Assessment of long-term and large spatial scale aquatic ecosystem restoration practices in China: reveals divergence recovery timeline and how urbanisation effects could be mitigated

Abstract

Ecosystem degradation and biodiversity loss have been caused by economic booms in developing countries over recent decades, and ecosystem restoration projects have been advanced in many countries. However, the post-restoration monitoring and evaluation of aquatic ecosystems across large spatial and temporal scales is underfunded or not well documented, especially outside of Europe and North America. The effectiveness of different approaches and indicators at large spatio-temporal scales (i.e., whole catchments) also remains poorly understood. Here, we first present a meta-analysis of abiotic and biotic indices to quantify post-restoration (2 month to 13 years) effects from reported aquatic restoration projects throughout the China-mainland, incorporating 39 lentic and 36 lotic ecosystems. Secondly, we assessed the effectiveness of a diverse array of 440 aquatic restoration projects (wastewater treatment, constructed wetlands, etc.) implemented and maintained from 2007 to 2017 across more than 2000 km2 of the northwest Taihu basin (Yixing, China). Synchronized investigations of water quality and invertebrate communities were conducted before and after restoration. Our analysis showed that: (1) decreases in dissolved nutrients (TN, NH4+-N, TP) post-restoration were rapid, but tended to slow after about 9.3 years; (2) 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; (3) Spatial heterogeneity, reflecting the effects of different restoration approaches (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; (4) Even though there was rapid urbanization at Yixing, nutrient (NH4+-N, TN, TP) concentrations and biological indices of benthic invertebrate (taxonomic richness, Shannon diversity, sensitive taxon density) improved significantly across most of the study area; (5) Improvements were associated with the type of restoration project, with projects targeting pollution-sources leading to the clearest ecosystem responses compared with those remediating pollution-sinks. Overall, our study suggests that 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. We also demonstrated that ecological damage caused by recent rapid economic development in China could potentially be mitigated by massive restoration investments synchronized across whole catchments, although these effects could be expected to be enhanced if urbanization rates were reduced at the same time.Related contents had been published see: (1) Fu, Hong, et al. "Mitigation of urbanization effects on aquatic ecosystems by synchronous ecological restoration." Water Research 204 (2021): 117587; (2) Fu, Hong, et al. "A meta-analysis of environmental responses to freshwater ecosystem restoration in China (1987–2018)." Environmental Pollution 316 (2023): 120589.