硝酸盐污染威胁着Barva和Colima多含水层系统,哥斯达黎加大都市区的主要饮用水源。在解决硝酸盐污染动态时,这项研究提出了一种结合多元统计分析的综合方法,水化学参数,污水排放,以及区域土地利用和土地覆盖模式,以评估污染的范围和程度,主要的生物地球化学过程,并完善以前仅从δ15NNO3信息得出的硝酸盐来源的解释。七年(2015-2022)分析了来自43个地点的714个地下水样品的硝酸盐和主要离子,包括对溶解的有机和无机碳的两次采样活动,亚硝酸盐,铵,FeTotal,MnTotal,和δ15NNO3分析。研究结果表明,城市和农业/城市地区的硝酸盐浓度升高,多次超过最高浓度水平,和氧化条件有利于无约束的Barva和局部约束的上科利马/下科利马含水层中的矿化和硝化过程。尽管浅层Barva含水层的农业和城市地区的硝酸盐含量和空间格局相似,但氮肥和城市废水的贡献相当。同位素分析和溶解有机碳(DOC)表明,在Barva和Colima含水层中,硝酸盐来源从农业地区转移到城市地区。主成分和层次聚类分析将土地利用联系起来,硝酸盐来源,和水质。三个不同的样本集群与森林/草地对齐,农业/城市,和城市土地利用,强调人为活动对地下水质量的影响,甚至在更深的科利马含水层中。这项研究挑战硝酸盐同位素混合模型,通过纳入DOC和其他水化学参数,提高识别污染源和评估污染空间范围的准确性。类似的结果,无论是否使用硝酸盐同位素,加强综合方法的有用性,提供一种实用且具有成本效益的替代方案。
Nitrate pollution threatens the Barva and Colima multi-aquifer system, the primary drinking water source in the Greater Metropolitan Area of Costa Rica. In addressing nitrate contamination dynamics, this study proposes an integrated approach by combining multivariate statistical analyses, hydrochemical parameters, sewage discharge, and regional land-use and land-cover patterns to assess the extent and degree of contamination, dominant biogeochemical processes, and refine the interpretation of nitrate sources previously derived solely from δ15NNO3 information. Over seven years (2015-2022), 714 groundwater samples from 43 sites were analyzed for nitrate and major ions, including two sampling campaigns for dissolved organic and inorganic carbon, nitrite, ammonium, FeTotal, MnTotal, and δ15NNO3 analyses. The findings presented elevated nitrate concentrations in urban and agricultural/urban areas, surpassing the Maximum Concentration Levels on several occasions, and oxidizing conditions favoring mineralization and nitrification processes in unconfined Barva and locally confined Upper Colima/Lower Colima aquifers. Similar nitrate contents and spatial patterns in agricultural and urban zones in the shallow Barva aquifer suggest comparable contributions from nitrogen fertilizers and urban wastewaters despite the gradual increase in urban land cover and the reduction of agricultural areas. Isotopic analyses and dissolved organic carbon (DOC) indicate a shift in nitrate sources from agricultural to urban areas in both Barva and Colima aquifers. Principal Component and Hierarchical Cluster Analyses link land use, nitrate sources, and water quality. Three distinct sample clusters aligned with forest/grassland, agricultural/urban, and urban land use, emphasizing the impact of anthropogenic activities on groundwater quality, even in the deeper Colima aquifers. The study challenges nitrate isotope mixing models, enhancing accuracy in identifying pollution sources and assessing the spatial extent of contamination by incorporating DOC and other hydrochemical parameters. Similar outcomes, with and without the use of nitrate isotopes, reinforce the usefulness of the integrated approach, providing a practical and cost-effective alternative.