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.

Atmospheric (210)Pb as a tracer for soil organic carbon transport in a coniferous forest

Core soils and falling litter samples were collected in a Japanese cypress forest (Chamaecyparis obtusa) to determine the litter-fed (210)Pbex and organic carbon transfer from the forest canopy to soil and their subsequent distribution. Of the canopy residing (210)Pbex pool, litterfall annually transports 53% to the forest floor while it adds 117 g m(-2) per year of organic carbon to the forest soil, implying that litterfall dynamics can influence the distribution of (210)Pbex and soil organic carbon (SOC). (210)Pbex and SOC showed identical profile shapes and strong correlation in spatial as well as along the soil depth, indicating that both are affected by a similar process. Given the ubiquitous natural source of (210)Pbex, it is plausible to infer that radiolead can be a possible tracer to study the SOC redistribution at regional and global scales.

Root uptake of lead by Norway spruce grown on 210Pb spiked soils

The root uptake of lead (Pb) by trees and the transfer of Pb by leaf litter deposition to the forest floor were investigated through a pot experiment with Norway spruce. Natural Pb and radio isotopic lead (210Pb) were determined in needles and twigs and in the pot soil spiked with 210Pb. Calculations of the specific activity in plant material and in the supporting pot soil showed that less than 2% of the Pb content of needles and twigs originates from root uptake and approximately 98% are deposited from the atmosphere. Atmospheric Pb has declined by a factor of 7 from 1980 to 2007 but is still a major pathway of Pb to vegetation and topsoils. The conclusion from the experiment is that the internal circulation of Pb through root uptake, translocation and litterfall, gives an insignificant input of Pb to the forest floor compared to atmospheric deposition.

Distribution of radiocesium and natural gamma emitters in pine needles in coniferious forest sites of Izmir

Using a high-resolution gamma-spectrometer system, the activity concentrations of 7Be, 137Cs, 40K and 226Ra were determined in the pine needles. Activity concentrations of the concerned radionuclides in the needle samples were as follows: 7Be, 24.6+/-2.40 to 210+/-7.21 Bq kg(-1), 40K, 23.5+/-12.4 to 287+/-15.6 Bq kg(-1), 226Ra, 0.44+/-0.12 to 12.3+/-2.18 Bq kg(-1), and 137Cs, 0.61+/-0.30 to 2.29+/-0.38 Bq kg(-1). It is found that the frequency distributions obtained for 7Be and 137Cs can be fitted to a normal distribution, and for 40K and 226Ra can be fitted to a log-normal distribution.