Ecological network analysis of watershed meta-ecosystems: A new perspective on quantifying the integrated watershed ecosystem

A watershed is an integrated ecosystem. In different disciplines, a watershed has been described as a geomorphic unit, a hydrological unit, an ecological unit, or a socio-economic unit and has been quantitatively described using different indicator systems. Until now, no general indicator system has existed that could quantitatively describe the geomorphic features, hydrologic features, ecological features and socio-economic features of an integrated watershed ecosystem (IWE) simultaneously. Here, we proposed a quantitative descriptive framework for an IWE (QDFIWE). This QDFIWE involved three steps: (1) constructing a watershed meta-ecosystem (WME) based on the hierarchical system of the watershed; (2) constructing flow networks based on the WME; and (3) identifying the holistic properties (such as spatial throughput, spatial organization and spatial resilience) of the WME through analyzing its flow networks based on ecological network analysis (ENA). Then, we applied this method to study the geomorphic topological structure, geomorphic spatial structure, natural water resource system and integrated water resource system of the Yangtze River basin. The results suggested that based on the QDFIWE, (1) one could construct different WMEs and corresponding flow networks for different requirements; (2) one could obtain time series of the holistic properties of an IWE to analyze its evolution; (3) one could compare, classify and cluster any number of IWEs through identifying their holistic properties according to similar strategies; and (4) one could determine or create more indicators, which could provide additional information, based on the holistic properties of an IWE. This study demonstrates that the QDFIWE is a general method of quantifying the holistic properties of all subsystems of an IWE simultaneously. Thus, the method can improve the understanding of the IWE.