Post-Impact Faunal Ecological Evaluation Of Ogbei Stream, Nkpologwu, Aguata Local Government Area, Anambra State, Nigeria

Abstract

The impact of concrete structure on the distribution and abundance of fauna and environmental variables were investigated in Ogbei Stream, Nkpologwu, Anambra State, Nigeria between May 2008 and April 2009. Zooplankton, macro-invertebrates and fish samples were collected fortnightly for a period of twelve months from six stations. The physico-chemical conditions were determined using standard methods. Zooplankton communities were sampled using a plankton net with mesh size 80 µm, collecting bottle, 300 ml plastic bottles and a seven (7) liter bucket. The macro-invertebrates were sampled using a scoop net, kick sampling technique, surber bottom stream sampler and a serrated core sampler (SCS). Fish sampling was done with nets. Water temperature in station 1 differed significantly (P < 0.05) from all other stations. Transparency was significantly different (P < 0.05) among the stations. T-test of seasonal variations of physical-chemical variables showed that all factors with the exception of conductivity, hardness, nitrate-nitrogen, phosphate-phosphorus and sodium were significantly different (P < 0.05). Pre- and post-impact data compared showed that hardness and transparency were significantly different (P < 0.05) in all the stations except Stations 1 and 3 respectively. Alkalinity and phosphate-phosphorus were significantly different (P < 0.05) in all the stations. Twenty eight (28) species of zooplankton distributed into seventeen 17 families and (7) orders were encountered in the stations. Brachionus patulus of the order Ploima was the most abundant taxon. The low zooplankton fauna experienced in Station 1 showed a strong evidence of impact arising from the concrete structure and human activities at that station. Physico-chemical parameters explained 89.4% of variation using principal component analysis (PCA). In the macro-invertebrate communities, five (5) classes were documented. Insecta was the dominant class. Of the forty-three (43) taxa identified, dipterans were dominant. The dominant taxon was Chironomous transvalensis (17.38%). Macro-invertebrates abundance was highest in Station 2 and lowest in Station 1. They occurred more in the dry season than in the rainy season. Diversity of macro-invertebrates was low in Station 1. Principal component analysis (PCA) of macro-invertebrates explained 86.5% variation in the data set. Macro-invertebrate abundance was low in post-impact study compared to pre-impact study due to perturbational stress arising from construction of concrete structure in Ogbei Stream. Fish were represented by six hundred and ninety-four (694) individuals belonging to fifteen (15) taxa and ten (10) families of six (6) orders with Cichlidae family (33.57%) being dominant quantitatively. Overall composition was dominated by Sarotherodon galilaeus (30.98%). Seasonally, Sarotherodon galilaeus (1.32 ± 0.128) was highest in the dry season. Principal component analysis explained 88.1% of the Pisces order and physico-chemical parameters. Conclusively, concrete structure did not only impact water quality adversely but also altered the distribution and abundance of zooplankton, macro-invertebrates and fish species in Ogbei Stream.