Climate change, urbanization, agricultural expansion – human activities are impacting ecosystems at an increasing rate and spatial scale. I am motivated to understand how watersheds are responding to these changes, and what the impacts are on how they transport, modify, and store nutrients and carbon. Across many different studies and field sites, a central theme is answering the question: How do hydrologic vs. ecological processes regulate nutrient export and carbon emissions at the watershed scale, and how does the balance of these controls respond to environmental change?
I address these questions using a combination of observational and experimental approaches in both the field and lab to better understand how watersheds work.
Effects of winter climate change on catchment hydrology and biogeochemistry How do changes in the distribution of precipitation as rain vs. snow impact the timing, magnitude and stoichiometry of nutrient export from watersheds?
Winter is an often understudied season, but is increasingly vulnerable to our changing climate. Warmer temperatures and changes in the form of precipitation as rain or snow have the potential to greatly alter ecosystem function. In particular, the conversion of winter precipitation from snow (which accumulates in areas with seasonal snowpack) to rain will likely have important consequences for runoff generation and nutrient export, with cascading implications for soil nutrient dynamics, terrestrial vegetation responses, and lake primary productivity.
We are investigating these question in set of watersheds in northern Vermont. Using a network of high-frequency sensors, we are studying how runoff is generated during rain on snow events and how important they are for nutrient mobilization and transport. By comparing rain on snow events to our understanding of snowmelt processes, we can understand how these watersheds may shift in the future.
Consequences of land use change on groundwater and surface water quality How does land use change effect runoff generation, nutrient export, and in-stream processing? What effect do nutrient legacies have on contemporary biogeochemical signals?
Land use change alters the supply of nutrients and carbon within landscapes, as well as the degree of aquatic-terrestrial connectivity. Studies across many different climatic regimes and land uses have shown complex effects of land use change on runoff generation, solute fluxes, greenhouse gas emissions, and in-stream processing – but ultimately these changes are often linked to diminished water quality and ecosystem function. It is critical to understand how reactive nutrient sinks within landscapes are responding to environmental change, and what role they may have in mediating nutrient dynamics.
One ongoing project in this area seeks to understand how riparian wetlands in agricultural and forested watersheds influence streamwater chemistry. We seek to understand how the ability of wetlands to mediate water quality is altered by land use and changing rainfall regimes, which may alter the balance of solute supply and transport.
Image from Phys.org
Intermittent streams: Characterizing the hydrologic and biogeochemical regime of non-perennial stream ecosystems How do intermittent streams transport and transform nutrients and organic matter? What are the spatial and temporal scales over which intermittent systems interact with and influence downstream perennial waters?
Intermittent streams make up over 50% of the global river network length, yet they remain understudied compared to their perennial counterparts. The vast majority of our understanding of how streams transport and transform nutrients and organic material has been based on studies of perennial streams, or systems in which surface water flow is present year-round. Climate change and anthropogenic pressure on water resources have the potential to increase stream intermittency in the future, making it increasingly important to understand the biogeochemical and hydrologic regimes of these dynamic systems.
We are investigating these questions in the Arkansas River watershed in western Kansas. We are combining geophysical, hydrologic, and biogeochemical measurements to understand how subsurface structure of intermittent streams determines the partitioning of flow between groundwater and surface water, and the consequences of intermittency on downstream water quality.
Coastal hydro-biogeochemistry How are terrestrially-derived solutes transformed along groundwater flowpaths in coastal ecosystems?
Coastal estuaries are the interface between uplands and the ocean and have the important role of intercepting, transforming, and transporting pollutants before entering the marine environment. While the importance of terrestrially-derived, nonpoint source nutrient pollution from rivers into coastal systems has been extensively characterized, the contribution and fate of pollutants from diffuse groundwater is less understood. Our team is focused on quantifying nitrogen fate and transport along shallow groundwater flowpaths at the aquatic-terrestrial interface in coastal watersheds draining into the Elkhorn Slough National Estuarine Reserve in Monterey, CA.