溅蚀过程中红壤团聚体周转路径的定量表征

为研究土壤团聚体的形成和破碎过程对于降雨侵蚀的响应机制，对降雨打击作用下不同粒径红壤团聚体在溅蚀过程中的周转路径进行了探讨。该研究基于稀土元素示踪法，对各粒径团聚体分别进行了标记，电感耦合等离子体质谱测定，实现全土样团聚体的周转路径追踪；然后通过室内模拟降雨试验，在90和30 mm/h降雨溅蚀条件下，对不同粒径大小团聚体（2～5、0.25～<2、0.053～<0.25、<0.053 mm）随降雨历时的周转变化规律进行了定量化研究。结果表明：稀土元素标记得到的标记团聚体效果较好且在湿筛过程中回收率达到90%以上，吸附稳定；不同降雨强度下，土壤团聚体的周转过程呈现出向破碎方向转化的趋势；90 mm/h降雨下团聚体更快发生破碎并到达稳定状态，其累积破碎率在降雨40 min后基本不发生改变，而30 mm/h下土壤团聚体会随降雨动能的累积逐步发生破碎；结合相关性分析可以发现小团聚体的变化对于整个溅蚀过程的累积破碎率和累积团聚率均表现出显著相关（P<0.01），>0.25 mm团聚体与其他粒级团聚体间的周转不显著相关（P>0.05），但<0.25 mm团聚体可能通过逐级团聚影响到其他粒级团聚体。不同团聚体在溅蚀过程中的双向转化过程，研究结果为侵蚀过程中土壤结构的动态变化模型提供理论参考。

Quantitative characterization of the turnover path of red soil aggregate in the splash process

Abstract: A soil aggregate is a cluster of primary soil particles that strongly adhere to each other. In view of the direct target of raindrop impact, the breakdown, formation, and stability of aggregates have been the key indicators of soil quality and functioning, particularly for the development of splash erosion. It is a high demand for a physical model of soil erosion associated with ecological degradation. However, little attention has been focused on transformation paths between aggregates with different sizes during the splash erosion. This study aims to quantify the mutual turnover path of red soil aggregates with different particle sizes during the splash erosion process under the various rainfall characteristics parameters. The quaternary red clay was first collected from Xian''ning in Hubei Province of China. A series of laboratory simulated rainfall experiments were then carried out with the controlled rainfall intensity (90 and 30 mm/h) and rain duration (20, 40, and 60 min). A quantitative characterization was also performed on the transformation of soil aggregates within different particle sizes (2-5 mm, large macroaggregates; 0.25-<2 mm, small macroaggregates; 0.053-<0.25 mm, microaggregates; and <0.053 mm, silt and clay fractions) under the Rare Earth Element (REE) concentration. The tested soil aggregates were labelled by the REE tracing associated with the wet sieving method. Among them, the REE was determined via the inductively coupled plasma mass spectrometry (ICP-MS). The splash erosion experiments were conducted in the improved Morgan''s splash pan. The mixture of labelled aggregates was filled in the horizontal pan for the same bulk density measured in the field. The results showed that the recovery rate was more than 90% in the labeled aggregates after the REE wet-mixing process, indicating the stable tracing performance. The turnover pathway of soil aggregates presented a dynamic tendency in the direction of fragmentation. Specifically, the turnover rate from small to microaggregates first reduced and then increased under the rain intensity of 30 mm/h, whereas, that increased and then decreased under 90 mm/h, both of which no path of large macroaggregates formation with the enrichment of microaggregates. The aggregates broke faster and reached a relatively stable state with an accumulated breakdown rate of 14%, indicating the minimal accumulated aggregation rate under heavy rainfall conditions. By contrast, the soil at 30 mm/h suffered a lasting and mild breakdown process with about half of macroaggregate under the accumulation of the kinetic energy of rainfall. The correlation analysis demonstrated that the small agglomerates behaved with a significant correlation with the cumulative fragmentation rate and agglomeration rate during the entire splash corrosion process (P<0.01), and the turnover paths were not significantly correlated between the aggregates whose diameters were >0.25 mm and others (P>0.05), while the aggregates whose diameters were <0.25 mm could affect the no-adjacent aggregates step by step (P<0.05). Consequently, the erosion-induced dynamics of the soil physical structure model can be largely enriched to combine the mixed transformation paths in opposite directions of different aggregates in the splash erosion.