ASSESSMENT OF THE ECOLOGICAL CONDITION OF LAKE AREKIT USING BENTHIC MACROINVERTEBRATES AS A BIOLOGICAL WATER QUALITY INDICATOR GURAGE ZONE ETHIOPIA

Abstract

The ultimate objective of this study was to determine the ecological condition of Lake Arekit using benthic macroinvertebrate communities and some selected physicochemical parameters. Both environmental and macroinvertebrate data were collected from three sampling sites between April and May 2023. Sampling sites were selected based on the degree of anthropogenic disturbance as high impaired (shore area/SS-site 1); moderately impaired (open area/OS-site-2); and less impaired (macrophyte area/vegetation area/MS- site-3). Water temperature, DO, pH, and conductivity, were measured using a portable mulitimeter probe. Turbidity and TDS were measured using measuring turbidometer. Inorganic nutrients were measured using APHA 1995 standardized method. Benthic macroinvertebrates were collected from the littoral region (sampling depth: 0-0.5 m) using standardized kick sampling with a hand D-frame net (28 cm x 30 cm in diameter) with a horizontal transect up to 10 meter from the shore towards the lake when the lake depth less than 0.5 m and diagonal transect when the lake depth greater than 0.5 m to maintain the consistency of sampling effort, a sample was obtained within 10 minutes at each site with three replicas. The results showed that the lake temperature and DO were ranged from 20.20C (at OS) to 20.80C (at SS) and 2.59 mg/L (at OS) to 5.68 mg/L (at SS), respectively. The lake was alkaline with a pH ranged from 7.07 to 8.82. The maximum and the minimum pH of the study lake were recorded at SS. The water turbidity of the lake was varied from minimum values of 3.95 NTU (at MS) to a maximum value of 43.23 NTU (SS). Major inorganic nutrients of the Lake Arekit did not showed a significant spatial effect (p>0.05). Nitrate and total phosphate (TP), correspondingly, were ranged between 2.71 mg/L and 108.18mg/L and 12.8 and 151.8 mg/L. In this study lake, a total of 620 benthic macroinvertebrate specimens comparing of six taxa were collected from all the three study sites. Notonectidae (39.19%) were comprised the highest taxa followed by Coenagrionidae (25.45%) and Chironomidae (20.64%). The occurrence of Hirunidae (5.8%), Gerridae (1.61%), and Begidae (0.64) were found low, all comprised less than 10% of the total taxa. All most all the benthic taxa found in the study lake were pollution tolerant, indicating that the lake water condition was highly impacted. The results of the physicochemical parameters and benthic invertebrates strongly suggested that the lake water of the study lake was polluted. This study proposes that management of anthropogenic activities, nonpoint sources of pollution, loss of natural riparian habitat, and occasional untreated point inflow are necessary.