Bathymetry and Siltation of Oyan Dam, Ogun State, Nigeria

Dams are reservoirs established for different reasons. Oyan dam, Ogun State, Nigeria was established and commissioned on the 29th March 1983 to supply water to Lagos State and Abeokuta for municipal uses, with power generation potentials to support Lower Ogun Irrigation Project. However, flooding has become an annual experience of downstream communities along Ogun river especially when the Oyan dam is opened; it has really becomes remarkable since the flood events of 2012. This project investigates the level of siltation and floods menace adjoining Oyan dam and its environ. An integrated methodology of bathymetric survey, total station traversing and satellite imagery were used to acquire geospatial locations of the dam features and other details within the dam through the process of traversing, heightening and detailing. The field investigation was conducted between January 2018 and January 2020 to determine dam bed topography with the deployment of integrated approach. The collected data were processed using Hydrologic Engineering Center’s River Analysis System (HEC-RAS), HYPACK software and ArcGIS 10.6 software. The maximum and minimum depth within the dam are -4.072m and -21.588m respectively. The cross sections are represented for each 200m length of the dam. Furthermore, volumetric analysis of sediment budget was computed to be 251.7x106m3 and compared with designed reservoir capacity of 270x106m3. From the study, a loss of about 18.2x106m3 approximately 6.7% was recorded. Satellite imagery shows the rate of change within Oyan dam and its catchment area downstream based on Triangulated Irregular Network (TIN) generated from Shuttle Radar Topography Mission (SRTM) the maximum and minimum elevation in the catchment are 29m and 182m respectively. The study recommends that deepen and training of Ogun river and all adjoining drainages system within the study corridor to retain more water when peak rainfall is recorded.

Heavy Metals Level in Clarias gariepinus (Catfish), Oreochromis niloticus (Tilapia) and Chrysichthys nigroditatus (Bagrid catfish) collected from Ogun River, Ogun State, Nigeria

Aquatic organisms such as fish are prone to contamination by water pollutants such as heavy metals. This study aims at assessing the levels of heavy metals in the fillet tissues of 75 fish samples comprising Clarias gariepinus (Catfish), Oreochromis niloticus (Tilapia) and Chrysichthys nigroditatus (Bagrid catfish) from five (5) different fishing locations along the Ogun River, Ogun State. The fillet tissues of the fish samples were digested and analysed for Zn, Pb, Fe, Cr and Cd using a Perkin Elmer, AAnalyst – 200 Atomic Absorption Spectrometer. The concentration of Zn in Clarias gariepinus, Oreochromis niloticus and Chrysichthys nigroditatus were 5.37±2.558, 6.58±2.35 and 5.11±1.55 respectively; while the levels of Pb in the species were Clarias gariepinus (1.30±3.099), Oreochromis niloticus (1.01±0.95) and Chrysichthys nigroditatus (0.35±0.59). Concentrations of Fe, Cr and Cd in the species were Clarias gariepinus (8.87±3.547, 0.08±0.098 and 0.09±0.100), Oreochromis niloticus (8.96±2.21, 0.12±0.11 and 0.11±0.11) and Chrysichthys nigroditatus (8.16±3.88, 0.11±0.11 and 0.11±0.11). The data revealed that most of these values were lower than FAO/WHO permissible except Pb and Cr. Some of the fish sampled may pose health hazards to the consumers. There is a need for constant monitoring of pollutants in Ogun River. Keywords: Heavy metals, Clarias gariepinus, Oreochromis niloticus, Chrysichthys nigroditatus, Ogun River

Characterization of tropical freshwater; River Ogun, Lagos Nigeria

Physico-chemical parameters and microbial contents of Ogun River at Magodo area, Lagos were investigated in relation to its safety for consumption. Water samples were weekly collected between August and December, 2016 at three equi-distance intervals for analysis on physico-chemical parameters, total bacterial count and biochemical tests following standard recommended procedures. Mean concentrations of the physico-chemical parameters were found in ranges for pH (6.68 ± 0.15 - 6.86 ± 0.21), temperature (26.78 ± 0.14 – 26.92 ± 0.31), electrical conductivity (355.40 ± 101.93 – 456.40 ± 115.77), total dissolved solids (166.80 ± 48.08 - 215.00 ± 54.29), dissolved oxygen (7.06 ± 0.01 - 7.08 ± 0.02), biochemical oxygen demand (25.59 ± 0.03 - 25.64 ± 0.01), chemical oxygen demand (98.75 ± 0.03 - 98.84 ± 0.02), total hardness (345.80 ± 1.28 - 349.40 ± 3.87), total alkalinity (9.28 ± 0.02 - 9.33 ± 0.02), nitrate (0.27 ± 0.00 - 0.28 ± 0.00), sulphate (0.55 ± 0.05 - 0.62 ± 0.00) and chloride (68.84 ± 0.77 - 74.97 ± 1.23). Total colony forming unit (Cfu) of bacteria in the river was found highest in descending order Centrimide Agar (CA) > Mac-Conkey Agar (MCA) > Plate Count Agar (PCA) > Mannitol Salt Agar (MSA) at the first and second serial dilution respectively. Biochemical tests showed the presence of Staphylococcus species, Escherichia coli, Pseudomonas aeruginosa, Proteus sp., Salmonella sp. and Baccillus sp. in the river. Variations in the microbial load and physico-chemical parameters in Ogun River as a result of different human activities around the river was found within the standard limits which makes the River safe for human consumption. Key words: River Ogun, microbial load, bacterial count, biochemical tests Trop.

Water Level and the Potentials for Wetland Formation and Sustainability in Lower Ogun River Floodplain, Nigeria

Identification, delineation and monitoring of wetlands which requires the understanding and application of their ecological characteristics are critical factors in wetland management and conservation. This study assessed the potentials of wetland formation and sustainability in the lower Ogun river basin by determining the levels of surface and ground water. The study area was divided into 1 km2 grids of 67 units using 0.052 % sampling intensity for the assessments in dry and wet seasons. Monthly water table levels were assessed in 50 cm soil pit while inundation levels were measured during the flooding event using staff gauge. Assessment was carried out for one year during which frequency and periodicity of water table and inundation events were recorded. Results revealed that low water table level ranged from 5 to 45cm of soil depth and occurred between August and September within 6 grids. Water table and surface water was recorded within a period of 2 – 10 weeks during the rainy season. The peak of water levels coincided with the peak of precipitation (> 200 mm) ranging from 30 to 280 cm between September and October while covering 28.75 km2. Conclusively, surface and groundwater levels were recorded during the rainy season having direct variation with the volume of precipitation for a duration that is long enough to support the formation of wetland hydrophytes and hydric soil. Keywords: Wetlands; Hydrology; Ground water; Surface water; Inundation; Precipitation

Histological, microbiological, physicochemical and heavy metals evaluation of effluent from Kara Cow Market, Ogun State, Nigeria in guppy fish (Poecilia reticulata)

The Ogun River is a sink for untreated effluents discharged from the Kara Cow Market, Ogun State. In this study, microbiological, physicochemical and heavy metals evaluation were carried out on effluent from the market. Standard methods were utilised for the examination of physicochemical and microbiological parameters of the effluent. The histological effects of sublethal concentrations of the effluent were assessed in the gills, intestine and skin of Poecilia reticulata (guppy fish) over a period of 56 days following standard methods and international ethical guidelines. None of the physicochemical parameters were within the set limits by the National Environmental Standards and Enforcement Agency (NESREA) for effluent discharges into surface waters. Coliforms, pathogens and fungi were observed in the effluent with a total plate count of 2.14 x 107 cfu/mL. The median lethal concentration (96 h LC50) of the effluent to P. reticulata was 71.50 mL/L (7.15%). Histological alterations such as distorted mucosal architecture with shortening and widening of intestinal villi were observed in the intestine of exposed groups of P. reticulata at day 56. The observed adverse physicochemical parameters, histological alterations and pathogenic microbes may pose ecological and public health risks to aquatic organisms and humans respectively. It is recommended that an effluent treatment plant should be installed at the market to reduce the pollutants load of the effluent before discharge into the Ogun River. Keywords: Effluents; histological effects; Kara Market; Ogun River; physicochemical parameters; pathogenic microorganisms; Poecilia reticulate