Estudo de microinvertebrados em um lago localizado em propriedade rural no município de Juiz de Fora, Minas Gerais

Abstract

On private properties, especially in rural areas, it is common to find water bodies within their boundaries. These aquatic systems can be classified as lotic ecosystems, such as streams and rivers, or lentic ecosystems, such as lakes and ponds. Environmental characterization of aquatic ecosystems must include not only the measurement of abiotic parameters but also biotic ones. Among the organisms inhabiting these ecosystems, benthic invertebrates are noteworthy. In this context, our objective was to conduct the environmental characterization of a lake located on a rural property in the municipality of Juiz de Fora, Minas Gerais, Brazil. Sediment samples were collected during both dry and rainy seasons using a D-frame net at four points within the lake, stored in plastic bags, and preserved in 85% ethanol, totaling eight samples. Specimens associated with the sediment were sorted under a stereomicroscope and identified using specific taxonomic keys. The variables temperature, dissolved oxygen, turbidity, conductivity, and pH were measured using a multiparameter probe. Sediment samples were analyzed for granulometric fractions and organic matter content. In total, 1,155 organisms belonging to 28 taxa were recorded. Chironomidae (56.58%) and Ceratopogonidae (25.64%) were the most abundant families, both belonging to the order Diptera. During the dry season, predators (61.87%) were the most abundant, followed by gatherers (32.57%) and filter feeders (2.62%). In the rainy season, predators (56.30%) and gatherers (29.77%) remained dominant; however, detritivores (8.02%) represented the third most abundant functional feeding group (FFG). Regarding abiotic variables, pH shifted from 6.7 in the dry season to 5.8 in the rainy season, indicating a slightly acidic environment. Based on the measured dissolved oxygen values, the lake was classified according to CONAMA Resolution 357/2005 as a Class 4 freshwater environment, suitable for landscape harmony. Sediment analysis revealed an average organic matter content of 8.78%, lower during the rainy season (6.9%), with coarse sand being the predominant granulometric fraction in both seasons. The results indicate that the proportion of FFGs was only slightly altered, maintaining its functional structure, with predators and gatherers being the most representative groups in both seasons. We believe this outcome is related to the fact that the studied lake is spring-fed, an aquatic ecosystem that tends to exhibit relatively stable environmental conditions compared to other surface waters.