Controls on Primary Production in the Colorado River Below Glen Canyon Dam
Primary production rates can have important implications for ecosystem food webs as well as nutrient and carbon cycling. Dams can fundamentally alter the temperature, clarity, and chemistry of river water and may thus affect rates of primary production downstream. For my postdoctoral work, I am collaborating with Charles Yackulic and Robert Hall as well as other scientists at the U.S. Geological Survey Grand Canyon Monitoring and Research Center to elucidate the patterns and controls on gross primary production in the stretch of the Colorado River directly downstream of Glen Canyon Dam.
Distinguishing Climate Related Effects on Natural Lakes versus Reservoirs: Towards a New Conceptual Model
Lakes and reservoirs integrate watershed and waterbody environmental change and are thus considered important climate change sentinels. Despite recognition that lakes and reservoirs differ in a number of key ways (e.g., managed outflow and landscape placement), there has been little quantification and synthesis of the differences between lakes and reservoirs. This project aims to compare and contrast the role of reservoirs versus natural lakes in modifying climate signals and is a collaborative effort with colleagues Nicole Hayes, Kristin Strock, Jessica Corman, and Roxanne Razavi. The collaboration was formed out of the 2014 Ecological Dissertations in the Aquatic Sciences Symposium.
Elusive Anaerobic Methane Oxidation Pathways in Lakes and Reservoirs
Although fresh waters are considered significant sources of methane to the atmosphere, the role of methane oxidation in regulating freshwater emissions is less well-studied than net methane emission. Anaerobic methane oxidation (AOM) plays an important role in regulating methane emissions from marine systems and its role in freshwater ecosystems is increasingly being appreciated as electron acceptors other than sulfate are recognized. This project aims to better characterize the role of anaerobic methane oxidation in the methane budget of lakes and reservoirs. Efforts to characterize methane oxidation dynamics in Lacamas Lake have been led by NIOZ Royal Netherlands Institute PhD student Sigrid van Grinsven. Additional synthesis work in collaboration with Daniel Reed and John Harrison aims to estimate the contribution of various electron acceptors to measured methane oxidation in Lacamas Lake and other eutrophic lake and reservoirs and considers the thermodynamic and kinetic constraints of organic electron acceptors (i.e. organic acids) in facilitating anaerobic methane oxidation.
Characterizing Greenhouse Gas Emissions From Water Reservoirs and Possible Mitigation Techniques via Control of Water Level Drawdown
Collectively, reservoirs created by dams are thought to be an important source of greenhouse gases to the atmosphere. Still, it remains challenging to estimate the magnitude of and controls on these emissions given the spatial and temporal heterogeneity in atmospheric emissions. My research aims to address these knowledge gaps at a variety of scales. My work with John Harrison, Keith Birchfield, and Maria Glavin in Lacamas Lake and in seven other Pacific Northwest reservoirs examines the role of water level drawdowns in controlling atmospheric methane emissions. In addition, I led an effort by an international team of scientists at Washington State University, U.S.A (John Harrison and Stephen Powers), the Chinese Academy of Sciences, China (Siyue Li), the U.S. Environmental Protection Agency (Jake Beaulieu), the University of Québec at Montréal, Canada (Tonya DelSontro), the Federal University of Juiz de Fora, Brazil (Nathan Barros), the Federal University of Minas Gerais, Brazil (José Bezerra-Neto), the Federal University of Rio de Janiero, Brazil (Marco dos Santos), and the University of Amsterdam (J. Arie Vonk). The result was a synthesis of all published studies on reservoir greenhouse gas emissions which has been highlighted by numerous media outlets including The Washington Post, Science, KQED Science, and the NPR radio show Science Friday and which was elected the Editor’s Choice article for the November 2016 issue of BioScience.
Integrating Biogeochemistry and Physics to Understand Hot Spots and Hot Moments for Nitrogen Transformation in Lakes and Reservoirs
Human activities have dramatically increased the rate at which nitrogen is made biologically available. In aquatic ecosystems, this excess nitrogen is associated with a number of negative ecosystem consequences. Denitrification is the main pathway whereby this nitrogen is removed, but the magnitude and controls on this process remain difficult to elucidate given current methodological constraints. Through intensive sampling of a local eutrophic reservoir (Lacamas Lake, WA), this project aims to develop a powerful measurement technique that combines approaches from fluid dynamics and biogeochemistry to quantify in situ denitrification rates. The project also characterizes the role of internal waves and physical mixing in determining hot spots and hot moments for denitrification. This interdisciplinary effort represents a collaboration between the Global Change and Watershed Biogeochemistry Lab (John Harrison) and the Environmental Hydrodynamics Lab (Stephen Henderson) at Washington State University.