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 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 and after and control and impacted (BACI) design. Upstream of each Restored reach there is a Control and a Reference reach. Four campaigns were carried out, two before and two 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 with 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 the 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 the 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 the Control reach and similar to the Reference reach, indicating the success of the study. Integr Environ Assess Manag 2023;19:648-662. © 2022 SETAC.

Massive mortality of the giant freshwater mussel Anodontites trapesialis (Lamarck, 1819) (Bivalvia: Mycetopodidae) during a severe drought in a Neotropical reservoir.

In 2012, a severe drought struck the southeastern of Brazil compromising the Paraná River Basin reservoirs. Here, we described how this climatic event promoted a massive mortality of the giant freshwater mussel Anodontites trapesialis in Furnas reservoir and reported the consequences of this phenomenon. In November 2012, three quarters of 100 m2 were sampled in this reservoir, where 812 dead shells of A. trapesialis were analyzed and measured (33 Ë« 133 mm). The species showed an aggregated distribution with high density ( X ¯ : 1.0 - 5.5 ind/m2). Despite the massive mortality detected in field, it was possible to find living specimens in a small channel in the studied area, allowing the species to survive the water level fluctuations. Large adult individuals (100 Ë« 124 mm) were more affected by drought than juveniles, accounting for about 90% of the dead mussels analyzed. Two years after the massive mortality event, water level was not reestablished and a terrestrial succession (with elevations in the concentration of organic matter and calcium in sediment) was observed in the studied area. We verified that the damming associated with extreme climatic events affect negatively the populations of A. trapesialis and should be faced as a conservationist problem.