Review of mechanism and quantifying methods of river system connectivity

"Connectivity" in a river ecosystem originated from landscape ecology, which plays a significant role in hydrological cycle, wildlife migration, and environment improvement. Now days, from the subjects of landscape, hydrology and ecology, many definitions of river system connectivity have been delimited as hydrological connectivity, landscape connectivity, and ecological connectivity, respectively, which are characterized as natural attribution. However, due to the role of human on a river system, river system connectivity should have social attributes and its concept should be extended to cover social connectivity as well. The connotation of connectivity could be illustrated from the mechanism of longitudinal connectivity and lateral connectivity and vertical connectivity. Particularly, these interaction mechanisms are dynamic. Many quantifying methods of connectivity, such as graphic method, hydrological and hydraulic method, landscape method, biological method and comprehensive index method, have been developed. However, as all these methods have their own limitation and disadvantages, they should be suited for many problems after being modified. In advance, it could be focused on research contents, methods and techniques. In the aspect of research contents, it should be significant to extend the connotation of the connectivity and investigate the responding mechanisms to many acting factors and develop the suitable measures of recovery connectivity. What's more, it should be paid attention to the fit scales and develop new methods and tools with integrated mathematic, landscape, hydrological models with GIS, network techniques and ect.