A decade on: the tailings legacy in Rio Doce water quality

In 2015, the collapse of the Fundão tailings dam released millions of cubic meters of mine waste into the Rio Doce Basin, causing profound and lasting environmental impacts. We analyzed 3 years of seasonal variation of water quality and metal concentrations across two middle Rio Doce sub-basins: one impacted by the tailings (Doce River) and a non-impacted reference system (Santo Antônio River). We hypothesized that tailings-associated variables (e.g., turbidity, Mn, As, Fe, Al) would differ in concentration and seasonality between the sub-basins, reflecting altered ecological responses nearly a decade after the collapse. Multivariate analyses (PCA, PERMANOVA) and mixed-effects models revealed significant spatial and temporal differences, with the impacted sub-basin showing persistently higher turbidity and metal loads, especially during the rainy season. Cluster analysis identified spatial groups corresponding to contamination gradients relative to the tailings source and confluence zones. Overall, our results demonstrate that the legacy of the tailings continues to shape water quality dynamics and suspended particulate matter in the Rio Doce system, highlighting the need for ongoing, spatially explicit monitoring to support ecosystem recovery and management.