摘要
The existing^(210)Pb_(ex)mass balance models for the assessment of cultivated soil erosion are based on an assumption that^(210)Pb_(ex)is quite evenly mixed within the plough layer.However,the amount of^(210)Pb_(ex)distributed in the soils below the plough depth,like a downward tail in the lower part of the^(210)Pb_(ex)profile,has been largely ignored.In fact,after the initial cultivation of undisturbed soils,^(210)Pb_(ex)will diffuse downward from plough layer to the plough pan layer due to the concentration gradient.Assuming^(210)Pb_(ex)inventory is constant,the depth distribution in the two layers of the cultivated soils will achieve a steady state after continuous cultivation for 10.37 years,when^(210)Pb_(ex)is evenly distributed in the soils of the plough layer with an exponential concentration decline with depth in the soils of the plough pan layer,and the^(210)Pb_(ex)concentration at any depth will be invariable with time.The work reported in this paper attempts to explain the formation of the^(210)Pb_(ex)tail in the soil profile below the plough depth by theoretical derivation of the^(210)Pb_(ex)depth distribution process in the two layers of the cultivated soils,propose a^(210)Pb_(ex)mass balance model considering^(210)Pb_(ex)diffusion based on the existing model,and discuss the influence of the^(210)Pb_(ex)tail to the existing model.
The existing 210Pbex mass balance models for the assessment of cultivated soil erosion are based on an assumption that 210Pbex is quite evenly mixed within the plough layer.However,the amount of 210Pbex distributed in the soils below the plough depth,like a downward tail in the lower part of the 210Pbex profile,has been largely ignored.In fact,after the initial cultivation of undisturbed soils,210Pbex will diffuse downward from plough layer to the plough pan layer due to the concentration gradient.Assuming 210Pbex inventory is constant,the depth distribution in the two layers of the cultivated soils will achieve a steady state after continuous cultivation for 10.37 years,when 210Pbex is evenly distributed in the soils of the plough layer with an exponential concentration decline with depth in the soils of the plough pan layer,and the 210Pbex concentration at any depth will be invariable with time.The work reported in this paper attempts to explain the formation of the 210Pbex tail in the soil profile below the plough depth by theoretical derivation of the 210Pbex depth distribution process in the two layers of the cultivated soils,propose a 210Pbex mass balance model considering 210Pbex diffusion based on the existing model,and discuss the influence of the 210Pbex tail to the existing model.
基金
Supported by National Natural Science Foundation of China(Nos.41102224 and 41101259)
