Examining human disturbances and inundation dynamics in China's marsh wetlands by using time series remote sensing data

The hydrological regime is one of the most significant characteristics of wetlands, which maintains the structural and functional integrity of wetland ecosystems. China experienced rapid economic development since the 1990s, which caused severe degradation of all types of wetlands, especially marsh wetlands that are easily converted through filling or draining. Therefore, it is crucial to examine the inundation alterations in marshes as well as the forces behind the changes. In this study, the inundation dynamics in marsh wetlands of China were documented using time-series Landsat observations from 1992 to 2018. Then, nighttime light data was utilized to indicate the intensity of urbanization and infrastructure construction, which was incorporated with historical statistics to conduct attribution analyses of wetland inundation changes. Great spatial heterogeneity in the water distribution and change trajectory was observed in different areas. Severe wetland desiccation took place in Inner Mongolia and East China, in which the inundation area decreased by 51.3 % and 20.9 %, respectively. By contrast, the water area in North China and Tibetan Plateau increased by 58.2 % and 21.0 %, respectively. Behind the tremendous changes, anthropogenic factors played dominant roles. The marsh wetlands in East China, North China, and Southwest China took up only 1.9 % of the total marsh area but accounted for 26.0 % of the entire nighttime light volume. In East China and Southwest China, urbanization and infrastructure construction had significantly negative effects on wetland inundation. Overgrazing or unregulated irrigation altered the original inundation dynamics of marsh wetlands in Inner Mongolia, Southwest China, the Tibetan plateau, and Northeast China. This study illustrated the possible driving forces behind wetland inundation changes, which could help to locate degrading marsh wetlands triggered by anthropogenic activities. Then, targeted management and conservation actions could be implemented.