Alternative stable state and its evaluation in wetland reconstruction based on landscape design

An alternative stable state is closely related to the health and sustainable development of ecosystems; however, knowledge of the alternative stable state and its quantitative evaluation in wetland reconstruction remains incomplete. In this study, we used landscape design to reconstruct an optimized ecological polder wetland and a lake wetland in the Yunmeng Marsh area, China, and the alternative stable states of the two wetland ecosystems were assessed from an ecosystem perspective via emergy/eco-exergy and fractal dimensions. The emergy densities for the optimized ecological polder wetland and the lake wetland were 2.35E+13 sej yr^-1 m^-3 and 2.18E+13 sej m^-3, and the emergy sustainability index (ESI) values were 216.57 and 193.31, respectively, indicating that the reconstructed wetland ecosystems were dominated by renewable energy flows and were highly sustainable. The eco-exergy density and emergy/eco-exergy ratio results showed that natural selection self-organized the reconstructed wetland ecosystems to tolerate environmental stresses and changes. In addition, the fractal dimensions of the morphology and contour of the polder wetland, which reflect the space occupation capacity of geometric and physical constraints in the wetland, were 1.57 and 1.75, and those of the lake wetland were 1.03 and 1.47, respectively. The synthetic evaluation results showed that the alternative stable states of both the optimized ecological polder wetland ecosystem and the lake wetland ecosystem were ecofriendly modes of wetland reconstruction, which can be implemented together to create a "lake-polder" ecosystem. Our study on the alternative stable states of wetland ecosystems is helpful for exploring the synergistic symbiosis between traditional culture and the ecological environment in China and other wetland-rich regions and countries with severe disturbances.