include a range of processing activities that call attention to anthropogenic connections to the environment (e.g., production, storage, and disposal of subsurface irrigation drainage, oil refining effluents, and waste shales), in addition to surface processes (weathering, erosion, and runoff), that can ultimately mediate contamination.
The Se sources model components are:
- oceanic depositional environments
- organic carbon-rich marine sediments
- anthropogenic activities that facilitate transfer to the environment
- waste components and source waters and
- affected receiving water bodies
The global distribution of organic-enriched sedimentary rocks (i.e., black shales, petroleum source rocks, phosphorites, and coals) (Figure 1) depends on the fundamental role of major and trace nutrients in determining primary productivity. Although black shales and their recoverable organic fractions as sources of trace elements are widely recognized, the implications of worldwide reservoirs, site-specific fluxes, and persistent biologic cycling of Se are not. Given the geographic distribution of these source rocks, Se emerges as a contaminant within specific regions of the globe that may limit mineral extraction and agricultural growth or exacerbate environmental toxicity.
Development of technologies for controlling Se pollution and predictive forecasts of ecological effects will become increasingly critical to commercial exploitation, as well as to faunal conservation. Based on our conceptual model, adoption of methodologies to protect fish and wildlife that recognize the full sequence of interacting processes from sources through food webs to vulnerable predators will advance risk management by including all considerations that cause systems to respond differently to Se contamination.
Development of an ecosystem-scale Se modeling methodology and its site-specific applications (e.g., San Francisco Bay-Delta Estuary, mountaintop coal mining areas) are examples of a new type of approach that predicts ecological Se effects based on dietary exposure and the major processes that determine how Se is processed through food webs to top fish and bird predator species.
A Se sources model that depicts anthropogenic activities that contribute to exposure in the environment.
Presser, T.S., Piper, D.Z., Bird, K.J., Skorupa, J.P., Hamilton, S.J., Detwiler, S.J. and Huebner, M.A., 2004, The Phosphoria Formation: a model for forecasting global selenium sources to the environment, in J. Hein, ed., Life Cycle of the Phosphoria Formation: From Deposition to the Post-Mining Environment: Elsevier, New York, p. 299-319.
Presser, T.S., Hardy, M.A., Huebner, M.A., and Lamothe, P., 2004, Selenium loading through the Blackfoot River watershed: linking sources to ecosystems: in J. Hein, ed., Life Cycle of the Phosphoria Formation, From Deposition to the Post-Mining Environment: Elsevier, New York, p. 437-466.
Skorupa, J.P., Detwiler, S., and Brassfield, R., 2002, Reconnaissance Survey of Selenium in Water and Avian Eggs at Selected Sites Within the Phosphate Mining Region Near Soda Springs, Idaho, May-June, 1999: U.S. Fish and Wildlife Report, U.S. Fish and Wildlife Service, Sacramento, California, 95 p.
Piper, D.Z., Skorupa, J.P., Presser, T.S., Hardy, M.A., Hamilton, S.J., Huebner, M.A., and Gulbrandsen, R.A., 2000, The Phosphoria Formation at the Hot Springs Mine in southeast Idaho: a source of trace elements to ground water, surface water, and biota: U. S. Geological Survey Open-File Report 00-050, 73 p.
For further information, contact:
Theresa S. Presser
National Research Program
U.S. Geological Survey, MS 435
345 Middlefield Road, Menlo Park, CA 94025
Joseph P. Skorupa
Division of Environmental Quality
U.S. Fish and Wildlife Service
134 Union Blvd., Denver, CO 80228