HYDROLOGICAL AND ECOLOGICAL FUNCTIONS OF WALLO WETLAND AND IMPLICATIONS TO THE DOWN STREAM LAKE CHAMO, ARBA MINCH, ETHIOPIA

Abstract

Wetlands are one of the most productive and essential areas with diverse environmental and economic benefits. They are also found as threatened habitats in different parts of the world. The present study was aimed to assess the regulatory, filtration and screening role of wetlands and valorize for better conservation. A total of six sampling sites were selected from Lake Abaya periphery immediately before joining the Wallo wetland and at the outlet of the wetland before joining river Kulfo. The water samples were taken at different strata and mixed to make them representative. Sampling was made from January to August, 2016; where overflow was observed significantly. The samples were analyzed for 14 (fourteen) selected physicochemical parameters. Standard methods for sampling, storage and analysis were done according to APHA. The study has revealed the existence of significant changes in terms of parameters like Dissolved Oxygen, Ionic Concentration, Heavy Metal removal, nutrient load and other physical parameters. The amount of dissolved oxygen has shown improvement by 13.6% from 5.88 to 7.99ppm after passing through the wetland. Removal efficiency of the wetland between inflow and outflow were higher for ionic concentrations like Electrical Conductivity, Salinity and TDS with 63.1, 40.7 and 54.4 removal percentage respectively. The heavy metals Mn, Cr, Cu, and Fe analysis showed a decrease in concentration from their inlet by average values of 43.1, 37.2 and 22.1and 12.5 percentages respectively. The water samples analyzed for nutrients (T-N and T-P) has also shown a decreasing tendency by 40.2 and 33.6% respectively when Lake Abaya water passes through the wetland and discharged to river Kulfo. The average water surface temperature recorded onsite has decreased from 29.2 o C at Lake Abaya to 25.95 o C at the outlet of the wetland. The physical parameters like TSS and Turbidity were found to be high at Lake Abaya and significantly decreased at the wetland outlet with 52.9 and 83.3% removals respectively and a slight decrease in pH. From the result it can be concluded that the wetland has shown remarkable efficiency in terms of screening the incoming suspended and dissolved materials; filtering nutrients and heavy metals; and regulating the temperature and pH of the water after passing through it. It can be said that overflowed Lake Abaya water which has different water chemistry from Lake Chamo has been regulated by the wetland beneath it before joining river Kulfo. It is recommended that the role of such wetlands which have paramount importance for their hydrological and ecological functions should not be overlooked. Hence, conservation efforts to such wetland ecosystems need to be strengthened.