The use of biological indices as surrogates for in-stream environmental quality has become increasingly common across the United States. The modern water quality monitoring criteria were developed in order to provide a system for measuring the “biological integrity” sought by the Clean Water Act (Karr et al., 1986). Davis and Simon (1995) describe the development and application of modern indices of biological integrity.
The most widely applied methods for assessing biological integrity involve collecting, counting, and enumerating species within a taxonomic group (typically fish or benthic macroinvertebrates such as aquatic insect larvae) and comparing the measured characteristics of the sampled community to a reference community using a scoring method. Standardized collection methods are codified for any local or regional area. Watershed areas are generally characterized within some defined biogeographic area (typically ecoregions). Habitat characterization is performed and usually compared to some concept of an expected habitat to support the assessed fish or macroinvertebrate community.
Scores calculated by these methods are unit-less numbers that represent the relative health and performance of the chosen community in that location. The most common versions of these scores are generally termed Indices of Biotic Integrity for stream fishes in North America (Karr et al., 1986). The IBI is a “multimetric” index based on adding subscores for different characteristics of the distribution and abundance of species within a sample. The indices incorporate measures of pollution tolerance, pollution intolerance, distribution of different feeding groups, and other characteristics of resident fish that provide measures of community composition and performance. The original IBI has been modified and incorporated across a range of watersheds and has been developed for other groups such as macroinvertebrates and even some terrestrial communities such as birds (see O’Connell et al., 1998).
The multimetric approach has been applied successfully in a regional and local context, such as the long term control plan for the City of Akron, Ohio.1 The methods are most successful where a good knowledge base exists about expected community composition within a regional or watershed area. Although some of the methods used to develop these indices can be standardized nationally, it is not possible to develop an index that can universally be applied across widely varying regions because of the different biota normally present in different habitats and climates. The National Research Council included multimetric indices in its review of biological and ecological indicators as a local or regional indicator (NRC, 2000). The Heinz Center has also included multi-metric indicators as a possible gauge of freshwater conditions nationally (by aggregation of regional scores) in its recent effort to provide a measure of ecosystem resources for the nation (Heinz Center, 2002).
The Ohio River Valley Water Sanitation Commission Compact (1948)2 states that the Ohio River should support and maintain a balanced, diverse, and healthy ecosystem. To determine whether pollution control efforts have achieved this objective, ORSANCO routinely conducts biological assessments that include the following components: (1) macroinvertebrate population reviews, (2) fish population studies, and (3) a fish tissue contaminants program. Macroinvertebrate populations provide perspective on aquatic life conditions in the river because many species are highly sensitive to pollution and are relatively immobile. The ORSANCO conducts macroinvertebrate sampling each year including site-specific studies, pool-wide studies, and river-wide surveys. Fish population studies have been a major component of ORSANCO monitoring activities throughout the history of the organization. Studies in 11 of 20 pools on the Ohio River below Pittsburgh have resulted in the collection of data for the development of biological criteria, or biocriteria, for the Ohio River. Methods employed included sampling fish in the chambers of locks at dams on the Ohio River and electrofishing. The fish tissue contaminants program of ORSANCO characterizes the levels of certain contaminants, such as pesticides or other organic chemicals, in Ohio River fish and provides a basis for determining the need for human health or fish consumption advisories.