You are here:
ECOLOGICAL ASSESSMENT OF ARIZONA'S STREAMS AND RIVERS, 2000-2004
Citation:
ROBINSON, A. T., N. V. PARETTI, AND G. E. CORDY. ECOLOGICAL ASSESSMENT OF ARIZONA'S STREAMS AND RIVERS, 2000-2004. Arizona Game and Fish Department, Research Branch, Phoenix, AZ, 2006.
Impact/Purpose:
To report on the ecological condition of Arizona's streams and rivers
Description:
The State of Arizona participated in a U.S. Environmental Protection Agency (EPA) ecological assessment of Western streams. One goal of the assessment was to report on the ecological condition of all Western perennial streams, except the `Great Rivers' such as the lower Columbia, Snake, Missouri, and Colorado rivers. Another goal was to identify and rank the importance of chemical physical, and biological disturbances affecting stream cognition. Having achieved these goals we can provide resource managers and decision makers with the information needed to conserve and manage the ecological condition of Arizona¿s streams.
To help address these goals, Arizona Game and Fish Department, U.S. Geological Survey, University of Arizona, Lockheed Martin, and EPA collected biological, chemical, and physical data from 47 perennial stream locations in Arizona. A probabilistic study design was used to select study sites to ensure results would be representative of all Arizona¿s perennial streams (an estimated 4,640 km stream length, 2,973 km of which was assessed). The ecological condition of each site was categorized as most-disturbed, intermediate, or least disturbed based on aquatic vertebrate and macroinvertebrate assemblage indicators; similar categories were assigned to each site based on levels of stressors. The results provide a snapshot of the ecological condition of streams in Arizona and in two broad climatic regions, Xeric and Mountains, within the state.
Most of Arizona's stream length was assessed to be in most-disturbed ecological condition (see figure below): 70% was in most-disturbed condition based on an aquatic vertebrate index of biotic integrity (IBI), and 57% was in most-disturbed based on a macroinvertebrate IBI. Within Arizona's two climatic regions, streams in the Mountains region tended to be in better condition than those in the Xeric climatic region.
Eleven stressors were examined which could potentially affect biotic integrity (see below). The importance of these stressors was evaluated by considering their relative extent (percentage of stream length in most-disturbed condition) and severity (the association with most-disturbed biotic integrity, as evaluated with relative risk). Statewide, non-native vertebrates had the greatest relative extent of any stressor examined, with 68% of stream length in most-disturbed condition. Salinity was the least extensive stressor, with 16% of stream length having high concentrations. A relative-risk analysis, however, indicated that high concentrations of salinity, total nitrogen and mercury in fish tissue, low levels of habitat complexity, and presence of Asian clam and crayfish were the stressors most associated with most-disturbed aquatic vertebrate condition. Of these stressors, non-native crayfish may be the best target for further study and possible management action because they were the most extensive (found in 33% of stream length) and were also associated with risk to the macroinvertebrate assemblage. It is our hope that information about the ecological condition of Arizona's streams presented in this report will be useful in developing management plans and priorities.