Species turnover and baseline shifts shape seasonal isotopic niches in a mining-impacted river basin

Fráguas, Patrícia Santos and de Carvalho, Débora Reis and Sperber, Carlos Frankl and Pompeu, Paulo Santos (2026) Species turnover and baseline shifts shape seasonal isotopic niches in a mining-impacted river basin. Water Biology and Security: 100665. ISSN 2772-7351 (In Press)

Abstract

In 2015, the Doce River basin was subjected to one of the largest environmental disasters with the collapse of the mining-tailings Fundão dam. The extensive impacts on the aquatic biota also affected fish trophic ecology. This study aims to evaluate the influence of seasonality on the trophic parameters of the fish community in the Doce River basin. Sampling sites were divided into three regions (control, near, and far from the dam rupture). Isotopic niches of the fish communities varied seasonally along the basin, but there were differences between regions. Control sites showed greater similarity in trophic niche and trophic diversity metrics between seasons. Contrastingly, sites closest to the dam rupture exhibited pronounced seasonal variation, with lower niche overlap and greater variability in trophic diversity metrics. However, when analyzing only the six fish species common to all regions and seasons, the significant regional differences in seasonal niche overlap were no longer evident. This result indicates that shifts in community species composition are the primary driver of the observed patterns at the community level, although changes in the isotopic values of food resources and in the proportions of the main consumed food items also play a role. Our findings demonstrate that the stronger seasonal shifts in the community isotopic niche near the impact site are not due to amplified dietary responses of resident species, but rather to a higher turnover in the species assemblage. This highlights the critical importance of considering taxonomic composition when interpreting community-wide isotopic metrics in impacted ecosystems. Stable isotopes’ results have proven to produce robust indications of changes in impacted environments. Such assessments are essential to understand mining-related impacts and guide restoration efforts in this basin.