Impact of the Mariana’s iron ore tailings spill upon cockroach (blattodea) communities of riparian forests in the Doce River Basin, Brazil
Authors:   , Harriman John Chidi 
Published: January 2024

In 2015, several thousand kilograms of iron ore mine tailings were discharged in the ecosystem, launched by the collapse of the Fundão dam in Mariana. This tailing buried villages, vegetation and animals and then moved over 800 km along the Doce River, causing ecological catastrophe on municipal councils it directly impacted. The activities of arthropods, such as nutrient cycling and decomposition that contribute to the functioning of ecosystems, might, thus, be compromised. This anthropogenic disturbance is speculated to influence the diversity of biotic communities. The impact of ecosystem degradation from the tailings are still unknown seven years after this disaster. We investigated the assumption that the abundance and the diversity of cockroaches decreased in areas that got in contact with the tailings’ flush along the Doce River’s channel. We also evaluated eventual covariates, such as distance to the river and amount of litter. We selected five locations along the Doce River basin including: Mariana, Rio Casca, Ipatinga, Conselheiro Pena, and Aimorés, all in Minas Gerais State, Brazil. We chose two(2) areas in each of these five regions; affected and unaffected. To test our hypothesis, we used analyses of co-variance (ANCOVA), adjusting generalized linear mixed models (GLMMs) with the following explanatory variables: affected or unaffected and its interaction with distance to the river, litter weight and litter heterogeneity, and distance to the origin of the disaster. These models were adjusted for: cockroach communities’ abundance, diversity and evenness. We also evaluated if the tailings’ passage alter cockroach species composition. There was a significant interaction effect between the affected x unaffected areas and distance to the origin of the disaster (Chi=5.1447, df=1, p=0.02332). In the unaffected areas, the abundance of cockroaches increased with the proximity to the origin of the disaster, as expected by an eventual dilution effect of the tailings, while in the affected areas, there was no impact of distance to origin on cockroach abundance (Chi = 0.2204; P = 0.6387). There was a substantial interaction between the treatments and other litter components (Chi= 4.8158, df = 5, p = 0.0282), which we interpret as correlated to the humus content in the litter, unto cockroach diversity, increasing with the local amount of humus in the litter. However, the increase was not significant in the affected areas. Unaffected areas had higher cockroach diversity, compared to affected areas. Cockroach diversity was higher in unaffected areas from three sampled regions (Ipatinga, Rio Casca, and Mariana), while only in our Rio Casca areas had the highest genus richness. There was a significant effect of the dilution effect (distance to the origin of the disaster) unto cockroach diversity (Chi= 4.1612, df=8, p=0.04136): in unaffected areas, cockroach communities’ evenness decreased with distance from the origin of the disaster. While a non-significant decreasing trend was also found along the affected gradient which decreased as the distance from the source of the tailing decreases. A significant interaction effect exists between distance to the river and cockroach communities’ evenness (Chi = 4.3381, df = 8, p = 0.03727). Keywords: Blattaria. Iron tailings. Abundance.