Temporal variation of suspended sediments and mineralogy using an improved automatic sampler system in the Riacho Fundo Stream, Brasília, Distrito Federal, Brazil

Abstract

This work aimed to contribute in the sedimentometric study of the Riacho Fundo stream, affluent of Lake Paranoá, Brasília, Federal District, and historically the main sediments exporter for the entire basin. For this purpose, the flow was measured by the acoustic method with the Sontek River Surveyour M9 equipment and an automatic sampler ISCO 6712 was used for water and sediment sampling, with collection at a fixed point and varying according to the height, in a water depth of 40 cm. The mineralogy of chosen sediment samples was assessed by X-ray diffraction. Also, simultaneous monitoring of the turbidity was carried out, with a floating multiparameter probe, likewise. The results are useful data for the location, since there is lack of data for reservoir sedimentation planning. Furthermore, the improved sampling method (floating probe) showed a better coefficient of determination (R² = 0,45) than the fixed sampling method (R² = 0,28). Thus, a good correlation could be reached between turbidity and concentration (R² = 0.92). Hysteresis was generally counterclockwise. The use of the automatic sampler allowed the identification of minerals in the suspended sediments, which are not identified in other studies in the region.