National Research Program
A holistic watershed approach in Boulder Creek, Colorado
Evaluating the flux of chemicals through watersheds is a challenge because of the diversity of chemical inputs, variability of water sources, and diversion of flow for agricultural, industrial, and domestic uses. Investigation of geochemical transformations requires a systematic evaluation of the spatial and temporal variation of hydrologic, landscape, and anthropogenic factors. In identifying contamination from anthropogenic activities, major-ion and trace-element contaminants have natural sources that must be taken into account. In contrast, identifying contamination by synthetic organic chemicals is more straightforward because they are not naturally occurring.
The 1160 km2 Boulder Creek Watershed in the Colorado Front Range encompasses a gradient of geology, ecotypes, and urbanization, features that make it ideal for assessing our ability to study natural and human-contributed constituents in water. Originating largely from snowfall, much of the water in Boulder Creek ends up being diverted for municipal and agricultural uses. The discharge of Boulder Creek after all the diversions is a fraction of its former volume. In a 2006 journal article, USGS scientists documented that the largest chemical input is from wastewater treatment effluent, which also accounts for as much as 75% of the flow. Ground-water inflows and storm-water runoff contribute more chemicals. Major-element and trace-element concentrations were found to be low in the relatively pristine headwaters, but increased through the urban corridor. Organic wastewater contaminants and pesticides were detected throughout Boulder Creek, although loads of anthropogenic-derived contaminants, including those from prescription drugs, increased as basin population density increased. The report notes that boron, gadolinium, and lithium were found to be useful inorganic tracers of anthropogenic inputs and documents that there is a suite of potential endocrine-disrupting chemicals in a reach of stream where native fish populations are showing indication of endocrine disruption.
A more complete summary of water quality in Boulder Creek is available in a 2006 USGS Circular. The circular provides an assessment of water quality in the watershed at the beginning of the 21st centuary and information about how it has changed over the past 160 years.
Barber, L.B., Murphy, S.F., Verplanck, P.L., Sandstrom, M.W., Taylor, H.E., and Furlong, E.T., 2006, Chemical loading into surface water along a hydrological, biogeochemical, and land use gradient: A holistic watershed approach: Environmental Science and Technology, v. 40, p. 475-486. (pdf format, 1784 kb, published by American Chemical Society; not subject to U.S. copyright)
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For additional information, see http://wwwbrr.cr.usgs.gov/projects/SWC_Boulder_Watershed/ or contact Larry B. Barber, firstname.lastname@example.org