Emergy and eco-exergy evaluation of wetland reconstruction based on ecological engineering approaches in the three Gorges Reservoir, China

Wetland reconstruction is an effective way to solve the severe environmental problems caused by natural disasters and human activities. In this study, we implemented three wetland reconstruction projects based on three ecological engineering approaches, the woodland and dike-pond complex (WDPC), the multifunctional and multistrip buffer complex (MMBC), and the multidimensional wetland complex (MWC), in the water-level fluctuation zone of Hanfeng Lake in the Three Gorges Reservoir (TGR), China. Then, the three wetland reconstruction projects were evaluated for quantity and quality by using the emergy and eco-exergy methods. The results showed that after the implementation of wetland reconstruction projects, the species biodiversity, water purification, slope protection and landscape effects were all greatly improved. The emergy density for each project was 3.40E + 17 sej yr−1 ha−1 for the WDPC, 4.49E + 17 sej yr−1 ha−1 for the MMBC, and 4.05E + 17 sej yr−1 ha−1 for the MWC. The emergy sustainability index (ESI) values for the three reconstructed wetland ecosystems were 163.35, 18.48 and 18.12. These results showed that the three projects, which were dominated by renewable energy flows, were highly sustainable over a long-term period. In addition, the eco-exergy density for each project was 1.29E + 12 j yr−1 ha−1 for the WDPC, 1.00E + 13 j yr−1 ha−1 for the MMBC, and 4.44E + 12 j yr−1 ha−1 for the MWC, and the emergy/exergy ratios were 2.64E + 05, 4.47E + 04 and 9.12E + 04, respectively. These results showed that the submergence-tolerant vegetation slowed the decrease in eco-exergy in the three reconstructed ecosystems and then slowed the reverse evolution speed of these ecosystems in the water-level fluctuation zone. The design concepts for these wetland reconstruction projects is a new approach in the TGR, which can serve as a demonstration and reference for other areas of the TGR and other countries of the world.