基于REE示踪的土壤团聚体破碎转化路径定量表征

土壤团聚体破碎转化路径是坡面侵蚀过程研究的难点问题之一。目前团聚体破碎转化路径的定量表征仍不明晰,一定程度上限制了土壤侵蚀过程中泥沙分选搬运机制的深入研究。基于大样带调查选取6种不同质地的典型农耕地土壤为研究对象,结合稀土元素(Rare Earth Elements,REE)示踪方法,综合分析不同粒径土壤团聚体(5~2,2~1,1~0.5,0.5~0.25,<0.25 mm)和不同径流扰动周期(24 h,7天)对REE吸附和解吸能力的影响,探究REE示踪不同粒径土壤团聚体破碎转化的可行性,定量表征了土壤团聚体破碎转化路径。结果表明:REE与土壤团聚体的实际吸附浓度低于施放浓度,2~1,1~0.5,0.5~0.25,<0.25 mm土壤团聚体的REE吸附浓度与黏粒含量呈显著正相关(P<0.05);径流扰动影响对吸附于土壤团聚体的REE解吸作用十分微弱,解吸浓度仅占REE实际吸附浓度的0.001%~0.139%。5~2,2~1,1~0.5,05~0.25,<0.25 mm土壤团聚体经过湿筛后向各粒径转化的路径基本相同,向<0.25 mm微团聚体转化为土壤团聚体破碎的主要路径。相较于粉粒、黏粒含量较高的土壤团聚体,砂粒含量较高的土壤团聚体向1~0.5,0.5~0.25 mm粒径的转化贡献率整体偏低。基于REE示踪得到的>0.25 mm各粒径团聚体质量整体被低估,低估范围为-27.96%^-11.08%;而<0.25 mm团聚体质量则被高估,高估范围为3.65%~22.73%。基于各粒径土壤团聚体的REE量化值建立了校正关系,可将计算相对误差降低至0.04%~16.24%。

Quantitative Transformation Pathways of Soil Aggregate Breakdown Using Rare Earth Element (REE) Tracer Method

Soil aggregation and transformation play an important role in soil erosion and vice versa. The quantifiably breakdown and transformation pathways of soil aggregate have not been clarified. The limitation hampers the in-depth study of sediment separation and transport mechanism of soil erosion processes. Recently, ¹³⁷Cs, ²¹⁰Pb, ⁷Be and magnetite tracer methods have been widely applied to soil erosion research at slope and small watershed scales. However, those methods are not suitable for tracking multiple erosion processes simultaneously. Six typical agricultural soils with different texture from Loess Plateau and black soil region in China were selected in this study. Rare earth elements (REE) tracer method was applied to quantify the transformation pathways of five soil aggregate fractions (5~2, 2~1, 1~0.5, 0.5~0.25, < 0.25 mm). The adsorption and desorption capacity of REE on different aggregates were analyzed with the simulated runoff disturbance cycles. Results showed that the actual adsorption concentration of REE and soil aggregates were lower than that of the application concentration. REE adsorption concentration of soil aggregates at 2~1, 1~0.5, 0.5~0.25 and < 0.25 mm were significantly positively correlated with the clay content (P<0.05). The effect of runoff disturbance on the desorption of REE adsorbed on soil aggregates was very weak, and the desorption concentration only accounted for 0.001%~0.139% of the actual adsorption concentration of REE. The transformation pathways among the 5~2, 2~1, 1~0.5, 0.5~0.25 and < 0.25 mm soil aggregates fractions were basically the same, converting to < 0.25 mm microaggregates was the main pathway. The transformation rate of soil aggregates with high sand content to 1~0.5 and 0.5~0.25 mm fractions was generally lower, compared with soil aggregates with high content of silt and clay. The REE tracer method underestimated the labeled > 0.25 mm aggregates, which ranged from -27.96% to -11.08%. However, < 0.25 mm aggregates was overestimated by 3.65%~22.73%. Based on the REE quantification values of soil aggregates of various particle sizes, a correction relationship was established, which could reduce the calculated relative error to 0.04%~16.24%.