Identification of ammonium source for groundwater in the piedmont zone with strong runoff of the Hohhot Basin based on nitrogen isotope

Jinyuan Liu; Jiongliang Yuan; Yilong Zhang; Hengxing Zhang; Yiqing Luo; Yuning Su

doi:10.1016/j.scitotenv.2023.163650

Identification of ammonium source for groundwater in the piedmont zone with strong runoff of the Hohhot Basin based on nitrogen isotope

Sci Total Environ. 2023 Jul 15:882:163650. doi: 10.1016/j.scitotenv.2023.163650. Epub 2023 Apr 23.

Authors

Jinyuan Liu¹, Jiongliang Yuan², Yilong Zhang³, Hengxing Zhang⁴, Yiqing Luo⁵, Yuning Su⁵

Affiliations

¹ Department of Environmental Science and Engineering, Beijing University of Chemical Technology, Beijing 100029, China; Hohhot Ecological Environment Bureau Comprehensive Protection Center, Hohhot 010000, China.
² Department of Environmental Science and Engineering, Beijing University of Chemical Technology, Beijing 100029, China. Electronic address: yuanjiongliangwz@163.com.
³ Institute of Hydrogeology and Environmental Geology, Chinese Academy of Geological Sciences, Shijiazhuang 050061, China; Key Laboratory of Groundwater Science and Engineering, Ministry of Natural Resources, Shijiazhuang 050061, China.
⁴ Institute of Hydrogeology and Environmental Geology, Chinese Academy of Geological Sciences, Shijiazhuang 050061, China; Key Laboratory of Groundwater Science and Engineering, Ministry of Natural Resources, Shijiazhuang 050061, China. Electronic address: hxzhang_iheg@sina.com.
⁵ Department of Environmental Science and Engineering, Beijing University of Chemical Technology, Beijing 100029, China.

PMID: 37094680
DOI: 10.1016/j.scitotenv.2023.163650

Abstract

Groundwater with high ammonium concentration (HANC groundwater), mostly caused by anthropogenic pollution, is widely distributed in China, which could also result from natural geological genesis. Groundwater in the piedmont zone with strong runoff in the central Hohhot Basin has featured its excessive ammonium concentration since the 1970s. Currently, chemical factories also serve as potential pollution sources. In this study, based on the nitrogen isotopic technique and combined with hydrochemical methods, the sources of high concentration ammonium in the groundwater was identified. The HANC groundwater is mainly distributed in the alluvial-proluvial fan and the interfan depression in the western and central parts of the study area, and a maximum ammonium concentration of 529.32 mg/L was observed in the groundwater in the mid-fan of the Baishitou Gully (BSTG) alluvial-proluvial fan. Although the BSTG mid-fan is part of the piedmont zone with strong runoff, some of the HANC groundwater in this area still presents the typical hydrochemical characteristics in the discharge area. Moreover, an extremely high concentration of volatile organic compounds was observed in groundwater in the BSTG alluvial-proluvial fan, which indicated significant anthropogenic pollution. Besides, ¹⁵N-NH₄⁺ is enriched in groundwater in the BSTG root-fan and the interfan depression, which is consistent with the situation of organic nitrogen and exchangeable ammonium in natural sediments, as well as the natural HANC groundwater in other regions of China. These δ¹⁵N-NH₄⁺ values indicate that the ammonium of the groundwater in the BSTG root-fan and the interfan depression is derived from natural sediments. The ¹⁵N-NH₄⁺ in groundwater is depleted in the BSTG mid-fan, and the δ¹⁵N-NH₄⁺ values are similar with those of the pollution sources from the chemical factories in the mid-fan. Both hydrochemical and nitrogen isotopic characteristics indicate significant pollution in the mid-fan, but the ammonium pollution is limited to the area near the chemical factories.

Keywords: Anthropogenic pollution; Groundwater ammonium source; Hohhot Basin; Natural sediments; Nitrogen isotope.