Spatial variation of the fish community in a mine tailings dam

Abstract It is expected that the spatial distribution of ichthyofauna in reservoirs within mining areas will be affected by environmental changes imposed by damming and the progressive deposition of tailings. In this context, we evaluated variations in the taxonomic and functional diversity of fish communities at five locations within the Gelado tailings dam, formed by a dammed stream in the Brazilian Amazon region. Among these locations, two are additionally affected by the continuous deposition of iron tailings. We sampled fish (collected using standardized gill nets) and environmental data in 2006, 2007, 2008, 2009, and 2021. We used linear mixed-effects models (GLMM) and permutational analysis of variance to assess differences in alpha and beta diversity among the different locations, respectively. We used the longitudinal gradient and expedition years to control for potential spatial and temporal autocorrelation effects during the analyses. Our results revealed that species composition varied significantly only between areas with and without tailings, while taxonomic structure, functional structure, and functional composition showed no variations among the different locations. The longitudinal gradient was significant only for functional evenness. Differences in species composition were due to variations in the abundance and capture frequency of Leporinus friderici, primarily in the area with tailing. Consequently, effects related to tailings deposition, along with the longitudinal gradient, exert a greater influence on the spatial structure of communities than local environmental variations, such as the presence of specific microhabitats. In conclusion, the fish community exhibited low species richness when compared to the regional species pool, an expected effect of the 45-year-old damming, and displayed an altered spatial structure in areas with continued deposition of iron tailings.