CaUses anD IMPaCTs of salInIZaTIon In THe loWeR PeCos RIVeR

absTRaCT—River salinization is a byproduct of water resource development that results from cumulative impacts of flow-regime modifications and crop irrigation. However, historical salinization in the Lower Pecos River is often attributed to natural, high-salinity groundwater. Here, evidence from literature and U.S. Geologi-cal Survey gaging stations is reviewed to summarize historical changes associated with water development that potentially contributed to Pecos River salinization. A suite of hydrological changes, initiated in the 1880s, likely contributed to streamflow salinization: (1) reduced flood frequency and magnitude, (2) diminished streamflow, (3) increased evapotranspiration, and (4) increased prevalence of natural, high-salinity groundwater. Saliniza-tion is presently highest where these cumulative impacts were greatest (Red Bluff Dam to Girvin, Texas). Prior to water-resource development, higher, fresher streamflows and periodic floods diluted natural, high-salinity groundwater inflows and continuously exported salts from the drainage. Predevelopment salinity was lo