Temporal pollution by nitrate (NO3), and discharge of springs in shallow crystalline aquifers: Case of Akok Ndoue catchment, Yaounde (Cameroon)

Abstract

Less than 30% of households in Yaounde have direct access to pipe-borne water. It is important to generate a time series on quality and quantity of spring water, which is an alternative source of water. Accordingly, temporal variation of NO3 and dissolved oxygen (DO), lag time of springs recharge by rainfall, discharge of springs and annual discharge of water from the Akok-Ndoue catchment was evaluated. Eleven springs, 3 wells and 1 rain gauge were investigated for 24 months. Flow rate, electrical conductivity, water temperature, DO, pH, water level in wells, rainfall amount and major ions were measured monthly. Temporally, the months of March, April, September and October are when the springs and shallow wells are polluted by NO3. Spatially, springs at lower altitudes are also susceptible to NO3 pollution. Rainfall depths from 125 to 275 and >275 mm/month recharge springs after 1 to 2 months, and less than 1 month, respectively. Moreover, when rainfall amount is <100 mm, it takes about 2 months for the discharge of the springs to decrease to less than 0.2 l/s. The springs were of category 5-7 on the Meinzer’s classification scheme. Recharge was estimated at 50 mm/year and the springs showed a wide range of variability with discharge that decreased with increase in elevation. Key words: Springs, Spatio-temporal pollution, discharge, crystalline aquifer, Yaounde, Cameroon