SALINITY CHANGE (2000-2020) DOWNSTREAM A RIVER IN CENTRAL CHIHUAHUA, MEXICO, AND ITS IMPACT TO SHALLOW GROUNDWATER

Two rivers (Rio San Pedro and Rio Conchos) provide irrigation water to an arid region in central Chihuahua. The water quality of these rivers is affected by natural and anthropogenic processes, among which input of irrigation returns and evaporation stand out. A baseline of the water quality for the affected river segments and its associated shallow aquifer was obtained using data from the official Mexican CONAGUA dataset and from various studies conducted in this area. 23 river sites and 14 wells were selected for this study since each had been sampled at least three (and up to 18) times during this period. Three wells (21% of wells) had consistently SAR (sodium absorption ratio) >9, a value that makes the water unfit for irrigation. Although the data were scattered, once put together, they were able to render a picture of salinity changes (both downstream and with respect to time) based on total dissolved solids (TDS), calcium (Ca), sodium (Na), and SAR values. In addition, the association of salinity with nitrate, fluoride, and arsenic was ascertained. The latter are parameters of concern because of their potential toxicity.