Efeitos do desmatamento e da poluição sobre a riqueza, densidade e composição de macroinvertebrados aquáticos de igarapés urbanos de Manaus,Amazonas

Abstract

The effects of deforestation and of organic poilution caused by domestic sewage 0 on the aquatic macroinvertebratesfauna and on Chironomidae were evaluated in m urban streams in Manaus In October and November 2003. In addition, the 0 frequency of deformities of the mandible and mentum were quantified in Chironomus (Chironomidae) in order to verify if any association existe with ® deforestation and with enrichment caused by total phosphorous (TP). Macroinvertebrates (including Chironomidae) were collected in the littoral and deep-water zones (treated here as benthic) with an aquatic net and a modified Petersen dredge, respectively. A total of 65 streams, three middie sections and three estuary sections of the three main microbasins in the urban area of Manaus 0 were sampled. Deforestation rates were estimated using a classified LANDSAT 0 sateilite image(2003); while poilution was estimated using the concentrations of total nitrogen (TN) and TP in the system. Other abiotic variables such as temperatura, velocity, depth, width, electrical conductivity, pH, and dissolved oxygen were aiso measured. Due to the small number of samples in the middie and estuary sections, it was not possible to detect the effect of deforestation and 0 poilution on the fauna in these stretches. High values of deforestation and TP were associated with reduction in richness and simplification of macroinvertebrate composition (p<0.05) in the streams in the study area. The resuits suggest that urban streams in Manaus, with few exceptions, are homogeneous with respect to composition, with species adapted to highly deforested and eutrophic environments. The taxa with the highest frequencies of occurrence and with the highest densities were Oligochaeta, Chironomus, Psychodidae and Ceratopogonidae. A separate analysis of the Chironomidae fauna led to the conclusion that this group is more sensitive than are macroinvertebrates in general to the perturbations evaluated in the study. In addition to this group undergoing a reduction In richness and a simplification of its composition, it aIso underwent a reduction in its density with increasing leveis of deforestation and TP and a reduction of the richness of littoral Chironomidae with an increase in TN.Taxa with the highest frequencies of occurrence and the highest densities were Oligochaeta, Chironomus, Psychodidae and Ceratopogonidae. In some streams, observed frequencies of deformities in Chironomus were higher (9 to 23%) than the frequencies accepted as natural(8%) in nature, however, these were not related to deforestation (p>0.05) and in benthic larvae they were negatively related to TP concentrations(p<0.05).