College of Resources and Environment, Southwest University, Chongqing, 400715, China; National Base of International S&T Collaboration on Water Environmental Monitoring and Simulation in TGR Region, Chongqing, 400716, China.
State Cultivation Base of Eco-agriculture for Southwest Mountainous Land, Field Scientific Observation & Research Base of Karst Eco-environments at Nanchuan in Chongqing, Ministry of Nature Resources of the People's Republic of China, School of Geographical Sciences, Southwest University, Chongqing, 400715, China.
Environ Pollut. 2022 Apr 15;299:118822. doi: 10.1016/j.envpol.2022.118822. Epub 2022 Jan 8.
Nitrate pollution in oxygenated karst aquifers is common due to nitrification and anthropogenic inputs. However, the shift of nitrogen sources influenced by enhanced rural tourism activities and land use changes are not well understood. In this study, hydrochemistry and dual nitrate isotopes of water samples from a rural karst basin in Chongqing, southwestern China were employed to investigate the nitrate fate and its decadal change during the periods from 2007-2008 and 2017-2019. The results showed that δN-NO and δO-NO values at the groundwater basin resurgence averaged 9 ± 3.4‰ and 2.5 ± 3.4‰, respectively, with a mean NO concentration of 19.7 ± 5.4 mg/L in 2017-2019, clearly exceeding natural background levels. The dual isotope results suggested that nitrification occurred at the sampled sites. From 2007-2008 to 2017-2019, the mean δN-NO values from the primary sink point and the resurgence of the underground river water samples increased from -0.2 ± 2.1 to 11.2 ± 4.8‰, 4.2 ± 0.9 to 9.0 ± 3.4‰, respectively. A Bayesian mixing model in R (MixSIAR) based on the isotopes revealed that soil organic nitrogen, and manure and sewage proportions for the groundwater increased by 34% and 23%, respectively, while chemical fertilizer and atmospheric precipitation proportions decreased by 32% and 25%, respectively. These decadal changes resulted from reforestation practices and enhanced rural tourism activities in the basin, which were evidenced by the change of land use patterns. The elevated nitrogen load from the rapid development of rural tourism is likely to increase this contamination in the near future if the infrastructure cannot meet the demands. The results from this study could contribute to minimizing environmental health risks in drinking water when rural tourism activities are increasing.
由于硝化作用和人为输入，富氧岩溶含水层中的硝酸盐污染很常见。然而，增强的农村旅游活动和土地利用变化对氮源的影响变化还没有得到很好的理解。在这项研究中，采用中国西南重庆市农村岩溶流域的水化学和双重硝酸盐同位素，研究了硝酸盐的归宿及其在 2007-2008 年和 2017-2019 年期间的十年来的变化。结果表明，2017-2019 年地下河泉域地下水的 δN-NO 和 δO-NO 值平均值分别为 9±3.4‰和 2.5±3.4‰，硝酸盐浓度平均值为 19.7±5.4mg/L，明显超过自然背景水平。双重同位素结果表明，采样点发生了硝化作用。从 2007-2008 年到 2017-2019 年，主汇点和地下河泉域水样的平均 δN-NO 值从-0.2±2.1‰增加到 11.2±4.8‰，从 4.2±0.9‰增加到 9.0±3.4‰。基于同位素的 R（MixSIAR）贝叶斯混合模型显示，地下水的土壤有机氮、粪肥和污水比例分别增加了 34%和 23%，而化肥和大气降水比例分别减少了 32%和 25%。这些十年来的变化是由于流域内的重新造林实践和农村旅游活动的增强造成的，这可以从土地利用模式的变化中得到证明。如果基础设施无法满足需求，农村旅游活动的快速发展所带来的氮负荷增加，可能会在不久的将来增加这种污染。本研究的结果有助于在农村旅游活动增加时，最大限度地降低饮用水的环境健康风险。
