DIVERSITY OF MACROINVERTEBRATES AND WATER QUALITY ALONG THE WALLO WETLAND GRADIENT, LAKE ABAYA, ETHIOPIA.

Abstract

Wetland is one of the most valuable and productive water body on earth, hosting the highest diversity of organisms that deliver fundamental ecosystem services. It is an act like the natural kidneys for the lakes, cleaning the water that flows into them. Wallo wetland is one of the most important natural wetland located at the out flow of Lake Abaya that flow into Kulfo River, where Kulfo River itself drains to Lake Chamo. However, the macroinvertebrates diversity and abundance of this essential wetland is not yet studied, moreover, the study on the function of Wallo wetland (removal efficiency) is limited. The aim of the present study was to investigate the diversity of macroinvertebrates and water quality along the Wallo wetland gradient from inflow to outflow. Physicochemical and macroinvertebrate samples were collected during end of wet season (Nov-Dec 2018) from 27 different locations along three different transects from the inflow to the outflow. Univariate analyses were performed in XLSTAT version 2015 software. The results show that the mean Total Suspended Solids (TSS), Total Phosphate (PO4), Nitrate (NO3-N), Ammonia (NH3-N) and Sulphate (SO4) were significantly different among the Inflow, Center and Outflow (p < 0.05). The NO3-N and SO4 at the inflow were significantly different from Center and Outflow (p < 0.05), whereas Center and Outflow did not show a significant difference (p > 0.05). The average removal efficiencies of TSS, NH4, TPO4 and NO3 were 61%, 91%, 72% and 81%, respectively. Dissolved oxygen (DO) at the Inflow, Center, and Outflow of Wallo wetland was recorded 7.62, 1.94 and 1.68 mg/L, such a sharp decline in DO was attributed to extensive water hyacinth and Azolla invasion at Center and Outflow. The Family Biotic Index showed that generally Wallo wetland was classified as polluted wetland (the Inflow sites fall into the poor, whereas the Center and Outflow sites were categorized as very poor). The poor macroinvertebrate diversity, declined water quality, and the profound water hyacinth and Azolla invasions are important anthropogenic disturbances that severely affect the ecological integrity of Wallo wetland, and also undermine the delivery of vital ecosystem services to Lakes Abaya and Chamo. Our results stress the urgent need for measures that prevent further deterioration of Wallo wetland. Mechanical removal of the invasive species (water hyacinth and Azollaand replanting of the indigenous wetland plants in the entire Wallo wetland should be a priority.