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Environmental Significace of the Groundwater-Surface Water Interaction Zone
Process Studies

Process Studies Campaign

Objectives and Scope:

  • Reveal how the history of inundation dynamics (e.g., inundation return frequency) influences the timescales of microbial and biogeochemical responses to re-inundation, with a focus on aerobic metabolism.
  • Reveal processes governing the character (e.g., thermodynamic favorability) of dissolved organic carbon (DOC) along subsurface flow paths and the influences of DOC character on microbial communities and rates of aerobic metabolism.
  • Translate concepts and knowledge—related to inundation history and DOC character—into biogeochemical reaction networks.
  • Provide robust spatiotemporal data streams that will 1) facilitate model calibration/evaluation from local to reach scales; and 2) link hydrologic exchange flows (HEFs) and rates of aerobic metabolism to hydromorphic and hydrogeologic settings.

The Process Studies Campaign is focused on understanding the processes underlying interactions among biogeochemical function, variable discharge, hydromorphology, and hydrogeology. This Campaign will primarily use field and laboratory data collection and experimentation. New conceptual understanding and data products generated by the Process Studies Campaign will inform local models in the Mechanistic Models Campaign (e.g., by providing local hydrogeology) and reach-scale models in the System Models Campaign (e.g., reach-scale spatiotemporal variation in organic C stocks). Model outputs from both the Mechanistic Models and System Models Campaigns will inform the design of experiments and monitoring networks (e.g., provide potential mechanisms governing observed reactive solute dynamics).

From a biogeochemical perspective, RC-C will emphasize the dominant processes observed to date within the field system. We will specifically emphasize aerobic metabolism—including respiration and nitrification—and the influences of DOC character. These processes and features were selected because 1) they have relevance to ecosystem health through influences on endangered anadromous fish, migratory birds, and broader river corridor food webs, 2) DOC delivers energy to drive major subsurface biogeochemical cycles, and 3) groundwater and surface water in our field system are usually aerobic. We have, however, observed anaerobic processes (e.g., denitrification, methanogenesis) in the field system, and will be expanding to new field sites within the Hanford Reach that may be dominated by different sets of processes. Field measurements will therefore include reactive solutes reflective of both aerobic and anaerobic processes (e.g., dissolved oxygen, nitrate, methane), while our manipulative experiments will initially focus on aerobic metabolism.

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