Incorporating functional metrics into the development of a diatom-based index of biotic integrity (D-IBI) in Thousand Islands Lake (TIL) catchment, China

[Display omitted] •Incorporate functional metrics into the development of a D-IBI.•Functional metrics differ significantly at the reference and impaired sites.•Most sites are in “Fair” and “Good” states.•The selection of metrics needs to remove the influence of spatial processes. Incorporating functional metrics into the development of a diatom-based index of biotic integrity (D-IBI) is conducive to a more comprehensive assessment of water quality and the degree of external impact on ecosystem function. A D-IBI was developed by incorporating functional metrics to candidate metrics. Four metrics were selected and divided into five levels to evaluate 147 sampling sites. By comparing the D-IBI scores in Thousand Islands Lake (TIL) catchment, we found that the total D-IBI score ranged from 20 to 100 (median was 45). Compared with reference sites, the resource competition of impaired sites was weaker, and the community was more stable. In response to basin damage, we recommend source protection, long-term monitoring, increased hydrological connectivity, and ecological management of small watersheds. For the assessment of water environmental health, we suggest that the functional metrics should be included in the biological assessment, and the candidate metrics that are greatly affected by the dispersal process should be excluded. Moreover, the assessment should be conducted at the multi-dimension level and watershed scale.