Evaluation of groundwater from drought-prone subtropical North America for irrigation and drinking quality assessments in the context of global warming
Résumé
Southeastern part of the Chihuahua Desert has always been drought-prone as southerly migrated ITCZ and enhanced ENSO since the early Holocene reduced the moisture supply. This arid region was inhabited by nomadic hunters since 10,500 years BP and agricultural activities started around 1500 years BP. The climate models predict temperature increase of 1-2°C and precipitation reduction of 10-20% in this region over the next couple of decades. The impacts of water scarcity might reduce the crop yield by half by the end of this century, exacerbating the immigration from Mexico to the USA. Additionally, the over-exploitation of groundwater in last decades for irrigation has drastically reduced the water table causing burning of subsurface peat layers and subsidence. We investigated groundwater from three sedimentary basins (El Potosi, Sandia and Cieneguilla), used extensively for agricultural activities, in order to identify the recharge regions and determine their suitability for irrigation and drinking purposes, following the guidelines of WHO as well as using Na% and sodium adsorption ratio and permeability index. These groundwater (pH:7.2-8.2; TDS: 168-1660 mg/L) are of Ca-HCO3 and Ca-SO4 types, due to interaction of recharging water with limestone-gypsum bearing catchment lithologies. Distributions of stable isotopes with respect to the local meteoric water line identify the recharge regions at Mountains of different elevations located to the east (i.e. Sierra Madre Oriental). This recharge, however, does not reach aquifers in central part of these basins due to over-extraction in basin margins. Groundwater from El Potosi is the most suitable for irrigation and drinking. Samples from the Sandia and Cieneguilla are characterized by high to very-high salinity hazard and some of them are also doubtful-unsuitable for irrigation based on the Wilcox diagram. Some samples from El Potosi and Sandia, however, contain nitrate and fluoride more than permissible limits of human consumption.