古日乃湖盆沉积物发育土壤盐分与碳酸钙积累机制

Characteristics and Mechanisms of the Accumulation of Salts and Calcium Carbonate in Sediment-derived Soils of the Gurinai Playa

干旱区湖泊是维持生态脆弱区环境平衡的重要载体,随着环境变化和人类对水土资源的不合理利用,我国干旱区湖泊日渐萎缩、干涸直至消失。湖泊干涸过程中,地下水位持续下降,风积物不断加积,土壤演化过程随之发生变化,但关于湖泊沉积物发育土壤演化特征的研究十分匮乏。本研究结合土壤发生学和地球化学方法分析了古日乃湖盆沉积物发育土壤的盐分与碳酸钙积累特征与机制。结果表明:盐分积累是古日乃湖盆土壤形成的主要特征,盐化土壤表层水溶性盐含量、Na^(+)浓度和钠吸附比分别为13.15~650.50 g·kg^(-1)、186.9~12114.7 mmol·L^(-1)、22.3~890.5(mmol·L^(-1))^(1/2),土壤具有高含盐量、高Na^(+)浓度与高钠吸附比,表现出强度盐化特征。古日乃湖盆干涸,土壤积盐过程由现代盐化向残积盐化演化,盐分类型由氯化物型、氯化物-硫酸盐型向硫酸盐-氯化物型、硫酸盐型转变。借助于与Ca地球化学行为相似的Sr同位素组成分析,表明土壤碳酸钙以次生碳酸钙为主,其占比超过碳酸钙总量的80%;土壤碳酸钙主要来源于母质和地下水,地下水持续供给Ca^(2+)是碳酸钙强度积累形成钙磐的基础。古日乃湖盆土壤盐分与碳酸钙积累特征可为评估环境变化背景下土壤的形成与演变,并为预测我国内陆河尾闾湖地区土壤与生态环境变化提供科学依据。

Lakes in arid areas play an important role in keeping the balance between ecology and environment of the fragile ecosystems therein.Unfortunately,the lakes in the arid regions of China are shrinking,drying up or even disappearing,due to changing environment and human’s abusive use of water and soil resources.【Objective】With the lake drying up,ground water table keeps on going down in depth and aeolian sediments build up,and consequently soil forming process begins to change.However,so far little has been reported in the literature about formation and development of sediment-derived soils in such an environment.【Method】In this study,both pedological and geochemical methods were applied to investigation of characteristics and mechanisms of salt and calcium carbonate accumulating in sediment-derived soils in the Gurinai Playa.【Result】Results show that the accumulation of various kinds of salts was the primary pedogenic process.Soil salt content,Na^(+)concentration and sodium absorption ratio in the surface soil layer of the sediment-derived soils in the Gurinai Playa reached 13.15~650.50 g·kg^(-1),186.9~12114.7 mmol·L^(-1)and 22.3~890.5(mmol·L^(-1))^(1/2),respectively,which suggest that the studied soils experienced strong salinization.In addition,with the Gurinai Playa drying up the accumulation of salts in the soils evolved from modern salinization to residual salinization,and soil salt composition gradually changed from Cl^(-),and Cl^(-)-SO_(4)^(2-)types in the initial stage of the soil evolution to SO_(4)^(2-)-Cl^(-),and SO_(4)^(2-)types in the more advanced stages.Given that Sr and Ca are quite similar in geochemical behavior,the analysis of composition of Sr isotopes demonstrates that secondary CaCO_(3)predominated in soil total CaCO_(3)accounting for over 80%.Moreover,soil CaCO_(3)in this area was primarily derived from calcareous sediments and groundwater.The continuous provision of Ca^(2+)by groundwater led to strong accumulation of CaCO_(3)and formation of Calcicpan.【Conclusion】Interpretation of the accumulation of salts and CaCO_(3)in soils during the drying progress of the Gurinai Playa provides a scientific basis for evaluating soil formation and evolution in relation to environmental changes,and for predicting changes in soils and ecological environment of the terminal lake areas of inland rivers.