Use of multiple isotopes to evaluate nitrate dynamics in groundwater under the barrier effect of underground cutoff wall
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RESEARCH ARTICLE
Use of multiple isotopes to evaluate nitrate dynamics in groundwater under the barrier effect of underground cutoff walls Pingping Kang 1,2 & Shaopeng Li 1 & Fuqiang Wang 1,3 & Heng Zhao 1 & Subing Lv 1,2 Received: 8 July 2019 / Accepted: 9 September 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Underground cutoff walls are useful in conserving groundwater and preventing seawater intrusion in coastal regions. However, the environmental effects of human activities on groundwater quality in the upstream area of the underground cutoff wall over the long term are not clear. In this study, combined analysis of multiple isotopes (δ15N-NO3−, δ18O-NO3−, δ2H, and δ18O-H2O) and nitrate concentrations was used to assess the effect of underground cutoff walls on nitrogen dynamics in groundwater in an agricultural area in China. We sampled groundwater wells in the upstream and downstream areas of the underground walls in April, July, and September. The results indicated that the underground cutoff walls hampered the horizontal groundwater flow, making the upstream groundwater a closed system, which led to an increase in the nitrate concentration and accelerated nitrification processes. Manure was the main nitrate source in the upstream groundwater, and its levels in the groundwater were similar during the three seasons, indicating that there was no difference in the nitrate sources in the upstream groundwater among the three seasons. Hence, further management measures for manure application may be critical for groundwater protection in the upstream area of underground cutoff walls. Keywords Groundwater . Underground cutoff wall . Multiple isotopesapproach . Isotope mixing model . Nitrogentransformation processes . Contribution of nitrate source
Introduction Nitrate (NO3−) has been recognized as an important nutrient for crop growth. However, nitrogen fertilizer application over relatively long periods has led to nitrate leaching and nitrate storage in groundwater (Van Meter Responsible Editor: Philippe Garrigues * Fuqiang Wang [email protected] 1
Department of Water Conservancy Engineering, North China University of Water Conservancy and Electric Power, Jinshuidong Road 36, Zhengzhou 450046, Henan Province, People’s Republic of China
2
Collaborative Innovation Center of Water Resources Efficient Utilization and Support Engineering, Jinshuidong Road 36, Zhengzhou 450046, Henan Province, People’s Republic of China
3
Henan Key Laboratory of Water Environment Simulation and Treatment, Jinshuidong Road 36, Zhengzhou 450046, Henan Province, People’s Republic of China
et al. 2017; Wang et al. 2019). This phenomenon may be more obvious in the upstream area of underground cutoff walls (Yoshimoto et al. 2013). Underground cutoff walls cut off horizontal water flow, which also prevents the horizontal out-migration of NO3− from upstream groundwater. This barrier may lead to the accumulation of the NO3− concentration in upstream groundwater (Yoshimoto et al. 2013) and prolong groundw
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