Abstract:
Wetland ecosystems are noted to play a critical role in water quality improvement by retaining pollutants in river water transiting through it. This study was therefore undertaken to determine the retention efficiency of selected wetland ecosystems within Lake Victoria Basin. Samples of water, soil/sediments and selected plant materials were collected from Kigwal/Kimondi, River Nyando and River Nzoia wetland ecosystems, digested and analyzed for residual halogenated and nonhalogenated hydrocarbons using Gas Chromatography - Mass Spectrometer (GC-MS) method. Seasonal values of physical parameters such as rainfall, temperature, pH, turbidity, and flow rate were measured in situ at the inflows, midpoints and at the outflows to the wetland ecosystems using LabQuest vernier calliper instrument. All results were recorded and analyzed for measure of central tendency using SPSS statistical program. Chi square ( ) was used to reject or retain the null hypothesis. From the analysis, 15 prominent residual halogenated and non-halogenated hydrocarbons were detected and quantified by GC-MS and they included: bendiocarb, benzene hexachloride (BHC), carbaryl, cypermethrin, deltamethrin/decis, diazinon, dieldrin, DDT, DDD, DDE, malathion, propoxur, sumithion, 5-phenylrhodanine,1,3,5-trichlorobenzene, 1-(2-phenoxybenzyl)hydrazine were detected and quantified. Their levels ranged from 5 to 242 ng/mL in water samples and 6 to 423 ng/mg in sediment and plant materials. These levels are above permissible levels of residual halogenated and nonhalogenated hydrocarbons reported by U.S. EPA and WHO and thus water quality of such ecosystems is highly compromised. Calculated seasonal retention efficiencies of the selected wetland ecosystems ranged from 3% to 88% with Kimondi/Kigwal wetland ecosystem recording high retention efficiency of 88% during rain season with River Nyando and River Nzoia wetland ecosystems having low seasonal retention efficiencies. There was overall relationship between measured physical parameters, levels of detected pollutants and retention efficiencies of the wetland ecosystems. It is recommended that a study be carried out to develop environmentally friendly molecules which can be used for pest control management practices with an aim of protecting wetland ecosystems from effects of chemical pesticides and hence improve retention efficiencies of natural tropical wetland ecosystems.
