Abstract
The study area is the Urucu Oil Province, Municipality of Coari, State of Amazonas, Brazil. This research represents a contribution to the hydrogeological knowledge in the northern region of Brazil, particularly in the central part of the Amazon rainforest, where researches on isotopic are still incipient. The primary goal was to determine, by stable isotopes 18O and 2H measurements, interrelationships between surface water and groundwater, in order to understand the origin and mechanisms of groundwater recharge and discharge. For this, samples of rainwater, superficial water and groundwater were collected between June 2008 and May 2009 for stable isotopic analyzes. This understanding is important in cases of eventual contaminations of the area, which could degrade the water resources. The results show that the superficial waters are typically light waters and have meteoric origin, and the groundwater recharge is by direct rainfall infiltration with primary evaporation before reaching the groundwater table in the Icá-Solimoes Aquifer System. The isotopic signatures similarities between groundwater and superficial waters indicate both waters’ contributions in the streams and, therefore, in the Urucu river.
Highlights
The use of stable isotopes in hydrogeology started in the 50s, with the pioneering works of Urey et al and Eps
The isotopic values for rainwater in the study area indicated a proximity to the Global Meteoric Water Line (GMWL) and the Meteoric Water Line for Marajó Island, but more negative, suggesting waters slightly lighter, due to the location of the study area being further from the ocean, causing more isotopic fractionation
The study suggests that the groundwater recharge is by direct rainfall infiltration
Summary
The use of stable isotopes in hydrogeology started in the 50s, with the pioneering works of Urey et al and Eps-How to cite this paper: de Souza, E.L., Galvão, P., de Almeida, R., Pinheiro, C., Baessa, M. and Cabral, M. (2015) Stable Isotopes Studies in the Urucu Oil Province, Amazon Region, Brazil. Through time, these studies have shown to be an effective way for investigating the complex hydrologic system on a range of spatial and temporal scales, providing quantitative information about surface-ground water interactions. The most relevant isotopes for atmospheric and hydrologic sciences are 18O for oxygen (corresponding to the most abundant isotope 16O), and 2H (or Deuterium, D) for hydrogen (corresponding to the most abundant isotope 1H) [2] [3] These isotopes, during evaporation and condensation phases, become enriched in one phase and depleted in the other. This separation of isotopes is named isotopic fractionation [3], and quantifying these processes is possible by calculating the large variability of their isotopic ratios (2H/H and 18O/16O)
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