A CONCEPTUAL-MODEL FOR ASSESSING ECOLOGICAL RISK TO WATER-QUALITY FUNCTION OF BOTTOMLAND HARDWOOD FORESTS

Ecological risk assessment provides a methodology for evaluating the t hreats to ecosystem function associated with environmental perturbatio ns or stressors. This report documents the development of a conceptual model for assessing the ecological risk to the water quality function (WQF) of bottomland hardwood riparian ecosystems (BHRE) in the Tifton -Vidalia upland (TVU) ecoregion of Georgia. Previous research has demo nstrated that mature BHRE are essential to maintaining water quality i n this portion of the coastal plain. The WQF of these ecosystems is co nsidered an assessment endpoint-an ecosystem function or set of functi ons that society chooses to value as evidenced by laws, regulations, o r common usage. Stressors operate on ecosystems at risk through an exp osure scenario to produce ecological effects that are linked to loss o f the desired function or assessment end point. The WQF of BHRE is at risk because of the ecological and environmental quality effects of a suite of chemical, physical, and biological stressors. The stressors a re related to nonpoint source pollution from adjacent land uses, espec ially agriculture; the conversion of BHRE to other land uses; and the encroachment of domestic animals into BHRE. Potential chemical, physic al, and biological stressors to BHRE are identified, and the methodolo gy for evaluating appropriate exposure scenarios is discussed. Field-s cale and watershed-scale measurement end points of most use in assessi ng the effects of stressors on the WQF are identified and discussed. T he product of this study is a conceptual model of how risks to the WQF of BHRE are produced and how the risk and associated uncertainties ca n be quantified.