PNNL

The Pacific Northwest National Laboratory (PNNL) River Corridor Hydrobiogeochemistry Scientific Focus Area (SFA) works to transform understanding of spatial and temporal dynamics in river corridor hydrobiogeochemical functions from molecular reaction to watershed and basin scales. The knowledge we gain is used to improve mechanistic representation of river corridor processes, and their response to disturbances, in multiscale models of integrated hydrobiogeochemical function.

Project successes

Over the past three years, the River Corridor Hydrobiogeochemistry SFA has intensively studied the interactions among variable river surface elevation (“river stage”), hydromorphic setting, and hydrogeologic heterogeneity. The pivotal link connecting these elements is hydrologic exchange flows (HEFs), the dynamic exchange of water and chemical constituents between river channels and adjacent environments. HEFs stimulate biogeochemical activity in the subsurface adjacent to the river channel through provision of nutrients, mixing of dissolved reactants, and exposure to microbes. Based on our studies, we have determined how these interactions influence river corridor hydrobiogeochemical function. Key findings and developments include:

• A new understanding of the roles of dissolved organic matter (DOM) chemistry in river corridor biogeochemical processes
• A new theory and methods to incorporate DOM chemistry and microbial data into biogeochemical reaction networks
• Elucidation of HEFs spatial patterns and their relationships to subsurface residence times and temperature regimes through field characterization and mechanistic numerical models
• Development of reduced-order models that can tractably quantify the effects of these reaction-scale mechanisms at reach and watershed scales.

Current priorities

There is strong evidence that river corridor hydrobiogeochemical processes are highly variable among different stream orders and climatic, ecological, and geographic settings. They are also hypothesized to be highly sensitive to a variety of environmental and anthropogenic disturbances including, for example, floods, drought, wildfire, land use changes, and water use and management. We are studying these processes across varying settings and scales with the ultimate goal of predicting system responses at scales relevant to national priority water challenges.

To accomplish our goal, we use integrated laboratory studies, and field studies along the Columbia River Basin, to build and inform our numerical modeling studies. In addition, we use community collaborations to extend our research themes to multiple basins across the contiguous United States. Our research focuses on understanding the controls on spatial and temporal variations in river corridor hydrobiogeochemistry, hydrobiogeochemical responses to wildfires and precipitation, and representation of river corridor hydrobiogeochemistry in numerical models from reaction to basin scales.

Long-term vision

Mechanistically link the impacts of disturbance on HEFs, molecular processes, and biogeochemistry, to watershed function across the continental U.S. basins. Central to this vision is the translation of fundamental process understanding into predictive, interoperable models that can be transferred across watersheds. The outcome will be fundamental knowledge to forecast and mitigate river corridor and watershed environmental issues that affect the functioning and operation of the nation’s complex energy–water systems.

Scientific grand challenge

Understand and quantify processes governing the cumulative effects of HEFs, DOM chemistry, microbial activity, and disturbances on river corridor hydrobiogeochemical functions at watershed to basin scales.

Overarching science questions

1. How do HEFs, DOM chemistry, microbial activity, and disturbances interactively influence river corridor hydrobiogeochemical function from reaction to basin scales?
2. How can mechanisms that govern river corridor hydrobiogeochemistry be efficiently and sufficiently represented in integrated land surface models at scales relevant to regional and national water challenges?

Acknowledgments

This research is supported by the U.S. Department of Energy (DOE), Office of Science, Biological and Environmental Research (BER) program. This contribution originates from the River Corridor Hydrobiogeochemistry Scientific Focus Area (SFA) at the Pacific Northwest National Laboratory (PNNL).

A portion of the research is performed within the Environmental Molecular Sciences Laboratory (EMSL), a DOE Office of Science User Facility sponsored by BER and located at the PNNL-Richland campus.