EAR-PF: Quantifying evaporation in Mono Basin: Bridging the gap between hydrologic modeling and paleoclimate records using triple oxygen and clumped isotope geochemistry

随着气候变化的加速和人口的增加，美国西部的淡水将成为一种日益宝贵的资源，其分配将变得更加有争议。为了能够帮助制定水资源管理决策的政策制定者和社区，我们必须能够更准确地预测流域的淡水资源未来将如何波动。加利福尼亚州东部的莫诺盆地分水岭是洛杉矶约1100万人的主要水源之一，是需要及时和了解科学情况的水管理战略的一个重要例子。该项目旨在提高我们对莫诺湖流域水文系统一个关键但通常缺乏约束的方面的了解：其标志性的终端湖泊莫诺湖因蒸发而损失的水量。对蒸发损失水量的错误估计可能导致现有和未来水资源的过度分配。该项目将结合强大的地球化学和水文模拟工具，以更好地量化莫诺湖流域的蒸发量，并扩大我们对近年来区域水文和气候变化的了解。这项研究将提供急需的信息，为水资源分配和保护决策提供信息，并提高对内华达山脉关键水资源如何受到人类活动的影响以及未来可能因全球气候变化而发生变化的理解。研究小组将与该区域的一个主要保护组织--莫诺湖委员会的外联和教育工作人员密切合作，为6-12年级的学生开发公民科学采样机会和以莫诺湖为重点的课程模块，以增加社区对水资源管理问题的参与，并加深对水文气候研究在决策中发挥的重要作用的理解。虽然水文质量平衡模型在估计关键流域的水文变异性方面提供了一个强大的工具，但仍有一些关键参数约束较差，例如蒸发损失的水量。缺乏对主要水库蒸发水损失的准确估计，给水文模型带来了很大的不确定性，并阻碍了对重要水资源未来变化性的准确预测。面对气候变化，加州东部的莫诺湖及其周围的分水岭象征着日益严重的水资源管理和保护问题。该项目旨在通过结合三重氧同位素地球化学、水文物质平衡模型和现场天气和环境(如温度、相对湿度)数据收集，解决对Mono盆地现代和历史蒸发水损失的更准确估计的需要。这项研究的第一个目标是量化现代莫诺盆地不同水库的同位素组成的时空变异性。这些同位素数据集将被用来评估同位素物质平衡模型在预测莫诺湖蒸发水损失和盆地水同位素组成演变方面的准确性。此外，该项目旨在通过从富含碳酸盐的沉积物中生成稳定的同位素替代数据，了解从大约100年的历史仪器数据中了解的天气和环境条件的影响是如何记录在Mono Lake沉积物记录中的。根据这些湖泊沉积物记录，可以估计莫诺湖近500年来的蒸发量和湖温变化。这项研究的预期结果是改进了对内华达山脉地区未来水文气候情景的模型模拟，并了解了稳定同位素替代品如何从干旱盆地捕获气候信号。此外，该项目将为湖泊沉积物记录中的水文气候信号提供一个解释框架，用于气候建模、古气候和古生态研究。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Freshwater in the Western United States will become an increasingly precious resource and its allocation will become even more contentious as climate change accelerates and human populations expand. To be able to assist the policymakers and communities who are making water resource management decisions, we must be able to more accurately predict how freshwater resources in watersheds will fluctuate in the future. The Mono Basin watershed in eastern California is one of the main water sources for approximately 11 million people in Los Angeles and presents an important example of the need for timely and science-informed water management strategies. This project aims to improve our understanding of a critical, but commonly poorly constrained, aspect of the Mono Basin hydrologic system: the amount of water lost due to evaporation from its iconic terminal lake, Mono Lake. Misestimation of water lost to evaporation can lead to the over-allocation of existing and future water resources. This project will combine powerful geochemical and hydrologic modeling tools to better quantify evaporation in the Mono Lake watershed and extend our understanding of the variability of regional hydrology and climate in recent history. This research will provide urgently needed information to inform water allocation and conservation decisions and improve the understanding of how critical Sierra Nevadan water resources have been affected by human activity and will likely vary in the future due to the changing global climate. The research team will work closely with the outreach and education staff of the Mono Lake Committee, a key conservation group in the region, to develop citizen-science sampling opportunities and Mono Basin-focused curriculum modules for 6-12th graders to increase community engagement in issues of water resource management and build a stronger understanding of the important role that hydroclimate research can play in policy decisions. While hydrologic mass balance modeling provides a powerful tool in estimating hydrologic variability of critical watersheds, there are key parameters that remain poorly constrained, such as amount of water lost to evaporation. The lack of an accurate estimate of evaporative water loss from major reservoirs creates large uncertainties for hydrologic models and hinders the accuracy of predicting future variability of important water resources. In the face of climate change, Mono Lake and its surrounding watershed in eastern California are emblematic of the increasingly serious issues of water management and conservation. This project aims to address the need for a more accurate estimate of modern and historic evaporative water loss in Mono Basin by combining triple oxygen isotope geochemistry, hydrologic mass balance modeling, and in-situ weather and environmental (e.g., temperature, relative humidity) data collection. The first objective of this study is to quantify the spatial and temporal variability of isotopic composition of various water reservoirs in the modern Mono Basin. These isotope datasets will be then used to assess the accuracy of an isotopically enabled mass balance model in predicting the evaporative water loss from Mono Lake and evolution of water isotope compositions in the basin. Additionally, this project aims to understand how the effects of weather and environmental conditions, known from ~100 years of historic instrumental data, are recorded in the Mono Lake sediment record through the generation of stable isotope proxy data from carbonate-rich sediments. From these lake sediment records, it will be possible to estimate the amount of evaporation and lake water temperature of Mono Lake varied in the last ~500 years. An anticipated outcome of this research is improvement of model simulations of future hydroclimate scenarios for the Sierra Nevada region and our understanding of how stable isotope proxies capture climate signals from arid basins. Additionally, the project will provide an interpretive framework for hydroclimate signals in lacustrine sediment records for use in climate modeling, paleoclimate, and paleoecology studies.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.