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

Abstract

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 population of Campsurus sp. Three sampling sites has been determined in each of the three lake regions (impacted, transition and natural); periodicity of samples has been chosen throughout the four periods of the flood pulse (high water, drawdown, low water and flood) between June 1996 and March 1997. The limnological variables measured were temperature, depth, dissolved oxygen and transparency (of water column), available phosphorus, total nitrogen and organic matter (in the sediment). Variables were organized by Pincipal Components Analysis (PCA). Density results for community of benthic macroinvertebrates 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 region Campsurus sp. was the group with the highest relative importance with regard to density and biomass