SEASONAL VARIATION IN ATMOSPHERIC DEPOSITION OF NITRATE, SULPHATE, LEAD, ZINC, AND COPPER IN SOUTHWESTERN NIGERIA

Abstract

Atmospheric and soil levels of nitrate-nitrogen (NO₃-N), sulphate (SO₄), lead (Pb), zinc (Zn), and copper (Cu) in southwestern Nigeria were determined. Rainfall and dust samples were collected at 2-week intervals and after a major rainfall and dust storm events at eight locations in a transect from the coast in Badagry to Ilorin, 300 km from the coast. The parameters were evaluated on monthly, seasonal, and annual bases for 2 years. The pH of the deposited materials varied with season and distance from the coast. Higher values were obtained in the dry season and in the hinterland. Soil pH followed a similar trend. The average annual depositions of NO₃-N, SO₄, Pb, Zn, and Cu ranged from 4.05 to 6.60, 2.58–5.85, 0.60–2.76, 0.96–2.52, and 0.39–2.79 kg ha⁻¹, respectively. Correspondingly the values in soil ranged from 7.45 to 15.65, 3.15–9.50, 1.65–3.35, 1.65–2.80, and 1.75–3.70 kg ha⁻¹. The values also varied with season. Relationships between deposited Pb and Cu and soil values were significant. It was concluded that harmattan dust and/or motorized traffic do contribute significantly to the soil levels of Pb and Cu and less significantly to the levels of pH, NO₃-N, SO₄, and Zn in the soil.

ACKNOWLEDGMENTS

The authors thank the University of Agriculture, Abeokuta, for providing financial support for this project in the form of a research grant from the Research and Development Centre (RESDEC).