Analysis of biological benchmarks for the Chishui River based on benthic integrity assessment

Environmental assessment was conducted at 26 sampling points along the main stream of the Chishui River, and 7 reference points were determined in the upper reaches and 4 in the middle and lower reaches. Through analysis of the distribution range of parameter values, discriminant ability analysis and redundancy analysis, 22 candidate indicators were screened. The ratio method was employed to calculate the scores of each parameter and the benthic macroinvertebrate integrity index (B-IBI) of all sampling points. Based on the B-IBI, the biological benchmark values of the Chishui River in different periods (dry season, wet season, and normal season) and different reaches (upper reaches, middle and lower reaches) were respectively formulated. The results showed that the core parameters in the dry season included the total number of taxonomic units, the number of EPT (Ephemeroptera, Plecoptera, and Trichoptera) taxonomic units, the relative abundance of predator individuals and the Pielou evenness index. The core parameters in the wet season included the total number of taxonomic units, the number of EPT taxonomic units, the Hilsenhoff biotic index, and the Margalef richness index. The core parameters in the normal water season included the total number of taxonomic units, the number of EPT taxonomic units, the percentage of EPT individuals, the Hilsenhoff biotic index, and the relative abundance of predator individuals. The biological benchmark values of the upper reaches and the middle and lower reaches of the Chishui River in the dry season were 6. 86 and 5. 04 respectively, those in the wet season were 6. 45 and 4. 43 respectively, and those in the normal season were 6. 65 and 6. 25 respectively.