资源环境科技发展态势分析平台

In many areas of the world, the surface of the earth is changing rapidly. This can affect the partitioning of precipitation into overland flow (OF) and infiltration. OF can reach the stream quickly and strongly influences the streamflow response to precipitation and can cause surface erosion. However, our knowledge of the changes in OF responses during landscape evolution is still limited. To investigate how hillslope aging affects OF, we studied three plots on four different aged moraines (several decades to ∼13.5 thousand years old) at a silicate and carbonate proglacial area in the Swiss Alps. We used sprinkling experiments to determine OF characteristics (such as the runoff ratio and timing) and used tracers (δ²H and NaCl) to identify the mixing of rainfall and soil water. Sediment concentrations and turbidity measurements provided an estimate of OF-driven erosion rates. The OF ratios were largest (42%) for the oldest moraines because the clay-rich layer at 20-40 cm below the surface caused saturated OF. However, OF was more frequent on the youngest moraines due to the high stone cover. Soil and vegetation development increased soil water retention capacity and pre-event water fractions for the old moraines, but decreased suspended sediment yield. The results show that OF characteristics and sediment transport change markedly during landscape evolution. This needs to be taken into account when simulating runoff and erosion responses for rapidly changing Alpine areas, and can - together with the outcomes for subsurface flow (companion paper) - be used to improve landscape evolution models.

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