Collaborative Research: Parsing out the controls of climate, geology, and land use on riverine (234U/238U) ratios in Texas river basins

该提案将研究铀同位素比率（234U/238U）的变化，这是一种自然发生且易于检测的地球化学特征，在德克萨斯州从西北流向东南的大型河流中。本研究旨在详细了解德克萨斯州河流流域的气候参数（如降雨和温度）、岩石类型（砂岩、页岩、石灰岩和蒸发岩）和土地用途（农业、城市和自然）的变化如何控制河流（234U/238U）比例。了解这一重要信息将促进以下方面的知识：1)天然岩石分解形成土壤并向流域释放溶质和矿物质养分的速度有多快；2)地表水如何与地下水相互作用，以及某些观察到的水质问题是否与农业或城市用水有关；3)如何解释地质记录中的（234U/238U）比率，如土壤、洞穴和钙华矿床中的碳酸盐，以重建过去的环境和水文条件。所获得的知识将推动低温地球化学、水文学、古气候学和环境科学等科学领域的发展，并对水资源管理产生重要的社会影响。这项研究将支持来自德克萨斯大学埃尔帕索分校（少数在职和卡内基R1大学）、俄勒冈州立大学/堪萨斯大学和埃尔帕索社区学院（大型城市社区学院）的4名早期至中期职业教师、3名研究生和8名本科生组成的团队。该提案将为研究生和本科生，特别是来自两个地理位置不同的地区（美国西南部和中部）的社区大学生提供宝贵的研究和教育机会，这些地区由于农业和城市发展而面临不同但同样紧迫的水和环境问题。研究人员将制定环境科学发展计划（ESPD），包括实地和实验室的实践培训、在线培训模块、面向公众的地质水文实地考察，以及在埃尔帕索举行的Kay Bailey Hutchison海水淡化厂和地球科学日的推广活动。这些经历将使学生培养必要的科学研究技能，为他们未来在地球科学、环境科学和关键地带科学领域的职业生涯做好准备。河流（234U/238U）比率对于促进对流域功能、生态系统服务、水可持续性、地表水和地下水管理以及全球碳和养分循环的理解具有巨大的潜力。然而，由于无法破译气候、岩性和土地利用梯度中控制（234U/238U）比率的众多机制，它们在解决许多关键的地球化学和水文问题方面的广泛采用受到了阻碍。在这里，研究人员将测试伞式假设，即河流（234U/238U）比率可以通过量化风化界面的α反冲和化学溶解因素来预测，这些因素受1)流域气候参数（降水和温度）的控制；2)风化基岩的岩性参数（如粒度、矿物耐候性等）；3)水停留次数；而土地利用（农业和城市发展）可以叠加这些自然特征。他们的方法是在一个关键的区域尺度上，利用德克萨斯河流域的强大环境和地质梯度，这些流域的大小从10到100公里不等，这将填补目前流域研究中存在的空白。他们将进行地球化学、地质和地理信息系统（GIS）联合研究，以调查德克萨斯州河流（234U/238U）比例对降水、岩性和土地利用的控制。他们还将首次在这些流域中观察到的U同位素分馏，在现有文献中测试（234U/238U）分馏模型。由于（234U/238U）分馏是在河流、流域和地质记录中普遍存在的特征，因此获得的知识将转移到德克萨斯州以外的地区。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This proposal will investigate the variations of uranium isotope ratios (234U/238U), a naturally occurring and easy-to-detect geochemical signature, in large Texas rivers that flow from northwest to southeast across the state. This study aims to understand in detail how changes of climate parameters (such as rainfall and temperature), rock type (sandstone, shale, limestone, and evaporite) and land uses (agricultural, urban, and natural) in Texas river basins control the river (234U/238U) ratios. Knowing this important information will advance knowledge of 1) how fast natural rocks break down to form soils and release solutes and mineral nutrients into river basins; 2) how surface water interacts with groundwater flow and whether certain observed water quality issues are related to agricultural or urban water uses; and 3) how to interpret (234U/238U) ratios in geological records such as carbonates in soils, caves, and travertine deposits to reconstruct past environmental and hydrological conditions. The gained knowledge will advance the scientific fields of low temperature geochemistry, hydrology, paleoclimatology, and environmental science with important societal impacts especially related to water resources management. This study will support a team of 4 early to mid-career faculty, 3 graduate, and 8 undergraduate students from University of Texas at El Paso (a minority serving and Carnegie R1 university), Oregon State University/University of Kansas, and El Paso Community College (a large urban community college). This proposal will provide a valuable research and education opportunity for graduate and undergraduate students, and especially community college students from two geographically distinct regions (Southwest and Central USA) facing different but equally pressing water and environmental issues due to agriculture and urban development. Investigators will develop environmental science development programs (ESPD) with hands-on training both in the field and laboratory, online training modules, geohydrological field trips for the general public, and outreach events with the Kay Bailey Hutchison Desalination Plant and Earth Science day at El Paso. These experiences will allow students to develop necessary scientific research skills for their future career in Geoscience, Environmental Science, and Critical Zone Science.Riverine (234U/238U) ratios have great potential to advance the understanding of watershed functions, ecosystem services, water sustainability, surface and groundwater management, and global carbon and nutrient cycles. However, their widespread adoption for solving many critical geochemical and hydrological issues has been hindered by the inability to decipher the multitude of mechanisms that control (234U/238U) ratios across climate, lithology, and land use gradients. Here, researchers will test the umbrella hypothesis that riverine (234U/238U) ratios can be predicted by quantifying factors of alpha recoil and chemical dissolution at the weathering interfaces that are controlled by 1) climate parameters (precipitation and temperature) of the watershed; 2) lithological parameters of the weathering bedrock (e.g., grain size and mineral weatherability); and 3) water residence times; while land uses (agriculture and urban development) can overprint these natural signatures. Their approach is to leverage the strong environmental and geologic gradients across Texas river basins with sizes ranging from 10s-100s of km, at a critical regional scale that will fill the gap existing in current watershed studies. They will conduct a combined geochemical, geological, and geographic information system (GIS) study to investigate the controls of precipitation, lithology, and land uses on the riverine (234U/238U) ratios in Texas. They will also test (234U/238U) fractionation models in the existing literature across this matrix of drivers for the first time with the observed U isotope fractionation in these watersheds. The gained knowledge will be transferable outside of Texas as (234U/238U) fractionation is a ubiquitous signature observed in rivers, watersheds, and the geological record.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.