Are fish assemblages recovering after the huge disaster of mining tailing dam collapse in Mariana (Brazil-MG)?

Assessing temporal shifts in trophic diversity in fish assemblages after the Fundão dam collapse

The rupture of the Fundão dam stands as one of the most significant environmental disasters of its kind on a global scale, profoundly affecting the aquatic ecosystem of Doce River Basin. By employing stable isotopes of carbon and nitrogen, we were able to trace matter and energy flow within ecosystems. In this study, we assessed the spatial and temporal variation, between 2020 and 2022, in species richness and trophic diversity in areas exposed (along a gradient in the main channel of the river) or unexposed (control sites in tributaries systems) to the mine ore tailings in the Doce River Basin. We tested the hypothesis that tailings reduce species richness, and that trophic stability is negatively affected by mining tailings. To estimate trophic stability for each sampling site, we calculated the standard ellipse area (SEA) and six community-wide metrics based on stable isotopes. The three regions studied presented distinct patterns on trophic diversity. Control sites exhibited stability in trophic metrics over time. Affected regions close to the rupture of the dam exhibited significant fluctuations on all six community-wide metrics analyzed than the affected regions farther from the rupture. Sites close to the rupture exhibited lower species richness, affecting mainly herbivores and piscivores. Our findings show the potential of using the isotopic approach in monitoring the ecological recovery of impacted ecosystems.

Five years after the collapse of the Fundão Dam: lessons from temporal monitoring of chemistry and acute toxicity

In November 2015, the Fundão Dam break released millions of tons of metal-rich tailings into the Doce River Basin (DRB), causing catastrophic damage and potential ecological effects that reached the Atlantic Ocean. This study aimed to evaluate the geochemistry and toxicity of water and sediments collected in the DRB from 2015 to 2019 and to determine the spatial and temporal trends. Water and sediment samples were analyzed for metals and As by inductively coupled plasma optical emission spectrometry (ICP-OES), and acute toxicity for Daphnia similis or D. magna. Results were explored using geochemical indices and correlation analyzes. Overall, higher concentrations of metals and As in water and sediments were observed immediately after dam breakage, but the levels exhibited a decreasing trend over time, although the levels of some elements such as As and Mn remained high in the upper DRB. The geochemical indices indicated mostly low to moderate contamination, and the enrichment factor (EF) demonstrated a higher enrichment of Mn in the upper DRB. Acute toxicity to water fleas (D. similis and D. magna) was occasionally observed in waters and sediments, but the reference samples were toxic, and the short-term effects were not correlated with metals and As. Overall, the results showed limited bioavailability of metals and As and a decreasing trend in their concentrations, indicating an ongoing recovery process in DRB. These results are important to decision-making regarding the disaster and actions for environmental restoration.

GIS modeling to investigate environmental change and degradation in Kohima district, North East Hill (NEH) region of India

As a part of the Himalayan mountains, the North East Hill (NEH) region of India is geophysically dynamic and seismotectonically active since its formation about 55 million years ago with a head-on collision of the Indian plate and the Eurasian plate. The region still has been underthrusting at a rate of 4.5-5 cm/year causing the reshaping and changing of its geophysical characteristics (geology, geomorphology, relief, slope gradient, drainage system, etc.), whereas anthropogenic activities, particularly shifting cultivation and technological intervention, have caused changes or degradation of the ecological environment (air, land, water, vegetation, crop pattern, climate, wildlife, etc.). Addressing this burning geoecological problem, a geospatial technology-based case study from the Kohima district of Nagaland in the North East Hill region of India is presented here. Through the development and integration of multiple GIS modules, this reconnaissance study suggests that continuous seismic activities (about 27 seismic events/year) along tectonic faults, thrusts, and lithological shear zones have been reshaping and changing the geophysical environment, whereas the ecological environment has been changing or degrading due to decreasing natural landscape and habitats (forest area, water bodies, and shrubs) at an annual rate of 5.91 km2 (0.60%), increasing built-up area, agricultural land, and wasteland at an annual rate of 2.73 km2 (0.28%), 2.69 km2 (0.27%), and 0.49 km2 (0.05%) respectively. Results also suggest that environmental degradation results in accelerated trends of climate change (rising temperature at the rate of 0.13 °C/year, decreasing annual rainy days at the rate of 2 days/year, decreasing annual rainfall at the rate of 9.55 cm/year, mounting climatic zones at the rate of 175 m/year) and its adverse impacts (increasing extreme rainfall events at the rate of 3 events/year and causing cloud burst, erosion, landslides, and floods) in the region.