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I qq9 f, CH ? eI a4. <br />71 t5 <br />" <br />A Method for Assessing Hydrologic Alter lon. -` <br />within Ecosystems <br />BRIAN D. RICHTER,' JEFFREY V. BAUMGARTNER,t JENNIFER POWELL,t <br />AND DAVID P. BRAUN$ <br />'The Nature Conservancy, P.O. Box 430, Hayden, CO 81639, U.S.A. <br />tThe Nature Conservancy, 2060 Broadway, Suite 230, Boulder, CO 80302, U.S.A. <br />tThe Nature Conservancy, 1815 N. Lynn Street, Arlington, VA 22209, U.S.A. <br />Abstract: Hydrologic regimes play a major role in determining the biotic composition, structure, an junc- <br />tion of aquatic, wetland, and riparian ecosystems. But human land and water uses. are substantially altering <br />hydrologic regimes around the world. Improved quantitative evaluations of human-induced hydrologic <br />changes are needed to advance research on the biotic implications of hydrologic alteration and to support <br />ecosystem management and restoration plans. We propose a method for assessing the degree of hydrologic al- <br />teration attributable to human influence within cut ecosystem. This method, referred to cis the "Indicators of <br />Hydrologic Alteration," is based upon an analysis of hydrologic data available either from existing measure- <br />ment points within tin ecosystem (such as at stream ga itges or wells) or model-generated data. We use 32 pa- <br />rameters, organized into five groups, to statistically characterize hydrologic variation within each year. These <br />32 parameters provide information on ecologically significant features of surface and ground water regimes <br />influencing aquatic, wetland, and riparian ecosystems. We then assess the hydrologic perturbations associ- <br />ated with activities such as dam operations, flow diversion, groundwater pumping, or intensive land-use con- <br />version by comparing ineasures of central tendency and dispersion for each parameter between user-defined <br />'Pre-impact" and '/lost-impact" time frames, generating 64 Indicators of Hydrologic Alteration. This method is <br />intended for use with other ecosystem metrics in inventories of ecosystem integrity, in planning ecosystem <br />management activities, and in setting and ]treasuring progress toward conservation or restoration goals. <br />Un Metro para Evaluar Alteraciones Hidrologicas dentro de Ecosisternas <br />Resumen: Los regiWenes bidrol6gicos juegan un papel importante en la determinaci6n de la composici6n de <br />la biota, la estructura y junci6n de ecosistemas acuciticos inundables y riparios. Sin embargo, el use de la <br />tierra y agua por parte del hombre estil alterando substanciabnente regimens bidrol6gicos. Se requieren me- <br />jores evaluaciones cuantitativas de los cambios hic/rolrigicos inducidos por el hombre Para avanzar en la in- <br />vestigaci6n de las intplicaciones de la alteraci6n hiclrol6gica sobre la biota yPara soportar planes de manejo <br />y restauraci6n del ecosistenta. Pmponemos un meto do para evaluar el grado de alteraci6n hidrol6gica atri- <br />buible a impactos htunanos dentro de tin ecosistenta. Este m6todo, denominado Indicadores de Alteraci6n <br />Hidrol6gica, se bass en el andlisis de datos hidrol6gicos disponibles ya sea de puntos de muestreo dentro de <br />tat ecosistema (tales conto mediciones de corrientes o pozos) o generados por modelos. Utilizamos .32 <br />pardmetros organizados en cinco gruuos, para ca racterizar estadisticamente la variaci6n hidrol6gica de <br />calla an`o. Estos .32 pardmetros proporcionan informaci6n de rangos ecoldgicamente significativos de los <br />regimenes de aguas superficiales y subterrdneas que influyen en ecosistentas actidticos, inundables y ripar- <br />ios. Se evaluaron las perturbaciones hidrol6gicas asociaclas con actividades tales como operaco6n de presas, <br />desviaci6n de flujos, bontbeo de agua subterrdnea o cambios en el use intensivo del suelo mediante la com- <br />pairaci6n de rnedidas de tendencia central), dispersitn para calla pardntetro, entre rangos de tiempo difini- <br />Paper submitted Jcaurat), 31. 199(; revised manuscript accepted August 14. 1996. <br />1163 <br />Con".1"a dun Biolop, Pa?_u 11(6-11-1