Assessment of Fluvial Sediments at Serra Azul Stream, Minas Gerais– Brazil

Aims: The goal of this study is to perform the characterization of bottom and in suspension sediments at Serra Azul stream. Chemical, mineralogical and grain size aspects were evaluated, as also the legal issues pertinent to this matter.

Study Design: Hydrosedimentological studies at Juatuba basin.

Place and Duration of Study: Juatuba basin – southeast part of Brazil, between December 2013 and October 2014.

Methodology: The bottom and in suspension sediments of Serra Azul stream were characterized through different techniques: x-ray diffraction, x-ray fluorescence and grain size analysis (using sieves and laser techniques). The environmental legislation was checked in order to see the values of the allowed concentrations of some heavy metals in the waters. Also, the data of a small hydrometric network were treated in order to obtain the natural flows of the water courses.

Results: Two elements found in the sediments in suspension were not found in bottom sediments: Chlorine and Bromine. Gallium, Lead, Barium and Nickel were not found in the bottom sediments samples in 2013, only in 2014. The concentration values of Chrome, Potassium, Sodium and Silicon became smaller in 2014, however for the other elements that were found, these values became bigger. The bottom sediments collected in the study area present values higher than the threshold above which a probable adverse effect on the biota is expected for Chrome and Nickel, in order of importance. When the global values of the dissolved constituents in surface waters were compared to the ones found at Juatuba basin, it was possible to verify that only for Iron and Aluminum the 2014 found values were bigger than the average elemental composition, according to a variety of sources and authors.

Conclusion: The transport of sediments in the studied area showed that some heavy metals are being transported towards the Serra Azul reservoir in concentrations higher than the allowed ones. Due to a long dry season in the study area, this transport is currently minimized, however the next rain station can generate a serious scenario. It is necessary to implement a permanent program in order to collect and analyze these sediments, inclusive in other parts of the basin. It is also necessary to solve the question concerning to the absence of a legislation for several other chemical elements found in the sediments.

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