Project Application of River Ecological Restoration Technology Based on Zoobenthos Communities

[Objective] Zoobenthos are the intermediate link in the food chain of river ecosystems, and promoting the restoration of healthy zoobenthos communities through the construction of suitable habitats is critical for river ecological restoration. Based on the living habits of zoobenthos, habitat modules suitable for the colonization of various zoobenthos species are designed and applied in experiments within the ecological restoration project of Fenghuang Creek to investigate the effectiveness of ecological restoration. [Methods] Prior to project implementation, zoobenthos samples were collected once from the river channel. One year after the completion of the project, when the river ecosystem was restored, zoobenthos samples within the modules were collected, with three sampling sites set up for this study. In addition, zoobenthos were collected from a river minimally affected by human activities to serve as a natural reference state. Collected zoobenthos samples were identified and counted, and ecological indicators were analyzed. A total of ten ecological indicators were analyzed to assess the restoration of zoobenthos communities. These indicators included: individual density and biomass density reflecting biomass characteristics; total number of taxa, number of sensitive taxa, and number of EPT taxa reflecting species richness; Shannon-Wiener diversity index, richness index, and evenness index reflecting community diversity; and biotic index (BI) and biological monitoring working party score (BMWP) reflecting environmental sensitivity. [Results] Among the biomass-related indicators, no significant change in individual density of zoobenthos was observed before and after the restoration project, and the values remained below 40% of those in the natural state. Biomass density, however, varied considerably among sampling sites after project implementation, with two sites exceeding twice and four times the values observed in the natural state, respectively. Regarding species richness-related indicators, the total number of taxa reached 60% of the natural state before project implementation. After the project, it increased slightly, ranging from 66.7% to 73.3% of the natural state, indicating a relatively small difference from the natural condition. Although the numbers of sensitive taxa and EPT taxa significantly increased after the project, they remained far below the natural state, with sensitive taxa at 30.0%-40.0% and EPT taxa at only 14.3% of the natural state. For species diversity-related indicators, slight increases were observed after project implementation compared with pre-project levels, and the gaps from the natural state were small, with some indicators even surpassing those of the natural state. Although indicators related to environmental sensitivity were improved after project implementation, they remained far below the natural state, with BI values at 41.5%-44.3% and BMWP scores at 55.7% of the natural state. [Conclusion] Following project implementation, the health of zoobenthos communities in the river shows a relatively pronounced restoration, but there remains a considerable gap compared with the natural state, mainly reflected in indicators closely associated with sensitive taxa—namely, the number of sensitive taxa, number of EPT taxa, BI value, and BMWP score. This can be attributed to the fact that the structure of zoobenthos communities is influenced not only by the river habitats but also by the types of surrounding terrestrial ecosystems. The reference site in this study is minimally affected by human activities, where the natural ecosystem is well preserved and suitable for the survival and reproduction of adult aquatic insects from sensitive taxa, resulting in a relatively rich assemblage of sensitive taxa. In contrast, the river under restoration is surrounded by villages and farmland, where terrestrial habitats and communities are relatively homogeneous, and the river ecosystem is frequently disturbed. Therefore, these conditions limit the development of sensitive zoobenthos taxa to a certain extent and make it difficult for community health to approach the natural state. Based on the analytical indicators used in this study, individual density, biomass density, Shannon-Wiener diversity index, richness index, and evenness index are relatively insensitive and fail to accurately reflect the differences before and after implementation or between post-implementation and natural state. In contrast, indicators related to sensitive taxa exhibit strong sensitivity and applicability in assessing zoobenthos community restoration and are recommended for use in similar studies or projects.