Macroinvertebrados bentônicos como indicadores de estressores ambientais e de serviços ecossistêmicos em reservatórios no semiárido

Abstract

Reservoirs are artificial ecosystems created by damming rivers and are primarily used to meet human needs when water is scarce. Population growth around reservoirs has led to environmental degradation from anthropogenic activities (agriculture, pasture, human occupation, industry, etc.), which can lead to a decline in the diversity of aquatic communities and a loss of processes and ecosystem services. With increasing climate change, more frequent drought scenarios are expected, leading to an increase in the number of reservoirs around the world. This work aims to assess how the benthic macroinvertebrate community in reservoirs responds to environmental stressors from different land use and occupation types, if their traits can serve as indicators of the stressors, how the land use and occupation influence the perception of the ecosystem services by the local population and how secondary production relates to these services. Therefore, this work is divided into four chapters with the following objectives: I) Evaluate the effects of land use and occupation patterns around reservoirs in physical and chemical variables, taxonomic and functional diversity, and secondary production of benthic macrofauna; II) Evaluate how gradients in physical and chemical variables affect the functional structure of the benthic macroinvertebrate community; III) Evaluate whether the ecosystem services of the benthic macrofauna are perceived by the population residing around the reservoirs, and what is the relationship between these services and the use and occupation of the land. Finally, didactic materials for scientific dissemination were developed to make the topics addressed in the thesis accessible to the general population. Environmental and benthic macrofaunal data were collected in six reservoirs in Northeastern Brazil in the Paraíba River basin (Sumé, Cordeiro, and Poções) and the Piranhas-Açu River basin (Cruzeta, Sabugí, and Passagem das Traíras) in 2014, 2015, and 2019, which suffered a severe drought. Overall, our results point that the development of anthropogenic activities adjacent to the reservoirs, such as agriculture, pasture and human occupation, negatively influenced the taxonomic and functional diversity of the macrobenthic community, either directly or indirectly (mediated by physical and chemical variables). However, agriculture, also an anthropic activity, influenced positively the benthic production, via increased nutrient concentrations. The increase in the environmental stressors selected functionally tolerant organisms with high resistance capacity. However, these were represented by dominant species, such as the exotic mollusc Melanoides tuberculatus, which resulted in low diversity in the most impacted reservoirs. This may compromise ecosystem functioning and raise concerns about adequate management of these systems. Land use and settlement also influenced the perception of ecosystem services by the local population, living near the reservoirs. Ecosystem services most recognized by the population were 84% provision, 12% cultural, and only 4% regulation and maintenance. In general, the presence of agriculture, pasture, open vegetation and trees/shrubs showed a significant relationship with the recognition of ecosystem services, especially those of provisioning. On the other hand, the identification of regulating and maintenance and cultural services showed a negative correlation with pasture, and a positive with open vegetation and trees/shrubs. The ecosystem services of benthic macrofauna were perceived indirectly by the population, through the potential of macroinvertebrates to facilitate services such as self-purification and decomposition in reservoirs. The ecosystem services most recognized by the population related to material benefits, highlighting the need for to inform these populations on the importance of other services provided by reservoirs and the role of benthic macroinvertebrates in maintaining those services. Also, the positive correlation between the secondary production of macrofauna and provisioning services suggests that this production may translate into higher energy available for sustaining these services through the trophic web. Finally, the results discussed here indicate that efficient management measures for the use and occupancy of lands adjacent to reservoirs are needed to ensure the maintenance of diversity and ecosystem services. In addition, the development of outreach and science education activities is needed to help people understand the importance of conserving benthic macroinvertebrates and reservoirs in providing ecosystem services. This thesis sought to cover a variety of areas, from community ecology to landscape ecology to ecosystem processes and social nature, to establish and explore connections between ecosystems and human populations.