Spatiotemporal variability of groundwater salinity and nitrate in a multi-aquifer system, Durango, Mexico

Groundwater resources in arid and semiarid areas worldwide are reaching critically low levels while the demand for drinking and irrigation water continues to increase. Agricultural and domestic waste are common sources of groundwater contamination, expressed primarily as salinity (e.g., EC, TDS, SAR, PI and Na%) and nitrate (as NO3-N). Salinity and NO3-N levels of a multi-aquifer system in a semiarid area within the state of Durango, Mexico, were spatially and temporally analyzed using GIS, Spearman correlation, and a double cluster analysis. Groundwater quality data were divided according to their location in either endorheic or exorheic basins and at two times, eight years apart, and the results were compared. Both groundwater salinity and NO3-N of endorheic basins were enriched about 2-fold compared with exorheic basins, whereas the variation with time was more subdued. Salinity and NO3-N in exorheic basins did not correlate, but salinity indices, TDS, and NO3-N correlated in endorheic basins. Salinity indices SAR, Na% and PI classified the water quality as suitable for irrigation, although only PI differentiated the water quality of exorheic from endorheic basins. Three clusters of wells, each with similar salinity values (high, moderate, and low), were identified. Mapping of these clusters hints at high salinity extending to the driest part of the studied area. The results shed light on the geochemical behavior and impact of anthropogenic contamination in water-scarce regions and on the urgency to implement water-saving strategies such as water-efficient irrigation practices and a reduction of nitrogen in irrigation returns, and animal and domestic waste flows.