ABSTRACT

This study was carried out to assess the quality of River Osse using the physico-chemistry, zooplankton and benthic macrofauna as indicators. The investigation was carried out over a period of two years from July 2000 to June 2002. Five stations made up of 1and 2 (upstream), 3(Gelegele port) and 4 and 5 (downstream) were studied. Air and surface water temperatures ranged between 26.1⁰C - 33.7⁰C and 25.2⁰C – 29.1⁰C respectively; Transparency, 38.0 - 225cm; Total suspended solids, 14.66 – 210.04mgl^-1; Total dissolved solids, 42.5 – 520.20mgl^-1; Total solids, 57.14 – 701.50mgl^-1; Turbidity, 2.3 - 58NTU; Hydrogen ion concentration (pH), 5.55 - 7.91; Dissolved oxygen, 4.40 – 11.60mgl^-1; Biochemical oxygen demand (BOD), 0.80 – 5.60 mgl^-1; Conductivity, 10.0 - 208µScm^-1; Alkalinity, 17.50 – 100.0mgCaCo₃^-1; chloride, 7.02 – 34.50mgl^-1; Sulphate, 0.02 – 0.43mgl^-1; Nitrate, 0.04 - 0.73mgl^-1; Phosphate, 0.28 - 3.52mgl^-1; Sodium, 0.18 – 19.1mgl^-1; Potassium, 0.11 - 6.2mgl^-1; Calcium, 1.11- 9.62mgl^-1 and magnesium, 0.20 -7.78 mgl^-1. Temporally, there was a clear pattern of seasonal variation in air and surface water temperatures, transparency, turbidity, total suspended solids, total dissolved solids, total solids, conductivity, chloride, alkalinity, nitrate, phosphate and potassium, while pH, dissolved oxygen, biochemical oxygen demand, sulphate, sodium, calcium and magnesium showed no distinct seasonality. Analysis of variance (ANOVA) revealed that there was a significant difference (P<0.05) between the means of air temperature, transparency, turbidity, total suspended solids, total dissolved solids, total solids, biochemical oxygen demand and nitrate in the study stations. A posteriori Duncan Multiple Range test revealed that air temperature of station 3 was significantly higher (P<0.05) than that of other stations; total dissolved solids, total suspended solids, total solids, and turbidity were significantly higher (P<0.05) at stations 4 and 5 than the others; transparency was significantly higher (P<0.05) at stations 1, 2 and 3 than stations 4 and 5; biochemical oxygen demand and nitrate were significantly higher at stations 4 and 1 respectively than those of other stations. Heavy metal concentrations in the river were low; Iron, 0.08 – 0.38mgl^-1; Lead 0.05 - 0.36mgl^-1; Chromium 0.01- 0.19mgl^-1; Copper 0.01- 0.28mgl^-1; Manganese 0.01 – 0.10mgl^-1; Zinc 0.23 – 2.98mgl^-1 and Cadmium 0.01 – 0.23mgl^-1. There was no seasonal variation in the values of heavy metals recorded. With the exception of zinc which was significantly higher (P<0.05) at stations 1 and 2 than those of other stations, all the other heavy metals were not significantly different (P>0.05) among the study stations. This was attributed to the high human activities in this station. The river was relatively homogenous across the study stations and all the parameters were within the WHO and FEPA standards for domestic usage.

A total of eighty-nine (89) invertebrate species and one (1) identified vertebrate species were encountered in this study. The species composition showed that thirty-one (31) zooplankton species were recorded at stations 1, 2 and 5, while twenty-nine (29) species and thirty-two (32) species were recorded at stations 3 and 4 respectively. Among the macrobenthic invertebrates, fifty-four (54) species were recorded at station 1, station 2 (52), station 3 (45), station 4 (48) and station 5 (46). Analysis of fauna abundance showed that of the 15,925 individuals recorded, zooplankton accounted for 9,355 individuals, while benthic macrofauna were 6,570. In station 1, zooplankton density was 2,964; station 2 (2,100); station 3 (1,032); station 4 (1,202) and station 5 (3,134), while the benthic macrofauna density in station 1 was 2,045; station 2 (1,526); station 3 (868); station 4 (963) and station 5 (1,320).

Analysis of variance (ANOVA) revealed that the overall density was significantly different (P<0.05) in the study stations. The overall density at stations 4 and 5 was low, and this was attributed to the activities of the industries located in these stations. The taxa richness for zooplankton was highest in station 4 and lowest in station 1. General diversity was highest in station 1 and least in station 3, while evenness was more in station 2 and lowest in station 5. Taxa richness for benthic macrofauna was highest in station 2 and lowest in station 5. General diversity was highest at station 1 and lowest at station 5, while evenness at stations 3 and 4 were higher than other stations. This study showed that the upstream stations were not perturbed, but stations 3 and 4 were highly perturbed due to the impact of the industries located here. Also, the degree of pollution in the river from organic source was minimal, while a high degree of self purification was observed.