EAR-PF: Transport and Fate of Riverine Organic Carbon in Grassland Ecosystems

Sarah Ellen Johnston博士被授予NSF EAR博士后奖学金，在莱斯布里奇大学、弗吉尼亚理工学院和州立大学开展与草原生态系统相关的研究和教育活动。北美的草原生态系统特别丰富，全球90%以上的草原生态系统被人类利用，是地球上受干扰最严重的系统之一。当人类活动改变景观时，流经草原的河流的化学成分和生态系统功能发生了戏剧性的变化。这个项目研究了加拿大阿尔伯塔省南部的一个河流系统，它流经没有改变的生态系统，以及那些被人类改变的生态系统。约翰斯顿博士将利用水化学和河流系统的模型，研究气候和人类活动(如农业改造)可能影响水系中碳循环的方式。这项工作将提供有关水化学，特别是有机碳的变化的信息，随着河流从河流源头的森林山区流向下游的农业和城市草原。这项研究的结果将描述人类在短时间(几周到几个月)和长时间(几年到几十年)对河流系统功能的影响。由此产生的数据将与北美各地的类似系统进行比较和缩放，以更好地了解草原河流系统对人类活动的脆弱性。这项研究将与当地社区的外联活动相结合，向年轻人宣传这一地区的水资源，并培训当地本科生在实地和实验室工作。此外，这里提出的工作将建立在现有社区联系的基础上，与地区分水岭委员会和尼西塔皮(黑脚)民族合作，分享由此产生的科学成果。这项研究将确定草原河流系统如何使用嵌套流域方法来循环碳，该方法整合了来自水文模型、化学技术、遥感和长期监测数据的数据，以表征一系列时间(周到十年)和空间尺度(从源头流到大河)的溶解有机物(DOM)。使用微生物培养技术评估从这些系统出口的DOM的命运，取决于来源材料的化学成分和环境条件，如水停留时间。在广泛的空间和时间尺度上使用技术方法的组合将在整个研究区域描绘DOM的来源、通量和命运。最终，这项研究试图确定整个南萨斯喀彻温河流域的短期和长期数据集的土地利用和气候振荡的影响，南萨斯喀彻温河流域是一个典型的草原分水岭。这项研究的结果将有助于建立一个框架，以评估土地利用和气候变化对草原河流系统提供的重要生态系统服务的综合影响。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。

Dr. Sarah Ellen Johnston has been granted an NSF EAR Postdoctoral Fellowship to carry out research and education activities related to grassland ecosystems at the University of Lethbridge and Virginia Polytechnic Institute and State University. Grassland ecosystems are particularly abundant in North America and, with over 90% converted to human use globally, are among the most disturbed systems on Earth. Rivers flowing through grasslands undergo dramatic changes in chemistry and ecosystem functioning when the landscape is altered by human activities. This project examines a river system in southern Alberta, Canada, which passes through ecosystems that are unaltered, as well as those that have been altered by humans. Using water chemistry and modelling of river systems, Dr. Johnston will investigate the ways that climate and human activities, such as agricultural modifications, may affect the cycling of carbon in the water system. The work will provide information about how water chemistry, in particular organic carbon, changes as the river moves from forested, mountainous terrain in the river headwaters to agricultural and urban grassland downstream. Findings from this research will characterize human effects on river system functioning over short (weeks to months) and long (years to decades) timescales. The resulting data will be compared and scaled to similar systems across North America to better understand the vulnerability of grassland river systems to human activities. This research will be paired with outreach to the local community to educate youth about water resources in this region, and to train local undergraduate students in the field and laboratory. Additionally, the work proposed here will build on existing community connections, partnering with the regional watershed council and the Niitsitapi (Blackfoot) Nation to share the resulting science. This study will define how grassland river systems cycle carbon using a nested watershed approach that integrates data from hydrologic modelling, chemical techniques, remote sensing, and long-term monitoring data to characterize dissolved organic matter (DOM) across a range of temporal (weekly to decadal) and spatial scales (headwater streams to a large river). The fate of DOM exported from these systems, assessed using microbial incubation techniques, depends on the chemical composition of source materials and environmental conditions such as water residence time. Using a combination of technical approaches across broad spatial and temporal scales will delineate sources, fluxes, and fates of DOM throughout the study region. Ultimately, this study seeks to define the impacts of land use and climate oscillations across short and long-term datasets throughout the South Saskatchewan River Basin, a model grassland watershed. The results of this study will help develop a framework to evaluate the ramifications of integrative effects of land use and climatic variability for important ecosystem services provided by grassland river systems.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.