Análise de intrusão salina e qualidade de água em aquífero costeiro na Vila de Algodoal (Ilha de Maiandeua, Pará)

Abstract

The increasing urbanization of coastal areas increases the demand for water resources and consequently leads to intensive exploitation of groundwater and anthropogenic impacts that result in groundwater quality degradation. The objective of this research was to assess potential saline intrusion and groundwater contamination in a marine protected area of sustainable use, Algodoal Village (Maiandeua, PA). For the first stage of the research, the quality of groundwater used for human consumption was evaluated based on current regulations (CONAMA Resolution 396/2008; Ministry of Health Ordinance 888/2021). Groundwater characterization was carried out using well water collected during rainy and less rainy periods (between 2021 and 2023), with in-situ physicochemical, microbiological, and major ion parameter analyses by chromatography. Topographic measurements and water table level measurements were also conducted. For the second stage, the results of a socio-environmental questionnaire applied to village residents were analyzed to ascertain their perception of water quality-related issues. Samples from the coastal aquifer presented average electrical conductivity (EC) values of 453 ± 1 µS/cm and total dissolved solids (TDS) of 225.8 ± 1 mg/L. The Cl⁻ ion showed an average concentration of 60 ± mg/L, with several wells exceeding the acceptable potability limit. Significant differences were observed for data collected in the first rainy period (March 2022), where EC averaged 290 µS/cm and TDS was 145 mg/L. The relationship between redox potential, ranging from 0.14 to 0.54 mV, and pH, ranging from 3.2 to 6.7, indicated a tendency toward a reducing acidic environment, typical of a subterranean transitional environment. All analyzed wells were contaminated with total and thermotolerant coliforms. Out of the 34 administered questionnaires, 52% indicated perception of some water quality problem, such as brackish water, for example. Poor water quality is locally associated with the process of saline intrusion and bacterial contamination due to proximity to septic tanks. The shallow depth of the wells (average of 12 m) exacerbates the poor groundwater quality in the village. It is concluded that the aquifer water is not recommended for human consumption, and saline intrusion occurs throughout the year, being more intense in the dry period.