长江三角洲古土壤有机元素组成及古环境意义

Composition of Organic Element of Paleosol in Changjiang Delta and Its Paleoenvironmental Implication

以长江三角洲第一古土壤层作为研究对象 ,分析古土壤的有机元素组成和变化 ,并结合微形态及其它分析工作 ,探讨其记录的古环境信息 .结果表明 ,古土壤层中成土程度强弱是影响有机质组成的主要因素 ,随着成土程度的增强 ,土壤m(C) /m (N)的比值也相应增加 ;此外 ,古土壤有机质组分还是土壤暴露时间的反映 ,土壤暴露成土时间越长则越有利于有机组分的降解和转化 ;区域古地理条件差异也是影响古土壤有机元素组成的重要因素 ,干旱透气良好的环境更有利于土壤有机质的分解与转化和增强脱氮作用 ,从而形成m (C) /m (N)的高值 .

Organic components have long been considered as an indispensable part of soil.It has significant influence on pedogenesis,physical character,chemical character and biological activity of soils.Nevertheless,few researches have emphasized on the relationship between soil organic components and pedogenesis.The study focused on the first layer of paleosol in Changjiang delta,and composition of organic element and its variation in the paleosol have been analyzed.Paleoenvironment information has been interpreted on the basis of organic element analysis,along with micromorphology analysis and previous studies.There are three strong pedogenetic horizons in the paleosol in the front of southern flank of Changjiang delta,and correspondingly organic components near these horizons are characterized with high carbon,low nitrogen content and high C/N ratio.High carbon content may be the consequence of carbon accumulation,while high C/N ratio resulted from degradation and denitrogenation of organic components.These processes are tightly related to pedogenesis.Extremely high C/N ratio horizon is also found in the paleosol,whereas micromorphological features indicate a relatively weak pedogenesis.Carbonate occuring in this horizon suggests more arid and well-exposed environment.Organic components in such an environment tend to be further denitrogenation.Organic element content of paleosol in the back of southern flank is different from that of front of southern flank in Changjiang delta.The latter bearing lower in C/N ratio indicates a more well-exposed environment.Such a difference is due to morphological diversity in the delta.In the upper part of the paleosol,the content of micromorphological feature decreases dramatically,indicating a drop in leaching.C/N ratio comparatively high in this horizon suggests a long period of exposure,which may be formed during the last glacial maximum.Both the carbon and the nitrogen contents increase rapidly in the overlying horizon suggest a shift toward warm and humid climate in postglacial period.