Stressor Identification (SI) at Contaminated Sites: Upper Arkansas River, Colorado (Final)

This report applies the U.S. EPA Stressor Identification (SI) methodology to evaluate impairments at a terrestrial contaminated site and to shed light on its utility in such an environment. The site chosen is in a highly mineralized area of the Colorado Rocky Mountains, consisting of the 500-year floodplain and adjacent irrigated lands of the Upper Arkansas River from the confluence of California Gulch to approximately 11 miles downstream. Impairments evaluated were barren areas in the floodplain (reduced vegetation), and reduced plant growth and plant species richness in meadows irrigated with water from the Upper Arkansas River. After a number of candidate causes were considered, the various lines of evidence support the interaction of elevated levels of extrinsic metal with decreased pH as the cause of the barren areas in the floodplain. Similar evaluation of reduced plant growth and plant species richness in the irrigated meadows leads to the conclusion that elevated levels of extrinsic metal is the cause. Aspects of the assessment process that may differ between aquatic and terrestrial systems include the critical variables that are measured, degree of development of bioassessment criteria, spatial heterogeneity and linearity of physico-chemical factors, and management practices. This project demonstrates the usefulness of the SI methodology for terrestrial systems.

This is the final report.

KRAVITZ, M. Stressor Identification (SI) at Contaminated Sites: Upper Arkansas River, Colorado (Final). U.S. Environmental Protection Agency, Office of Research and Development, National Center for Environmental Assessment, Washington, DC, EPA/600/R-08/029, 2011.