Final Publication: Karr, J.R. 1997. Measuring biological integrity. In Principles of conservation biology, ed. G.K. Meffe and C.R. Carroll, 483-485. Sunderland, MA: Sinauer.

Environmental change has always been a reality, and it is continuous. Change on Earth is driven by wind and water; geological activity; astronomical events; and the work of microorganisms, plants, and animals. These forces are active everywhere, and at all scales in space and time. Usually the forces with the greatest potential for cataclysmic change are rare like volcanic eruptions; local, like tornadoes or lightning fires; or slow to play out, like the advance and retreat of ice sheets.

Over the past two centuries, however, this pattern has changed. The activity of one species, Homo Sapiens, has become the principle driver of change on the Earth's surface. Human influences are massive; they are incessant; and they are global. For the first time, a biological agent -- a single species at that -- rivals geophysical forces in shaping the Earth.

Human-caused change may be positive, neutral, or negative. The challenge faced by conservation biologists and other environmental scientists is to detect and interpret change and to distinguish among those alternatives; they must understand and explain the causes and consequences of change, especially those that alter living systems. Resource and environmental managers want to detect and treat changes that have negative consequences; at the same time, they want to avoid wasting resources to treat changes without negative consequences.

Historically, negative consequences -- that is, risks -- were identified and assessed in terms of their effects on human health; a toxic chemical spill clearly presents a direct risk to human well-being, for example. But direct risks to human health are not the only environmental risks that society faces; other, ecological risks also pose a threat to well-being.

Human actions that increase ecological risks range from toxic spills and excessive nutrient release in agricultural runoff to destruction and fragmentation of natural habitats and the introduction of exotic species. For decades, modern society has behaved as if it were immune to ecological risks; conventional wisdom held that risks could easily be detected and then remedied before serious damage occurred. This behavior has left a legacy of degraded environments.

To effectively restore degraded areas, or to protect existing high-quality areas, one must be able to define the attributes of "normal," undegraded, "healthy" habitats as a model. Otherwise, how can one objectively assess whether mitigation or restoration techniques are succeeding? One way of setting a baseline and measuring restoration success is to define the normal "biological integrity" of a system, and then measure deviations from it.

The phrase biological integrity was first used in 1972 to establish the goal of the Clean Water Act: "to restore and maintain the chemical, physical, and biological integrity of the Nation's waters." This mandate clearly established a legal foundation for protecting aquatic biota. Unfortunately, the vision of biological integrity was not reflected in the act's implementing regulations.

Integrity implies an unimpaired condition, or the quality or state of being complete or undivided. Biological integrity is defined as "the ability to support and maintain a balanced, integrated, adaptive biological system having the full range of elements (genes, species, and assemblages) and processes (mutation, demography, biotic interactions, nutrient and energy dynamics, and metapopulation processes) expected in the natural habitat of a region" (Karr 1996). Inherent in this definition is that: (1) living systems act over a variety of scales from individuals to landscapes; (2) a fully functioning living system includes items one can count (the elements of biodiversity) plus the processes that generate and maintain them; and (3) living systems are embedded in dynamic evolutionary and biogeographic contexts that influence and are influenced by their physical and chemical environments.

Unfortunately, regulations implementing the Clean Water Act were aimed at controlling or reducing release of chemical contaminants (pollution) and thereby protecting human health; the integrity of biological communities was ignored (Karr 1991). As a result, aquatic organisms and aquatic environments have declined precipitously in recent decades. The present water resource crisis extends far beyond pollutant-caused degradation of water quality; in addition, we face loss of species, homogenized biological assemblages, and lost fisheries. Water resource programs have not and are not protecting biological integrity in the nation's waters because society continually fails to see rivers, and the landscapes they drain, in their entirety. Until an integrative perspective dominates our collective conscience, the condition of rivers will continue to decline.

Under section 305(b) of the Clean Water Act, states are required to report the status of water resources within their boundaries, yet the dominance of numerical chemical criteria in water quality standards results in chronic underreporting of actual degradation. In one state, conventional chemical evaluations failed to detect 50% of the damage to surface waters when compared with more comprehensive, sensitive, and objective assessment provided by biological evaluations.

Today more resource managers are recognizing the weaknesses of the chemical contaminant approach, and state and federal agencies are moving to incorporate sophisticated biological criteria -- numerical values or narrative expressions that describe the characteristics of a living aquatic assemblage.

To implement biological criteria, managers need formal methods for sampling the biota of streams, evaluating the resulting data, and clearly describing the condition of sampled stream reaches. I developed a measurement system, called the index of biological integrity (IBI), to fill this need. The complexity of biological systems, and the varied impacts humans have on them, require a broadly based, multimetric index that integrates information from individual, population, and assemblage levels.

IBI, like conventional economic indexes such as the index of leading economic indicators, provides a convenient measure of the status of a complex system. Both require an index time or baseline state against which future conditions are assessed. For IBI, that baseline -- biological integrity -- is the condition at a site with a biota that is the product of evolutionary and biogeographic processes in the relative absence of the effects of modern human activity.

IBI metrics are chosen because they reflect specific and predictable responses of the stream biota to human activities across the landscapes those streams drain. These responses are similar to dose-response curves measured by toxicologists; an organism's response varies with the dose of a toxic compound. Because they provide an integrative measure of the cumulative impacts of all human activities in a study watershed, IBI metrics can be viewed as ecological dose-response curves. IBI is based in empirically defined metrics because (1) such metrics are biologically and ecologically meaningful; (2) they increase or decrease as human influence increases; (3) they are sensitive to a range of stresses; (4) they distinguish stress-induced variation from natural and sampling variation; (5) they are relevant to societal concerns; and (6) they are easy to measure and interpret.

IBI metrics evaluate species richness; indicator taxa (stress intolerant and tolerant); relative abundances of trophic guilds and other species groups; presence of exotic species; or the incidence of hybridization, disease, and anomalies such as lesions, tumors, or fin erosion (fish) and head capsule abnormality (stream insects).

To determine an IBI for a stream, metric values from the stream are compared with values expected for a relatively undisturbed stream of similar size in the same geographic region. Each metric is assigned a value of 5, 3, or 1 depending on whether the condition is comparable to, deviates somewhat from, or deviates strongly from the "undisturbed" reference condition. Metric scores are then summed to yield an index (based on 9 metrics for western streams) that ranges from a low of 9 to a high of 45 for faunas equivalent to those in pristine or relatively undisturbed areas.

IBI or its conceptual clones are now used on six continents and in freshwater and marine systems. In 1996, 47 U.S. states are adapting biological criteria to assess the condition of water resources. The Ohio Environmental Protection Agency, for example, uses IBI to establish and maintain use designations for water bodies and to support their so-called section 319 Clean Water Act non-point-source program, section 305(b) CWA water quality inventory reports, and national pollution discharge elimination system (NPDES) discharge permits. The conceptual underpinnings of IBI have now been applied to a variety of aquatic environments (Davis and Simon 1995), including large rivers, lakes estuaries, wetlands, riparian corridors, and reservoirs. Taxa studied in developing IBIs have included algae, benthic invertebrates, and fishes (Ohio EPA 1988; Lyons et al. 1995; Fore et al. 1996).

An important key to successful restoration, mitigation and conservation efforts is having an objective way to assess and compare the biological integrity of damaged sites. IBI provides a tool for doing so and, at the same time, allows managers to set specific biological integrity targets for restoration programs.

FIGURE 1 Biological responses across a gradient of human influence in watersheds are "ecological dose-response" curves. Human influence is measured as chemical pollutants or dams and weirs in a watershed and the amount of riparian corridor removed. As Human influence increases, the number of Trichoptera (caddisfly) taxa in Japanese streams declines (A) and the number of invertebrates tolerant of input of organic effluent, sedimentation, and reduced oxygen levels in streams increases (B).

LITERATURE CITED

Davis, W.S. and T.P. Simon, eds. 1995 Biological Assessment and Criteria: Tools for Water Resource Planning and Decision Making. Lewis, Boca Raton, FL. [14]

Fore, L.S., J.R. Karr, and R.W. Wisseman. 1996 Assessing invertebrate responses to human activities: Evaluating alternative approaches. J.N. Am. Benthol. Soc. 15:212-231. [14]

Karr, J.R. 1001 Biological integrity: A long neglected aspect of water resource management. Ecol Appl. 1:66-84. [14]

Karr, J.R. 1996. Ecological integrity and ecological health are not the same. Pp. 97-109 in P.C. Schulze, ed. Engineering Within Ecological Constraints. National Academy Press, Washington, D.C. [14]

Lyons, J., S. Navarro-Perez, P.A. Cochran, E. Santana-C., and M. Guzman-Arroyo. 1995. Index of biotic integrity based on fish assemblages for the conservation of streams and rivers in west central Mexico. Conserv. Biol. 9:569-584. [14]

Ohio Environmental Protection Agency. 1988. Biological Criteria for the Protection of Aquatic Life. Ohio EPA, Division of Water Quality Monitoring and Assessment, Surface Water Section, Columbus, Ohio. [14]

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