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Seminar 2022-11-08 by Dr. Liwen Wu

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08 November 2022, 1:05 PM


Speaker: Dr. Liwen Wu

Time: 10:45-11:30

Location: ES354

Surface water and groundwater interactions in terrestrial and coastal hydrologic systems across varying spatiotemporal scales

Interactions between surface water bodies (rivers and oceans) and their surrounding aquifers (alluvial and coastal) vary significantly over space and time, constraining the exchange of water, energy, and solutes, and therefore the biogeochemical transformations taking place within sediments. Of particular interest is the interface between surface water and groundwater, known as hyporheic zones. Hyporheic zones are often characterized by marked physical and biogeochemical gradients that drive the exchanges between surface water and groundwater. The local and cumulative implications of this tightly coupled process strongly depend on characteristics of drivers (i.e., discharge and temperature of the water column) and modulators (i.e., hydraulic and thermal properties of the sediment). With this in mind, we perform a systematic numerical and field analysis of hyporheic responses to understand how the temporal variability of river discharge and temperature affect flow and heat transport within hyporheic zones. We identify typical time series of river discharge and temperature from gauging stations along the headwater region of Mississippi River Basin, which are characterized by different degrees of flow alteration, to drive a physics-based model of the hyporheic exchange process. Our results indicate that coupled groundwater flow and heat transport significantly affects the dynamic response of hyporheic zones, resulting in substantial differences in exchange rates and characteristic time scales of hyporheic exchange processes. Similar methods are applied to coastal aquifers, where we found temperature stratifications in the near-shore waters due to heated water discharge from nuclear plants are the key player determining the aerobic respiration rates in coastal aquifers. These findings shed light on fundamental processes modulating surface water groundwater exchanges in both terrestrial and costal systems with important implications for biogeochemical transformations along river corridors and coastal zones.

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