Abstract
The objective of this research was to identify and quantify the primary processes responsible for the increase in salinity observed in the alluvial aquifer during the dry season. Multivariate statistical analysis and inverse geochemical modeling were used to simulate possible salinization mechanisms in the alluvial aquifer. For this, by quantifying electrical conductivity and the concentrations of the ions Ca2+, Mg2+, Na+, K+, Cl-, HCO3- and SO42- in waters from the crystalline basement near the study area, water reservoirs near the alluvial aquifer and the studied alluvial aquifer, groups were formed and discriminant analysis was applied. Significance tests showed that direct evaporation has not only an influence on the alluvial aquifer, but also a mean volumetric contribution of 15.8% from waters of the crystalline basement, accompanied by processes of salt dissolution and precipitation, which would also justify the increase in salinity observed in the alluvial aquifer in the dry period.
Highlights
In the state of Ceará, there are thousands of wells providing water essentially for irrigation and human consumption, which are the main source of water supply in some of these areas.In general, the quality of the water in these wells is directly related to the geological formation of the region
Water with high salt concentration is usually found in areas of crystalline rock formation (Silva Júnior et al, 1999; Lopes et al, 2008), while water with low salt concentration is found in areas of sedimentary rocks (Andrade Júnior et al, 2006; Silva et al, 2007)
For all the other wells, the simulations were performed for the same hypothesis and in all of them the results show mole transfers similar to the ones found for the P10 well, with volumetric contributions of water from the fissure aquifer ranging from 1.53 to 27.99% to the enrichment of salts in the water of the alluvial aquifer
Summary
In the state of Ceará, there are thousands of wells providing water essentially for irrigation and human consumption, which are the main source of water supply in some of these areas.In general, the quality of the water in these wells is directly related to the geological formation of the region. Due to its easy exploitation and good quality, when compared with water stored in crevices of crystalline rocks, the water from the alluvial aquifer of the Forquilha River becomes an important source for both human and animal consumption, as well as to irrigate small plantations, such as maize and bean. The conservative characteristic of the chloride ion (Svensson et al, 2012) makes its measurement a parameter usually used to identify deterioration in water quality (Richter & Kreitler, 1993; Manwell & Ryan, 2006; Lucas et al, 2010) This ion was used in this study as a tracer of the water from crystalline crevices, which is rich in chloride
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