Water Quality Assessment of Densu, Birim and Ayensu Rivers in the Okyeman Area

Abstract

The water quality assessment conducted in the Densu, Birim and Ayensu Basins of Ghana in the Okyeman area between August 2005 and June 2006 identified human and agricultural activities as the main sources of pollution. All the pH values for the rivers ranged from 6.5–8.5. The average turbidity levels in Densu Basin were higher than that of Ayensu and Birim basins. The low turbidity of Ayensu Basin is an indication of higher primary productivity. The conductivity levels in the river basins followed the order: Densu > Ayensu > Birim. The order is depended on the human activities in each basin. Ammonia-Nitrogen (NH -N) followed this order in terms of 3 mean levels in the river basins: Densu (0.356 mg/l) > Birim (0.267 mg/l) > Ayensu (0.161 mg/l). The 2005 NH -N 3 levels were lower than that of the 2006. This was a reflection of the impact of increased human and agricultural activities in the year 2006. Nitrate-Nitrogen (NO -N). The basin had a mean NO -N concentration of 1.89 mg/l  3 3 for Densu, 2.55 mg/l for Birim and 2.63 mg/l for Ayensu with ranges of 0.01–3.96 mg/l, 0.21–6.48 mg/l and 0.001–8.17 mg/l, respectively. All the mean nutrient values for Densu, Birim and Ayensu were not significantly different at 95% from each other (NH₄ -N, p < 0.089; NO₃-N, p < 0.385; NO₂-N p < 0.203; PO₄-P p < 0.188.) Total hardness and TDS also showed a similar pattern of Densu > Ayensu > Birim. This was as a result of more domestic activities impacting on Densu Basin compared with all other basins. The classification of the water quality index (WQI) system showed in 2005 that all the three basins were in class II, which was fairly good quality. The Ayensu basin was of best quality. The 2006 results indicated that all the stations fell under class III. This showed a deterioration of the state of the rivers in 2006. The WQI also confirmed the fact that Densu Basin was the most polluted compared to that of Birim and Ayensu.