Effects of an oil spill and discharge of domestic sewage on the insect fauna of Cururu stream, Manaus, AM, Brazil Os efeitos de um vazamento de óleo e despejo de esgoto doméstico na fauna de insetos do igarapé Cururu, em Manaus, Amazonas, Brasil

• Published in: Brazilian journal of biology 2006-02, Vol.66 (1a), p.35-44
• Main Authors: S. R. M. Couceiro, B. R. Forsberg, N. Hamada, R. L. M. Ferreira
• Format: Article
• Language: English
• Subjects: Amazonia; Amazônia; esgoto; impacto urbano; macroinvertebrados; macroinvertebrates; oil spill; sewage; urban impact; vazamento de óleo
• ISSN: 1519-6984; 1678-4375
• DOI: 10.1590/S1519-69842006000100006

Assemblages of aquatic and edaphic insects in three streams in Central Amazonia were used to evaluate the impact on one of the streams (Cururu) caused by an oil spill that occurred in August 1999. The Cururu stream had already been impacted by domestic sewage. These three streams were evaluated during four different periods of the regional hydrological cycle (falling-, low-, rising- and high-water), from September 2000 to May 2001. An Eckman dredge, an aquatic entomological net and a manual auger were used to collect insects, which were used to estimate the taxonomic richness (at the family level) and insect density in each stream. Anoxic and eutrophic conditions were determined in each stream based on the mean concentration of dissolved oxygen, total nitrogen and phosphorus. Richness and abundance of insect fauna were higher in the Cristalino stream (not impacted) than in the Bom Jardim stream (impacted by domestic sewage) and in the Cururu stream, with the exception of samples collected along the stream banks (littoral fauna). The mean dissolved oxygen was lower in the Cururu stream than in the other two, while the mean concentrations of total nitrogen and phosphorus were higher. These elements showed intermediate values in the Bom Jardim stream, while the opposite pattern was observed in the Cristalino stream, with higher concentrations of dissolved oxygen and lower concentrations of total nitrogen and phosphorus. The concentrations of these variables reflect the modifications resulting from anthropogenic eutrophication caused by the discharge of domestic sewage into Bom Jardim and Cururu and by the oil spill in Cururu, which negatively affected the richness and abundance of insects in these streams.As assembléias de insetos aquáticos e edáficos de três igarapés da Amazônia Central foram utilizadas para avaliar o impacto sofrido por um deles (igarapé Cururu), após um vazamento de óleo derivado de petróleo, ocorrido em agosto de 1999. O igarapé Cururu já era impactado pelo despejo de esgoto doméstico. A avaliação desses sistemas foi realizada em quatro diferentes períodos do ciclo hidrológico da região (vazante, seca, enchente e cheia), entre setembro de 2000 e maio de 2001. Os insetos foram coletados com draga Eckman, rede entomológica aquática e trado, e utilizados para estimar a riqueza taxonômica (nível de família) e a densidade de insetos em cada sistema. Os efeitos de anóxia e os efeitos da eutroficação foram mensurados pelas médias de concentração