Seasonal changes in physico-chemical parameters and nutrient load of river sediments in Ibadan City, Nigeria

Seasonal variations in ecological parameters exert a profound effect on the distribution and population density of both animal and plant species (Odum, 1971). The productivity in terms of planktonic biomass in freshwater bodies is regulated by various physico-chemical factors viz., temperature, transparency, pH, total hardness, nitrates, phosphates etc. A field study was conducted (October 2003 and March 2004) to develop a data-base on seasonal changes of physico-chemical parameters and nutrient load of the river sediment in Ibadan metropolis. Quantitative samples of sediments were collected during dry and rainy seasons from 11 stations and analyzed for various physico-chemical parameters and nutrient load. All (except dissolved oxygen) physico-chemical parameters assessed in this study were higher than the recommended standard (EPA, 2002). The nutrient load of pore water of Ibadan river system sediments during rainy and dry seasons was found in the range of: phosphate (2.23-16.2 ppm and 0.35-2.8 ppm respectively); nitrate (0.22 to 0.9 ppm and 0.47-3.3 ppm respectively); Nitrite (0.2-0.42 ppm and 0.03-0.3 ppm respectively); Total nitrogen (0.13-0.9ppm and 0.47- 3.4 ppm respectively) and sulphate (70-99.4 ppm and 26.6-120 ppm respectively). The levels of parameters downstream were significantly elevated than the corresponding levels upstream. This result suggests that the water quality of Ibadan river system is adversely affected and impaired by the discharge of domestic, agricultural and industrial wastes, which is the usual practice in Ibadan. The data generated from this study will guide potential remediation and other management decisions.