ABSTRACT

Broader significance.

Elevated salt content (salinity) in the Rio Grande River, which serves as a critical source of irrigation water in the semi-arid southwestern US, has led to severe reductions in crop productivity and an accumulation of salts in soils. These pressing salinity problems have also been observed for other arid rivers worldwide. In this study, the research team will determine the sources of salinity in the Rio Grande. This study has implications for informing land and water management practices, and as such can contribute to ensuring maintance of U.S. agriculture and the longevity of freshwater supplies. Notably, this work is applicable to understanding processes affecting salinity in related systems worldwide. In addition to the potential utility of this work for US agriculture and water resources, this has impact scientifically in that it focuses on the development of a new geochemical tool for understanding near-surface / surface water flow paths and transit times. This tool can potentially be applied to water systems across the US and beyond, again providing information that may assist in water resource management in both natural and managed systems.

This project will integrate expertise and resources in environmental isotope research from four institutions at both national and international levels: U. of Texas El Paso (UTEP; minority serving public university), U. of Arizona, U. of Tennessee, and the Institut de Physique du Globe de Paris (IPGP). By training two graduate and three undergraduate students, the project will contribute to the training of a future US STEM workforce. Notably, a UTEP student will also gain international professional experience by working with the IPGP in France with a highly-regarded top research group in isotope geochemistry. In addition to this international experience, the student will receive training in isotope geochemistry methods and will bring this knowledge back to the US research team. This international collaborative component of the work will be supported by NSF International Science and Engineering. Outreach activities will also bring cutting-edge research topics such as interactions between human and water, soils, and environments, as well as local pressing environmental problems to the attention of U.S. high school students, teachers and general public in the rapidly growing and diverse El Paso region.


Technical description.

The research will revisit an important salinity issue in the semi-arid portion of the lower Rio Grande watershed in New Mexico and Texas. The goals of this project are: 1) to fingerprint and quantify salinity sources in the lower Rio Grande in New Mexico and Texas using emerging isotopic (uranium), traditional isotopic (boron, sulfur, strontium), and elemental (major dissolved ions) tracers, with a concerted effort on understanding impacts related to human activities; and 2) to understand the controlling factors on uranium and sulfur isotope variations in natural streams in the Jemez River Basin Critical Zone Observatory (JRB-CZO), a headwater region of the Rio Grande with limited human activities. The combination of the above isotopic and solute tracers has particular resolving powers in distinguishing salinity from agriculture, urban activities, and geologic sources. The gained insights will improve our understanding of human impacts on water quality and elemental cycles, one of the most pressing issues facing the Earth Sciences community. This study will also advance our understanding of the controlling factors on uranium and sulfur isotope variations in headwater streams in the Jemez River Basin. Such information will provide an important natural baseline to understand human-impacted waters. With the multi-tracer approach, we will achieve the following objectives: 1) to characterize the U, S, B and Sr isotope and major element signatures in anthropogenic and natural salinity sources in the Rio Grande watershed; 2) to establish both spatial and temporal variations of these tracers in the Rio Grande and to quantify the contributions from various salinity end members with mass balance constraints; 3) to link U and S isotope variations in natural streams to different water sources that have evolved via different flow paths controlled by climatic, geological and hydrologic conditions.

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