Water quality of the Gualaxo do Norte and Carmo rivers after the Fundão dam collapse, Mariana, MG

Abstract We investigated the effects of Fe-mining tailings of the Fundão dam on water quality, concerning physical and chemical parameters, aiming to infer the recovery process of the affected areas, and prospects of water quality in the coming years. Water quality data from the Gualaxo do Norte and Carmo rivers were evaluated in three moments: (i) before the dam rupture (1999–2000); (ii) one year after the rupture of the Fundão dam (2016); and (iii) after the implementation of recover mitigation activities (2017–2019). Concerning the variables evaluated, the mean concentrations of Fe and Mn were higher in the dry period, and increasing turbidity was detected in the rainy season. The turbidity, even after the recovery measures, peaked at 300 and 400 NTU in 2017 and 2019, respectively. The concentrations of dissolved Fe, Mn and Cr, closely related to the tailings, decreased with rainfall by a dilution mechanism. Conversely, the concentrations of Cd, Al, Zn, and Cu increased in the rainy season, probably by greater erosion. The implementation of the recovery actions at the Gualaxo do Norte headwaters are helping to reduce the Mn and Fe concentrations and turbidity downriver, all associated with the Fe-mining tailings.