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

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.