What are the seasonal controls on stream-riparian groundwater exchange during baseflow recession in headwater catchments?

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ABSTRACT"This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)."Hyporheic zones and riparian zones play important roles in catchment-scale budgets of nutrients, heat, and energy. Significant research has been conducted on the biogeochemical and hydrologic functions of both hyporheic and riparian zones, though often in isolation from each other. Here, we seek to determine how dynamic valley-bottom hydrology is controlled by valley morphology and gradient, and how this in turn influences hyporheic exchange throughout summer baseflow recession in headwater catchments. We pose the following research questions:1) How do down-valley and cross-valley vectors of subsurface flow change through seasonal baseflow recession?2) How are these changes controlled by valley-scale morphology and gradient?3) How spatially consistent are the patterns of down- and cross-valley vectors? 4) How does the extent of hyporheic exchange change during seasonal baseflow recession? We will address these questions by combining field methods, groundwater flow and transport modeling, stream solute transport modeling, and integrated analyses of tracer data and geophysical surveys of stream tracer distribution in the subsurface. This research will significantly enhance our ability to predict and quantify the hydrology of stream-groundwater exchange. We propose to conduct a workshop at the Shale Hills Critical Zone Observatory to bring together hydrologists and geophysicists to define the cutting edge and future directions of hydrogeophysics in stream-groundwater interactions. We will additionally train two graduate students and two undergraduate students in hydrology, groundwater modeling, geophysics, and solute transport. We will actively recruit from under-represented applicants to Penn State.