The Muddy Creek watershed, part of the Upper Colorado River watershed, is a semi-arid catchment in a sagebrush steppe ecosystem. A synoptic watershed assessment was conducted in 2010 to identify areas within the watershed that are more susceptible to mobilization of trace elements that occur in soils forming on marine shale. Samples of soil, stream sediment, and water were collected and assayed for major elements and a suite of trace elements. Formation waters discharged from two wells within the watershed were sampled in 2011 to evaluate their potential contribution of organic carbon, nitrogen (N) species, and trace elements to surface waters.
In FY2012, analyses of the soil, rock, and water samples collected in 2010 and 2011 were completed. Soil nutrients were present in low concentrations throughout the watershed, with the exception of the headwater sampling site. Stream sediments also were nutrient poor, with low concentrations of organic carbon (less than 0.05-1.4 percent carbon) and no detectable concentrations of N. Concentrations of selenium (Se), derived primarily from the weathering of exposed shale, increased with increasing carbon (C) in stream sediments and alluvial soils. This correlation is consistent with the tendency of Se to bind to organic matter. Soils formed directly from Se-bearing shales did not exhibit the same relationship between Se and organic C. Concentrations in surface waters of dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) were 280-840 and 12-40 µM (micromoles), respectively. Concentrations of Se and DOC in groundwater collected from two wells were not unusually elevated, but concentrations of inorganic nitrogen (Well 1: 60 micrometers [µM] of N-NH4+; Well 2: 13 µM of N-NO3) were elevated relative to stream concentrations (less than 4 µM of N-NH4+ + N-NO3-). Introducing groundwater containing DOC:TDN ratios of 0.8-1.5 µM, where N is dominantly inorganic, to streams with DOC:total nitrogen of greater than 20 µM where N is dominantly organic, could lead to shifts in stream ecosystems and the type of organic matter present. Project personnel have drafted or submitted several manuscripts to peer-reviewed journals.
Products Completed in FY2012
Products Completed in FY2011
Products Completed in FY2010
McDougal, R., Grauch, R., Holloway, J., Plumlee, G., Stillings, L., and Tuttle, L. 2010. Development of Assessment Methods in Support of U.S. Geological Survey Integrated Science -- Wyoming Landscape Conservation Initiative, presented at the Energy Resources and Produced Waters Conference -- Water Quality, Management, Treatment, and Use, Laramie, Wyo., May 25-26, 2010, Laramie, Wyo., University of Wyoming [presented by R. McDougal].
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