浙江东部玄武岩发育土壤剖面风化特征

Weathering characteristics of soil profiles from basalt in eastern Zhejiang Province

【目的】探究浙江省东部玄武岩发育土壤的发生演化过程,对当前亚热带地区土壤的发生和演变提供更全面的认识,从而有利于促进对该区域土地资源的高效利用。【方法】选取新昌-嵊州盆地4个玄武岩风化壳母质发育土壤剖面,分析土壤的常量元素组成、化学风化指标[化学蚀变指数(ICIA)、化学风化指数(ICIW)]和元素迁移率。【结果】①不同土壤剖面中常量元素质量分数以二氧化硅(SiO2)、氧化铝(Al2O3)和三氧化二铁(Fe2O3)为主,三者质量分数可达79%以上。②ICIA为42.81%~87.37%,ICIW为45.04%~91.43%,两者均指示中等强度化学风化。③大多数土壤样品的常量元迁移率为负值。钙(Ca)、钾(K)、镁(Mg)、钠(Na)等易溶元素大量淋失,在剖面中的迁移率表现为明显的负值(最小值可达-99%),铝(Al)、铁(Fe)、钛(Ti)元素在部分剖面的淀积层(B)相对富集,迁移率>0。常量元素的迁移率随土壤深度呈逐渐降低的趋势。【结论】①研究区不同剖面土壤样品的化学组成具有较好的一致性。②研究区较为湿热环境下,土壤经历了较为强烈的化学风化过程。③土壤发育过程符合亚热带地区脱硅富铝铁的基本成土过程。各剖面土壤常量元素迁移率随土壤深度的变化规律,揭示了基岩发育土壤自下而上的风化渐进特征。

[Objective]This study aims to explore the soil genesis of soil profiles from basalt in eastern Zhejiang Province,and to provide a comprehensive understanding of soil genesis in subtropical regions for efficient use of land resources.[Method]Four soil profiles developed from basalt in Xinchang-Shengzhou Basin were selected.The major element composition,chemical weathering indexes[chemical index of alteration(ICIA),chemical index of weathering(ICIW)]and element migration of soil were analyzed.[Result](1)The main components in different profiles were SiO2,Al2O3,and Fe2O3,whose total content reached over 79%.(2)ICIA value was 42.81%-87.37%,and ICIW value was 45.04%-91.43%,both indicating moderate strength of chemical weathering.(3)The major element migration of most soil samples was negative.Ca,K,Mg and Na were leached out of the soil in large quantities and the mobility in the profile was significantly negative(up to a minimum value of-99%).Al,Fe and Ti elements were relatively enriched in the deposition layer(B)of some profiles,and the migration rate was over zero.The major element migration gradually decreased with soil depth.[Conclusion](1)The chemical composition of the soil samples in different profiles was consistent.(2)The soil in the study area experienced a relatively strong chemical weathering process under the humid and hot environment.(3)The soil genesis conformed to the desilicification and allitization basic soil formation process in subtropical regions.The law of major element migration changing with soil depth in each profile suggested the gradual bottom-up weathering characteristics of the soil developed from the bedrock.