A METHOD FOR ASSESSING HYDROLOGIC ALTERATION WITHIN ECOSYSTEMS

Hydrologic regimes play a major role in determining the biotic composi tion, structure, and function of aquatic, wetland, and riparian ecosys tems. But human land and water uses are substantially altering hydrolo gic regimes around the world. Improved quantitative evaluations of hum an-induced hydrologic changes are needed to advance research on the bi otic implications of hydrologic alteration and to support ecosystem ma nagement and restoration plans. We propose a method for assessing the degree of hydrologic alteration attributable to human influence within an ecosystem. This method, referred to as the ''indicators of Hydrolo gic Alteration'' is based upon an analysis of hydrologic data availabl e either from existing measurement points within an ecosystem (such as at stream gauges or wells) or model-generated data. We use 32 paramet ers provide information on ecologically significant features of surfac e and ground water regimes influencing aquatic, wetland, and riparian ecosystems. We then assess the hydrologic perturbations associated wit h activities such as dam operations, flow diversion, groundwater pumpi ng, or intensive land-use conversion by comparing measures of central tendency and dispersion for each parameter between user-defined ''pre- impact'' and ''post-impact'' time frames, generating 64 Indicators of Hydrologic Alteration. This method is intended for use with other ecos ystem metrics in inventories of ecosystem integrity, in planning ecosy stem management activities, and in setting and measuring progress towa rd conservation or restoration goals.