Influence of environmental factors on fish and macroinvertebrate assemblages of natural wetlands in the Gilgel Gibe watershed, Southwest Ethiopia

Abstract

Natural wetlands of Gilgel Gibe watershed in the southwestern Ethiopia have various socioeconomic and ecological values such as habitat for a variety of plant and animal species, and water source for human and livestock consumption. Although these values and services are appreciated, wetlands in the catchment are subject to increasing anthropogenic disturbances. The objective of this study was to determine the effects of these anthropogenic disturbances on water and habitat quality, fish and macroinvertebrate assemblages. A cross-sectional study was carried out from March to April 2014 in three wetlands located in Gilgel Gibe watershed. A total of 23 sites were sampled. Canonical Correspondence Analysis (CCA) and multiple linear regression models were used to identify influencing variables on macroinvertebrate and fish communities. A total of 4,349 macroinvertebrate individuals belonging to 11 orders and 33 families were collected. The most abundant orders were Hemiptera 2478(57%), Coleoptera 557(13%), Diptera 438(10%), Odonata 389(9%) and Ephemeroptera 361(8%) represented by 24 families. 760 different fish specimens were collected. Oreochromis niloticus was the dominant species which accounts 77.5 % followed by Labeo forskalii (18.16 %), Garra dambeensis (3.42), Garra chebera (0.79%) and Labeobarbus intermedius (0.13 %). CCA analysis clearly indicated that environmental factors such as concentration of DO, TSS, ammonium, chloride, turbidity, water temperature, secchi depth, conductivity, water depth, sludge depth and pH influence the structure of wetland fish and macroinvertebrate communities. Furthermore, Macroinvertebrate descriptor was best predicted (R2 = 0.55) by water depth and sludge depth whereas fish descriptor was best predicted (R2 = 0.53) by sludge depth, ammonium and TSS. These variables provided clear interpretations of water quality and habitat deterioration of natural wetlands in the Gilgel Gibe watershed due to human impacts from catchment land use. Therefore, creation of awareness for proper utilization of natural wetlands and their related ecosystem services in the Gilgel Gibe watershed, where wetland resources are being lost at a high rate, and continue to be at high risk due to expansion of agricultural and other development activities. The finding of this study can complement the previous studies on wetlands and surrounding watersheds to prepare a complete monitoring tools and metrics which can give results to make informed decisions for management and restoration of wetland ecosystem.