For decades scientists have been trying to understand why there is an great increase in salt content from ~40mg/L at the headwaters of the Rio Grande in Colorado to ~1500 mg/L in El Paso, TX. The increased salinity has limited its use as city drinking water and agricultural irrigation water. The saline water causes problems such as increased soil salinity and reduction of crop productivity. This project focuses on pinpointing sources of salinity in the Rio Grande and its relationships to the fault systems within the Mesilla Bolson using a combination of water geochemistry and geophysical data.
Previous studies suggest multi-source contribution of salt to the overall salinity of the Rio Grande. This study has attempted to assess two main sources: 1) natural upwelling of saline groundwater through subsurface faults; and 2) return flows from the agricultural fields after irrigation with Rio Grande water and groundwater. Previous gravity studies have exposed a complex fault network throughout the Mesilla Bolson. This study has combined these datasets with new geophysical investigations to infer groundwater flow paths along the fault systems. Modeling the flow system of the Mesilla Bolson and its relationship to the Rio Grande can expose a potential salt influx from the faults of the Mesilla Bolson. Furthermore, the geochemistry of groundwater samples will be used to distinguish salinity sources from the natural groundwater upwelling and the agricultural return flows to the Rio Grande.
