The influence of hyporheic upwelling fluxes on inorganic nitrogen concentrations in the pore water of the Weihe River.

Hyporheic zone is an important region of nitrogen removal in river systems. Hyporheic exchange generally leads to heterogeneous redox environments, which are conducive to nitrogen transformation. This study seeks to determine the influence of hyporheic upwelling fluxes on inorganic nitrogen (NH 4 + , NO 3 − , and NO 2 − ) concentrations in the sediment pore water of the Weihe River, China. The patterns and magnitudes of hyporheic water exchange on 12 August 2016 were derived by a one-dimensional heat transport model, and inorganic nitrogen concentrations in the pore water, surface water, and groundwater were obtained. The results indicated that hyporheic water exchange was characterized by upwelling at each point during the test period. Moreover, NH 4 + dominated the hyporheic zone from 0 to 45 cm, likely due to organic nitrogen mineralization. Additionally, a non-linear relationship was observed between NH 4 + concentrations and upwelling fluxes. This relationship was derived by analyzing the effect of upwelling on biogeochemical activity and nitrogen transformation. Notably, increasing upwelling fluxes less than 400 mm/d resulted in high NH 4 + concentrations, whereas fluxes exceeding 400 mm/d led to low NH 4 + concentrations. Overall, the variations in inorganic nitrogen associated with hyporheic water exchange are of great importance for controlling nitrogen pollution and maintaining sustainable health in river systems. [ABSTRACT FROM AUTHOR]