Impacts of different pond-to-wetland restoration methods on macrofauna in the Liao River Estuary, China

Aims: A pond-to-wetland restoration project along the Liao River Estuary was launched in 2015 to improve coastal ecological protection. However, the recovery effects on macrofauna and the underlying mechanisms associated with different pond-to-wetland restoration methods remain unclear. We analyze the macrofaunal community characteristics and their relationships with environmental factors to assess the effects of different pond-to-wetland restoration methods on macrofauna recovery. Methods: Macrofauna and environmental factors in May (spring) and September (autumn) 2023 were taken for our analysis. We used 82 sampling points across three types of restored pond sites with increasing degrees of pond-to-wetland restoration (unleveled, semi-leveled, and fully leveled pond dike sites) and a natural Suaeda salsa control site in the Liao River Estuary. We analyzed the community structure, biodiversity, and their relationships with environmental factors using classical taxonomy, biodiversity indices, non-metric multidimensional scaling, analysis of similarities, and nonlinear regression analysis. Results: We collected a total of 21 macrofauna species and classify these into 3 phyla, 5 classes, and 16 families. The dominant species are Ilyoplax deschampsi, Assiminea latericea, and Capitella capitata in spring and Assiminea latericea, Assiminea sp., and Capitella capitata in autumn. In spring, the species biomass in the semi-leveled pond dike area is significantly higher than in the unleveled and fully leveled pond dike area. In autumn, the species density in the fully leveled pond dike area is significantly higher than in the unleveled and semi-leveled area. Further, biomass is significantly higher than in the unleveled area with an evenness index significantly lower than in the semi-leveled area. There are significant differences in macrofaunal community structure among the different restored pond dike areas in both seasons. We also find elevation, sediment, temperature, sand content, and total nitrogen content are significantly related to macrofauna distribution. Conclusion: The species density, biomass, and diversity index values for macrofauna rose as the degree of pond-to-wetland restoration increased. Still, the semi-leveled pond dike area showed a biomass recovery similar to that of the fully leveled pond dike area and has favorable biodiversity index results. These results suggest that the semi-leveled pond dike approach may be the most suitable option after taking into account resource consumption, project duration, and restoration effects.