The influence of climate-induced alterations in dissolved organic material on metal toxicity and UV radiation in Rocky Mountain streams

W.H. Clements¹, M. Appel², J. Barron¹, M.L. Brooks¹, W. Johnston¹, D.R. Kashian¹, D.M. McKnight², J. Meyer³, B. Prusha⁴, T.S. Schmidt¹, and R.E. Zuellig¹. ¹Colorado State University, Fort Collins, CO 80523, ²University of Colorado, Boulder, CO 80309, ³University of Wyoming, Laramie, WY 82071, ⁴North Carolina Division of Water Quality, Raleigh, NC 27699

Benthic communities in high elevation streams of the Rocky Mountains are subjected to intense levels of ultraviolet radiation (UVR) because of shallow depth and naturally low levels of light- attenuating organic materials. Benthic communities in many of these streams are simultaneously exposed to elevated metals from abandoned mines, the toxicity and bioavailability of which are also determined by dissolved organic materials (DOM). This research examined the influence of climate-induced changes in hydrology and DOM on responses of stream ecosystems to UVR and heavy metals. We integrated climate and hydrologic modeling with an intensive field monitoring and experimental program to test the hypothesis that climate-induced changes in DOM increased exposure to UVR and bioavailability of metals. Seasonal monitoring of 21 streams showed that the concentration of DOM was related to stream discharge and the amount of riparian vegetation. Because of lower concentrations of DOM, lower binding affinity, and reduced light attenuation, metal bioavailability and UVR exposure to benthic communities increased during low flow conditions. Field and microcosm experiments conducted in late summer supported the hypothesis that UVR and metals impacted benthic communities. These results demonstrate that interactions between UVR and other anthropogenic stressors may structure aquatic communities in Rocky Mountain streams.