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Response mechanisms of nitrate and ammonia nitrogen concentrations to hydrological processes in the riparian hyporheic zone of pastoral areas北大核心CSCD
作者单位:1.School of Ecology and Environment, Inner Mongolia Key Laboratory of River and Lake Ecology, Inner Mongolia University, Inner Mongolia, Hohhot010020;2.Key Laboratory of Ecology, Resource Use of the Mongolian Plateau, Ministry of Education, Inner Mongolia, Hohhot010020;
摘    要:In pastoral and irrigated agricultural areas, nitrogen-containing livestock, poultry manure, and nitrogen fertilizers can enter the surface water and groundwater from the soil, and this is the main source of non- point source pollution in basins. The riparian hyporheic zone acts as an effective barrier to reduce the nitrogen pollution load. Understanding the mechanisms of the migration, transformation, and removal of nitrogen in riparian hyporheic zones is key to controlling nitrogen pollution in the whole basin. In this study, an upper reach of the Xilin River, located in typical pastoral areas, was selected and its water levels, ammonia (NH+4) and nitrate (NO-3) concentrations, as well as the related environmental factors of the river water and riparian groundwater during the summer flood season, were continuously monitored. Based on the high- solution measurements, a water flow and nitrogen reactive transport model of the riparian hyporheic zones was established using FEFLOW. The model fitted using the measured data was found to accurately reproduce the water level dynamics and two main nitrogen concentrations in the riparian hyporheic zone. The results indicate that there is a high risk of nitrogen pollution in the riparian zones during the summer flood season. The NH+4concentration in the riparian zones can increase from 0.2 mg · L ? 1before rainfall events to 7.23 mg · L ? 1after rainfall events, and the NO-3concentration can increase from 1 mg · L ? 1to 8.27 mg · L ? 1. Both measured and simulated results show that the nitrogen dynamics in the hyporheic zone are closely related to hydrological processes such as rainfall events and groundwater-surface water exchange. During rainfall events, NO-3with high mobility was found to infiltrate from the river and the ground surface into the riparian zone due to the leaching effect, resulting in a significant increase in the concentration. Meanwhile, the groundwater- river water exchange enhanced by rainfall events can further regulate NO-3and NH+4concentrations in the riparian hyporheic zone by controlling the input of nutrients and affecting the biogeochemical nitrogen cycles. This study preliminarily reveals the buffering mechanisms of pastoral riparian zones in the hydrological and biogeochemical processes involving nitrogen and provides scientific references for the nitrogen pollution control in pastoral areas. © 2023 Editorial office of Arid Zone Research. All rights reserved.

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