Nitrogen dynamics in the Hyporheic zones of complex 3-D bedforms

Abstract:

The hyporheic zone (HZ) is a biogeochemically active zone that hosts the coupled reactions of organic carbon oxidation, nitrification, and denitrification. These N transformations could either produce or consume NO₃^－ and thus the HZ could serve as a NO₃^－sink or source in the fluvial system. The reactants within the hyporheic zone are transported through advection by flow induced by bedform topography. However, most previous studies have focused on two-dimensional (2-D) and simple bedforms. Recent studies showed that even a simple 3-D bedform would have a higher hyporheic flux and a slightly larger volume or exchange zone depth, and thus a different residence time compared to its equivalent 2-D bedform. This implies that the competition between reactant supply and demand for the 3-D bedforms might be different from 2-D bedforms. In this study we will investigate the ecological role of HZ with much more complex and more natural 3-D bedforms through numerical simulations. We are investigating synthetic but realistic complex bedforms considering the superimposition of smaller dunes upon larger dunes. The goal of the study is improve our understanding and the prediction of the ecological function of HZ as a nitrate sink or source for a natural system.