| The water-level fluctuation zone in the Three Gorges Reservoir is a transitional zone between the land and water body in the Three Gorges Reservoir.It is an important ecological security barrier in the Three Gorges Reservoir.It maintains the long-term stable operation and ecosystem health of the Three Gorges Reservoir,and protects the ecological security of the middle and upper reaches of the Yangtze River and even the whole Yangtze River Basin.The water-level fluctuation zone in the Three Gorges Reservoir is a unique,dynamic and complex ecosystem.It is also the most sensitive and vulnerable area in the Three Gorges Reservoir area,and its ecological environment problems are complex.For the sake of ecological security and sustainable development of the Three Gorges Reservoir and even the whole Yangtze River Basin,it is of great practical significance to carry out ecological restoration of the water level fluctuation zone in the Three Gorges Reservoir.In this study,four ecological restoration models in the water-level fluctuation zone of the Three Gorges Reservoir,i.e.,Urban dike-pond and woodland complex（UDPWC）system model,Multifunctional and multistrip buffer complex（MMBC）system model,Multidimensional wetland complex（MWC）system model,and Mulberry-fir woodland and dike-pond complex（MFWDPC）system model,were selected as the research objects.Then,the ecological restoration effects were evaluated by using the emergy and eco-exergy methods,the complexity mechanism of ecological restoration in the water-level fluctuation zone was analyzed based on the fractal theory,edge of chaos theory and other complexity science.The goal was to explore the ecological restoration mode to adapt to the water-level fluctuation in the Three Gorges Reservoir and provide basic data and theoretical reference for the ecological protection and restoration.The main contents and research results are summarized as follows:（1）After restoration,the biodiversity,water purification capacity,slope protection capacity and landscape effect of the four ecosystems in the water-level fluctuation zone were significantly improved.Emergy evaluation showed that the renewable resources such as solar energy,wind,rain,soil and plants were the main input streams,while species diversity,water purification,slope protection capacity and tourism income were the main output streams;the ecological restoration systems were based on the function of ecological services,and their environmental loading ratios were low（0.08,0.29,0.26and 0.04 respectively）,emergy yield ratios were high（13.30,5.34,4.79 and 27.18respectively）,and emergy sustainability indexes were high（163.35,18.48,18.12 and708.88 respectively）.Due to the implementation of ecological restoration,the emergy density of the four ecosystems increased,which were 1.15E+16sej yr-1 ha-1,8.52E+16sej yr-1 ha-1,1.01E+16sej yr-1 ha-1 and 3.96E+17sej yr-1 ha-1,respectively,and the dike-ponds and submergence-tolerant vegetation had increased the emergy of the ecological restoration system in the water-level fluctuation zone and played an important role in the ecological restoration system.（2）The distributions of species composition and genetic information C value of the four ecological restoration systems were similar,but there were some differences.Eco-exergy evaluation showed that the MFWDPC system and the MMBC system had larger eco-exergy values of 2.41E+14J yr-1and 7.03E+13J yr-1,respectively,and the eco-exergy of the MFWDPC system was mainly from natural weeds,while the eco-exergy of the MMBC system was mainly from trees;the specific eco-exergy of the MMBC system was the largest,which was 5.48E+08J yr-1 and mainly from trees;the exergy/emergy ratio of the MMBC system was the largest,which was 2.24E-03;the self-organization degree,order degree and stability of the ecological restoration systems in the water-level fluctuation zone were better,especially the MMBC system.On the whole,natural weeds had rich genetic information C value,while trees had huge biomass,which indicated that trees and natural weeds layer with huge biomass and rich genetic information occupied a large proportion in ecological and structural layers,and they played an important role in the development and maintenance of ecosystem complexity and stability.（3）After flooding in winter,the eco-exergy,specific eco-exergy and exergy/emergy ratio of the four ecosystems decreased,indicating that their self-organization level were low.However,in the high water level period,the submergence-tolerant vegetation slowed down the decline rate of the eco-exergy in the four ecological restoration systems,which were 4.87%,16.69%,12.16%and 3.46%respectively.In addition,the dike-ponds and submergence-tolerant vegetation alleviated the emergy difference caused by the water level fluctuation,changed the flow and distribution of the energy in the ecosystems,and improved the self-regulation and self-sustaining abilities of the ecosystems in the water-level fluctuation zone to cope with complex hydrological stress.Therefore,the four ecological restoration systems are elastic and self-sustaining ecosystems,which can cope with the pressure and change of complex water environment.At the same time,introducing of flood tolerant plants with large biomass and abundant genetic information,then improving the eco-exergy and specific eco-exergy should be the thermodynamic goal of the ecological restoration in the water-level fluctuation zone.（4）Among the four ecosystems in the water-level fluctuation zone,the fractal dimensions of herbaceous plants（box dimensions were 1.61 and 1.58）and trees（box dimensions were 1.83 and 1.56,and information dimensions were 2.00 and 1.68）in the MMBC system and the MFWDPC system were larger,and they had significant correlations with the specific eco-exergy.The fractal dimension of landscape morphology in the UDPWC system and the MFWDPC system were relatively larger,and their box dimensions were 1.52 and 1.47 respectively,and they had significant correlations with the dike-ponds density.The fractal dimensions of soil in the four ecosystems were different,but the differences were not significant;compared with the soil on the dike-ponds,the fractal dimensions of the soil in the dike-ponds and woodland were larger,and the box dimension were 1.81 and 1.79,showing a thinning feature and a significant correlation with the soil organic matter.Fractal results showed that in the process of ecological restoration,the plants with larger fractal dimension and specific eco-exergy should be added,and the spatial distribution pattern of trees should be optimized;the water land shorelines and dike-ponds with larger fractal dimension should be designed,and the length of water land shorelines and density of dike-ponds should be increased;the dike-ponds project and woodland project should be implemented to increase soil organic matter,improve soil fertility,improve the fractal dimension of soil microstructure,and then increase the complexity of ecological restoration system in the water-level fluctuation zone.（5）The power spectrum exponent and fractal dimension of the time series at 4.72m in the Hanfeng lake where the UDPWC system,MMBC system and MWC system are located were 1.35 and 1.82,respectively,and the power spectrum showed good continuity and wide peak characteristics,which was close to the edge of chaos,with higher complexity and adaptability.However,the power spectrum exponent and fractal dimension of the time series at 30m water level fluctuation in the Pengxi River where the MFWDPC system is located were 1.56 and 1.72,respectively,and the power spectrum showed local discontinuity and peak characteristics,which deviated from the edge of chaos,with lower complexity and adaptability.These results showed that the fluctuation of water level in the Hanfeng lake had a relatively small impact on the ecological restoration system,but it had also shown the characteristic of weakening complexity,and some restoration measures need to be taken to increase the complexity of the ecological restoration system.However,the fluctuation of water level in the Pengxi River had a relatively serious impact on the ecological restoration system,and it was difficult to grasp the law and internal mechanism,so some measures must be taken to increase the complexity of ecological restoration system.In addition,the implementation of dike-pond project and woodland project,as well as the introduction of large biomass and rich genetic information of flood tolerant plants,can not only increase the emergy and eco-exergy of the water level fluctuating zone ecosystem,but also improve the fractal dimension of the ecosystem,thus increasing the complexity of the water level fluctuating zone ecosystem and enhancing its ability to cope with water level changes.（6）Complex system has the ability to self-organize order and chaos into stable equilibrium state,and has the greatest complexity and the strongest adaptability.The higher eco-exergy the ecosystem has,the more it can control the most complex behavior at the edge of chaos.Therefore,the ecological restoration of the water-level fluctuation zone is to make the ecosystem produce more eco-exergy and information through self-organization.The edge of chaos and the butterfly effect play important roles in the evolution of the ecological restoration system in the water-level fluctuation zone,so it is necessary to avoid blindly changing the components of the ecological restoration system.Therefore,to help the ecosystem restore and maintain the chaotic edge state in a short time and make it more self-organized,resilient and adaptive are the goals of ecological restoration of the water-level fluctuation zone.（7）Based on the studies of emergy evaluation,eco-exergy evaluation,and complexity mechanism of the four ecological restoration systems,some regulation principles and countermeasures for the ecological restoration are put forward.The regulation principles mainly include integrity restoration principle,complexity restoration principle,self-organization restoration principle,near nature restoration principle and manual assistance restoration principle,etc.;the countermeasures mainly include wetland dike-ponds group design,fractal interface regulation design,energy quality improvement design,multi-functional optimization design and river-wetland complexity design,etc. |
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