Collaborative research: a multi-tracer (U, S, B, and Sr) approach to fingerprint and quantify anthropogenic salinity sources in the semi-arid Rio Grande watershed

在半干旱的美国西南部，格兰德河是灌溉用水的重要来源，它的含盐量(盐度)升高导致作物产量严重下降，土壤中盐分积累。这些紧迫的盐碱化问题也在世界各地的其他干旱河流中观察到。在这项研究中，研究小组将确定格兰德河的盐分来源。这项研究对土地和水资源管理实践具有指导意义，因此有助于确保美国农业的维持和淡水供应的持久性。值得注意的是，这项工作适用于了解影响全世界相关系统盐度的过程。除了这项工作对美国农业和水资源的潜在效用外，这项工作还具有科学影响，因为它侧重于开发一种新的地球化学工具，用于了解近地表/地表水的流动路径和传输时间。这一工具有可能应用于美国及其他地区的水系统，再次提供可能有助于自然和管理系统中水资源管理的信息。该项目将整合国内和国际上四个机构在环境同位素研究方面的专业知识和资源：德克萨斯州埃尔帕索大学(UTEP；少数族裔服务的公立大学)、亚利桑那大学、田纳西大学和巴黎物理研究所(IPGP)。通过培训两名研究生和三名本科生，该项目将为培养未来的美国STEM劳动力做出贡献。值得注意的是，UTEP的一名学生还将通过与法国IPGP合作，与一个在同位素地球化学方面备受尊敬的顶级研究小组合作，获得国际专业经验。除了这一国际经验外，该学生还将接受同位素地球化学方法的培训，并将这些知识带回美国研究团队。这项工作的国际合作部分将由NSF国际科学和工程部门提供支持。外展活动还将把前沿研究主题，如人与水、土壤和环境之间的相互作用，以及当地紧迫的环境问题，引起快速发展和多样化的埃尔帕索地区的美国高中生、教师和普通公众的注意。这项研究将重新探讨新墨西哥州和德克萨斯州格兰德河下游分水岭半干旱部分的一个重要的盐分问题。这个项目的目标是：1)利用新出现的同位素(铀)、传统同位素(硼、硫、锶)和元素(主要溶解离子)示踪剂，识别和量化新墨西哥州和得克萨斯州格兰德河下游的盐度来源，共同努力了解与人类活动有关的影响；以及2)了解杰梅兹河流域临界区观测站天然溪流中铀和硫同位素变化的控制因素，这是格兰德河流域人类活动有限的源头地区。上述同位素和溶质示踪剂的组合在区分盐分与农业、城市活动和地质来源方面具有独特的分辨能力。所获得的见解将提高我们对人类对水质和元素循环的影响的理解，这是地球科学界面临的最紧迫的问题之一。这项研究也将加深我们对杰梅兹河流域源头溪流铀、硫同位素变化的控制因素的认识。这些信息将为了解受人类影响的水域提供重要的自然基线。通过多重示踪方法，我们将实现以下目标：1)表征格兰德河流域人为和自然盐度来源的U、S、B和Sr同位素和主要元素特征；2)建立这些示踪剂在格兰德河流域的时空变化，并量化不同盐度终端成员在质量平衡约束下的贡献；3)将自然溪流中U和S同位素的变化与不同的水源联系起来，这些水源是通过受气候、地质和水文条件控制的不同流动路径演变而来的。

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.