ABSTRACT
This study was carried out from February to November 2001 to investigate the physico-chemical characteristics and crustacean zooplankton of the Utor River in Emu, Edo State. Four stations were studied from upstream to downstream with a distance of about 400 metres between stations. A total of twenty-eight physico–chemical characteristics were studied. Air and water surface temperatures ranged from 26.0OC to 33.0OC and 25.0OC to 27.5 OC respectively and showed seasonal variations. Transparency (0.11m – 0.90m) and suspended solids (2.59mg-1 – 74.27mg-1) showed inverse relationship. Depth ranged from 56cm to 208cm, while turbidity ranged from 1.16NTU to 54.50NTU. Dissolved solids ranged between 5.50mg-1 and 78.40mg-1, suspended solids ranged from 2.59mg-1 to 74.27mg-1 and total solids ranged between 8.59mg-1 and 112.30mg-1. Hydrogen ion concentration (pH) values ranged from 4.22 to 7.02; there was no clear observation of spatial and temporal variations. Alkalinity range was from 15.00mg-1 to 75.00mg –1. Dissolved oxygen value ranged from 3.80mg-1 to 10.00mg –1, while the biochemical oxygen demand (1.2mg-1 and 4.8mg-1) indicated no form of pollution or stress on the water body. Conductivity and chloride values ranged from 9.0 to 110.0 and 10.53mg-1 to 52.65mg-1 respectively. Calcium and magnesium had a ranges of 0.00mg-1 to 0.51mg-1 and 0.24mg-1 to 11.67mg-1 respectively while sodium and potassium had values ranging from 1.88mg-1 to 27.05mg-1 and 0.91mg-1 to 18.50mg-1 respectively. The nutrient status of the water body was measured as the soluble portions of phosphates and nitrates. Phosphate and nitrate values ranged from 0.26mg-1 to 1.90mg-1 and 0.03mg-1 to 1.04mg-1 respectively, while sulphate and total alkalinity values also ranged from 0.03mg-1 to 0.70mg-1 and 15.0mg-1 to 75.0mg-1 respectively during the period of sampling. Iron ranged from 0.08mg-1 to 058mg-1; lead ranged from 0.03mg-1 to 0.83mg-1, chromium ranged from 0.01mg-1 to 0.40 mg-1; copper ranged from 0.03mg-1 to 0.66mg-1; cadmium ranged from 0.00mg-1 to 0.51mg-1 and zinc ranged from 0.32mg-1 to 1.63mg-1. There was a clear pattern of seasonal variation in air and water temperature, transparency, turbidity, total suspended solids, total dissolved solids, total solids, conductivity, chloride, alkalinity, nitrate, phosphate, sulphate, potassium, sodium, calcium, magnesium, iron, cupper and cadmium while pH, dissolved oxygen, biochemical oxygen demand, lead, chromium and zinc showed no seasonality. Analyses of variance (ANOVA) revealed that there was significant difference (P<0.05) between the means of transparency and depth in the study stations. A posteriori Duncan Multiple test revealed that the transparency of station 1 was significantly higher than that of the other stations; the value of depth in stations 4 and 1 had no significant difference, while that of stations 2 and 3 were significantly different. The water of River Utor is relatively low in its assemblage of crustacean zooplankton. A total of 11 crustacean zooplankton species belonging to 9 genera in 5 families and 3 orders were encountered during the study period. The family Cyclopoidae was the dominant group in the order Cyclopoida while the family Chydoridae was the only family recorded in the order Cladocera. All the eleven taxa were recorded in all stations. Station 1 was most abundant and recorded the highest number of individuals (113); this was followed by 95 individuals in station 2, 92 individuals in station 4 and 80 individuals in station 3. In all stations, the Copepoda were more abundant than the Cladocera and Harpacticoida. The order Copepoda were made up of six taxa, Cladocera were made up of four taxa, while the order Harpacticoida consisted of only one taxon. The species composition showed that 23 cladocerans were recorded in station1; station 2 recorded 29, station 3 recorded 25 and station 4 recorded 26 cladocerans. Also the species composition showed that 90 copepods were recorded in station1, 66 were recorded in station 2, 55 were recorded in station 3 and 66 copepods were recorded in station 4. Analyses of variance (ANOVA) revealed that the overall density of copepods was not significantly different (P<0.05) between the study stations. All the species recorded were almost evenly distributed in all the stations. The study also showed that there was no evidence of water pollution recorded in any of the stations. The river was relatively homogenous across the different stations and all the parameters were within the WHO, FEPA and NAFDAC recommended standards for domestic use.
