Response of traditional and taxonomic distinctness diversity indices of benthic macroinvertebrates to environmental degradation gradient in a large Chinese shallow lake

A variety of biodiversity metrics are available to assess the quality of aquatic ecosystems. However, different types of metrics perform with considerable variation and provide various information involved in ecosystem conditions. Taxonomic distinctness (TD) indices have been recommended as desirable measures for assessing environmental degradation, but their utility based on lake macroinvertebrates is still largely unknown. Here, we evaluated the response of traditional and taxonomic distinctness diversity indices (the average taxonomic distinctness, Δ⁺, and variation in taxonomic distinctness, Λ⁺) of benthic macroinvertebrates to environmental degradation gradient in Lake Taihu, the third largest freshwater lake in China. Benthic assemblages responded markedly to human disturbances, with significance among-region differences in community composition throughout four seasons. The traditional biodiversity indices (Shannon-Wiener diversity and Pielou's evenness) showed high sensitivity in discriminating anthropogenic impacts, with highest values in macrophytic region but lowest values in eutrophic region. In contrast, Δ⁺ and Λ⁺ did not perform well in distinguishing sites subjected to different disturbance levels. The Pearson correlation and multiple regression analysis both indicated that traditional biodiversity metrics (Shannon-Wiener diversity, taxon richness, and Pielou's evenness) responded more readily to water quality variables (Secchi depth, electrical conductivity, and comprehensive trophic level index) than Δ⁺ and Λ⁺. Despite the weak correlations between TD indices of benthic macroinvertebrates and water quality in the present study, we suggest that the TD indices should still be considered in bioassessment programs because they provide useful complementary information on traditional diversity indices.