Using Remote Sensing, Geochemical, and Isotopic Data to Quantify the Impact of Agricultural Practices in an Overexploited Aquifer in Northwest Mexico.

Water management with near-real-time data in arid zones is particularly critical where water resources from overexploited aquifers exist. Intensive agricultural practices in the Bustillos' Lake basin in Northern Mexico in the last 40 years have resulted in an overexploited aquifer that is being mined and its groundwater levels lowered at a 2m/yr rate. The watershed containing the aquifer has an area of 3,390 km², from which an approximated 55,500 ha are destined to irrigation of corn and apple orchards. Satellite products are a versatile tool enabling the monitoring of natural resources in general, and water resources in particular. In this work we used products from MODIS, TRMM and GRACE to solve the water balance equation to quantify discharge and recharge processes of the Bustillos' Lake watershed. To investigate the impact of agricultural practices on the water dynamics of the aquifer, we carried out time series analysis at a quasi-monthly and annual scales and estimated the net discharge of the aquifer to exceed the recharge by at least twice as much. Our analyses indicate that small recharge events occur at the end of the agricultural cycle when climatic conditions favor the deep infiltration of moisture from precipitation pulses and possibly the remnants of water from small ditches and reservoirs scattered throughout the agricultural valley. Nevertheless, our results suggest that these small recharge events are insufficient to neutralize the net drawdown of the aquifer levels from the high discharge from irrigation during the growing cycle of the crops. This reflects the unsustainability of the current water usage in the aquifer. Geochemical and isotopic tracers are being collected and analyzed to investigate the surface and groundwater flow systems in the Bustillos' Lake watershed. Samples from precipitation, surface water (lakes and streams), and groundwater (wells and springs) are being analyzed for metal and water stable isotopes (δ ¹⁸O and δ²H) to identify water-rock interaction, groundwater sources and flow paths, as well as for estimating residence times. The combination of remote sensing and geochemical data is being used to build a conceptual model of the watershed-aquifer system flow-paths in the basin to inform stakeholders and improve water management and agricultural practices of the region.