Ori stream (one of the tributaries of River Oba, Iwo, Osun State, Nigeria) was studied from October to December 2013 with the aim of providing baseline information on its water quality, phytoplankton primary productivity and invertebrate faunal composition. Plankton samples were collected by towing plankton net over a 2 metres horizontal distance, while benthic macroinvertebrate samples were collected by kick-sampling technique. Hydrological and some physico-chemical variables were determined in-situ, and water samples collected for further physico-chemical analyses in the laboratory. A total of 17 phytoplankton species, seven species of zooplankton and eight species of benthic macroinvertebrates were recorded. The upper reach of the stream was the most polluted with the presence of biological indicators of poor water quality, while the lower reach recorded some biological indicators of good water quality. Although the upper reach recorded the highest gross primary productivity, the highest net primary productivity was recorded at the stream's lower reach. Water quality typically decreased from the upper reach of the stream towards the middle reach but later picked up at the lower reach before discharging into River Oba. The physico-chemical and biotic nature of the different reaches were a reflection of human activities in and around the stream.

(Fe, Mn, Zn, Cu, Cr and Ni) were below or equal to the limits set by WHO for drinking and domestic water while the toxic metals (Pb, Hg, As and Cd), recorded values higher than the safe limits set by WHO hence, the water sources are capable of constituting serious health hazards.

ABSTRACT:The status of arsenic in Aiba Reservoir, Iwo, Nigeria was assessed to determine its levels and distribution in water, sediment and tissues of fish. Total arsenic was estimated by atomic absorption spectrophotometry. The mean levels detected for reservoir water (1.50 ± 0.22ppb) and sediment (2.00 ± 0.17ppb) were below the World Health Organization recommended limit of 0.01mg/L (10ppb) for drinking water. Arsenic in sediments significantly followed (r = 0.588, p = 0.002, n = 24) the level of contamination of water. The distribution of arsenic in reservoir water shows significant spatial and temporal heterogeneity; while that for sediment shows temporal homogeneity. Mean As levels for fish kidney (15.72 ± 4.14ppb) and liver (12.04 ± 2.73ppb) were significantly higher than levels for fish gills (2.03 ± 0.34ppb) and muscle (1.46 ± 0.13ppb). The first and second Canonical Variate showed 49.82% and 34.75% between-species variation respectively. This report suggests that fish at the lower level of the food web have higher levels of As compared to those at a higher trophic status. The current low levels of arsenic in the abiotic component of the reservoir suggest that contamination is mainly from anthropogenic rather than from natural sources. This report suggests seasonal, municipal and agricultural sources of arsenic contamination of Aiba Reservoir. ©JASEM http://dx