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DE-SC0021402: Effects of Surface Water Fluctuations and Sediment Movement on Hyporheic Zone Biogeochemistry and Microbial Communities

Award Status: Active
  • Institution: Virginia Polytechnic Institute and State University, Blacksburg, VA
  • DUNS: 003137015
  • PM: Bayer, Paul
  • Most Recent Award Date: 07/15/2021
  • Number of Support Periods: 2
  • PI: Hester, Erich
  • Current Budget Period: 09/01/2021 - 08/31/2022
  • Current Project Period: 09/01/2020 - 08/31/2022
  • Supplement Budget Period: N/A

Public Abstract

Effects of Surface Water Fluctuations and Sediment Movement on Hyporheic Zone Biogeochemistry and Microbial Communities


Erich T. Hester, Virginia Tech (Principal Investigator)

Kyle Strom and Mark A. Widdowson, Virginia Tech (Co-Investigators)

The hyporheic zone (HZ) is the region in sediment beneath and adjacent to streams, rivers, and riverine estuaries where groundwater (GW) and surface water (SW) mix.  The HZ provides habitat to aquatic organisms and improves water quality in watersheds.  Water quality improvements are due to beneficial reactions carried out by microbes such as bacteria in the sediment.  Much prior research has investigated these reactions in the HZ, but it generally assumed that sediment is immobile, and rates of reaction do not change over time.  Yet key unique aspects of the HZ include 1) the impact of SW water level fluctuations (due to storms, dam operations, etc) which alter supplies of key chemicals needed for these reactions (such as carbon and oxygen), and 2) continually shifting sediment on river bottoms that affect exchange patterns.  Both of these controls should substantially influence beneficial reactions in the HZ, yet remain poorly understood.  As a result, modeling tools that can predict how such reactions will vary with natural conditions and human actions currently do not exist.

Our project will initiate the development of such modeling tools that simulate the effects of SW water level fluctuations and sediment migration on distribution of microbes in the sediment which will allow us to better simulate the beneficial chemical reactions.  This exploratory grant will focus on 1) SW water level fluctuations and river bottom sediment movement that occur during non-storm conditions for much of the year, 2) riverbed dunes which are common riverbed sediment features that induce HZ exchange which often dominates HZ effects on watershed water quality, and 3) the effects of carbon infusion from SW and sediment movement on microbial distribution and hence beneficial reactions that remove excess nitrogen (a widespread nutrient that is a pollutant at high concentrations).  This exploratory project will then serve as a springboard to future projects that will extend this approach in multiple directions.

Our technical objectives are to 1) create and test a modeling approach that simulates migration of sediment dunes along river bottoms, 2) add SW and GW water flow and exchange across river bottoms to the model, including reactions and microbial growth, and 3) use the developed models to test the following hypotheses: H1) increases in SW flow velocity and water level during modest river stage fluctuations (e.g., from daily hydropower operation) increase dune migration speed which in turn controls spatial variation in carbon intrusion from SW into the HZ, and hence HZ microbial communities and rates of nitrogen reactions; and H2) intrusion of seasonably-variable carbon and microbes from SW into the dune-induced HZ impacts the spatial distribution and activity of HZ microbial communities, again regulating rates of nitrogen reactions.

We plan two tasks to test Hypotheses H1 and H2.  Task 1 will entail model development to address Objectives 1 and 2.  For Objective 1, we will link a SW model (e.g., FLUENT/OpenFOAM) to a GW model (MODFLOW/SEAM3D) to simulate processes pertinent to H1 and then adapt the GW component of the model to a moving frame of reference to add processes pertinent to H2, i.e. migration of dunes and their impact on hyporheic zone flow and transport.  For Objective 2, we will add microbial growth and migration to the modeling approach. Task 2 will use the models developed in Task 1 to test H1 and H2, thus addressing Objective 3.

This proposal aligns with the Subsurface Biogeochemical Research program priority to quantify and predict how water movement in watersheds drives fine-scale chemical processes in surface-subsurface systems that is the focus of the Pacific Northwest National Laboratory Science Focus Area program.  Our long-term vision is to use this exploratory grant to provide the foundation for longer term research efforts to continue model development toward a more comprehensive systems-based approach to simulate the effects of dynamic river conditions on HZ water exchange, sediment migration, chemical reactions, and microbe migration and growth, in turn providing input to larger watershed-scale models. 

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