Development of a multicommunity index of biotic integrity for ecological health assessments of water—A case study of a mountain watershed in eastern China

• A multicommunity biological integrity index (Mc-IBI) assessment method was developed. • The structure of biological community in the mountain watershed was analyzed. • The t-SNE method was used to integrate biological communities and calculate the Mc-IBI score. • The tributaries in the mountain watershed exhibited better ecological health level than the trunk streams and reservoirs. • Compared with the single-community indices, Mc-IBI provides a more comprehensive ecological health assessment for watersheds. The evaluation of water ecological health provides a scientific foundation for water resource management, ecological protection, and restoration in river basins. The index of biological integrity (IBI) is a popular method, but a single-community IBIs may not fully reflect aquatic ecosystem health. In this study, a multicommunity index of biological integrity (Mc-IBI) was proposed as an indicator for aquatic ecosystem health assessment at the regional watershed scale. Mc-IBI was established based on benthos, phytoplankton, zooplankton, and epiphytic algae collected from 44 sampling sites in a mountainous small watershed in central Hangzhou (Zhejiang Province, China). A candidate indicator pool comprising 137 potential indicators was constructed on the basis of the distribution characteristics of the biological communities. Through distribution range analysis, discriminability testing, and redundancy testing, 17 core indicators, including benthic taxa, copepod taxa, and the Simpson index, were selected. The weight of each biological community at each sampling point was determined using the low-dimensional space obtained after dimensionality reduction with the t-SNE method, and the final Mc-IBI values were derived by assigning scores based on these weights. The ecological health of the small mountainous watershed, evaluated via the Mc-IBI, was classified as “good” (63.58 ± 8.52). Comparing with the individual IBIs, the Mc-IBI integrates multiple biological communities to enable a more comprehensive evaluation of aquatic ecosystem health at the regional watershed scale.