Mecanismos dominantes na salinização de água em rochas anisotrópicas com base em razões iônicas e número fuzzy, em área do Sertão Central no Ceará.

Abstract

In this research, the interpretation of ionic ratios served as basis for explaining the dominant mechanisms that contribute to the salinization of groundwater in anisotropic medium. The use of ionic ratios using major, minor or trace elements has been a good tool to estimate the origin of salinity in groundwater. From these ratios, it is possible to infer about the dominant phenomena in the generation of solutes, whether endogenous or exogenous. In this study, the analysis of ionic ratios was weighted via "Fuzzy Systems Theory" or Fuzzy Logic. The study area was under tropical semi-arid climate and located in the central portion (Sertão Central) of the State of Ceará, Northeast Brazil. The area is located between two municipalities: Quixadá and Quixeramobim. The following coordinates bound them: 4º57'18 "and 5º10'34" of latitude S and 38º48'42 "and 39º11'01" W longitude. The water points, mostly wells, were previously grouped according to the geological unit where they were located. The study revealed that the salinity of the groundwater is a result of the joint action of several factors, suggesting successive stages of evolution of the hydrogeochemical composition. Results indicated the interaction between water and rock as the dominant mechanism in the Juatama geological unit. However, at the present stage of knowledge, rock weathering does not explain alone the high salinities in water samples from the Acopiara unit, especially in relation to the anionic content. The use of the fuzzy method presented a good approximation to interpret the natural hydrogeochemical environment, demonstrating the importance of compatible scale mapping. The study should be complemented with the use of environmental isotopes, since these have a deterministic character, while the fuzzy theory provides a mapping of an interval information.