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ASSOCIATIONS AMONG WATERSHED- AND SITE-SCALE DISTURBANCES INDICATORS AND FISH ASSEMBLAGES AT LEAST- AND MOST-DISTURBED STREAM AND RIVER SITES IN WESTERN USA
Citation:
Whittier, T R., J L. Stoddard, R M. Hughes, AND G. A. Lomnicky. ASSOCIATIONS AMONG WATERSHED- AND SITE-SCALE DISTURBANCES INDICATORS AND FISH ASSEMBLAGES AT LEAST- AND MOST-DISTURBED STREAM AND RIVER SITES IN WESTERN USA. Presented at American Fisheries Society meeting, Madison, WI, August 22-27, 2004.
Description:
At broad scales, the kinds and intensity of human disturbance to streams vary with natural gradients (e.g., elevation). While fish assemblages vary with both human and natural gradients, ecological condition assessments need to partition out the natural gradients to evaluate human disturbance. We defined least-disturbed conditions for each of four water chemistry, watershed, and site-scale indicators of disturbance, for 500+ Environmental Monitoring and Assessment Program (EMAP) sites in the Western Forested Mountains, Arid Lands, and Plains ecoregions. For each indicator, the definition of least-disturbed and most-disturbed was adjusted for the site's location on the primary natural gradients. For example, the least-disturbed condition for phosphorus in eastern Plains streams allowed up to 100 micrograms/L total P, while in western Plains sites < 30 micrograms/L total P was required. Sites were scored by the number of times they met the least-disturbed or most-disturbed condition for the 12 disturbance indicators. In the Mountains and Arid Lands, elevation, slope and stream size were the primary natural gradients, while longitude was the dominant gradient in the Plains. The importance of disturbance types varied regionally and along natural gradients. For example, watershed-scale disturbance measures did not distinguish between least- and most-disturbed sites for small streams at higher elevations, but were important for larger streams and at lower elevations.