Tidal riparian zones function as critical biogeochemical control points in estuarine networks, regulating the flux of terrestrial nitrogen to coastal waters. However, the oscillatory nature of tidal forcing creates a complex reactive transport regime where the influx of nitrate-rich surface water is counteracted by the simultaneous delivery of dissolved oxygen, a potent inhibitor of denitrification. While the hydraulic dynamics of these systems are well-characterized, the role of bank morphology in modulating the trade-off between residence time and redox zonation remains poorly understood. In this study, we employ a two-dimensional, variably saturated reactive transport model coupled with Triple-Monod kinetics to investigate the hydro-biogeochemical efficacy of riparian banks under varying geomorphic and hydraulic conditions. Our results demonstrate a profound decoupling between theoretical transport timescales and realized biogeochemical function. Across a wide range of hydraulic conductivities (  to  m/d), the system exhibits negligible removal efficiency ( ), indicative of a kinetic “oxic trap” where tidal excursion lengths are insufficient to deplete oxygen and establish stable anoxia. Despite this low efficiency, we identify a strong geomorphic control on cumulative mass removal. Flatter bank slopes ( ) expand the intertidal wedge volume, linearly increasing the effective reactive surface area and compensating for kinetic inefficiencies. We propose a revised dimensionless framework that accounts for this geometric buffering, challenging the applicability of standard Damköhler numbers in oxygen-sensitive tidal environments. These findings suggest that river restoration strategies prioritizing bank regrading (profile flattening) may offer substantial water quality benefits by maximizing the volumetric capacity of the intertidal reactor, even under suboptimal redox conditions

Dr. Gu is a tenured Associate Professor at Duke Kunshan University. Before joining Duke Kunshan University, he held a faculty position as a professor at Beijing Normal University and a tenured Associate Professor at Appalachian State University in the United States. He has led and contributed to numerous research projects funded by the U.S. National Science Foundation, the U.S. Department of Energy, the National Natural Science Foundation of China, and China's Ministry of Science and Technology through international cooperation projects, joint funds, and key research and development projects. He has served as a panel member for the U.S. National Science Foundation and as a committee member of the University of North Carolina system within the Consortium of Universities for the Advancement of Hydrologic Science. Additionally, he is an Associate Editor of HydroResearch. Dr. Gu’s contributions to the field have been recognized with several awards, including the Outstanding Reviewer Award for Water Resources Research by the American Geophysical Union in 2017 and the Wachovia Environmental Research Award in 2012 for his exceptional contributions to Appalachian environmental research. His research interests span contaminant transport within the earth's critical zone (soil-plant-air-water complex), groundwater-surface water interactions, biogeomorphiic feedback in salt marsh, soil global warming potential, and urban hydrology.