110 YEARS OF RESEARCH ON THE SALINIZATION OF THE RÍO GRANDE

The salinity of the Río Grande increases from very dilute at its headwaters in the San Juan Mountains of Colorado to barely usable for irrigation before it dries up south of El Paso, Texas. In Mahdi Hantush's day, New Mexico Tech researchers confronted several questions. What is the cause of this progressive salinization? Have human activities caused it to increase? These questions are only beginning to be fully answered. Application of environmental tracers, including Cl/Br, ³⁶Cl, ¹⁸O, ²H, and Sr and U isotopes has shown, that in addition to evapotranspiration, tributary salt inflows, and wastewater inflows, seepage of connate and geothermal brines has added significantly to the salinization of the river. Surprisingly, salt burdens have decreased substantially over the Twentieth Century. This decrease appears to be a result of the improvement of agricultural drainage early in the century. The most feasible approach to maintaining current TDS levels is projects that reduce undesirable evapotranspiration. Interception and deep disposal of subsurface brine might also play a role in reducing salinity.