Environmental health surveillance: indicators for freshwater ecosystems.

The relationship between the health of human populations and the state of the ecosystems in which they live is profoundly complex. As most environmental indicators relevant to human health depend on evidence of a direct cause and effect relationship, there are few indicators of the less direct consequences of environmental degradation on human health. Indicators of the direct consequence of contaminants in freshwater ecosystems on human health are highlighted in this paper and candidate indicators for environmental health are provided. Many of the indicators included here are from the State Of the Lakes Ecosystem Conference (SOLEC) program. SOLEC conferences in the past (1994 and 1996) examined the state of various components of the ecosystem through the use of ad hoc indicators, and provided subjective assessments of certain environmental conditions. At SOLEC 98, a comprehensive suite of 80 Great Lakes ecosystem health indicators was presented for review, refinement and acceptance. Candidate indicators for freshwater systems and environmental health presented here are organized following the "Pressure-State-Response" framework and cover the areas of drinking water, recreational water, freshwater food sources, and the availability of freshwater for economic activities.