基于网络分析的湿地水文关系研究——以美国奥克弗诺基流域为例

Network-based Analysis on Hydrological Relationships of A Wetland System—A Case Study of Okefenokee Basin,USA

湿地与周边水文系统通过复杂的水文过程相互联系和影响,具有整体性和复杂性。研究湿地与周边水文系统相互作用过程和机理,对湿地保护和恢复起着重要的作用。以美国奥克弗诺基(Okefenokee)流域为案例,构建包含沼泽地表水、沼泽地下水、高地地表水和高地地下水4个水文子系统的流域水文网络模型,采用生态网络分析方法中的效用、控制和单位元分析研究水文单元间作用关系。控制分析的结果显示,高地地表水和地下水两个子系统对沼泽地表水和地下水子系统的支持程度达到100%。无论是沼泽还是松林高地,其地表水和地下水之间存在高度的相互依赖和互补性。效用分析结果表明,沼泽地表水和高地地下水之间存在着互利的水文关系。而单位元分析结果显示,沼泽地下水深层渗漏和高地松树生态系统的蒸散过程是袭夺流域湿地系统水资源的重要一环。上述结果表明,生态网络分析方法可以有效地分析水文单元之间的作用过程、描述水文单元之间直接和间接的水文关系,可以用于流域湿地水资源管理。

Wetlands are not isolated spaces but complex habitats with complex hydrologic connections all around.Especially,subsystems of wetlands（e.g.,surface water,underground water） are hydraulically interconnected and form a specific network structure that displays integral characteristics in different spatial and temporal scales.The protection and restoration of wetlands require information on processes and mechanism of interactions among hydrological units inside and outside wetlands.Studies on individual subsystems are far from enough to develop effective protection and restoration policies for wetlands.To operate valid water resources management and ecological management,we should understand the ecological relationships of these interconnected hydrological subsystems firstly.In this study,we developed a hydrological relationship assessment framework in which the ecological network analysis（ENA） was employed.Three functional analyses,utility analysis,control analysis and unit environ analysis,in ENA were used to characterize hydrological relationships among four subsystems.The Okefenokee Swamp in USA was taken as an example.We aim to highlight the importance of maintenance the integrity of these associated subsystems.Holistic knowledge of controlling relations is important for the understanding of system structure and function.Through the results of control analysis,we quantified the static flow control and dependencies on both donor and recipient-oriented processes in a holistic way.Results showed that the control parameter of cn 13,cn 14,cn 23 and cn 24 equal to 1.0,respectively,indicating the swamp depended totally on upland during their hydrological interactions.The dependence of upland underground water（component 2） on upland surface（component 1） was 85.9%,indicating there are intensive interactions between the above two subsystems.The independency between system components within the system is extremely important for wetland system survival although little exchanges took placed.Utility analysis considers that a gain of resources provides positive utility and a loss of resources provides negative utility.The method identifies both direct and indirect qualitative and quantitative ecological relationships in a network,thereby revealing the integration and complexity of ecosystem behaviors.Results of utility analysis indicate there are three types of ecological relationships between hydrological subsystems,including exploitation,neutralism and mutualism.An example of exploitation can be given as（D 21,D 12） =（-0.664,0.860）,indicating upland groundwater got a net positive utility of 0.860 from upland surface and upland surface got a net negative utility of-0.664 from upland groundwater.Neutralism appeared in the relationship between（D 41,D 14）=（0,0）,indicating there is no direct hydrological exchanges between upland surface and swamp subsurface.An interesting phenomenon is the hydrological relationships between swamp subsurface and upland surface changed from neutralism to mutualism,indicating two hydrological components benefited each others from indirect transactions.It reflects the fact that hydrological modification should be planned under an integral framework.Results of unit environ analysis reflect that water flows out of system through seepage of swamp and evapotranspiration of upland.It is concluded that the proposed methods can provide effective ways to examine the hydrologic components＇interdependencies in a wetland system and contributes to the basin-wide wetlands protection and water resources management.