Sodium adsorption ratios and salinity levels in nine Texas aquifers: Implications for irrigated agriculture

This study evaluated sodium and salinity irrigation hazards for Texas' nine major aquifers. Sodium adsorption ratios (SAR's) and electrical conductivity levels (EC's) were calculated at 5,442 water wells. Aquifer median SAR's varied widely, from 0.3 (Edwards Balcones Fault Zone) to 8.5 (Carrizo-Wilcox). The percentage of SAR observations exceeding 17.5 ranged from 0.0 (Seymour Aquifer) to 36.3 (Carrizo-Wilcox Aquifer). There was a significant positive correlation between SAR and well depth in four aquifers and a significant negative correlation in four aquifers. Median EC's ranged from 545 umhos/cm (Edwards Balcones Fault Zone Aquifer) to 2,280 umhos/cm (Cenozoic Pecos Alluvium Aquifer). Respectively, 12.1% and 95.1% of the observations exceeded 750 umhos/cm in the Edwards Balcones Fault Zone and Cenozoic Pecos Alluvium Aquifers. EC and well depth were significantly positively correlated in two aquifers and significantly negatively correlated in five aquifers. Several factors control SAR's and EC's in Texas aquifers, including rock/sediment composition, groundwater chemical evolution, and seepage from nearby formations. Probable human controls include irrigation return flow, oil field brine, and pumping-induced saltwater intrusion. The Trinity, Carrizo-Wilcox, Gulf Coast, Cenozoic Pecos Alluvium, Seymour, and HuecoMesilla Bolson Aquifers have the greatest potential for sodium or salinity irrigation problems