Impact Of Farming Activities On The Water Quality Of The Pratu River And Its Tributaries In The Muni-Pomadzi Wetland

ABSTRACT The Muni-Pomadze wetland in the Central Region of Ghana is one of five internationally-recognised coastal wetlands (Ramsar sites) in Ghana under the Convention on Wetlands of International Importance. The wetland is known for its rich variety of biodiversity and unpolluted ecosystem and is fed by a main river called Pratu along with its tributaries (Ntakofa and Muni Rivers) that flows into the Muni lagoon. However, the need to produce enough food to feed the ever increasing population has led to the extensive use of land especially along the banks of the rivers that feed the wetland for farming activities. This disturbing issue coupled with other anthropogenic activities has led to an increasing level of pollution in the wetland resulting in water quality degradation in the river catchment. This has consequently diminished both the local and international significance of the wetland. In this light, this research sought to assess the impact of farming and other anthropogenic activities along the Pratu River and its tributaries and consequently the Muni lagoon in the wetland by determining the source, types and level of pollution existing in the river basin. Water samples from the Pratu River, Ntakofa River and the Muni lagoon were analysed for physico – chemical parameters (pH, Temperature, Electric Conductivity, Salinity, Total Dissolved Solids, Alkalinity, Dissolved Oxygen, Biological Oxygen Demand, Chemical Oxygen Demand and Total Hardness) using titrimetry, Hach Sension 5 Conductometer and Hach pH Meter; trace metals (Iron, Copper, Zinc, Lead, Cadmium, Cromium and Mercury) using the Atomic Absorption Spectrometer; ions (Na, Ca, K, Mg, Cl- , ) using the Flame Photometry, UV-Visible Spectrophotometry and titrimetry. Pesticide residues (Organochlorines, Organophosphates and Synthetic Pyrethroids) were also xi analysed using the Gas Chromatography–Electron Capture and Pulse Flame Photometric Detections. Results of the physical analysis showed high concentration of EC ( 20655.77 µS/cm, 16822.32 µS/cm and 55600 µS/cm respectively), TDS, (13761.77 mg/L, 10775.89 mg/L and 33333.33 mg/L respectively) and salinity (14.95, 11.79 and 37.33 respectively) depicting a high level of dissolved ions in the basin. High levels of total hardness were 3833.85 mg/L, 2942.222 mg/L and 6933.333 mg/L respectively and COD were 10.35 mg/L, 14.31mg/L and 13.8mg/L respectively. This may be attributed to the high levels of dissolved ions and anthropogenic activities involving farming practices, illegal gold mining operations, domestic effluents and other chemical effluents that enter the river through surface run-off. Major cationic dominance pattern for the basin was Na>Ca>K>Mg and that of the anions were Cl > . The observed pattern shows that Na and Cl concentrations are dominant in the basin. This condition may be attributed to the effect of aerosols from the sea and Na and Cl ions which may be present in the soils close to the river banks (evidenced by salt-like precipitates on the soil surface). Results of trace metals and pesticide analysis in the sediment of the river basin showed that, most of the metals and the pesticides found were all adhered to the soil sediment in low concentrations hence may not pose a threat to the river‘s quality. Sodium Adsorption Ratio (SAR) was measured in the basin. 21.02, 29.44 and 51.02 respectively for the three parts of the basin showed that the river is not suitable for irrigation (results were >13). However continual use of the river as a source of irrigation may cause stunted growth of the crops resulting in low yield. This may necessitate increased fertilizer use and consequently impact the river by eutrophication. Based on these findings, it is recommended that further water quality analysis be conducted on the river on an annual xii basis in order to ascertain the pollution progress of the river and its impact on the wetland. Secondly, SAR measurements should be conducted on the soils of the farmlands to give more detailed information on the degree of sodicity of the soil. This will help the farmers make an informed decision on best farming practices.