ABSTRACT
Osun River is important for domestic, recreational and other activities. It flows along a channel
that may be polluted by inputs from industrial, agricultural and other anthropogenic activities
thereby limiting its normal use for drinking, fishing, recreation and other purposes. Available
literature on the river quality is limited in scope, frequency of sampling and duration of studies.
Therefore, a study of the river and its tributaries was carried out to determine the spatial and
temporal variations of physicochemical characteristics of its water and sediment.
Surface water and sediments were sampled bimonthly from July 2006 to May 2008 at upstream
and downstream points of the main river course and 31 tributaries. Sampling was by compositing
at each point of 90 locations for surface water and 63 identified locations for sediment, where
possible. Water samples were analysed for alkalinity, hardness, ammonia, anions, Dissolved
Oxygen (DO), Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD), heavy
metals and turbidity. Sediment samples were analysed for organic carbon, particle size and
selected heavy metals using APHA methods. Location-based and overall data obtained were
fitted into a time series model using a number cruncher statistical system, and applied to predict
contaminant concentrations up to year 2018. The Pratti model was applied to determine
locational pollution classes (Class 1-5) based on gross organic pollutants and ammonia.
Statistical evaluation of data involved use of principal component analysis, analysis of variance
and Student’s t-test at p = 0.05.
The concentrations (mg/L) of alkalinity, hardness, ammonia, nitrate, phosphate and chloride
were 93±130, 116±120, 4.2±6.6, 1.8±1.5, 0.15±0.23 and 54±110 respectively. Those of DO,
BOD, COD, lead, copper, cadmium and zinc were 7.9±3.0, 6.9±7.5, 135±120, 0.003±0.004,
0.003±0.004, 0.002±0.003, 0.07±0.10 mg/L respectively and turbidity, 34±43 FTU. Values of
parameters for upstream locations did not differ significantly from downstream points, indicating
randomness of contaminant inputs. Turbidity, sulphate and DO were higher during the wet
seasons while phosphate, nitrate and BOD were higher in the dry seasons. Metal levels correlated
positively between water and sediment, with coefficients ranging between 0.75 for Cu and 0.99
for Co. Highest concentration factors in sediment were 233 (Pb) and 171 (Zn). Inter-element
association in sediment was high only for Pb/Cu (r =+0.72). Two locations fitted into Class 4
(grossly polluted) of the Pratti scale, while thirty-one were Class 3 (slightly polluted) which was
UNIVERSITY OF IBADAN LIBRARY
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indicative of pollution derived from mild industrial and agricultural impacts. Fifty-three locations
were acceptable (Class 2), and four excellent (Class 1). Time series modelling fitted well for
nitrate (R2= 0.79), phosphate (R2= 0.84) and BOD (R2= 0.71) data and gave their 2018 predicted
values of 19.2, 18.1 and 21.9 mg/L respectively. Comparison with WHO guidelines indicated
that 37.0% of sampling points for surface water were unfit for drinking mostly due to high
turbidities, but suitable for irrigation. Metal levels in sediment were within international limits.
Osun River and its tributaries have been adversely impacted upon by non-point pollutant inputs.
Further deterioration in the near future was predicted, and heavy metal pollution is not yet a
significant problem in the river basin.
ABIDEMI, O (2021). Spatial And Temporal Variations Of Physicochemical Characteristics Of Surfacewater And Sediment Of Osun River In Southwestern Nigeria. Afribary. Retrieved from https://afribary.com/works/spatial-and-temporal-variations-of-physicochemical-characteristics-of-surfacewater-and-sediment-of-osun-river-in-southwestern-nigeria
ABIDEMI, OLAYIWOLA "Spatial And Temporal Variations Of Physicochemical Characteristics Of Surfacewater And Sediment Of Osun River In Southwestern Nigeria" Afribary. Afribary, 22 Apr. 2021, https://afribary.com/works/spatial-and-temporal-variations-of-physicochemical-characteristics-of-surfacewater-and-sediment-of-osun-river-in-southwestern-nigeria. Accessed 23 Dec. 2024.
ABIDEMI, OLAYIWOLA . "Spatial And Temporal Variations Of Physicochemical Characteristics Of Surfacewater And Sediment Of Osun River In Southwestern Nigeria". Afribary, Afribary, 22 Apr. 2021. Web. 23 Dec. 2024. < https://afribary.com/works/spatial-and-temporal-variations-of-physicochemical-characteristics-of-surfacewater-and-sediment-of-osun-river-in-southwestern-nigeria >.
ABIDEMI, OLAYIWOLA . "Spatial And Temporal Variations Of Physicochemical Characteristics Of Surfacewater And Sediment Of Osun River In Southwestern Nigeria" Afribary (2021). Accessed December 23, 2024. https://afribary.com/works/spatial-and-temporal-variations-of-physicochemical-characteristics-of-surfacewater-and-sediment-of-osun-river-in-southwestern-nigeria