University of Waterloo, Department of Earth and Environmental Sciences, Waterloo, Ontario, N2T 0A4, Canada.
Université de Carthage, Institut Supérieur des Technologies de L'Environnement de L'Urbanisme et de Bâtiment, Tunis, 2035, Tunisia.
J Environ Manage. 2023 Nov 1;345:118803. doi: 10.1016/j.jenvman.2023.118803. Epub 2023 Aug 21.
In coastal salinized groundwater systems, contamination from various nitrate (NO) inputs combined with complex hydrogeochemical processes make it difficult to distinguish NO sources and identify potential NO transformtation processes. Effective field-based NO studies in coastal areas are needed to improve the understanding of NO contamination dynamics in groundwater of such complex coastal systems. This study focuses on a typical Mediterranean coastal agricultural area, located in Tunisia, experiencing substantial NO contamination from multiple anthropogenic sources. Here, multiple isotopic tracers (δO, δH, δN, δO, and δB) combined with a Bayesian isotope MixSIAR model are used (i) to identify the major NO sources and their contributions, and (ii) to describe the potential NO transformation processes. The measured NO concentrations in groundwater are above the natural baseline threshold, suggesting anthropogenic influence. The measured isotopic composition of NO indicates that manure, soil organic matter, and sewage are the potential sources of NO, while δB values constrain the NO contamination to manure; a finding that is supported by the results of MixSIAR model revealing that manure-derived NO dominates over other likely sources. Nitrate derived from manure in the study area is attributed to organic fertilizers used to promote crop growth, and livestock that deposit manure directly on the ground surface. Evidence for ongoing denitrification in groundwaters of the study area is supported by an enrichment in both N and O in the remaining NO, although isotopic mass balances between the measured and the theoretical δO values also suggest the occurrence of nitrification. The simultaneous occurrence of these biogeochemical processes with heterogeneous distribution across the study area reflect the complexity of interactions within the investigated coastal aquifer. The multiple isotopic tracer approach used here can identify the effect of multiple NO anthropogenic activities in coastal environments, which is fundamental for sustainable groundwater resources management.
在沿海地区的盐化地下水中，各种硝酸盐（NO）输入源与复杂的水文地球化学过程相结合，使得区分 NO 来源和识别潜在的 NO 转化过程变得困难。需要在沿海地区开展有效的基于现场的 NO 研究，以提高对这种复杂沿海系统地下水中 NO 污染动态的认识。本研究以突尼斯一个典型的地中海沿海农业区为重点，该地区受到多种人为来源的大量 NO 污染。在这里，结合贝叶斯同位素混合模型，使用多种同位素示踪剂（δO、δH、δN、δO 和 δB）（i）确定主要的 NO 来源及其贡献，（ii）描述潜在的 NO 转化过程。地下水中测量的 NO 浓度高于自然基线阈值，表明存在人为影响。NO 的测量同位素组成表明，粪肥、土壤有机质和污水是 NO 的潜在来源，而 δB 值则将 NO 污染限制在粪肥中；MixSIAR 模型的结果支持这一发现，表明粪肥来源的 NO 比其他可能的来源更占主导地位。研究区域内来源于粪肥的硝酸盐归因于用于促进作物生长的有机肥料和直接在地面上沉积粪肥的牲畜。研究区域地下水中持续反硝化的证据得到了支持，因为剩余的 NO 中 N 和 O 都得到了富集，尽管实测和理论 δO 值之间的同位素质量平衡也表明硝化作用的发生。这些生物地球化学过程在研究区域内的异质分布中同时发生，反映了所研究沿海含水层内相互作用的复杂性。这里使用的多同位素示踪剂方法可以识别沿海环境中多种人为 NO 活动的影响，这对可持续的地下水资源管理至关重要。
