Responses of Sediment Yield to Vegetation Cover Changes in the Poyang Lake Drainage Area, China

摘要

Ascertaining the relationships between sediment transport processes and vegetation cover is essential for watershed soil and water conservation. However, it is not easy to realize this target on a large scale. In this study, the location-weighted landscape contrast index (LCI) based on the “source-sink” theory of ecological processes was introduced to unravel the response of sediment yield to vegetation cover changes in the Poyang Lake drainage area (the largest freshwater lake in China). A modified location-weighted landscape contrast index (mLCI) was proposed to improve the accuracy and efficiency of the LCI. The average vegetation fraction of the study area significantly increased from 46.2% in Period I (1992–1994) to 76.5% in Period II (2004–2006) and then slightly decreased to 73.2% in Period III (2011–2013). From Period I to Period II, the area-specific sediment yield (ASY) sharply decreased by 55%. In Period II, the “source” vegetation patches were found further away from the water bodies, and were more likely to be located on gentler slopes than in Period I. From Period II to Period III, the ASY sharply increased by 83%. In Period III, “source” patches were found closer to the water bodies than in Period II, whereas the “sink” patches were found further away from the water bodies. The high statistical correlation between LCIs/mLCIs and ASY indicated a sensitive response of the sediment yield to vegetation cover changes that significantly altered the sediment transport processes in the study area. The ASY was better correlated with the mLCI than with the LCI. Three key harnessing sub-watersheds of the Ganjiang watershed were identified by calculating the mLCIs: Qingfengshan, Yuanhe, and Jinjiang. This study supported watershed ecological management in the Poyang Lake drainage area and provided a methodology reference for future sediment transport process studies.