Investigation of factors controlling the runoff generation mechanism using isotope tracing in large-scale nested basins

Abstract

In the Yellow River source area (SAYR), a large-scale isotope hydrological monitoring effort of landscape heterogeneity was implemented. To assess and determine whether permafrost has a controlling influence on hydrological processes in the watersheds, the IsoSource and MixSIAR models were used to partition runoff during permafrost thaw season in five nested basins (from 20,930 km2 to 121,972 km2). The analysis results showed that there were significant differences in the factors controlling runoff generation in the five basins, as well as significant differences in runoff sources between upper watersheds with predominantly permafrost cover and lower watersheds with predominantly seasonal frozen soil cover. The influence of permafrost on runoff generation was significantly reduced with increasing basin size. Soil permeability was influenced by permafrost thawing which impacted runoff generation in the permafrost zone. However, this only became effective under a specific combination of landscape characteristics and topography. In basins with less permafrost cover, the topographic characteristics and conditions of the catchment itself controlled the runoff generation mechanism. In general, the presence of permafrost influences the runoff generation, but the extent of the influence depends on the characteristics of the basin itself and, in particular, the control of topography increases with the scale of the basin.