Assessment of Ecological Health Using Benthic Macroinvertebrates and Hydrological Alteration in Gilgel Abay River Ethiopia
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Date
2024-06
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Addis Ababa University
Abstract
Bio-monitoring and hydrological flow alterations are currently given due attention as they appropriately reflect the health of aquatic ecosystems. This study aimed to assess the ecological health of the Gilgel Abay River using benthic macroinvertebrates and hydrological flow-alteration metrics. Flow alteration analysis was monitored using the Indicators of Hydrological Alteration (IHA) with observed discharge data gathered from 1979 to 2020. Five sampling sites were selected based on major stressors including; water abstraction for irrigation, deforestation, fishing, cloth washing, bathing, swimming, spiritual purpose, livestock watering, grazing, and the accessibility of the sites for sampling. In-situ environmental variables such as dissolved oxygen, pH, temperature, and conductivity were measurement using a multiline-probe system (HQ40d) and the nutrients including, nitrate, nitrite, soluble reactive phosphorus,and total suspended solid laboratory analysis were carried out in 2023 folowing APHA, 1995 protocol. Benthic macroinvertebrate samples were collected following a multi-habitat sampling approach and identified to family level except in the case of Chironomidae which were identified to species level. Both 1-day and 90 days durations of high flow and low flow had a decreasing trend over the past 42 years (1979–2020). The environmental flow component analysis found four large floods (i.e., 1980, 1986, 1988, and 1994), but no large flood was recorded after 1995. The low flow conditions of the stream flow were equal to 15.81m3s-1 for 95% of the time in the flow duration curve. Highest concentrations of NO3- (4.25 mg/l), TSS (0.065 mg/l), NH4+ (0.622 mg/l), were recorded at the Telifa site, while lowest levels of soluble reactive phosphorus (0.395±0.5 mg/l), NO3- (1.23 mg/l), NO2- (0.008 mg/l) and the highest concentration of dissolved oxygen (7.74 mg/l) were recorded at the reference site. Redundancy analysis indicated that dissolved oxygen, NO2-, TSS, NO3-, and pH directly impacted macroinvertebrates distribution. All environmental variables except NH4+ and SRP have significantly different among sampling sites. The overall qualitative habitat assessment values of the river was 59.3%, indicating Class D (largely modified) based on the intensity of human influence. A total of 28 family benthic macroinvertebrate taxa under 9 orders were collected. The families Caenidae, Hydropsychidae, Heptageniidae, Tricorythidae, and Naucoridae were frequently encountered in minimally impacted upstream sampling sites and considered as indicators of relatively minimally impacted sites. The family Chironomidae was dominant in highly impacted sites and can be considered as indicators of impaired conditions. Polypedilum wittei was dominant in highly agricultural activities impacted sites and can be considered as an indicator of highly polluted sites in the study river. Metrics composed of %Ephemeroptera and Trichoptera, percent dominant taxon, %Diptera individuals, Shannon-Wiener diversity index (H), total number of taxa (family), percent dominant functional group, ETHbios, and habitat quality assessment score were able to differentiate reference sites, and agriculturally impacted sites. Altered river flows in the Gilgel Abay likely harm aquatic life. Studies should focus on water requirements for the ecosystem, bank stability, and local community-centred approaches to watershed conservation structures.
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Keywords
Benthic Macroinvertebrate, Bioindicator, Environmental Flow, Functional Feeding Groups, Hydrological Regime