I am interested in how flowing water and gravity shape the surface of the Earth in the past and how they may do so in the future. Much of my research focuses on the impact of climate change and land use on the hydrology and geomorphology of rivers. Through my postdoc, dissertation, masters research, and various interdisciplinary collaborations, I seek to better understand how natural processes of rivers support healthy freshwater ecosystems, how these processes may shift under a changing climate, and how they are impacted by society. I am highly interested in research that can inform the sustainability of freshwater resources, restoration of the structure and function of rivers, and conservation of the environment. I’ve had the opportunity to work on a variety of projects, some of which are described below.
Hydrologic controls on river migration, bank erosion, and spatial variability of microbial decomposition of organic carbon across the floodplain.
During my postdoc at Los Alamos National Laboratory, I continue to examine sediment and organic carbon dynamics along river corridors in collaboration with the Lawrence Berkeley National Laboratory and the Rocky Mountain Biological Laboratory. I use remotely sensed imagery, lidar, and extensive fieldwork to quantify migration of the East River over 60 years. Extending measured stream flow at our study site using a USGS gauge at a nearby site, I examine the role of various aspects of the snowmelt-dominated flow regime (e.g., the magnitude, frequency, duration, timing, and rate of change) on bank erosion and the floodplain sediment budget. I am also using modeled stream flow output from different scenarios anticipated under a changing climate to estimate the potential changes in erosion as hydrologic regimes shift till 2099. Working with collaborators at the Environmental Molecular Sciences Laboratory in the Pacific Northwest National Laboratory who use use fourier transform ion cyclotron resonance mass spectrometry and nuclear magnetic resonance, I am examining the physical controls on the spatiotemporal variability in chemical composition of organic carbon in the soil and water and quantifying the relative decomposition by microbes with increasing distance downstream, across the floodplains, and through time as flows change. This work links landscape-scale geomorphic and hydrologic processes with microscopic processes, quantifies ecosystem services of floodplains and help determine the role of rivers in the terrestrial carbon cycle. This understanding will provide the basis for understanding the past and estimating how these processes might change with changes in hydrology, land use, and climate in the future.
Geologic, biogeomorphic, and hydrologic influences on sediment dynamics and floodplain sediment residence time in mountainous headwater streams of the Colorado Rocky Mountains
My dissertation research in Rocky Mountain National Park, Colorado and surrounding areas examined the influence of valley and channel form on the storage and turnover time of floodplain sediment and associated carbon in mountainous headwater streams. This work entailed extensive fieldwork for soil sampling and wood surveys along numerous headwater channels of the Big Thompson River and N. St. Vrain Creek to quantify carbon storage in confined to unconfined valley segments and differing channel planform including single thread and multithread channels. I used radiocarbon ages of charcoal from floodplain sediment to estimate floodplain sediment turn over time across an elevation gradient in the Colorado Front Range. Older ages in glaciated valleys at high elevation show that headwater streams have longer floodplain sediment residence time than lower elevation streams in this mountainous region, but severe wildfire greatly alters the geomorphic disturbance of floodplains at high elevation. Aerial lidar before and after the 2013 flood in the Front Range was used to calculate volume of eroded material. Stepwise multiple linear regression of 155 study reaches indicated that contributing drainage area, valley confinement and stream power are the strongest predictors of floodplain disturbance. This research has implications for channel, landscape, and ecological response to climate change and land-use changes. This work also showed that increased channel complexity resulting from large wood jams and beaver dams likely influence the decomposition of organic carbon, as described below.
Geomorphic controls on carbon community composition and microbial processing in mountainous headwater streams
Although the valley and channel form plays a role in the retention of organic carbon in mountainous headwater streams, only a portion of this carbon may be stored for long periods of time (i.e., 100′s – 1000′s or years). A significant amount of this organic carbon serves as the foundation for foodwebs within mountainous ecoregions. Together with another I-WATER Fellow (Laurel Lynch) and Tim Fegel, at the USFS Rocky Mountain Research Station, we examined the dissolved organic carbon composition along confined, single thread and complex multithread channels at a subset of my study sites. This research suggests that complex channel form increases the metabolism of organic carbon, providing hot spots for aquatic and riparian ecosystem food chains and an important ecosystem service, filtration of OC from surface waters.
Assessing social-ecological systems to find balance between environmental and community freshwater needs
As a NSF IGERT Fellow in the Integrated Water, Atmosphere, Ecosystem, Education and Research Program (I-WATER), I had many opportunities to collaborate across disciplines regarding challenges confronting freshwater resources and the balance between ecological and societal needs. These experiences included working with engineers, economists, biogeochemists, soil scientists, ecologists, sociologists, geophysicists, and geographers on projects included frameworks for environmental flows to stimulate riparian and aquatic ecosystems. Ecological recommendations for environmental flows often include unrealistic goals that can not necessarily be met under societal demand for freshwater. I worked with David Martin, Dylan Harrison-Atlas, and LeRoy Poff to develop a framework that allows integration of stakeholder, community, and policy requirements and values to determine the exposure, sensitivity, and adaptive capacity of freshwater social-ecological systems. This approach can provide more realistic recommendations for releasing flows through rivers that can help stimulate the ecosystem by mimicking components of the natural flow regime. I’ve also worked with LeRoy Poff and Brian Bledsoe as a member of a Global Challenges Research Team in the School of Global Environmental Sustainability at Colorado State to develop recommendations for mitigation of nutrient pollution of freshwater in the South Platte River basin.
Hydrogeomorphic classification and sediment regimes of ephemeral channels in arid regions
My M.S. research in fluvial geomorphology at CSU under Ellen Wohl involved the development of a geomorphic classification of ephemeral streams in arid regions. I surveyed 101 study reaches on military land in southwestern Arizona and used various multivariate statistical approaches to test a classification that distinguished five channel types based on reach-scale channel geometry and hydraulics. This work informs a broader interdisciplinary effort to examine the ecohydrologic characteristics and ecosystem sensitivity of riparian vegetation in arid-region ephemeral streams of the southwestern U.S. Continued collaboration found that distinct vegetation communities are present along the 5 channel types. With experience from this research, I have recently co-authored a chapter title Geomorphology and Sediment Regimes of Intermittent Rivers and Ephemeral Streams in a textbook titled Intermittent Rivers and Ephemeral Streams: Ecology and Management.