The dynamic evolvement and hydrological driving factors of marsh in Nenjiang River basin

Based on ArcGIS spatial analysis tools and four wetland remote sensing images from 1978, 1990, 2000 and 2008, the Nenjiang River basin can divided into 43 subbasins using the Soil and Water Assessment Tool (SWAT) model.A contrastive analysis is performed on marsh wetlands to investigate the differences between information on rainfall and runoff and wetland degradation provided by remote sensing images.Further analysis is done on the subbasins with serious issues on wetland loss and degradation.On the other hand, two land-use maps are used to generate the land-use transition matrix of the Nenjiang River basin.The result shows that the marsh wetlands in the f Nenjiang River basin have degraded seriously during the period 1978—2008, especially between 1990 and 2000.This can be closely related to the changes in precipitation and runoff, as well as the influence of human activities such as the conversion of land-use changes and water conservancy constructions.Furthermore, the variation of marsh areas and the basin runoff coefficient exhibit a significant positive correlation at the level of 0.01, and the Pearson correlation is 0.90. Under the influences of climate changes and human activities on the hydrological processes and water resources, the wetland areas have gradually been shrinking over the years, causing a negative impact on the balance of the wetland ecosystem in the Nenjiang River basin.