AN ENVIRONMENTAL QUALITY INDEX FOR THE GREAT LAKES¹

Abstract

ABSTRACT: To facilitate communication on the environmental quality of lakes, particularly among policy makers and the general public, a new index for summarizing technical information is presented. The index is designed for the nearshore waters of the North American Great Lakes, but the concept is applicable to other temperate lakes with relatively good water quality. The index is based on nine physical (p), chemical (C), biological (B), and toxic substance (T) variables. Raw data are converted to subindex values by mathematically defined functions based on national or international objectives. Subindex values are multiplied by weighting factors and added to yield a final score ranging from 0, worst quality, to 100, highest quality. Letters with subscripts following the index score indicate the types and numbers of Variables whose values are equal to or worse than the objective — e.g., 70 C 1 P 1 indicates that one chemical and one physical variable exceeded the objective. For 18 nearshore locations in the Great Lakes, index scores ranged from 98 at two stations in Lake Superior to 30 C 2 P 1 B 2 T 1 off Point Mouillee in Lake Erie. If properly utilized, the index should be a useful tool to help managers evaluate the response of the Great Lakes to the multibillion dollar cleanup efforts conducted during the 1970's.