Spreading and accumulation of river-borne sediments in the coastal ocean after the environmental disaster at the Doce River in Brazil

Abstract

This study is focused on the fate of a large volume of mine slurry discharged from the Doce River (DR) to the coastal ocean after the worst environmental disaster in Brazilian which occurred in November 2015. We used Eulerian (ROMS) and Lagrangian (STRiPE) numerical models, as well as satellite remote sensing data, to study the spreading and seafloor accumulation of fine river-borne sediments during the initial six months following the disaster. We show that the regions of intense sediment accumulation were determined by spreading patterns of the surface-advected DR plume. The river discharge rate governed the plume surface area, while its position depended on local wind forcing conditions. The spreading of sediments carried by the DR plume was dominated by southward transport caused by prevailing upwelling-favorable northeasterly winds during the study period. Under high discharge conditions, river-borne sediments were transported over 100 km southward from the DR mouth and reached the outer shelf. In contrast, sediments were arrested near the mouth during drought periods and remained on the inner shelf. As a result, fine river-borne sediments accumulated on the seafloor, mainly in the large shallow shelf area southward from the DR mouth. Conversely, only a small fraction of residue was deposited northward. Thus, the Environmental Protection Area (EPA) of Costa das Algas, located 40 km southward from the DR, potentially exhibited more susceptibility to sediment arrival. On the other hand, their influence on Abrolhos Marine National Park, located 200 km northeastward from the DR mouth, was presumably minimal.

Historical contamination with a current problem: Can mining tailings enhance coastal arsenic pollution?

“…Different letters indicate significant differences among samplings (Kruskal-Wallis, p < 0.05); and between wet and dry conditions (Mann-Whitney, p < 0.05) contaminants associated with them, mainly when they coincide with great wave height (Longhini et al, 2022;Quaresma et al, 2020); however dry conditions are marked by enhanced resuspension events and release of metals and As from the sediment to the water column (Longhini et al, 2022). This is also supported by the pattern of Rio Doce plume dispersion that was transported as far as 100 km south from the river mouth under heightened discharge conditions in January 2016 (Lemos et al, 2022).…”

“…Colatina fluviometric stations (codes 56994505 and 56994500) were considered for the search. Colatina is the main station with continuous data for Rio Doce discharge, and it has been used for the most important studies of the streamflow of this riverine system (e.g., Lemos et al, 2022; Oliveira & Quaresma, 2017).…”

“…The latter conditions favor the resuspension of modern sediments and the transport and deposition in the North Sector, whereas the Central Sector acts as a bypass where depositional processes are less verified (Quaresma et al, 2015). In this sense, the southward transport of sediments and the Rio Doce plume was dominant on the continental shelf after the disaster, mostly because of upwelling-favorable winds from the north quadrant (Lemos et al, 2022). No significant differences were observed for As concentrations among the isobaths (Kruskal-Wallis, p > 0.08086; Supporting Information: Table S4).…”