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Environmental Significace of the Groundwater-Surface Water Interaction Zone

Hydrobiogeochemical and Ecological Impacts of Hydrologic Exchange Flows

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We are developing predictive understanding of the processes that govern influences of hydrologic exchange flows on water quality, nutrient dynamics, and ecosystem health in dynamic river corridor systems. Exchange of water between rivers and the surrounding subsurface environments (hydrologic exchange flows or HEFs) are a vital aspect of watershed function. HEFs lead to enhanced biogeochemical activity (accounting for up to 96% of respiration within river ecosystems) and modulate water temperatures, thus playing a key role in water quality, nutrient dynamics, and ecosystem health. However, these complex processes are not well understood, particularly in the context of large managed rivers with highly variable discharge, and are poorly represented in system-scale quantitative models. Using the 75 km Hanford Reach of the Columbia River as our research domain, we have developed fundamental understanding in several areas including

  • Effects of groundwater-surface water mixing on ecological assembly processes, biogeochemical rates, and balance among metabolic pathways
  • River water pathways and impacts on contaminant plume mobility
  • Physical controls on HEFs at kilometer scales
  • Impacts of microbial regulation processes on biogeochemical rates in response to changing environmental conditions
  • The nature, speciation, and energetics of organic carbon driving biogeochemical processes.

We are building on this foundation to develop a fundamental and comprehensive scientific understanding of the influences of HEFs (in particular as driven by river discharge variations) on river corridor biogeochemical and ecological functions and to integrate this new-found scientific understanding into a first-of-kind hydrobiogeochemical model of the river corridor, linked as a critical component of watershed systems models. Accordingly, we pursue the resolution of fundamental scientific hypotheses designed to advance understanding of coupled hydrobiogeochemical processes. At the same time, we are developing a hierarchical multiscale modeling framework that will integrate scientific understanding into a predictive watershed modeling capability with wide applicability. New predictive understanding of HEFs and biogeochemistry in the river corridor will play a key role in reduction of uncertainties associated with major Earth system biogeochemical fluxes, improving predictions of environmental and human impacts on water quality and riverine ecosystems, and supporting environmentally responsible management of linked energy-water systems.

Scientific Grand Challenge: Develop fundamental understanding of the processes that govern influences of hydrologic exchange flows (HEFs) on water quality, nutrient dynamics, and ecosystem health in dynamic river corridor systems.

Motivating Science Question: What are the hydrobiogeochemical processes that link river stage fluctuations and hydromorphic and hydrogeological setting to distributions of hydrologic exchange fluxes, residence times, and reaction rates?

Mission Grand Challenge: Provide a mechanistic basis for predictive understanding of river corridor function, and incorporate this new understanding into community watershed modeling frameworks.

Motivating Science Question: What are the manifestations of mechanistic processes at larger scales, and what is the appropriate representation of fundamental processes in system-scale predictive hydrobiogeochemical models.



This research is supported by the U.S. Department of Energy (DOE), Office of Biological and Environmental Research (BER), as part of BER's Subsurface Biogeochemistry Research Program (SBR). This contribution originates from the SBR 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 PNNL.


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