Bioassessment, the Human Disturbance Gradient, and Applicability to Environmental Decisions

Abstract

A recommended procedure to develop scientifically valid biological assessment tools includes these following steps: • Classify aquatic systems into meaningful units. • Sample target biota across a human disturbance gradient (to define biological expectations). • Select relevant biological attributes that provide a reliable signal about human effects. • Extract and interpret patterns in the data. • Communicate results to policy makers. We discuss a system, known as the Human Disturbance Gradient, which establishes criteria, independent from the biology, to determine which sites are impaired by humans vs. those that are not. The HDG consists of land use information, hydrologic modification scores, habitat assessment scores, and water quality data. The HDG can be used to determine which attributes of biological community structure are effective discriminators of adverse human effects. These measures, known as metrics, should: • Provide meaningful measures of ecological structure or function. • Show a strong and consistent correlation with human disturbance. • Be statistically robust, with low measurement error. • Represent multiple categories of biological organization. • Be cost-effective to measure.Show responses that are not redundant with other metrics. An example of this procedure involving the recalibration of the Stream Condition Index and BioRecon methods is presented, as well as discussion of the applicability of bioassessment to environmental decisions. (51 slides in Powerpoint presentation.)