Thermodynamic based indicators illustrate how a run-of-river impoundment in neotropical savanna attracts invasive species and alters the benthic macroinvertebrate assemblages' complexity.
Hydropower dams are widespread sources of anthropogenic alteration on lotic ecosystems, found in most hydrological basins system in the world. Our objective was to assess how such a run-of-river dam influences benthic macroinvertebrate assemblages in a neotropical river under a deactivated run of river dam. For that we tested four hypotheses: (1) a run-of-river dam diminishes the local diversity of the benthic macroinvertebrate assemblages; (2) the presence of the dam results in a more propitious habitat to the establishment of invasive species; (3) the presence of the dam results in a lower complexity of local benthic macroinvertebrate assemblages; (4) the ecological impacts are restricted to the sites directly affected by the dam. While the presence of the dam lowers the benthic macroinvertebrate assemblages' diversity in its reservoir, the diversity downstream next to the dam actually increases. The habitats directly affected by the dam also supported much higher biomass proportion of invasive species. By using eco-exergy and specific eco-exergy indicators, we were able to assess the complexity of benthic macroinvertebrate assemblages and the assemblages in the reservoir appeared to be enhanced by the presence of invasive species. These results illustrate that deactivated run-of-river dams still alter significantly the structure of lotic benthic macroinvertebrate assemblages and that is advisable a management intervention for decommissioning of the dam. Finally, our results show that exergy based indicators may improve our comprehension of ecological systems' functioning in regards of ecological impacts of small dams, supporting environmental sustainable practices.