Larvas de Odonata como bioindicadores de qualidade ambiental de cursos d água no cerrado

Abstract

Biological monitoring is an effective method for determining the quality of water because it uses the community structure as an indicator of the degree of pollution. Among the groups of invertebrates that are used as bioindicators, deserve mention insects of the Odonata order. These insects have aquatic larval stage and are present in diverse aquatic environments such as rivers, streams, lakes and even temporary ponds or marshes. In aquatic environments associated with the Cerrado it is still fairly limited the number of studies performed with macroinvertebrates, mainly Odonata. The aim of this study was to evaluate the potential of Odonata larvae as bioindicators of the quality of Cerrado watercourses, testing the following hypotheses: i) there is correspondence between assemblage parameters (richness and diversity) of Odonata and indices of environmental integrity related to the characteristics of water and habitat structure, and ii) abiotic factors such as pH, temperature, dissolved oxygen, and others are crucial to the presence of certain genera of Odonata in the watercourses. The study was conducted in 12 watercourses in Uberlândia and Uberaba (MG Brazil), with different levels of conservation. For the evaluation of water quality samples were collected for analysis of the following parameters: apparent color, biochemical oxygen demand, total phosphorus, nitrate, dissolved oxygen, pH, total solids, turbidity, temperature and fecal coliforms. For the evaluation of ecological conditions of the sites studied we applied a rapid assessment protocol. The data on the use and occupation of the areas was obtained by photointerpretation of current satellite images (sensor images of Landsat TM 05/10/2010 - Scene 220, orbit 072). For the sampling of Odonata larvae in each watercourse were selected stretches of 100 m. This section was divided into 20 segments of 5 m, and to perform the sampling were randomly selected five of these segments. In each selected segment, a sample was obtained, using a D-type network with a mesh of 0.25 mm. A standardized sampling effort of six minutes was used in each segment, dragging the net along the sediment and riparian vegetation. To characterize the Odonata larval communities richness and diversity were used. To evaluate the relationship of environmental indicators with the descriptors of the Odonata assemblages a PCA was used. To evaluate the relationship between the assemblages of Odonata larvae and physico-chemical parameters of water a CCA was used. We recorded 101 individuals, belonging to six families and 21 genera. The highest abundances were recorded in Liso, Óleo and São José streams, and the Liso and São José streams also had the highest richness. There was a predominance of genera belonging to the family Libellulidae. In PCA, there was a negative correlation between the metrics of environmental integrity and descriptors of Odonata assemblage. The Axis 1 of PCA explained 58.18% of the variance, while Axis 2 explained only 29.66%. The CCA did not show significant results for any of the axes. Thus, there was no significant relationship between the abundance of taxa and variation in environmental parameters for the water bodies studied. However, there was a trend of some genera to occur at better environmental conditions, while others are more tolerant. These results obtained, although not conclusive, indicate that the genera of Odonata have the potencial to be used as environmental quality bioindicators.