Use of δ18O, δ 13C and NO3−to identify hydrogeochemical processes related to contamination in an aquifer located in central Mexico

• Published in: Acta geochimica 2022, Vol.41 (3), p.367-392
• Main Authors: Morales-Arredondo, José Iván, Hernández, María Aurora Armienta, Juárez-Aparicio, Fátima, Landa-Arreguín, Jorge Federico, Flores-Ocampo, Itzamna Zaknite
• Format: Article
• Language: English
• Subjects: Aquifers; Biodegradation; Calcite; Carbon dioxide; Carbon sources; Carbonates; Chemical composition; Contamination; Denitrification; Earth and Environmental Science; Earth Sciences; Geochemistry; Groundwater; Groundwater flow; Hydrogeochemistry; Isotopes; Nitrification; Original Article; Pollution; Rocks; Soil contamination; Water analysis; Water sampling
• ISSN: 2096-0956; 2365-7499
• DOI: 10.1007/s11631-021-00519-6

In this work, an isotopic analysis of δ 18 O, δ 13 C, and NO 3 − concentrations was carried out to identify the origin and the processes related to the contamination of an aquifer located in the state of Guanajuato, Mexico. The research identified the possible sources of δ 13 C in groundwater. During groundwater flow, CO 2 participates in different hydrogeochemical reactions in which the dissolution of carbonates or biochemical processes related to biodegradation stand out. Isotopic data of δ 13 C, δ 18 O, and the hydrogeochemical behavior of NO 3 − and HCO 3 − in water, in addition to isotopic data and the chemical composition of limestones in the study area, were determined to establish the isotopic signature and the processes undergone by the rocks. The isotopic signature of rock and water samples indicated that metamorphic limestones contributed with carbon dioxide to deep groundwater, while in the upper aquifer, bacterial metabolic reactions during nitrification–denitrification could modify the isotopic signature of δ 13 C in some wells, although atmospheric contribution also plays a role. The modification of the carbon isotopic component is related to the precipitation of calcite in specific regions of the study area, input of atmospheric CO 2 , and soil (e. g. the possible participation of C4-type plants in the assimilation-release of carbon). This process is not confirmed or completely ruled out in this study since agriculture is excessively developed throughout the region. The joint interpretation of isotopic values and the hydrogeochemical behavior of major and conservative elements help in identifying possible pollution processes in which different carbon sources are related.