ackground and Objectives: One of the most reliable scientific methods for investigating the effects of human activities on river water quality and for assessing the ecological health of aquatic ecosystems is biological monitoring based on aquatic insects. These organisms are widely recognized as the most common and effective bioindicators in biomonitoring programs. Therefore, the present study aimed to assess the response and performance of EPT (Ephemeroptera, Plecoptera, and Trichoptera) and Diptera aquatic insect communities to variations in water quality in the Gargar River, Khuzestan Province, using biological indices.
Methods: This study was conducted on a seasonal basis in 2018 (1397) at five sampling stations along the Gargar River, a branch of the Karun River, in Khuzestan Province, Iran. Benthic macroinvertebrate communities were collected using Petersen grab and Surber samplers, each with a sampling area of 225 cm². The collected samples were washed through a 500-µm mesh sieve and stained with Rose Bengal (1 g L⁻¹) for 45 min. Subsequently, the samples were preserved in 96% ethanol and then identified and enumerated. Physicochemical parameters of the water, including temperature, dissolved oxygen, salinity, and pH, were measured in situ using a multiparameter probe. Diversity metrics, including total taxa richness, EPT richness (Ephemeroptera, Plecoptera, and Trichoptera), and the EPT/CHIR abundance ratio, were calculated. Statistical analyses were performed using PAST software (version 2.17), SPSS (version 21), and Microsoft Excel 2010. The normality of data distribution was evaluated using the Kolmogorov–Smirnov test. Differences in measured parameters among seasons and sampling stations were assessed using one-way analysis of variance (one-way ANOVA). Mean comparisons were conducted using Duncan’s multiple range test at a 95% confidence level (α = 0.05).
Findings: In this study, a total of 25 species belonging to 5 genera, 27 families, and 4 classes of aquatic insects were identified and enumerated. The highest relative abundances were recorded for Diptera (71.0%), followed by Ephemeroptera (24.0%) and Trichoptera (5.4%) of the total aquatic insect community. According to the Hilsenhoff biotic index, water quality at the studied sites was classified into four categories: good, fairly poor, poor, and very poor. The highest abundance was observed for the genus Austrosimulium sp. (family Simuliidae) within the order Diptera. The highest and lowest values of the total taxa richness index were recorded at Stations 2 and 3, respectively. During the study period, high EPT richness values were observed only at Stations 2 and 1. Station 1 exhibited the highest EPT/CHIR abundance ratio, indicating the most favorable ecological condition among the studied stations based on this metric. Based on the Shannon diversity index, all sampling stations were classified as having poor to bad ecological quality.
Conclusion: Based on the Hilsenhoff biotic index, the water quality of the study area was classified into four categories: good, fairly poor, poor, and very poor. In addition, the Shannon diversity index assessed the studied stations as having poor to bad ecological quality. Considering the results of the present study, and given that physicochemical indices typically reflect rapid and short-term variations and are unable to capture long-term biological responses of benthic communities, it can be concluded that the use of aquatic insects, particularly EPT taxa and Diptera, as biological indicators represents an appropriate and reliable approach for water quality assessment
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