Aquatic macrophytes in Ethiopian Rift Valley Lake Koka: Biological management option to reduce sediment loading

Abstract

Nowadays, due to deforestation, poor soil management and improper farming techniques, reservoir and lake sedimentation is a serious problem in Ethiopia. Despite the severity of the problem, there is no documented study on the use of macrophytes as a biological management option for sediment loading. A sediment trap field experiment was conducted from July to September 2017 to assess the efficiency of macrophytes in reducing sedimentation problem in Lake Koka. During the study period (90 days) on average a total of 1140 g DW m−2 sediment was deposited at the vegetated stations and 336 g DW m−2 at the open water site. The corresponding values for resuspension were 906 g DW m−2 and 1680 g DW m−2, respectively. Compared with the non-vegetated area, all macrophytes significantly facilitated sedimentation and reduced resuspension (P < 0.05). The order of the macrophytes in their sediment trapping efficiency was Echinochloa stagnina>Typha angustifolia > Eichhornia crassipes = Leptochloa caerulescens and the corresponding order for restraining resuspension was T. angustifolia > E. stagnina >E. crassipes = L. caerulescens. Generally, E. stagnina and T. angustifolia were better in trapping sediment and preventing resuspension. Development and maintenance of wetlands with these aquatic macrophytes may be an effective management tool for reducing the sediment load on Lake Koka, but would need further studies on the effect of wind velocity and direction on their efficiency.