Avaliação da integridade ecológica de riachos urbanos reabilitados

Abstract

Urban streams are affected by a complex combination of stressors (e.g., garbage disposal, water pollution, canalization), which modify the physical habitat, water characteristics, the composition of biological communities and ecological processes, thus altering the structure and functioning of ecosystems. Rehabilitation projects have been developed in several countries with the objective of recovering urban streams. However, this is still an incipient subject in tropical regions. Most studies address structural aspects, such as water quality, sediment control and flood events, without considering indicators of ecosystem functioning. Here, we evaluate the structure and functioning of urban streams rehabilitated 15 years ago in comparison to streams in the best available ecological conditions (reference), streams with moderate habitat alteration (consolidated), and severely degraded streams. We found higher habitat diversity and riparian zone integrity, richness of sensitive macroinvertebrate taxa, and macroinvertebrate biotic index (multimetric) scores in the rehabilitated compared to the degraded streams. Additionally, we found lower primary production, nutrient concentrations, sediment deposition, and siltation in rehabilitated streams compared to degraded streams. However, comparing the rehabilitated streams with the consolidated ones, we found a higher primary production in the rehabilitated streams. We also found lower habitat diversity, richness of sensitive macroinvertebrates and macroinvertebrate indices, and higher primary production in rehabilitated streams compared to streams under reference conditions. These results show that the rehabilitated streams are in better structural and functional conditions than the degraded ones, but they do not differ significantly from the consolidated ones, nor did they reach a condition similar to the reference ones. We conclude that rehabilitation is effective in reducing the state of degradation, evidenced by the structure and functioning of the ecosystem. Furthermore, the combined use of functional and structural indicators allowed a comprehensive assessment of the ecological integrity of streams and allowed the detection of differences among categories of urban streams beyond those detected based on structural indicators of water quality. The rehabilitation of urban streams is a prospect for improving ecological quality in South America and, potentially, could inspire other countries in the southern hemisphere to follow the example that will allow recovering some of the ecosystem services that rehabilitated urban streams can provide to urban populations.