利用燃煤飞灰作为时间标记物评价坡耕地黑土侵蚀物质和有机碳的再分配

燃煤飞灰(以下简称飞灰)作为时间标记物克服了放射性同位素137Cs示踪方法不能鉴定大气核爆炸之前的土壤再分布过程这一缺陷。本文利用土体中的飞灰研究坡耕地黑土有机碳的时空再分布特征。尝试建立飞灰在土壤中分层的方法,根据飞灰和土壤有机碳(SOC)随土壤深度的分布特征鉴定土壤堆积厚度,以及堆积土壤的相对年代。结果表明:用飞灰示踪技术鉴定的埋藏土壤表层与SOC含量随深度变化确定的埋藏表层吻合较好,景观中低洼部位在飞灰出现前就有一定的土壤堆积。各地貌部位坡肩侵蚀最为严重,有机碳含量最低;坡顶坡度较小,侵蚀微弱;坡脚和坡足发生沉积。土壤沉积速率在1.01~5.56mm a-1之间。研究结果还表明堆积部位埋藏层的SOC含量较高,说明有相当数量的有机碳被隐遁在目前的耕作层之下。因此,在评价农田土壤作为大气CO2“源”或“汇”时应该考虑景观中土壤物质迁移和埋藏作用的影响。

ASSESSMENT OF REDISTRIBUTION OF EROSION MATERIAL AND SOIL ORGANIC CARBON USING FLY ASH AS A TIME MARKER AT A SLOPING FIELD IN BLACK SOIL REGION

Using fly ash as a tracer overcomes the limitation that the ¹³⁷Cs tracer method has in explaining the processes of soil redistribution prior to a nuclear explosion in the atmosphere.In this study fly ash was used as a time marker to study spatial and temporal characterist ics of the redistribution of soil organic carbon(SOC)in Black soil,Northeast China.Attempts were made to build up a methodology to determine thickness of accumulated layers and the soils underneath using fly ash.Results showed that the method was capable of est imating relative age of the accumulated materials.The surface of the buried soil determined by the fly ash technology was in consistency with that obtained with the method based on variation of SOC concentration with the depth in profiles.The results also indicated that redistribution of soils in the study area occurred prior to the use of steam locomotive.Among the studying geomorphic positions,at the shoulder-slope erosion was the strongest and the content of SOC was the lowest.There was no obvious erosion at the summit because of small slope gradient.Redeposition also took place at backslope,foot-slope and toe slope.The rate of soil deposition ranged between 1.01~5.56 mm a^-1.The study also found that the content of SOC in buried surface layers was higher than that in the plowed layer,which indicated that there was much organic carbon sequestered below the plowed layer.The effects of soil transport and burial need to be considered in assessing agricultural soils as carbon resource or sink of atmospheric CO₂.