Dynamics and integrity of wetland network in estuary

a r t i c l e i n f o The increasing fragmentation and degradation tendency of estuarine wetlands due to rapid urbanization in coastal areas exert the urgent need to quantify the structural characteristic of wetland network, which involves the fragmentized wetland patches for wetland restoration and conservation. Although wetland networks have already been used for conservation planning on a regional scale, the variation of connectivity and structural characteristic has not been well studied. Therefore, this study gathered data from Landsat TM/ETM+ images to construct the wetland network and employed the graph theoretical analysis to characterize the network evolution, structural connectivity changes, and network integrity alteration in the Pearl River Estuary, South China. The wetland network integrity was defined in the study, including structural connectivity and several functional attributes , the variation of six generated networks during 1979 to 2009 was analyzed as well. The wetland network exhibited a weakening topology over time, which is indicated by a significant decrease in the degree distribution, connectivity, and clustering coefficient. The diminishing trends of wetland network integrity reveal that although the latest wetland network can still protect the regional environment, the weakening phenomenon in its topol-ogy and integrity would reduce the ability of estuarine wetland network to resist external interference. Estuarine wetlands improve water quality and provide habitat for wildlife (Mitsch and Gosselink, 2000; Moreno et al., 2007). However, the structure and function of estuarine wetlands have been greatly changed under the synthetic effect of human activities (Evan et al. The existing wetland pattern on the regional scale might not meet wildlife requirements for habitat because of fragmentation and ecological process change Estuarine wetlands can support rich ecological functions if good linkages exist between the adjacent wetlands when barriers to water flow and movement of animals are only few (Boys et al. Related studies have suggested that enhancing the connectivity of wetlands is a key measure of biodiversity conservation and may be one of the most effective approaches to counteract the potentially adverse effects of habitat fragmen-According to the graph theoretic approach, wetland networks could reflect the connected relationships between the kinds of wetlands based on the network index (e.g., shortest path index) to access ecological functions of wetland networks (Lookingbill et al., 2010a). The connec-tivity characteristics could illuminate critical nodes and specific links, which should be protected preferentially to improve physical, chemical, and biological processes within wetland networks (Fath …