Density and biomass of Campsurus sp (Ephemeroptera) and other macroinvertebrates in an Amazonian lake impacted by bauxite tailings (Lago Batata, Para, Brazil)

For 10 years (1979 to 1989) the Lake Batata received about 18 million cubic meters per year of effluent from the washing of bauxite. About 30 % of its area was impacted. The main goal of this study has been the to evaluation of the effects of the bauxite tailing dumping on the density and biomass of the benthic macroinvertebrates community and, especially, on the populatio n of Campsurus sp. Three sampling sites has been determined in each of the three lake regions (impacted, transition and natural); periodicity of sampl es has been chosen throughout the four periods of the flood pulse thigh wat er, drawdown, low water and flood) between June 1996 and March 1997. The li mnological variables measured were temperature, depth, dissolved oxygen and transparency (of water column), available phosphorus, total nitrogen and o rganic matter (in the sediment). Variables were organized by Pincipal Compo nents Analysis (PCA). Density results for community of benthic macroinverte brates were significantly lower (Kruskal-Wallis, p < 0,05) in the impacted region; the highest values were found in the natural and transition regions . Ostracoda, Chaoboridae, Oligochaeta and Chironomidae were the predominant taxonomic groups in the natural and transition regions; in the impacted re gion Campsurus sp. was the group with the highest relative importance with regard to density and biomass.