A meta-analysis of environmental responses to freshwater ecosystem restoration in China (1987-2018)

Understanding how abiotic and biotic components respond to aquatic ecosystem restoration is pivotal for sus-tainable development in the face of economic development and global environmental change. However, the post -restoration monitoring and evaluation of aquatic ecosystems across large spatial and temporal scales is under-funded or not well documented, especially outside of Europe and North America. We present a meta-analysis of abiotic and biotic indices to quantify post-restoration (2 months-13 years) effects from reported aquatic resto-ration projects throughout the China-mainland, incorporating 39 lentic and 36 lotic ecosystems. Decreases in dissolved nutrients (total nitrogen, ammonia nitrogen and total phosphorus) post-restoration were rapid, but tended to slow down after about 9.3 years. Response ratios summarizing biodiversity responses (incorporating phytoplankton, invertebrates, vascular plants, fish and birds) typically lagged behind abiotic changes, suggesting longer timescales are needed for biotic indices to recover. Time since restoration interacted with lentic project size showing that, even with the same proportional efforts of restoration, larger lentic ecosystems responded much more slowly than smaller ones. Spatial heterogeneity, reflecting the effects of different restoration ap-proaches (e.g., sewage interception, polluted sediment dredging, artificial wetlands, etc.), had a significantly stronger effect on biotic than abiotic indices, particularly in rivers compared to standing waters. This reflects the complexity of fluvial ecosystem dynamics and hints at a limitation in the reinstatement of ecological processes in these systems to overcome issues such as dispersal limitations. Overall, the different timelines and processes by which abiotic and biotic indices recover after restoration should be taken into account when defining restoration targets and monitoring programs. Our study illustrates the value of long-term aquatic ecosystem monitoring, especially in China given the scale and magnitude of ongoing restoration investments in the country.

Automated summary

Understanding the response of abiotic and biotic components to aquatic ecosystem restoration is crucial for sustainable development in the face of economic growth and global environmental change. However, post-restoration monitoring and evaluation of aquatic ecosystems are lacking in funding and documentation, particularly outside of Europe and North America. This study presents a meta-analysis of abiotic and biotic indices in aquatic restoration projects in mainland China, revealing rapid decreases in dissolved nutrients post-restoration but slower recovery times for biodiversity indices. The findings emphasize the importance of long-term monitoring and considering different timelines and processes for restoration targets and programs.