Effects of irrigation on the physico-chemical quality of water in irrigated areas: The Upper Osin Catchment, Kwara State, Nigeria

摘要

High demand for water is driving potentially unsustainable practices and competition for water resources between various sectors in developing areas. As a result of improved quality of life and population growth, increase in demand for fresh water is anticipated in all African countries in all sectors, over the next 10 years. This study examines the effects of dry season irrigation farming (fadama) on the physical and chemical quality of the River Osin which receives both surface and subsurface flow from irrigated areas in the Upper Osin Catchment, Kwara State, Nigeria. A total of 90 samples were obtained from Upstream (UPS), Irrigated area (IRG) and Downstream (DNS) segments of the river in the dry and rainy seasons. Water samples were analysed for pH, conductivity, total dissolved solids (TDS), suspended solids, dissolved organic matter (DOM), pesticides (ionic basic type), Na~+, K~+, Mg~(2+),Cl~-, NO_3~-, PO_4~(3-), Ca~(2+) and HCO_3~-. The results indicate that values of agricultural pollutants such as pesticides (CuSO_4), NO_3~- and PO_4~(3-) were significantly higher at IRG than at UPS, and decreased slightly at DNS, while all other anions and cations except DOM reached peak values at DNS. Agricultural pollutants (NO_3~-, PO_4~(3-) and pesticides) contributed significantly to poor water quality observed at IRG and DNS segments but the values are within acceptable tolerance range at UPS. The findings further indicate that irrigation practice degrades the quality of water at IRG and DNS segments. As a result, a holistic approach to agriculture and water resource management is recommended to ensure sustainable water resources development in the catchment.