Biogeochemical Mechanisms of HCO<sub>3</sub>–Ca Water and NO<sub>3</sub><sup>−</sup> Pollution in a Typical Piedmont Agricultural Area: Insights from Nitrification and Carbonate Weathering
Water hardening and NO<sub>3</sub><sup>−</sup> pollution have affected water quality globally. These environmental problems threaten social sustainability and human health, especially in piedmont agricultural areas. The aim of this study is to determine the biogeochemical mec...
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MDPI AG
2025-05-01
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| author | Li Xu Bo Xin Wei Liu Haoyang Liu Guoli Yang Guizhen Hao |
| author_facet | Li Xu Bo Xin Wei Liu Haoyang Liu Guoli Yang Guizhen Hao |
| author_sort | Li Xu |
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| description | Water hardening and NO<sub>3</sub><sup>−</sup> pollution have affected water quality globally. These environmental problems threaten social sustainability and human health, especially in piedmont agricultural areas. The aim of this study is to determine the biogeochemical mechanisms of HCO<sup>3</sup>–Ca water and NO<sub>3</sub><sup>−</sup> pollution in a typical piedmont agricultural area (Qingshui River, Zhangjiakou, China). Here, an extensive biogeochemical investigation was conducted in a typical piedmont agricultural area (Qingshui River, China) using multiple hydrochemical, isotopic (δ<sup>2</sup>H-H<sub>2</sub>O, δ<sup>18</sup>O-H<sub>2</sub>O and δ<sup>13</sup>C-DIC) and molecular-biological proxies in combination with a forward model. In the region upstream of the Qingshui River, riverine hydrochemistry was dominated by HCO<sub>3</sub>–Ca water, with only NO<sub>3</sub><sup>−</sup> concentrations (3.08–52.8 mg/L) exceeding the acceptable limit (10 mg/L as N) for drinking water quality. The riverine hydrochemistry responsible for the formation of HCO<sub>3</sub>–Ca water was mainly driven by carbonate dissolution, with a contribution rate of 49.8 ± 3.96%. Riverine NO<sub>3</sub><sup>−</sup> was mainly derived from agricultural NH<sub>4</sub><sup>+</sup> emissions rather than NO<sub>3</sub><sup>−</sup> emissions, originating from sources such as manure, domestic sewage, soil nitrogen and NH<sub>4</sub><sup>+</sup>-synthetic fertilizer. Under the rapid hydrodynamic conditions and aerobic water environment of the piedmont area, NH<sub>4</sub><sup>+</sup>-containing pollutants were converted to HNO<sub>3</sub> by nitrifying bacteria (e.g., <i>Flavobacterium</i> and <i>Fluviimonas</i>). Carbonate (especially calcite) was preferentially and rapidly dissolved by the produced HNO<sub>3</sub>, which was attributed to the strong acidity of HNO<sub>3</sub>. Therefore, higher levels of Ca<sup>2+</sup>, Mg<sup>2+</sup>, HCO<sub>3</sub><sup>−</sup> and NO<sub>3</sub><sup>−</sup> were simultaneously released into river water, causing riverine HCO<sub>3</sub>–Ca water and NO<sub>3</sub><sup>−</sup> pollution in the A-RW. In contrast, these biogeochemical mechanisms did not occur significantly in the downstream region of the river due to the cement-hardened river channels and strict discharge management. These findings highlight the influence of agricultural HNO<sub>3</sub> on HCO<sub>3</sub>–Ca water and NO<sub>3</sub><sup>−</sup> pollution in the Qingshui River and further improve the understanding of riverine hydrochemical evolution and water pollution in piedmont agricultural areas. |
| format | Article |
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| spelling | doaj-art-3c44bfbab2ff4238b3e5e05b9108cd9d2025-08-20T02:34:02ZengMDPI AGToxics2305-63042025-05-0113539410.3390/toxics13050394Biogeochemical Mechanisms of HCO<sub>3</sub>–Ca Water and NO<sub>3</sub><sup>−</sup> Pollution in a Typical Piedmont Agricultural Area: Insights from Nitrification and Carbonate WeatheringLi Xu0Bo Xin1Wei Liu2Haoyang Liu3Guoli Yang4Guizhen Hao5School of Energy and Environmental Engineering, Hebei University of Engineering, Handan 056038, ChinaZhangcheng Ecological Environmental Protection and Restoration Technology Innovation Center, No. 3 Geological Brigade of Hebei Geology and Mineral Exploration Bureau, Zhangjiakou 075000, ChinaHebei Key Laboratory of Water Quality Engineering and Comprehensive Utilization of Water Resources, Hebei University of Architecture, Zhangjiakou 075000, ChinaHebei Key Laboratory of Water Quality Engineering and Comprehensive Utilization of Water Resources, Hebei University of Architecture, Zhangjiakou 075000, ChinaHebei Key Laboratory of Water Quality Engineering and Comprehensive Utilization of Water Resources, Hebei University of Architecture, Zhangjiakou 075000, ChinaHebei Key Laboratory of Water Quality Engineering and Comprehensive Utilization of Water Resources, Hebei University of Architecture, Zhangjiakou 075000, ChinaWater hardening and NO<sub>3</sub><sup>−</sup> pollution have affected water quality globally. These environmental problems threaten social sustainability and human health, especially in piedmont agricultural areas. The aim of this study is to determine the biogeochemical mechanisms of HCO<sup>3</sup>–Ca water and NO<sub>3</sub><sup>−</sup> pollution in a typical piedmont agricultural area (Qingshui River, Zhangjiakou, China). Here, an extensive biogeochemical investigation was conducted in a typical piedmont agricultural area (Qingshui River, China) using multiple hydrochemical, isotopic (δ<sup>2</sup>H-H<sub>2</sub>O, δ<sup>18</sup>O-H<sub>2</sub>O and δ<sup>13</sup>C-DIC) and molecular-biological proxies in combination with a forward model. In the region upstream of the Qingshui River, riverine hydrochemistry was dominated by HCO<sub>3</sub>–Ca water, with only NO<sub>3</sub><sup>−</sup> concentrations (3.08–52.8 mg/L) exceeding the acceptable limit (10 mg/L as N) for drinking water quality. The riverine hydrochemistry responsible for the formation of HCO<sub>3</sub>–Ca water was mainly driven by carbonate dissolution, with a contribution rate of 49.8 ± 3.96%. Riverine NO<sub>3</sub><sup>−</sup> was mainly derived from agricultural NH<sub>4</sub><sup>+</sup> emissions rather than NO<sub>3</sub><sup>−</sup> emissions, originating from sources such as manure, domestic sewage, soil nitrogen and NH<sub>4</sub><sup>+</sup>-synthetic fertilizer. Under the rapid hydrodynamic conditions and aerobic water environment of the piedmont area, NH<sub>4</sub><sup>+</sup>-containing pollutants were converted to HNO<sub>3</sub> by nitrifying bacteria (e.g., <i>Flavobacterium</i> and <i>Fluviimonas</i>). Carbonate (especially calcite) was preferentially and rapidly dissolved by the produced HNO<sub>3</sub>, which was attributed to the strong acidity of HNO<sub>3</sub>. Therefore, higher levels of Ca<sup>2+</sup>, Mg<sup>2+</sup>, HCO<sub>3</sub><sup>−</sup> and NO<sub>3</sub><sup>−</sup> were simultaneously released into river water, causing riverine HCO<sub>3</sub>–Ca water and NO<sub>3</sub><sup>−</sup> pollution in the A-RW. In contrast, these biogeochemical mechanisms did not occur significantly in the downstream region of the river due to the cement-hardened river channels and strict discharge management. These findings highlight the influence of agricultural HNO<sub>3</sub> on HCO<sub>3</sub>–Ca water and NO<sub>3</sub><sup>−</sup> pollution in the Qingshui River and further improve the understanding of riverine hydrochemical evolution and water pollution in piedmont agricultural areas.https://www.mdpi.com/2305-6304/13/5/394HCO<sub>3</sub>–Ca waterNO<sub>3</sub><sup>−</sup> pollutionagricultural ammoniumnitrificationcarbonate dissolutionpiedmont area |
| spellingShingle | Li Xu Bo Xin Wei Liu Haoyang Liu Guoli Yang Guizhen Hao Biogeochemical Mechanisms of HCO<sub>3</sub>–Ca Water and NO<sub>3</sub><sup>−</sup> Pollution in a Typical Piedmont Agricultural Area: Insights from Nitrification and Carbonate Weathering Toxics HCO<sub>3</sub>–Ca water NO<sub>3</sub><sup>−</sup> pollution agricultural ammonium nitrification carbonate dissolution piedmont area |
| title | Biogeochemical Mechanisms of HCO<sub>3</sub>–Ca Water and NO<sub>3</sub><sup>−</sup> Pollution in a Typical Piedmont Agricultural Area: Insights from Nitrification and Carbonate Weathering |
| title_full | Biogeochemical Mechanisms of HCO<sub>3</sub>–Ca Water and NO<sub>3</sub><sup>−</sup> Pollution in a Typical Piedmont Agricultural Area: Insights from Nitrification and Carbonate Weathering |
| title_fullStr | Biogeochemical Mechanisms of HCO<sub>3</sub>–Ca Water and NO<sub>3</sub><sup>−</sup> Pollution in a Typical Piedmont Agricultural Area: Insights from Nitrification and Carbonate Weathering |
| title_full_unstemmed | Biogeochemical Mechanisms of HCO<sub>3</sub>–Ca Water and NO<sub>3</sub><sup>−</sup> Pollution in a Typical Piedmont Agricultural Area: Insights from Nitrification and Carbonate Weathering |
| title_short | Biogeochemical Mechanisms of HCO<sub>3</sub>–Ca Water and NO<sub>3</sub><sup>−</sup> Pollution in a Typical Piedmont Agricultural Area: Insights from Nitrification and Carbonate Weathering |
| title_sort | biogeochemical mechanisms of hco sub 3 sub ca water and no sub 3 sub sup sup pollution in a typical piedmont agricultural area insights from nitrification and carbonate weathering |
| topic | HCO<sub>3</sub>–Ca water NO<sub>3</sub><sup>−</sup> pollution agricultural ammonium nitrification carbonate dissolution piedmont area |
| url | https://www.mdpi.com/2305-6304/13/5/394 |
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