Abstract: Changes in zoobenthos can effectively indicate the damage to river ecosystems and are commonly used in aquatic ecological health assessments. We investigated the zoobenthos in the lower reaches of the Dongjiang River. For the first time, we establish a benthic-index of biotic integrity (B-IBI) evaluation system for assessing damaged rivers in this region, and explore the main factors influencing aquatic ecological health. The results demonstrate that the B-IBI values of reference sites range from 2.23 to 3.53, indicating excellent or good conditions. In contrast, the B-IBI values of damaged rivers range from 0.04 to 2.61, with most of them being in poor health, including both poor and very poor states accounting for 45%. Dissolved oxygen, COD_Cr, BOD₅, ammonia nitrogen, total phosphorus, and anionic surfactants exhibit significant correlations with B-IBI values. Water pollution emerges as the primary cause for the deterioration of river ecosystems. Additionally, the high-intensity development and construction activities around rivers negatively impact zoobenthos, particularly aquatic insect communities. For tidal reaches, we recommend selecting targeted parameters to construct an evaluation system and establish evaluation standards when conducting B-IBI assessments.

Key words: river ecological system, aquatic ecological health assessment, lower reaches of Dongjiang River, zoobenthos, Benthic-Index of Biotic Integrity