Water quality studies on two irrigation-associated rivers in southern Ghana

Abstract

The water quality of two rivers, Ayensu and Okyi-Amisa, associated with irrigation in southern Ghana were assessed in a bid to determine impacts downstream of the irrigated farmlands. Both have man-made reservoirs on their tributaries which flow under gravity into farmlands before entering the main river. A variety of inorganic fertilisers as well as pesticides are used to treat soil and crops on these farmlands which drain into the rivers. Physico-chemical parameters comprising temperature, transparency, pH, alkalinity, conductivity, dissolved oxygen, biochemical oxygen demand, ammonia-nitrogen, nitrite-nitrogen and nitrate-nitrogen were determined for the rivers before reaching the irrigation areas and also downstream of the irrigated farmlands. The alkalinity (CaCO3) and conductivity values obtained for the terminal irrigation drain of the Ayensu system showed marked higher values in comparison with values from the river samples. The physico-chemical parameters are discussed in relation to irrigation activities, coastal lagoons and other general impacts downstream.

JOURNAL OF THE GHANA SCIENCE ASSOCIATION Volume 1 Number 2, January (1999) pp. 100-109