Diversity and response of Benthic Macroinvertebrates to Natural and Induced Environmental Stresses in Aiba Stream, Iwo, Southwestern Nigeria

Abstract

Aiba stream, a tropical stream in southwestern Nigeria, was investigated on monthly basis from November 2012 to April 2013 with a view to comparing their response with the Biological Monitoring Working Party (BMWP) score system already in use in some eco-regions. The diversity and response of benthic macroinvertebartes were used in assessing the biological water quality and health status of the stream. Samples were collected from four different stations using the Kick Sampling Technique. All the specimens collected were preserved in 70% alcohol solution and later identified in the laboratory using relevant identification guides. Predatory invertebrates like water scorpions (Nepa and Rana spp.) and dragonfly nymphs (Macromia sp.) were sorted out in-situ and stored separately. Nineteen taxa of macroinvertebrates were recorded comprising three Phyla, four classes and 17 families. The overall Shannon-Weiner diversity and Margalef’s indices of the stream indicated that the stream was organically polluted, as evidenced by the presence of some pollution-tolerant macroinvertebrates (e.g. Families Stratiomyidae, Nepidae, Planorbidae, Chironomidae and Syrphidae). Although there were some similarities between the BMWP score system and the response of the benthic macroinvertebrate families to environmental stress, a disparity was also observed between the two which underscores the need to carry out intensive research in this regard and adapt a BMWP score system for regional freshwaters in the tropics.