Assement of the impact of Lafenwa Market waste on the zooplankton and phytoplankton diversity in Ogun River, Abeokuta, Ogun State, Nigeria.
This study investigated types of waste generated and patterns of waste disposal in relation to activities in Lafenwa market, Abeokuta, Ogun State, Nigeria. It also characterised the abundance of plankton species and physico-chemical properties in the adjoining Ogun River. This was with a view to determining the impact of market waste on the physico-chemical and biological quality of the receiving river. A preliminary survey of the market was carried out to determine patterns of daily activities in different sectors of the market. A structured questionnaire was administered on 5% of randomly selected individuals from each sector to collect information on the type of waste generated, and patterns of disposing such waste. Polythene bags were assigned to each selected individual to collect waste generated for six consecutive days. The bags were retrieved each morning and waste weighed using a standard weighing balance. Plankton samples were collected from eight sampling stations (two upstream, three within the market, and three downstream) once every three months for 12 months and analysed for plankton species diversity and number. Twenty litres of each water sample was strained through a fine meshed plankton net (mesh size = 45 µm) to a concentrate volume of 30 ml and preserved with 5% formalin solution. Water samples for the analysis of physico-chemical properties were collected in 2-L plastic bottles and returned to the laboratory and analysed using both instrumentation and non-instrumentation methods. Data were analysed using ANOVA and correlation coefficient. Ninety-nine of 150 selected respondents (66.0%) disposed their waste directly to dumpsite and 22.7% directly to Ogun River. The major types of waste generated were polythene, vegetables, food waste, smoke/ashes, paper/carton, waste water and chaff. Rice milling sector generated the heaviest mean waste weight of 1,527.5 kg and saloon sector the least (6.95 kg). The differences were statistically significant at p < 0.05. Seven genera and thirty-seven species of phytoplankton recorded were Bacillariophyta and Chlorophyta (14 species each), Cyanophyta (5 species), Chrysophyta, Dinophyta, Euglenophyta, and Rhodophyta (1 species each). The most abundant phytoplankton was Skeletonemacostatum (54.68 ± 19.49 org/m3), while the least was Gyrosigmafasciola (1.56 ± 1.56 org/m3). Similarly, four genera and 10 species of zooplankton were recorded namely, Rotifers (4 species), Copepoda (3 species), Insecta (2 species), and Cladocera(1 species). The most abundant zooplankton were Chaoborussp (31.25 ± 10.4 org/m3), while the least was Eudiaptomussp (4.69 ± 2.62 org/m3). Phytoplankton species abundance decreased from upstream to downstream while zooplankton followed an inverse direction. The peak abundance of biological indicators of pollution (Oscillatoriasp 87.5 ± 37.5 org/m3, Nitzchiasp 62.5 ± 36.29 org/m3, Brachionusdimiadiatus 41.67 ± 14.86 org/m3 and Euglena sp 6.25 ± 6.25 or/m3) was recorded at the market area while the least upstream (29.17 ± 37.5 org/m3, 33.33 ± 17.77 org/m3, 0 ± 0 org/m3, 4.17 ± 4.17 org/m3) respectively. Mean biochemical oxygen demand ranged from 2.90 ± 0.40 mg/l (upstream) to 6.80 ± 1.92 mg/l (market) while the dissolved oxygen ranged from 3.80 ± 0.41 mg/l (upstream) to 5.00 ± 0.73 mg/l (market). The correlation coefficients showed both negative and positive statistical significance between plankton species and some physico-chemical parameters. The study concluded that the peak abundance of biological indicators of pollution at the market area was a clear indication of pollution due to direct waste disposal to the river.