Research On Ecological Network Of Desert Oasis Based On Complex Network Theory

Taking Denko County,a typical area in the desert oasis region as a case study,based on multi-temporal remotely sensed images,long-term time series groundwater depth data and meteorological data,the minimum cumulative resistance surface model suitable for Denko County was constructed first,followed by the proposition of the potential ecological network for Denko County by coupling density factor with distance factor from urbanization and groundwater distribution,in this study.Furthermore,the spatial structure of extracted potential ecological was analyzed through the utilization of data assimilation algorithm,point pattern analysis method and skeleton tree extraction algorithm.And by means of basic static statistical indicators,correlation indicators,importance indicators and connectivity indicators of complex networks,we analyzed the topological features of potential ecological networks.Ultimately,the BCBS model would be utilized to optimize the spatial structure of potential ecological networks and analyze the connectivity robustness and restoration robustness of potential ecological networks before and after optimization.Then we used force-oriented model and set 11 scenarios to achieve multi-field damage simulation of the potential ecological network and detailed analysis of the typical region selected.The main results are as follows.(1).From 2000 to 2014,the area of urban areas in 2014 was almost three times that of 2000 after 14 years of urbanization and urban planning area will increase to 62.10km2 by 2025.The city boundary has undergone a process from natural expansion to scientific planning.The trend lines of 17 wells logs are divided into 5 categories,which contains monotonic decreasing trend,monotonic rising trend,the trend of falling first and then rising,the trend of rising first and then falling,and the trend of rising first,then falling and finally rising again.The downward trend appeared in the northern and western parts of Denko County,and upward trend could be seen in the middle and southeast regions.There are three typical areas in Denko County with dramatic changes and the first one is in Lake Nalin in the southern part of the study area.There is a second area in the Narenbrugge district located in the western part and the third is the center of Bayan Galle Town.The analysis of three regions reveals that positive human interference has a positive effect on groundwater.Conversely,massive use of groundwater by human could lead to a drop in the groundwater level and even a groundwater funnel.(2).The construction of ecological resistance surface under ecological protection model and economic development model was implemented based on ecological resistance evaluation system.The extracted potential ecological network in Denko County includes 391 ecological source sites,47466 potential ecological corridors and 667 potential patch nodes.In accordance with this,the ecological network security pattern is divided into three levels based on the development boundary of urban area of Denko County.(3).In the simulation of ecological land use change based on ecological source changes,the introduction of Ensemble Kalman Filter could reduce the accumulation of errors and improve the accuracy of simulation.The total simulation accuracy of EnKF-MCRP model has reached 82.4%and it is of great importance for the introduction of ecological source changes into ecological resistance surface model.The seven ecological source areas are clustered and distributed on a small scale and evenly distributed on a large scale.However,the distribution pattern of ecological source nodes,which are highly aggregated at small scales and tend to be uniform at large scales,can ensure the stable development of ecological source areas in the arid and semi-arid desert oasis ecologically fragile areas and guarantee the stability of regional environment.The skeleton corridor extracted by the modified Kruskal algorithm is consistent with actual situation.(4).In the potential ecological network of Denko County,average per ecological node has a direct connection with other 6 ecological nodes.The degree distribution presents an obvious power distribution,except for the ecological nodes with degrees 0 and 1:f(x)=55.75×e^(-0.40x).The scale-free property manifests itself in potential ecological networks.Any two nodes are not connected,and the clustering coefficient is 0.3692,which does not have the characteristics of a small-world network.The ecological network is positively related,that is,the nodes with high degree of compatibility are more inclined to cluster compared with nodes with smaller degrees of integration and there is no obvious hierarchy in the network.The northeastern part of Denko County is mainly distributed with more important nodes,with a network clear number of 19.The spatial structure of potential ecological network extracted cannot be regarded as the most stable structure.(5).Before the optimization,the current coverage rate of the node was 65.23%,and current uniformity of node distribution was 0.5378.After the optimization of the layout of ecological nodes,the area of blind spots has been reduced by 484.46km2.Compared with pre-optimization,the coverage rate increases by 22.56%,and the distribution uniformity of optimized nodes decreases to 0.3978,which indicates that the uniformity of node distribution is highly degraded and the spatial distribution of ecological nodes is more uniform in Denko County after optimization.In the optimized ecological network,each ecological node has a direct connected relation with other 16 nodes on average,and the degree distribution scattered point exhibites a certain degree of Poisson distribution features,with small-world characteristics and scale-free characteristics.Any two ecological nodes could communicate with each other through about 7 conversions and the number of important nodes in the network had increased by 10.It is found that the optimized ecological network is equipped with stronger anti-strike ability and connectivity capability under malicious attacks and random attacks,and the restoring robustness of nodes and edges becomes more powerful.(6).Based on the force-oriented model of complex ecological networks,the ecological network has been gradually destroyed with the transition from(1,0)mode to(0,1)mode in 11 scenarios.Taking a typical area of local circle as an example,the patch grid of ecological source sites disappears and skeleton corridor breaks by degrees with the transformation of the model,leading to a great destruction of the ecological network under(0,1)mode eventually.It could be inferred that ecological network would suffer great damage if large-scale land development is carried out in arid and semi-arid areas under current conditions.In(0.9,0.1)mode,the destruction occurs at the edge of desert,but there is an expansion of ecological network within the circle.Under the constraints of existing natural resources,the space for development of economy in Denko County is present but not too large.