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E xchange of water between rivers and the surrounding subsur- face environments is a vital aspect of watershed function. ese hydrologic exchange flows (HEFs) lead to enhanced biogeo- chemical 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 computational models. A Scientific Focus Area (SFA) project led by Pacific Northwest National Labora- tory (PNNL) is addressing these challenges. e project is supported by the Department of Energy’s (DOE) Office of Biological and Envi- ronmental Research (BER) as part of BER’s Subsurface Biogeochem- ical Research (SBR) program. e project’s field site is a free-flowing section of the Columbia River (called the Hanford Reach) in eastern Washington state. Research activities are being conducted in the river corridor, which includes the surface water channel and other functionally connected features such as the hyporheic zone, near-shore groundwater aquifer, riparian zone, and vadose zone. e biogeochemical functioning of the river corridor and solute transport both within and through the corridor are con- trolled by the local groundwater gradient, variable river discharge, sub- surface material properties, and river channel morphology. Changes in river discharge occur seasonally (with maximum river stage occurring in spring from snowmelt) and daily (driven primarily by variations in hydropower production at upstream dams). is variable dis- charge causes fluctuations in river stage (water surface elevation) that control the spatial distribution, magnitude, and direction of HEFs. Consequently, the system’s biogeochemistry and ecology are highly dynamic and strongly interconnected with hydrologic processes. Translating Process Understanding Across Scales SFA research includes fundamental process identification and quantification, integration of modeling and experimentation River Corridor and Watershed Hydrobiogeochemistry Scientific Focus Area Developing a predictive understanding of hydrologic exchange flows and their influence on river corridor and watershed function sbrsfa.pnnl.gov Office of Biological and Environmental Research science.energy.gov/ber/ Columbia River Field Site. The Hanford Reach is a 70-km stretch of the Columbia River. It is bordered by agriculture on the east and north and the Hanford site on the west and south. It has many islands, an active riparian zone, and complex channel physiography. Hydrologic Exchange Flows. Conceptual river corridor diagram showing various types and scales of HEFs. Key Scientific Questions PNNL SBR SFA researchers are developing mechanistic understanding of coupled hydrologic and biogeochemical processes in large, dynamic rivers and associated watersheds and translating that understanding into multiscale numerical models. Key questions include: What are the hydrobiogeochemical processes that link river stage fluctuations and hydromorphic and hydrogeological setting to distributions of HEFs, residence times, and reaction rates? 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?

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Page 1: River Corridor and Watershed Hydrobiogeochemistry ... › docs › PNNL_SBR_SFA_Flyer_April_2018.pdf · as the hyporheic zone, near-shore groundwater aquifer, riparian zone, and vadose

Exchange of water between rivers and the surrounding subsur-face environments is a vital aspect of watershed function. These hydrologic exchange flows (HEFs) lead to enhanced biogeo-

chemical 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 computational models. A Scientific Focus Area (SFA) project led by Pacific Northwest National Labora-tory (PNNL) is addressing these challenges. The project is supported by the Department of Energy’s (DOE) Office of Biological and Envi-ronmental Research (BER) as part of BER’s Subsurface Biogeochem-ical Research (SBR) program.

The project’s field site is a free-flowing section of the Columbia River (called the Hanford Reach) in eastern Washington state. Research activities are being conducted in the river corridor, which includes the surface water channel and other functionally connected features such as the hyporheic zone, near-shore groundwater aquifer, riparian zone, and vadose zone. The biogeochemical functioning of the river corridor and solute transport both within and through the corridor are con-trolled by the local groundwater gradient, variable river discharge, sub-surface material properties, and river channel morphology. Changes in river discharge occur seasonally (with maximum river stage occurring in spring from snowmelt) and daily (driven primarily by variations in hydropower production at upstream dams). This variable dis-charge causes fluctuations in river stage (water surface elevation) that control the spatial distribution, magnitude, and direction of HEFs.

Consequently, the system’s biogeochemistry and ecology are highly dynamic and strongly interconnected with hydrologic processes.

Translating Process Understanding Across Scales SFA research includes fundamental process identification and quantification, integration of modeling and experimentation

River Corridor and Watershed Hydrobiogeochemistry Scientific Focus Area

Developing a predictive understanding of hydrologic exchange flows and their influence on river corridor and watershed function

sbrsfa.pnnl.gov

Office of Biological and Environmental Research science.energy.gov/ber/

Columbia River Field Site. The Hanford Reach is a 70-km stretch of the Columbia River. It is bordered by agriculture on the east and north and the Hanford site on the west and south. It has many islands, an active riparian zone, and complex channel physiography.

Hydrologic Exchange Flows. Conceptual river corridor diagram showing various types and scales of HEFs.

Key Scientific QuestionsPNNL SBR SFA researchers are developing mechanistic understanding of coupled hydrologic and biogeochemical processes in large, dynamic rivers and associated watersheds and translating that understanding into multiscale numerical models.

Key questions include:

• What are the hydrobiogeochemical processes that link river stage fluctuations and hydromorphic and hydrogeological setting to distributions of HEFs, residence times, and reaction rates?

• 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?

Page 2: River Corridor and Watershed Hydrobiogeochemistry ... › docs › PNNL_SBR_SFA_Flyer_April_2018.pdf · as the hyporheic zone, near-shore groundwater aquifer, riparian zone, and vadose

at multiple physical scales, and implementation of a novel and computationally efficient multiscale modeling framework. This framework incorporates new process understanding into local-scale, high-resolution mechanistic models, which, in turn, are used to formulate simplified (reduced-order) models applicable at system scales. Accordingly, research activities are organized and integrated around process studies, mechanistic models, and system models.

Process studies advance state-of-the-science hydrobiogeochemical process understanding across scales. This activity emphasizes field observations and experiments in the river corridor to study the effects of variable river discharge on key biogeochemical and ecological processes.

Mechanistic models apply new process understanding to elucidate mechanisms and characteristic component behaviors. This activity emphasizes high-resolution, local (km-scale and smaller) numerical models in the river corridor.

System models develop and link reduced-complexity model com-ponents to understand and predict system responses to natural and anthropogenic perturbations. This activity emphasizes reach- and watershed-scale numerical model development and integration.

Toward Predictive UnderstandingThe PNNL SBR SFA aims to develop a fundamental and comprehen-sive scientific understanding of HEF influences (particularly those driven by river discharge variations) on river corridor biogeochemical and ecological functions. Findings are integrated into a first-of-its-kind hydrobiogeochemical model of the river corridor, which is a critical component of watershed systems models. This new, predictive understanding of HEFs and biogeochemistry in the river corridor will play a key role in reducing uncertainties associated with major Earth system biogeochemical fluxes, improving predictions of environ-mental and human impacts on water quality and riverine ecosystems, and supporting environmentally responsible management of linked energy-water systems.

For more information about the River Corridor and Watershed Hydrobiogeochemistry SFA, go to sbrsfa.pnnl.gov.

River Corridor and Watershed Hydrobiogeochemistry SFA sbrsfa.pnnl.gov

Subsurface Biogeochemical Research doesbr.org

Climate and Environmental Sciences Division science.energy.gov/ber/ research/cesd/

DOE Office of Biological and Environmental Research science.energy.gov/ber/

DOE Office of Science science.energy.gov

U.S. Department of Energy energy.gov

April 2018

Contacts and Websites Principal InvestigatorsTim Scheibe, [email protected], 509.371.7633 Xingyuan Chen, [email protected], 509.371.7510James Stegen, [email protected], 509.371.6763BER Program ManagersDavid Lesmes, [email protected], 301.903.2977 Paul Bayer, [email protected], 301.903.5324

Linking Across Scales. Research activities are designed to translate the effects of coupled hydrobiogeochemical processes at the local scale to predict their cumulative impact at reach and watershed scales.

Community EngagementThe Hanford Reach is a rich environment for research because of existing extensive and diverse datasets combined with natural and anthropogenic factors driving hydrology and biogeochemistry. Active engagement between PNNL SBR SFA researchers and university and laboratory collaborators is leading to a community of researchers that can more effectively solve scientific challenges.

An example is the Worldwide Hydrobiogeochemical Observation Network for Dynamic River Systems (WHONDRS; whondrs.pnnl.gov), which is coordinated by PNNL SBR SFA researchers. WHONDRS is a global consortium of researchers aimed at understanding how high-frequency river stage variations influence river corridor function across a wide range of geographical settings. The consortium is developing new instrumentation to estimate HEFs in dynamic rivers and protocols for sample collection that will extend new process understanding to many other systems worldwide.

Peeper Installation. PNNL SBR SFA researchers work with collaborators from Ohio State University to install instruments that measure the products of biogeochemical reactions in the hyporheic zone. [Courtesy Kelly Wrighton, Ohio State University]