渭河源流域源汇景观演变对径流泥沙的影响

探讨源汇景观演变特征与径流泥沙的关系对定量识别源汇景观功能对生态过程的影响具有重要的科学意义。以位于黄土高原和西秦岭山地交错区域的渭河源为例,分析了流域源汇景观格局演变与降雨耦合驱动对径流和泥沙的影响,结果表明:(1)研究区1982—2017年汇景观比例逐渐增加并超过源景观,源汇景观功能演变主要发生在黄土丘陵区,源汇景观负荷比指数呈逐年下降趋势;(2)影响流域径流和泥沙的主要因素不同,洪峰流量与含沙量主要受源景观面积比例和源汇景观负荷比的影响,呈显著的下降趋势,而径流量仅与降水量存在相关性;(3)基于信息理论方法的相对重要性分析表明,降雨对流域径流量的相对重要性高于源汇景观负荷比,而源汇景观负荷比对洪峰流量和含沙量的相对重要性较高,传输距离和海拔分布对径流泥沙和洪峰流量具有重要影响。在长时间尺度上,源汇景观格局演变影响了径流及泥沙特征,并且对泥沙影响的相对重要性高于径流。源汇景观合理的时空分布可以有效调控水土流失过程,对黄土高原生态可持续发展具有重要意义。

Impacts of source and sink landscape dynamics on runoff and sediment in the source watershed of the Weihe River

Identifying the relationships among characteristics of the source and sink landscape and runoff and sediment will help quantifying the interactions between landscape pattern and ecological processes. This study analyzed the coupled impacts from changes in the source sink landscape and precipitation patterns on runoff and sediment at the source watershed of the Weihe River, which located in the ecotone of the Loess Plateau and the western Qinling Mountain. The location-weighted landscape index (LWLI) based on the Source-sink Landscape Model (SSLM) was used to quantitatively characterize the changes of landscape pattern. The results included:(1) the area proportion of the sink landscapes increased from 1982 to 2017 and became larger than the source landscapes. The changes of source and sink landscape mainly happened in the hilly regions of the Loess Plateau. The LWLI decreased from 1982 to 2017, with substantial decrease between 1995 and 2010. (2) The major factors affecting runoff and sediment were explicitly different. The peak flow and sediment concentration substantially decreased from 1982 to 2017 and had close correlations with area proportion of "source" landscapes and the LWLI values. However, the amount of annual runoff fluctuated during the study period due to variation of precipitation and had limited correlation with changes of the landscape pattern. (3) The LWLI had close relationships with peak flow and sediment concentration by comparing the relative variable importance of landscape to climatic factors, while precipitation was the major factor affecting runoff. Moreover, characteristics of landscape pattern were regulated by latitude and migration distance and had stronger impacts on runoff and sediment concentration than slope in the study area. Results of the study suggested that changes in the pattern of "source-sink" landscape and precipitation had significant influences on river channel runoff and sediment at a long-time scale, but their importance to runoff and sediment were obviously different. The reasonable planning of "source" and "sink" landscapes could effectively control soil and water loss at the watershed scale. For land use planning and policy-making, optimization of landscape configuration should be considered to improve water and soil conservation.