Science and Engineering Faculty, School of Earth Environmental and Biological Science, Queensland University of Technology, GPO Box 2434, Brisbane, 4001, QLD, Australia.
School of Environmental and Biological Science (SEBS), Islamic Azad University, Zanjan Branch, Zanjan, Iran.
J Environ Manage. 2018 Sep 15;222:54-65. doi: 10.1016/j.jenvman.2018.05.022. Epub 2018 May 23.
Denitrification has documented as a promising pathway to permanently remove nitrate from a system. Numerous studies have used the isotope fractionation technique (IFT) to evaluate the denitrification rate in the constructed wetlands (CWs), but the potential of IFT method to quantify the denitrification rate in hyporheic zone (saturated sediments beneath a stream) is still challenging. Thus, more studies are required to investigate that if measurements of the natural abundance of δN-NO and δO-NO (IFT) can be employed to calculate the fate of nitrate in hyporheic zone. Therefore, in this study, the possibility of the IFT to quantify the hyporheic-denitrification rate was investigated. Then, the results were verified by the combined application of the pre-established net Sediment N flux and multi-linear regression analysis (p < 0.01). Finally, the groundwater bacterial groups (Fecal coliform (FC) and Escherichia coli (EC)), and the mass balance isotope mixing model were used to investigate the dominant sources of hyporheic-nitrate. The IFT reveals that denitrification contributes 74.1% and 29.1% of the hyporheic-nitrate removal during dry and wet seasons, respectively. The multi-linear regression analysis, considering at 99% confidence interval (R = 92.1%; n = 44; p < 0.01), slightly overestimates the rate and the percent contribution of denitrification in the dry season (475.15 ± 101.18 μmol/m2d; 80.7%) and underestimates it during the wet season (205.072 ± 35.39 μmol/m2d; 24.01%). The analysis of EC and FC demonstrates that manure (41.9 ± 4.2%) and sewage (54.1 ± 8.9%) are the dominant contributors of the hyporheic-nitrate load. In addition, the results achieved by the analysis of the fecal bacterial indicators (EC and FC) were confirmed by NO/Cl vs Cl diagram. This study provides an alternative-initiative framework to accurately quantify the spatio-seasonal variations in the hyporheic-nitrate sources and hyporheic-denitrification rate that enables decision-makers to apply appropriate and targeted strategies to regulate nitrate load in river-aquifer systems.
反硝化作用已被证明是一种从系统中永久性去除硝酸盐的很有前途的途径。许多研究都使用同位素分馏技术（IFT）来评估人工湿地（CWs）中的反硝化速率，但 IFT 方法量化底流区（溪流下的饱和沉积物）反硝化速率的潜力仍然具有挑战性。因此，需要更多的研究来探讨是否可以使用自然丰度 δN-NO 和 δO-NO（IFT）的测量值来计算底流区硝酸盐的归宿。因此，在本研究中，研究了 IFT 定量底流区反硝化速率的可能性。然后，通过联合应用预先建立的净沉积物 N 通量和多元线性回归分析（p<0.01）对结果进行了验证。最后，利用地下水细菌群（粪大肠菌群（FC）和大肠杆菌（EC））和质量平衡同位素混合模型来研究底流区硝酸盐的主要来源。IFT 表明，在旱季和雨季，反硝化作用分别贡献了底流区硝酸盐去除的 74.1%和 29.1%。多元线性回归分析（置信区间为 99%，R=92.1%；n=44；p<0.01）略微高估了旱季反硝化作用的速率和贡献百分比（475.15±101.18 μmol/m2d；80.7%），而低估了雨季的速率和贡献百分比（205.072±35.39 μmol/m2d；24.01%）。EC 和 FC 的分析表明，粪便（41.9±4.2%）和污水（54.1±8.9%）是底流区硝酸盐负荷的主要来源。此外，通过对粪便细菌指标（EC 和 FC）的分析结果得到了证实，通过 NO/Cl 与 Cl 关系图得到了证实。本研究提供了一种替代的主动框架，可以准确量化底流区硝酸盐来源和底流区反硝化速率的时空变化，使决策者能够应用适当和有针对性的策略来调节河流-含水层系统中的硝酸盐负荷。
