Insetos aquáticos bioindicadores: influência de efluentes de piscicultura sobre um córrego pampeano, Uruguaiana, Brasil

Abstract

Water bodies undergo strong impacts due to disorderly increase of human activities. Among then, the pisciculture is considered polluting even in accordance with environmental rules, casting organic contaminants coming from fish’s excreta, leftover feed and fertilization. Accordingly, benthic insects have often been used in evaluation of environmental impacts and in biological biomonitoring of aquatic ecosystems. Therefore, this study aimed assess the water quality and the likely effects of pollution from effluents of Pisciculture sector of Federal University of Pampa (UNIPAMPA, Uruguaiana campus) in a segment of the stream Arroio Felizardo, though of the aquatic insects bioindicators. Were performed four sampling (January, February, July, August 2012) in three points of the stream: upstream (P01), in the effluent discharge site (P02), and downstream (P03), 500 meters distant from each other. For the insect capture were used driftnets, for approximately one hour in each point, and five efforts with scanning network of 1 mm mesh. Were sampled the three points in the same day. Were also measured the water physicochemical characteristics (Conductivity, pH, temperature, total ammonia and dissolved oxygen). The insects ware fixed in ethyl alcohol (70%), and subsequently identified at family level. Were used the biotic indices Biological Monitoring Working Party – BMWP and Family Biotic Index – FBI for assessment of water quality. Were collected 351 exemplars from 14 families. The most frequent were Coenagrionidae (Odonata) and Chironomidae (Diptera), totaling 35% of total. The water temperature remained around of 24.7 °C, with pH of 7.87, nitrite 0.1 mg/L and ammonia 1.0 mg/L. The physicochemical parameters for all points of study are in accordance with Classification of Freshwater Bodies (CONAMA 357/05), with exception for dissolved oxygen in summer period. The inorganic parameters have been with values within the allowed. However the biotic indices suggest the direct influence of pisciculture effluents over the aquatic insect fauna in P02 and rank the waters of the stream with quality between doubtful and acceptable (BMWP) and between good and reasonable (FBI). There are evidences of moderates effects of water pollution, or with some organic pollution confirmed by such indices. According with our results, the Arroio Felizardo remains with your waters identified in class II (Brazilian legislation), even suffering the influence of pisciculture effluents.