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 function.
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.
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.
AIMS - Aquatic Intermittency effects on Microbiomes in Streams: The AIMS project is an exciting new multi-state EPSCoR grant that is focused on understanding the role of stream intermittency in controlling water quantity and quality across the Mountain West, Great Plains, and Southeastern Forest ecosystems. This collaboration will span 7 institutions and will integrate datasets on hydrology, biogeochemistry, and microbial communities in three biomes to test the overarching hypothesis that physical drivers (e.g. climate, hydrology) interact with biological drivers (e.g. microbial communities, biogeochemistry) to control water quality in intermittent streams across the United States. Core Collaborators: Sam Zipper (KGS/KU), Amy Burgin (KU), and many more!
Spatial variability and subsurface controls of groundwater recharge and nutrient mobilization in the Arkansas River: We are investigating how stream intermittency influences groundwater recharge and water quality in the Arkansas River watershed in western Kansas, a large intermittent river influenced by groundwater depletion. 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. This work is supported by a grant from the Kansas Water Resources Institute. Core Collaborators: Sam Zipper (KGS/KU), Chi Zhang (KU)
Photo from Missisquoi River Basin Association
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.
Sleeper's River (VT), one of the study sites for this project, at the second-highest peak stormflow on record. Photo: James Shanley
Critical Zone Resiliency to Environmental Change How does critical zone structure control the multidimensional response of ecosystems to disturbances, and thereby regulates ecosystem resilience and resistance?
The critical zone (CZ), Earth's near-surface layer that spans from bedrock to the tree canopy, is being increasingly affected by numerous types of anthropogenic change that have the potential to trigger ecosystem state changes. However the structure of the CZ may mediate how resilient or resistant ecosystems are to multiple, interacting disturbances. Our Critical Zone Observatory Network cluster seeks to understand what CZ properties and climate characteristics regulate water, carbon, and nutrient retention and how CZ properties, disturbance history, and land use affect resistance and resilience to more intense, large-scale disturbances under a changing climate and anthropogenic pressure. We will address these questions at a range of scales spanning from the catchment to the continental US, and using diverse tools including complex systems analyses and watershed modeling.
One facet of this work will be focused in the northeastern US and will explore how streamwater nutrient export has responded to the interacting disturbances of acidification and increasing frequency of extreme precipitation events and what CZ attributes may promote resilient responses to these disturbances.
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. Our research team combines empirical field data, ex-situ lab experiments, and reactive transport modeling to address these questions. This work is supported by grants from California SeaGrant and the Department of Energy Subsurface Biogeochemical Research Division (abstract).