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

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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.