Objective Passing through nature reserves, rural agricultural areas and urban construction areas successively, regional river blue-green space is typically characterized by external differentiation and internal integrity. With its natural process and spatial function closely linked, regional river blue-green space plays the role of multi-scale support constraint and multi-dimensional regional coordination in territorial spatial planning. As an important ecologically sensitive space, regional river blue-green corridor network can support the supply of territorial natural ecological resources as a whole, the protection and restoration of ecological space, the efficiency of rainfall flood regulation and storage, the health of ecosystem in urban and rural watersheds, and can constrain the unlimited sprawl of city and the planning and spatial layout of construction land to guide the formation of sustainable urban spatial forms and promote the intensive development of territorial space. The river blue-green space has multiple functional values in such fields as ecology, society, economy and culture. Through reasonable planning and management, the river blue-green space can be used as a "connector" to coordinate the conflicts between protected areas and development areas, construction land and non-construction land, ecological function and social function, etc. The research on the collaborative planning of river blue-green space is of important significance to the conservation and exploitation of natural resources under the background of territorial spatial planning.

Methods Through literature research and case studies, this research summarizes the differences in the transformation characteristics of regional river blue-green space, and develops approaches for the collaborative planning and management thereof.

Results The differences in internal natural characteristics are reflected in longitudinal spaces (such as source zone, transfer zone and sedimentary zone), lateral spaces (such as river channel, flood plain, slope area and highland area), vertical spaces (such as surface water, diving layer and groundwater) and seasonal changes of natural factors. The differences in external construction demands are reflected in the riparian areas associated with urban and rural areas, such as nature reserves, rural agricultural areas, and urban construction areas, which respectively undertake such functions as habitat maintenance, agricultural production, residence, industry, commerce and leisure. The differences in regional overall spatial transformation are reflected in the transformation rules for river blue-green space in such aspects as functional pattern, associated land utilization, and basic element characteristics. On the basis of recognizing the characteristic differences of regional river blue-green space, the research proposes a collaborative planning approach in terms of space and function. According to relevant socio-economic indicators, the research conducts transect zoning at three levels as follows: the overall transect zoning of the river network at the urban and rural regional level, the river longitudinal transect zoning at the central town level, and the lateral transect zoning of river reach at the block site level. In combination with the natural ecological characteristics, current construction problems and urban-rural development demands of the river blue-green space in each zone, the research coordinates the dominant and secondary composite functions of the river blue-green space in transect zones as a whole and the longitudinal transect zones based on the interpretation of the synergy-tradeoff relationship between various ecological service functions. At the level of urban and rural areas, the research puts forward a model for collaborative planning and layout of river blue-green space at multiple scales. In addition, the research builds an overall support system of river blue-green space, which covers water conservation areas, hydrological corridors, and hydrological priorities. According to the overall functional positioning of the overall transect zoning, the research confirms the layout types and locations of conservation areas, corridors and hydrological priorities. At the level of central town, the research forms the longitudinal land layout pattern of the river blue-green space. Under the composite functional objective of longitudinal transect zoning, the research summarizes the guidelines for the layout of land types of the river blue-green space in such aspects as layout location, layout scale, layout form and compatible combination to form a coupled and coordinated layout mode for construction land and non-built land in river area of central town. At the level of block site, the research implements management and control over the lateral ecological interface of the river blue-green space and the fine interface design matching the composite functional objectives. Specifically, the research manages and controls the boundary, patch form and greenway of the ecological interface, and establishes the main control indicators of the lateral ecological interface, such as the proportion of trees and shrubs, the form of revetment, the ratio of inner patch edge, and the width of greenway and green street.

Conclusion There exists obvious spatial heterogeneity in the supply and demand of ecosystem services in the regional river blue-green space. It is necessary to integrate the differences in ecological characteristics and social demands, and carry out the identification of differences in urban-rural regional characteristics and the collaborative planning and management of regional river blue-green space. Based on transect zoning, the research clarifies the the composite functions of and the spatial layout of land utilization by river blue-green space, and develops the strategies for collaborative planning at different levels for different river sections and corresponding control factor indexes, so as to form planning and management approaches for the effective protection and utilization of regional river blue-green space. The collaborative planning of regional river blue-green space attaches importance to both the internal adaptation to the evolution of riparian ecosystem, and the external formation of related environmental impacts and satisfaction of urban-rural development function demands, which not only ensures the healthy operation of the internal ecosystem of the river corridor, but also improves the external composite service function.