Relevance of macroinvertebrate communities as a water quality monitoring tool in ecosystems under harsh environmental conditions in the Rift Valley region.

Abstract

Ecological assessment was performed in different thermal springs located in the Ethiopian Rift Valley area: Gergedi, Sodere, Halaba, and Gara. We assessed the habitat conditions, physicochemical characteristics, and macroinvertebrate composition at 12 sampling sites in four thermal spring systems. The physicochemical properties of the water samples varied among the sampling stations. Temperature ranged from 38.5 to 90°C among the 12 sites. Dissolved oxygen, which is essential to aquatic ecosystem normal functioning, was not detected at three sampling sites. An average of 109 macroinvertebrates were identified in three sampling campaigns. Relatively higher macroinvertebrate abundance 94 (86.2%) was registered in Gergedi than any other thermal spring sites. The macroinvertebrate abundance was 9 (8.3%) and 6 (5.5%) for the Gara and Sodere thermal springs. No macroinvertebrate communities were observed in all sites of Halaba thermal spring. From all macroinvertebrate groups, 82 (75.2%) were dipterans, 20 (18.4%) Oligochaeta, 5 (4.6%) Gastropoda, and the rest Hemipterans and Coleopterans, which comprises 2 (1.8%) individuals. Chironomidae was the dominant invertebrate taxa at all sites, and when the water temperature exceeds 42°C, it becomes the only taxon in the thermal springs. Macroinvertebrates were absent in thermal springs where the water temperature is 52°C or higher. Other diversity measures were not sensitive enough to discriminate sampling sites regardless of physicochemical variabilities except the richness and abundance. Water temperature, chloride, pH, and phosphate were identified as major determinants of macroinvertebrate richness in the Ethiopian Rift Valley region.