In the Yangtze River Delta, the nitrate released from intensive agricultural and industrial activities has overburdened the river system and posed risks to ecological health through eutrophication. Though the riparian zone offers a natural approach to mitigate nitrate pollution, how tidal fluctuations affect those functions remains unclear. Examining a tidal river riparian near the Yangtze River Estuary, this study seeks to understand the tides’ influence on riparian buffer, regarding microbial community, geochemical patterns, and the overall nitrate removal. Our soil samples, collected at different distances from the river and depths, show a significant difference (p < 0.05) in microbial composition between the riverward and the landward areas. Adapting to the unique environmental conditions, the microbial community near the river exhibits a higher diversity with more anaerobic taxa. Also, the functional genes and their related pathways predicted by PICRUSt2 demonstrate high metabolic versatility, which is consistent with the various riverine nutrient inputs we observed. However, when it comes to denitrification, the key functional genes (narG, nirK, norB, nosZ, etc.) are generally less abundant in the riverward area. This contrast suggests that, despite the anaerobic conditions created by the tides, the active river water-groundwater interactions and the riverine nutrients interrupt and weaken nitrate removal. Furthermore, the limited amount of nitric oxide reductase-encoded norB leads to incomplete denitrification, as the riparian also shows nitrite accumulation. Our findings portray how tidal fluctuations affect microbial nitrate removal and can be instructive to conservation efforts along tidal rivers. In the face of climate change, the rising sea level rings an alarm because the changing hydrodynamics of tidal rivers can further disturb the riparian and increase nitrate pollution.

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.