Limnologia, distribuição e composição da fauna de Oligochaeta (Annelida: Clitellata) e larvas de Chironomidae (Diptera) do Lago dos Manacás, município de Juiz de Fora, MG

Abstract

The aim of this study was to verify the existence of the spatial and temporal variation of abiotic variables and know the structure of Chironomidae and Oligochaeta assembléia of the Manacás lake in months that compound the dry and rainy period and from this variable to evaluate the water quality of the environment. Three collects have been done, two in dry season (august/09 and july/10) and one in the wet season (february/10) in two transects each with five sampling points., Sediment samples has been collected by a bottom sampler Petersen. Three replicates have been made in each sample point for analysis of macroinvertebrates. Sediment samples were also obtained for analysis of particle size and organic matter. Water samples were obtained from the bottom with a bottle of Van Dorn. To analyse of the environment trofic status was calculated the trofic status index (TSI) of the Carlson and the presence and abundance of the pollution indicators taxa. Limnological parameters showed no significant variations among the sampling sites and among transects. However significant differences were detected between samples collected, with the exception of oxygen, dissolved organic carbon and pH. The particle size was mainly composed of fine sediment with a high percentage of organic matter. The assembléia found was composed of 25 taxa and 1007 organisms. The higher richness and diversity was obtained in the first collection in August 2009 and the lower density and number of taxa was found to the rainy season. Chironomids were the most abundant organisms during all period of collection. The marginal points (I and V) differed significantly with respect the assemblage only in transect A in the first collection in the others, the margins were considered equal. In August 2009 could be seen a large number of taxa adominantes. During this period the main dominant taxa was Caladomyia ortoni. In 2010 adominantes taxa were not observed, and Polypedilum were dominant in this period. The index to determine the trophic status of Manacás Lake rated this environment as oligotrophic, mesotrophic and eutrophic during the period of collection. The abiotic variables varied temporally changing environmental conditions and structure of the assembléia of Chironomidae and Oligochaeta. The concentrations of nutrients increased significantly showing that the lake goes through a process of change in water quality. The low abundance of the organisms found in the lake was considered common, already observed on others places. Although the trofic status index to show the water quality of Manacás lake is in bad conditions the absence and/or the low density of taxa considered how pollution indicators do not confirm this data.