Abstract

The study of the chemical composition of rain water was conducted in Ile – Ife and environs, an agrarian, commercial, residential and semi-industrialised center of Osun state Nigeria. This was with a view to assessing the impact of land use activities on rain water composition and the temporal variation of rainwater chemistry. Physico-chemical parameters such as Turbidity, pH, TDS, Conductivity, Oxygen parameters, Alkalinity, Acidity, Hardness and Major ions (Ca²⁺, Mg²⁺, K⁺, Na⁺, NO₃^-, SO₄^-, HCO₃^-) were determined, predominant ions were identified. Turbidity, pH, Conductivity, TDS, D.O B.O.D, Alkalinity, Acidity Hardness ranged between 2.90 - 42.84 NTU, 5.65 - 7.40, 6.71 – 122.33 µScm^-1, 4.10 –73.27 mg/L, 3.60 – 10.60 mg/L, 0.13 – 7.20 mg/L, 0.33 – 22.0 mg/L, 2.00 – 15.00 mg/L, 0.04 – 1.23 CaCO₃mg/l respectively. The dominant ions detected in the study were HCO₃^-, Mg²⁺, Na⁺ and Ca²⁺. Generally, the mean concentration of ions as expressed in milli-equivalent per Litre showed order of dominance as HCO₃^- > NO₃^- > SO₄^2- for the anions and Mg²⁺ > Na⁺ > Ca²⁺ > K⁺ for cations. The study concluded that land use activities had influence on all the chemical composition of rain water in the study area but more on pH, alkalinity, acidity, bicarbonate. Except sulphate and Nitrate, all other parameters recorded high values in dry season.

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