Short-term hydromorphological and ecological responses of using woody structures for river restoration in a tailing-impacted tropical river.

Gualaxo do Norte River (GNR), in southeastern Brazil, was impacted by iron ore tailings from the Fundão Dam rupture (November 2015). The deposition of tailings on the riverbed has changed the hydrogeomorphological characteristics of the GNR, resulting in a decrease in the diversity of physical habitats and the ecological biodiversity. As part of the process of restoration and management of this damaged ecosystem, the river restoration project ReNaturalize was implemented to restructure the geomorphological characteristics and the physical habitat, and to enhance the reestablishment of biota, mainly for macroinvertebrates and fishes. For this goal, 203 wooden structures, such as tree trunks, branches and grass were installed in two sections of GNR (T6R and T7R), totaling 1.8 km long. The effectiveness of the project was evaluated by an assessment that followed a before/after and control/impacted (BACI) design. Upstream of each Restored reach there is a Control and a Reference reach. Four campaigns were carried out, 2 before and 2 after the restoration process. After 14 months of the woody installation, an increase in hydraulic retention in the restored reaches was observed (T6R-20.2%; T7R-63.5%), when compared to the control reaches, which favored the accumulation of sediments (T6R-388 metric tons; T7R-396 metric tons). This enhanced the formation of natural tailings barriers and promoted enrichment of substrate types (T6R-39.2%; T7R-43%). The benthic macroinvertebrate community showed an increase in the total abundance (T6 - 110%), including the most sensitive groups (T6R-124%; T7R-124%). For fish, the increase was up to 81.38% with hand nets capture, indicating recruitment of juveniles; and the abundance and the biomass of some species were also higher (up to 100%) than the Control reaches. The results indicated that the Restored reach is already qualitatively and quantitatively better than Control reach and similar to the Reference reach, indicating the success of the study. This article is protected by copyright. All rights reserved. Integr Environ Assess Manag 2022;00:0-0. © 2022 SETAC.