Beryllium-7 in vegetation, soil, sediment and runoff on the northern Loess Plateau

Abstract

Beryllium-7 (7Be), as a potentially powerful tracer, was widely used to document soil redistribution and identify sediment sources in recent decades, but the quantity and distribution of 7Be in vegetation, soil, sediment and runoff on the Loess Plateau have not been fully described. In this study, we measured 7Be in vegetation, soil, sediment and runoff on the northern Loess Plateau of China and analyzed its variations during the rainy season to assess the potential of the 7Be method for documenting soil redistribution and identifying sediment sources in a wide range of environments. The results indicated that vegetation, soil, and sediment samples showed higher levels and larger variations of 7Be activities during the rainy season. The drying plants showed 7Be mass activity that was more than three times higher than that of living and semi-decomposed plants. 7Be mass activity in plants and sediment was much higher than in the soil. 7Be activity in runoff water with a few submicron suspended particles varied slightly and was far lower than in plant, soil and sediment samples. The cumulative precipitation generally determined 7Be inventory held by plants and soil. An inverse relationship was found between the 7Be mass activity in sediment and the sediment amount. Globally, approximate 30% of the total 7Be was held by plants in both the herbaceous and subshrub plots. Approximate 10% of the total 7Be was lost with sediment from the bare plot. A very small proportion of 7Be (1.18%–3.20%) was lost with runoff, and the vast majority of 7Be was retained in the slope soil at the end of rainy season. Vegetation cover and soil erosion significantly affected the spatial distribution and variations of the 7Be inventory in soil, providing a necessary condition for the development of a 7Be method to document soil erosion on slopes with vegetation.