7405 - Laserfiche WebLink

Home Browse Search

26 BIOLOGICAL REPORT 90(5) The IBI: A Quantitative, Easily Communicated Assessment of the Health and Complexity of Entire Fish Communities1 by Robert M. Hughes U.S. Environmental Protection Agency Environmental Research Laboratory NSI Technology Services Corporation 200 SW 35th Street Corvallis, Oregon 97333 Two basic questions face biologists interested in assessing and predicting impacts on stream ecosys- tems: Why do we need assessments of biological communities? How can data on biological commu- nities (species and abundances) be made useful for nonbiologists (decision-makers and the public)? Answers to these questions are central to im- plementing the Clean Water Act. Although the act requires restoration and maintenance of biological integrity (Section 101) and biological assessment (Sections 105, 303, 304, 305, 404), biological integ- rity remains poorly defined and rarely measured. States are required to establish water quality stan- dards consisting of designated biological uses (broad goals) and criteria (which if met are presumed to pro- tect the uses); however, both the uses and the na- tional chemical criteria are inaccurate. Uses such as aquatic life and warmwater fish are so broad as to be met by any form of aquatic life or species of fish, in any abundance. Nationally established chemical criteria ignore naturally occurring differences in conventional water quality parameters, such as dissolved oxygen, pH, and the ionic character of waters. The ionic character of waters is particularly important because it affects the activity of toxic chemicals. Equally important, single-chemical criteria do not consider combined-chemical effects, which may mitigate or magnify results. Single-species toxicity tests may not be appropriate or sensitive measures of ecosystem effects because test species may not IThis paper was funded by the U.S. Environmental Protection Agency through Contract 68-C8-0006 to NSI Technology Services Corporation. It has been subjected to EP A's peer and administrative review and approved for publication. An earlier draft benefited from reviews by M. Bain, J. Kurtenbach, 1. Schlosser, and D. Vanna-Miller. be representative of indigenous species or the most sensitive species and because populations can be devastated by indirect effects on competitors, predators, and prey. Furthermore, criteria exist for only a small number of chemicals. It is too expen- sive to develop specific criteria for every site, and it would create immense regulatory problems if they were developed. Water quality monitoring data are difficult to interpret because of the lack of an ap- propriate sampling and reporting framework and because of the weak link between water quality and ecosystem structure and function. Finally, there are many other factors besides toxics that may limit at- tainment of biological integrity. Like toxics, physical habitat conditions are also surrogate measures of the communities that agen- cies are mandated to protect. Although physical and chemical conditions are necessary for understanding and explaining biological conditions, biological monitoring is preferable in many cases because it provides a direct assessment of the biological com- munity. Moreover, the biota reflect the integrated chemical and physical quality of an area, and they often can be assessed at lower cost than physico- chemical habitat parameters, such as priority pollutants and species-specific habitat. Millions of dollars have been spent on chemical monitoring and on the development of in stream flow models; still, there is only limited quantitative information regard- ing the health of the resident biota at those sites. In the southeastern United States (unlike the West, where the methodology developed), meeting in- stream flow requirements for game fish or a small number of nongame species is underprotective of the entire fish assemblage because (I) most game species have wider habitat-flow tolerances (e.g., centrar- chids vs. salmonids), (2) many nongame species have narrower habitat tolerances than the game species, ~