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<br />Abstract: Hydrologic regimes play a major role in detennining the biotic composition, <br /> <br />structure, and function of aquatic, wetland, and riparian ecosystems. However, human land. <br /> <br />and water uses are substantially altering hydrologic regimes around the world. Improved. .; <br /> <br />quantitative evaluations of human-induced hydrologic changes would greatly benefit the.~",-.o <br /> <br />development of ecosystem management. and:restoration plans. To facilitate such improv$...... .' <br />-.' ~--. <br /> <br />hydrologic evaluations, we propose a method for assessing the degree of hydrologic altClu!i!!P. <br /> <br />attributable to human impacts within an ecosystem. This method, referred to as the Ind(~ <br /> <br />of Hydrologic Alteration (IHA), is based upon an analysis of hydrologic data available.~ ...>; <br />-. :;~.t~~~;;;_"-<,:,, <br />existing measurement points within an ecosystem (such as at Streamgauges or wells) .~"A'; :' <br /> <br />32 different parameters, organized into five groups, to statistically characterize hydrologic <br /> <br />variation within each year. These 32 parameters provide information on some of the most;;.;....:; <br /> <br />ecologically significant features of surface and ground water regimes influencing aquatic, ."d <br /> <br />wetland, and riparian ecosystems. . The hydrologic perturbations associated with activities-:sucJr <br /> <br />as dam operations, flpw diversion, ground water pumping, or intensive land use conversw,1f!ii;.;; ""c. <br /> <br />are then assessed by comparing measures of central tendency and dispersion for each, <br /> <br />'~d <br />-...~.. <br /> <br />-'-O_'C.__ <br /> <br />parameter, between user-defined "jJre-impact" and "post.impact" timeframes, generati1!&.~l ".' ,. <br />. - . . <br /> <br />different "I'!f1icators of Hydrologic Alteration. " The IHA method is intended to be useti ~'1IiIf'~'\'~ <br /> <br />:~'.': ",",,~::::~-,~; <br /> <br />conjunctively with other ecosystem metrics in inventories of ecosystem integrity, in plann~h <br /> <br />ecosystem management activities, and in setting and measuring progress towards conserv~ <br /> <br />or restoration goals. <br /> <br />,-,-.-., <br /> <br />.-',..-< <br />