Coastal regions are quite populous, causing coastal aquifers to be overexploited, due to which contamination of these aquifers is observed. The municipality of Belém, located on the eastern edge of the Amazon Forest, is severely deficient with respect to sanitation services, resulting in contamination by domestic wastewater becoming a widespread problem. Furthermore, groundwater overexploitation induces the migration of the saline wedge into the continent. To evaluate the natural and anthropic processes controlling the water quality, we conducted a large-scale (152 samples) hydrochemical analysis, stable isotope analysis, ¹⁴C dating of the Belém region. We also performed geochemical simulations to assess the mass balance of the identified process governing the water hydrochemistry. We found that the groundwater of the studied area may be classified into eight groups (based on hydrochemistry and sampled aquifer) or five hydrochemical clusters (solely as per hydrochemical affinity). The natural composition of siliciclastic aquifers Post-Barreiras and Barreiras (Cluster 1) is less mineralized, closely resembling rainwater, composed by recent groundwater recharge. In urban areas of Belém, nitrate contamination is quite significant (Cluster 2), while some samples present noticeable salinization induced by excessive groundwater pumping (Cluster 3). The TDS of deep samples of Barreiras and Pirabas (Clusters 4 and 5) increase as depth and groundwater age increases by the dissolution of calcite, dolomite, and pyrite. Our results allowed us to characterize the natural composition of the water and to measure the intense process deterioration of the water quality of the shallow aquifers.

沿海地区人口众多，导致沿海含水层被过度开发，因此观察到这些含水层受到污染。位于亚马逊森林东部边缘的贝伦市严重缺乏卫生服务，导致生活废水污染成为一个普遍问题。此外，地下水过度开采导致咸楔迁移到大陆。为了评估控制水质的自然和人为过程，我们进行了大规模（152 个样品）水化学分析、稳定同位素分析、¹⁴贝伦地区的 C 测年。我们还进行了地球化学模拟，以评估确定的控制水水化学过程的质量平衡。我们发现研究区的地下水可分为八组（基于水化学和采样含水层）或五个水化学簇（仅根据水化学亲和力）。Post-Barreiras 和 Barreiras（集群 1）的硅质碎屑含水层的天然成分矿化程度较低，与雨水非常相似，由最近的地下水补给组成。在贝伦市区，硝酸盐污染非常严重（聚类 2），而一些样本由于过度抽取地下水而出现明显的盐渍化（聚类 3）。由于方解石、白云石和黄铁矿的溶解，Barreiras 和 Pirabas（集群 4 和 5）深层样品的 TDS 随着深度和地下水年龄的增加而增加。我们的结果使我们能够表征水的自然组成，并测量浅层含水层水质的剧烈恶化过程。