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The study aimed at determining spatial and temporal changes in physico-chemical water quality and planktonic composition in relation to rainfall patterns was carried out in Osinmo reservoir, an impoundment on the Ataro River, Osun State, Nigeria, over a period of six months (May-October 2011). The effect of rains and reservoir zonation on the investigated parameters varied widely. A wide range of DO, BOD 5 , organic carbon and transparency values was recorded both temporally and spatially. The rainfall pattern affected four out of the nine investigated chemical parameters (conductivity, alkalinity, carbonate and organic carbon). Water conductivity was found to be highly variable during the three phases of the annual rainy season. The lacustrine zone was characterised by the highest content of organic carbon, considerably differing from that in other zones, and the greatest abundance of plankton followed by that in the transitional zone. The variation in plankton abundance was highly significant (p < 0.05) temporally, but showed no significance (p > 0.05) spatially. The fluctuations recorded, particularly in conductivity and organic carbon concentrations, showed that the influx into the reservoir via rainfall should be monitored in order to prevent reservoir pollution.Buvo tiriamas kritulių poveikis vandens fizinių-cheminių parametrų ir planktono struktūros kaitai. Tyrimai atlikti 2011 m. gegužės-spalio mėnesiais Nigerijoje, Osuno valstijoje esančioje Osinmo vandens saugykloje, atsiradusioje užtvenkus Ataro upę. Deguonies koncentracija, biocheminis deguonies poreikis, organinės anglies kiekis vandenyje ir vandens skaidrumas skyrėsi priklausomai nuo kritulių periodiškumo ir saugyklos vietos. Kritulių periodiškumas turėjo įtakos keturiems iš 9 tirtų cheminių vandens parametrų (laidumui, šarmingumui, karbonatų ir organinės anglies kiekiui). Lietingojo periodo metu labai kito vandens laidumas. Ežerinėje (giliausioje) vandens saugyklos zonoje nustatytas didžiausias organinės anglies kiekis (ženkliai besiskiriantis nuo kitų zonų), joje buvo gausiausia planktono. Planktono gausumo pokyčiai laike buvo patikimi (p < 0,05). Vandens parametrų pokyčiai rodo, kad siekiant išvengti vandens taršos saugykloje, būtina stebėti kritulių sukeltą vandens prietaką.

Reservoir fishes contribute significantly to freshwater fish resources in Nigeria. The composition, size variation and relative abundance of fishes in Opa reservoir, Southwest Nigeria, were investigated to establish the ecological balance of the various trophic groups of fishes in the reservoir. The study was carried out in view of recent reports on the decline in the quality and quantity of water in the aging reservoir. Fishes were collected from the reservoir monthly for twelve months using monofilament gill nets and wire cages. The fishes were identified to species level and the ecological balance of the fish community was calculated as a ratio of the forage to the carnivore groups by number and by weight. Data were subjected to statistical analysis using the Stata 13 software. 1915 fishes belonging to 17 species and 10 families were collected from the reservoir. The fish composition was dominated by the family cichlidae, with its 7 species accounting for 89.8% of the total catch. There were 2 species of clariidae, which made 6.2% of the total catch. The ecological balance of the fish community was 3.4 (by number) and 6.2 (by weight). The result obtained revealed that the fish community in the reservoir is ecologically balanced. Comparative analysis of the fish composition of the Opa reservoir with reports from other reservoirs in Southwest Nigeria showed that the reservoir has more fish species than most of the other reservoirs around. The study concludes that the reservoir still supports a rich, diverse and ecologically balanced fish community. It is recommended that the management of these fish resources should be key in the holistic management of the aging Opa reservoir.

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The taxonomic composition and community structure of zooplankton faunae of selected earthen fishponds in Ife North Local Government Area of Osun State, Nigeria were investigated for a period of two years sampling every other month. The study was based on three sets of fishponds with regards to fertilization practice and water flow regime. These include non flow-through ponds that received organic and inorganic fertilizers (FNF); flow-through ponds that received organic and inorganic fertilizers (FF) and unfertilized flowthrough ponds. The zooplankton fauna of the fishponds comprised of 81 species belonging to three phyla namely Rotifera (62 species belonging to 16 families and two orders), Arthropoda (6 cladocerans, 2 copepods, 6 ostracods, 4 insecta and one arachnid species) and Protozoa which was represented by only one species. Zooplankton species richness indices were generally higher in the flow-through ponds than in the non flow through ponds with some species occurring only in the fertilized flow-through ponds. The flow-through pond had the highest number of species 54, while the least number of species 37 was recorded from the non flowthrough pond. The fertilized non-flow-through ponds also had the .highest mean abundance of 36762 ± 56162 ind/m 3 , followed by fertilized flow-through ponds (34346 ± 40784 ind/m 3 ) and non-fertilized flow-through ponds (16006 ± 41263 ind/m 3 ) descending order. The means in zooplankton abundance among the ponds were, however, not statistically significant. The fertilized ponds supported zooplankton abundance while continuous water flow as observed in the flow-through had direct influence on diversity and species richness. Hence to achieve the desired effect of pond fertilization on its primary productivity, this must be accompanied by adequate water flowage especially in shallow fish ponds.

The present study investigated the ecological status of Opa reservoir, Obafemi Awolowo University, Ile Ife, Nigeria, based on the spatial and temporal variations in abundance and distribution of zooplankton. 72 samples were collected monthly with a quantitative net zooplankton from both the surface and bottom levels in three stations established at the dam site (Lacustrine), mid-lake (Transition) and inflow (Riverine) over a period of an annual cycle. A total of fifty-four (54) species were recorded from the reservoir comprising Rotifera (57.41%) > Arthropoda (33.33%) > Protozoa (5.56%) > Ciliophora (1.85%) = Cnidaria (1.85%), in the order of abundance. The least number of species (47) was recorded at the Transition station, while the highest number of species (49) occurred at the Lacustrine zone. Of all the zooplankton recorded, four species had significant spatial variation, while nine displayed seasonal variations during the study period (p ≤ 0.05). The highest species richness was observed in Transition surface station (4.18), followed by Lacustrine surface station (3.80) and Riverine surface station (3.23). Shannon's index showed that zooplankton species were more diverse during the rainy season than dry season. The highest Trophic State Index (TSI CR ) with respect to Rotifer abundance occurred in Transition surface, followed by Riverine surface and the least occurred in Transition bottom portion. The mean TSI CR value obtained was 65.20, indicative of hyper-eutrophic, while the mean TSI CL value with respect to cyclopoida-calanoida obtained was 58.07 also revealing eutrophic status of the study area. Opa reservoir comprises mainly Rotifers and its TSI CR showed the lake as eutrophic, tending towards becoming hyper-eutrophic, which could speed up the aging of the lake.

The study determines the physico-chemical parameters of water from Odo-Ebo River with a view to providing information on the effects of discharge from carwash on the River’s water quality. Samples (48) for physico-chemical water quality were collected monthly over a period of an annual cycle (February 2015–January 2016) from four stations, namely: upstream (about 500 m before the carwash), two discharge points (1st and 2nd discharge points), and downstream (about 500 m after the carwash). The discharge points had higher mean values in 9 out of the 13 investigated water quality parameters, especially plant nutrient ions (phosphate, nitrate, and sulphate), with the discharge points significantly differing from the other stations in terms of phosphate concentration and apparent colour. This led to reduction in dissolved oxygen and zooplankton abundance, changes in apparent water colour, and increase in COD at the effluent receiving points. Furthermore, the higher mean values of dissolved oxygen, BOD5, turbidity, and true colour recorded upstream and downstream were reflections of higher biological productivity and organic detritus at these stations as compared to discharge points. The specific presence of some eutrophic species at the discharge points has only further proven the negative effects the effluent from the carwash had on the river, thus posing a potential threat to its aquatic organisms’ diversity. This eutrophication effect was observed downstream as an increase in zooplankton abundance and diversity. Therefore, environmental protection regulations are needed to reduce anthropogenic influence on the rivers in Nigeria.