Assessing Relative Risks to Ecological Systems: A Methodology and Results at the National Scale. M. Harwell, Rosenstiel School of Marine and Atmos. Sci., Univ. of Miami; and S. Sanzone, U.S. EPA Science Advisory Board
As part of the EPA Science Advisory Board’s project to update and expand the 1990 report, Reducing Risk, the Ecological Risk Subcommittee developed and tested a methodology for assessing relative risks to ecological systems. The methodology, which was applied to relative risks at the national scale, begins with a stressor-based assessment of the co-occurrence of stress and effect regimes for at-risk systems so that ecosystem effect intensities are related to observed stressor levels in the real world. Ecosystem effects, an aggregate of effects on various endpoints for at-risk system types, are grouped into high, medium, and low intensity, each of which is assigned a numerical score. A series of multiplicative factors was then applied to adjust the initial co-occurrence score, taking into account proportion of the resource class at risk, existence of "hotspots" of high effects, temporal considerations such as duration of the stress/effects and system recovery potential, species depletion potential, and special ecological significance of at-risk system or effects. The result is a list of ranked relative ecological risks, which are subsequently placed into narrative risk categories of Highest, High, Medium, and Low Ecological Risks. The application of the methodology on the national scale, including evaluation of 34 ecological stressors, produced a risk ranking that placed physical and biological stressors at the top, with many of the traditional EPA-regulated chemical pollutants falling in the medium to low ecological risk categories.