Fine natural sediments like clay particles are transported in rivers and deposited in riverbeds. Historically, these particles are considered wash-load, i.e., passive material that travels in suspension, having little to no interaction with other river processes. However, river water enters the porous beds, bringing with it those fine particles that are filtrated and immobilized in the riverbed. Over time, they accumulate and clog the riverbed voids, dramatically attenuating hyporheic exchange and diminishing the connection between surface and groundwater. Hyporheic exchange is crucial for microbially mediated transformations, such as carbon and nitrogen cycling. Despite the long stretches of land that rivers span, these biogeochemical transformations occur at limited hot spots in hyporheic zones, right on the areas that are prone to clogging.

During this seminar, I will present how coupling surface water flow, hyporheic exchange, and clogging led us to determine that surface water turbulence plays a vital role in the deposition of fine particles in riverbeds and the subsequent attenuation of hyporheic exchange. These new insights will be essential to quantify better the role of rivers in carbon and nitrogen cycling estimations, and future work will be directed at upscaling these soil-grain scale processes into basic-scale models.

Lieu
Laboratoire METIS, Sorbonne Université, Campus Pierre et Marie Curie
4, place Jussieu 75005 Paris
Salle Darcy, tour 46-56, 3^e étage.