Assessment of ecological health using benthic macroinvertebrates and physico-chemical parameters in Gilgel Abay River, Ethiopia

Abstract

Biomonitoring is currently given due attention as it appropriately reflects the health of aquatic ecosystems. There is little research on the Gilgel Abay River to assess its ecological status using biological organisms. The aim of this study was to assess the ecological health of the Gilgel Abay River using benthic macroinvertebrates and physico-chemical parameters. Five sampling sites were selected based on major stressors and accessibility of the sites for sampling. In situ physico-chemical parameters measurement and nutrient analyses were conducted in 2023. Benthic macroinvertebrate samples were collected following a multi-habitat sampling approach and identified to the family level except Chironomidae were species level. Highest concentrations of NO₃⁻ (4.25 mg/L) and TSS (0.065 mg/L) were recorded at the Telifa site, while lowest levels of NO₃⁻ (1.23 mg/L) and NO₂⁻ (0.008 mg/L) and highest concentration of dissolved oxygen (7.74 mg/L) were recorded at the slightly impacted site. Absence of pollution intolerant taxa, fewer numbers of tolerant taxa and collector-gatherer functional feeding groups are evident of the impacted sites. While sensitive to modestly tolerant taxa and scrapers functional feeding groups were frequently encountered in upstream sites. According to ETHbios; 2 (S1, S2) sites were classified as slight ecological disturbance, 3 (S3, S4, S5) as significant ecological degradation. Redundancy analysis indicated that pH, DO, CD, NO₃⁻, NO₂⁻, and TSS significantly impacted the distribution of macroinvertebrates. This finding highlights the ecological degradation of the Gilgel Abay River, underscoring the need for watershed conservation and stabilization of riverbanks with active participation of local communities to safeguard the river’s health.