Influence of hydrological flows from tropical watersheds on the dynamics of Cu and Zn in sediments.

This work aimed to evaluate, on a spatial and temporal scale, the effect of the flow on the concentrations of Cu and Zn in sediments from two water bodies (the Alvorada and Mandaguari Rivers). Five sediment-sampling periods were conducted, under four different streams in each sampling point (shallow/fast (SF), shallow/slow (SS), deep/fast (DF), deep/slow (DS)). Each sampling point represented the spring, the middle, and the mouth of the evaluated rivers. Some climatic variables were also evaluated, such as monthly temperature and rainfall. In addition, temperature, pH, dissolved oxygen (DO), and total solids were evaluated. Cu and Zn concentrations were obtained by FAAS. Cu and Zn levels are affected by the speed and depth of the water column. The quality of the sediments is affected by human activities in the surroundings, and according to legislation, levels of Cu and Zn in sediments offer risks of medium and high effects to aquatic biota. The highest accumulation of Cu in sediments occurs during October (221 mg kg-1) and December 2015 (225 mg kg-1), which coincides with the period of implantation of the soybean crop in the region, as well as the rain period. The increase of Cu in these periods suggests the occurrence of erosion. It can be concluded that Cu and Zn are found in large quantities in sediments, offering risk to the aquatic organisms. Cu levels exhibited direct relation with the sampling periods, with higher concentrations in rainy periods, while Zn concentrations suffer influence of the water column velocity and depth.