Beryllium-7 activity concentration in plants on the Loess Plateau, China

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.

Beryllium-7 measurements of wind erosion on sloping fields in the wind-water erosion crisscross region on the Chinese Loess Plateau

Soil erosion is complex in the wind-water erosion crisscross region of the Chinese Loess Plateau, as interleaving of wind and water erosion occurs on both temporal and spatial scales. It is difficult to distinguish wind erosion from the total erosion in previous studies due to the untraceable of aeolian particles and the limitation of feasible methods and techniques. This study used beryllium-7 measurements to study wind erosion in the wind-water erosion crisscross region on the Chinese Loess Plateau arms to delineate wind erosion distribution, to analyze its implication to erosive winds and surface microrelief, and to determine correlations between erosion rates and slope gradients. Results obtained using beryllium-7 measurements based on observation plots were verified with saltating particle collection method, and were also verified on a field scale. Results indicated that the effective resultant erosion wind was from northward, which was proved by the eight-directional distributed saltating particles. The microrelief of the ground surface contributed to the formation of high or low erosion centers. Wind erosion rates increased with a linear (R²≥0.95) or exponential (R²≥0.83) fitting increase in the slope gradients as reported in previous studies. Compared to wind erosion on field scale, both the plots and fields exhibited similar distribution patterns in wind erosion isolines. We also determined that the wind erosion rate for two fields estimated, based on equations developed from plot scale was acceptable. This study validates the feasibility of beryllium-7 measurements for soil-wind erosion field experiments and the potential to expand this approach to real field conditions.