LIMNOLOGICAL CHARACTERISTICS OF KURUDU AND KARSHI RESERVOIRS, IN FEDERAL CAPITAL TERRITORYABUJA, NIGERIA

Abstract

Limnological characteristics of Kurudu and Karshi reservoirs in Federal Capital Territory, Abuja, Nigeria was conducted from January 2018 to December 2019. The aim of this study was to assess physicochemical parameters, phytoplankton and zooplankton communities of the reservoirs. Water Samples were collected from three sampling stations and analyzed using standard methods, procedures and instruments. The results of physico-chemical parameters in Kurudu reservoir had a mean value of ; temperature (25.1±1.8ºC), pH (6.9±0.3), transparency (0.9±0.2m), turbidity (26.0±13.4), Electrical Conductivity (EC) (166.0±17.2µS/cm), Dissolved Oxygen (DO) (6.0±0.2mg/l), Biochemical Oxygen Demand (BOD) (3.2±0.3 mg/l), Nitrate-Nitrogen (NO3-,) (6.1±0.4mg/l), Phosphate (PO4-) (0.2±0.0 mg/l), Iron (Fe2+) (0.1±0.0 mg/l) and Lead (Pb2+) (0.0bdl). In Karshi reservoir, the mean values were; temperature (26.0±1.9ºC), pH (7.1±0.3), transparency (1.2±0.4m), turbidity (40.1±15.5NTU), EC (105.4±31.9µS/cm), DO (6.2±0.4mg/l), BOD (5.7±0.6mg/l), NO3- (6.7±0.9mg/l), PO4- (0.1±0.0 mg/l), Fe2+(0.1±0.0mg/l) and Pb2+(0.0bdl). Mean values of physicochemical parameters were within the recommended WHO limits except for turbidity and nitrate that were above WHO limits in Kurudu and Karshi reservoirs. Phosphate was also above WHO limit in Kurudu reservoir. Phytoplankton assemblage in in Kurudu and Karshi reservoirs comprised of six phytoplankton phyla belonging to 7 classes, 23 families and 42 species. In Kurudu reservoir, Zygnemataphyceae class was the most abundant (2737 Org/l) while Chrysophyceae was the least abundant (171 Org/l) whereas Chlorophyceae (1791 Org/l) was the most abundant and Chrysophyceae was the least abundant (24 Org/l) in Karshi reservoir. Four Zooplankton groups comprising of 19 species were identified during the study; Rotifera was the most abundant ((2149 Org/l) while Copepoda (1170 Org/l) was the least abundant in Kurudu reservoir while in Karshi reservoir Rotifera was the most abundant (1100 Org/l) and Ostracods (428 Org/l) was the least abundant. Calculated diversity indices indicated a diverse and hetereogenous assemblage of plankton. Analysis of Variance (ANOVA) indicated that physico-chemical parameters in both reservoirs were strongly influenced by seasonal variation while Phytoplankton and Zooplankton abundance in both reservoirs was strongly influenced by stations and monthly variation as shown in the p-value of ANOVA. Pearson correlation analysis showed a significant relationship between plankton and water quality parameter. This study has shown that the reservoirs fall within “good/average” water quality, with class II level of pollution which is indicative of moderate pollution especially during the rainy season. Transparency, turbidity, EC, BOD, Iron concentration, DO and BOD are the major abiotic factors influencing the reservoirs. Comparative study of reservoir revealed that limnological data varied differently to reflect reservoir morphology, size, inflows, varying anthropogenic activities, seasons etc. Effective monitoring of reservoir and regulation of activities in and around the reservoir are recommended if Sustainable Development Goals (SDG)are to be achieved and for sustainable use of the reservoir.