Macroinvertebrados bentônicos como ferramenta na avaliação da qualidade ecológica de reservatórios tropicais

Abstract

Assessment of aquatic ecosystem quality is becoming increasingly important for managers and researchers. The general objective of this thesis was to adapt and develop different methodologies aiming toward the development of tools to assess the ecological quality of reservoirs, through the use of the littoral benthic macroinvertebrate communities. To do this: i) morphological deformities in Chironomidae mouthparts were tested for their use as tools in environmental assessments; ii) through allometric relationships, a statistical model was established to estimate the biomass of alien species Melanoides tuberculatus (Thiaridae, Gastropoda); iii) the influence of physical habitat structural complexity on benthic macroinvertebrate communities was assessed; iv) an approach was proposed to select sites with maximum ecological potential in urban reservoirs; v) an evaluation of the water quality was developed, tested and proposed, based on a predictive statistical model, as well it was proposed an assessment of water quality in ecological status classes; and vi) an evaluation and comparison of the performance of diversity, eco-exergy and specific eco-exergy indices in reservoirs. This thesis consists of 6 chapters based on data collected over two years (2009 - 2010), in three urban reservoirs in the watershed of Paraopeba, Minas Gerais, Brazil. Chapter 1 describes the morphological deformities in the mentum of Chironomidae larval (Diptera, Insecta) in three reservoirs under different trophic impacts. In Serra Azul, 6.9% of the mentum were deformed in the dry season, whereas in the Ibirité and Vargem das Flores 6% of the mentum were deformed. The higher percentage of deformities in the Chironominae sub-family individuals in Serra Azul (>6%) may be a response to background high concentrations of sedimentary manganese there due to the matrix rock geological origin. Thus, it was concluded that Chironomidae mouthpart deformities can not be used as impact indicators because they may be related to natural origins (genetic factors or even due to the sediments' chemical composition). In Chapter 2, a statistical model was proposed to estimate the biomass of Melanoides tuberculatus (Thiaridae, Gastropoda). Measurements of the total length and shell opening of 70 individuals were obtained and correlated with the biomass values for construction of exponential and power-function models. Both models showed high coefficients of determination but the exponential model was the better biomass predictor, with a coefficient of determination over 93%. The modeling used in this study provides an important tool to determine the biomass of M. tuberculatus in eutrophic reservoirs. Chapter 3 focused on the influence of habitat structure complexity on benthic macroinvertebrate communities. To assess this, the USEPA physical habitat protocol was adapted and modified. The results of the variables measured by the protocol found that the macroinvertebrate community in Serra Azul was significantly influenced by the shrub understory and bank angle. In Ibirité and Vargem das Flores the variables of land cover, human disturbance and aquatic macrophytes showed significant relation with the benthic macroinvertebrate communities. Information obtained through the use of the habitat protocol provided complementary information for reservoir monitoring and may help to guide reservoir rehabilitation programs. In Chapter 4, reference sites were selected with maximum ecological potential, based on an a posteriori classification of pressure variables for the reference sites characterization. Twenty-eight sites with high ecological status were selected and divided in two sub-groups. The results showed that the environmental indicators that best explained the distribution of benthic communities in sites with high ecological status were: bottom substrate type, presence of gravel/boulders, coarse sand, silt/clay or muck, depth and shoreline substrate zone, and these variables discriminated Macroinvertebrados bentônicos como ferramenta na avaliação da qualidade ecológica de reservatórios tropicais 96% of the distribution of the communities. These two subsets of biological communities and respective environmental conditions are a basis for future development of a quantitative assessment system to monitor tropical reservoirs. Chapter 5 it was tested the value of an assessment tool based on the structure of benthic invertebrate communities to evaluate the Ecological Potential of urban reservoirs. For that, it was designed a conceptual assessment scheme based on the Reference Condition Approach and developed a statistical model based on 28 sites classified as having maximum ecological potential. Sixty-two disturbed sites were used to test the model. The results showed that the use of 3 classes of ecological status classification is possible to significantly distinguish different levels of pressure to which the sites are submitted. It was demonstrated that the benthic communities in reservoirs can also be used as an assessment of water quality. Chapter 6 focused on testing the ability of Eco-exergy, Specific Eco-exergy, Shannon-Wiener, and Margalef indices to distinguish between reference and impaired sites. The results showed that the Shannon-Wiener, Margalef, and Eco-energy indices significantly distinguished reference sites from highly disturbed sites. Therefore, it was noted that the diversity and Eco-exergy indices are ecological indicators and offer information of the state and environmental health of urban reservoirs. The results of this thesis highlight the value of using biological indicators to assess the ecological quality of reservoirs and demonstrate that other tools, indices and other predictive models can also be used to assess the reservoirs ecological quality as a component of biomonitoring programs