Lessons Learned for Bioassessment

View some of the premises from Karr and Chu (1999)

Proper classification of sites is key

"The point of classification is to group places where the biology is similar in the absence of human disturbance and where the responses are similar after human disturbance. In some cases, these groupings may coincide with ecoregion boundaries; in others, they may cross these boundaries. To evaluate sites over time and place, we need groupings that will give reliable metrics and accurate criteria for scoring metrics to represent biological condition."

Measuring the wrong things sidetracks biological monitoring

"A bewildering variety of biological attributes can be measured, but only a few provide useful signals about the impact of human activities on local and regional biological systems. Variation may be natural or human induced, and natural variation may come from temporal (diurnal, seasonal, annual) or spatial sources (stream size, channel type), or both. Biological monitoring must separate human effects from natural variation by discovering, testing, and using those biological attributes that can be measured with precision to provide reliable information about biological condition. Some attributes are poor candidates for monitoring metrics because of their underlying biology. In particular, abundance, density, and production vary too much to use in multimetric indexes, even when human influence is minimal, and they (especially production) may also be very difficult to measure. Estimated density or species abundance at a site is affected by three sources of variance: sampling efficiency, natural events, and human activities.

Reference condition must be defined properly

"The goal of biological assessment is to detect and understand change in biological systems that results from the actions of human society. But change with respect to what? Just as economic analyses define a standard (e.g., 1950 dollars) against which economic activity can be judged, biological assessment must have a standard against which the conditions at one or more sites of interest can be evaluated. This standard, or reference condition, provides the baseline for site evaluation. In multimetric biological assessment, reference condition equates with biological integrity - defined as the condition at sites able to support and maintain a balanced, integrated, and adaptive biological system having the full range of elements and processes expected for a region."

Statistical decision rules are no substitute for biological judgement

"Ecologists tend to overuse tests of significance. It is not enough to detect differences in lieu of determining an impact's magnitude and cause or of understanding its consequences. It would be wiser to decide first what is biologically relevant and then use hypothesis testing to look for biologically relevant effects, not merely run a general "search for significance". Overreliance on statistical correlation, t-tests, or other statistical models can short-circuit the process of looking at data and asking whether they make sense and what they show. Dependence on p-values can divert scientists and managers from exploring the biology responsible for the patterns in data, no matter when or by whom they were collected." Learn more about some pitfalls when over-relying upon statistical test and ignoring biological judgement from Karr and Chu's (1999) Premise 33. Also, learn how simple graphs provide astonishing insights into patterns of biological response from Karr and Chu's (1999) Premise 10.

(from "Restoring Life in Running Waters" by James R. Karr and Ellen W. Chu)

Don't miss Developing Biological Indicators: Lessons Learned from Mid-Atlantic Streams (html, EPA/903/R-03/003, March 2003) on the MAIA Web site.