Knowledge Resource Center for Ecological Environment in Arid Area
| 黑河流域土壤碳酸盐地球化学特征及其发生学意义 | |
| 其他题名 | Geochemical characteristics of soil carbonate in the Heihe River Basin and their pedogenic implications |
| 杨帆 | |
| 出版年 | 2018 |
| 学位类型 | 博士 |
| 导师 | 张甘霖 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 以碳酸钙为主的碳酸盐是土壤中重要的物质组成，对土壤物理、化学和生物性状有着重要的影响。碳酸钙的淋溶淀积过程是干旱、半干旱地区主要成土过程，其形态特征和剖面分布是判定土壤发育程度的重要标志和区分土壤类型的重要指标。次生碳酸钙还是土壤发育的历史信息记载，可以指示土壤年龄，用作重建古气候和古生态环境。土壤碳酸钙的来源、次生碳酸钙的形成过程及其影响因素是土壤发生学研究的重要内容。另外，碳酸盐作为土壤无机碳的主要组成，它通过溶蚀/风化到再结晶与大气CO2之间进行物质交换，影响全球碳的生物地球化学循环。黑河流域是我国西北干旱区第二大内陆河流域，其土壤碳酸盐的组成和分布详细特征还不清楚。流域内景观分异强烈、成土因素组合多样，是研究土壤碳酸盐地球化学特征分异的理想区域。明确不同景观土壤碳酸盐演变规律，对理解干旱区土壤形成和发育具有重要的理论意义；次生碳酸盐的辨别，尤其是次生碳酸钙与原生碳酸钙的区分对土壤无机碳库的精确估算和固碳效应的科学评估具有迫切的现实意义。黑河流域具有高山－绿洲－荒漠的景观格局，本研究根据相似的成土因素组合将其划分为10种景观单元。分析了不同景观单元土壤碳酸盐的含量（碳酸钙含量）、密度（无机碳密度）及其剖面分布；基于土壤碳酸钙含量的剖面分布特征，获得了9个代表性剖面进行土壤碳酸盐元素和同位素地球化学、土壤次生碳酸钙形成过程及其速率的研究；结合土壤碳酸钙潜在物源和成土模式对不同景观单元土壤碳酸钙的来源进行解析。结果表明：（1）成土环境的不同引起景观间土壤CaCO3含量和土壤无机碳密度的差异极显著。土体CaCO3含量大小顺序为荒漠化草原＞干草原＞河西走廊绿洲＞山地草原＞干盐湖＞阿拉善戈壁＞沙漠＞山地森林＞亚高山灌丛草甸＞高山草甸；不同景观1米土壤无机碳密度为0.22~20.22 kg C m-2，其变化趋势与土体CaCO3含量一致。根据剖面各发生层CaCO3含量将土壤碳酸钙的分布归并为均一型、淀积型和逐渐增加型；此外，无机碳占土壤碳库的比重随土壤深度的增加而增加，表明碳酸盐主要分布于深层土壤。黑河流域土壤碳酸钙的影响因素较为复杂。干旱环境下（年均降雨量MAP＜200 mm），土壤CaCO3含量与气候因子的相关性检验不显著，母质是土壤CaCO3含量的主控因素；（类）黄土母质发育的土壤CaCO3含量随温度的增加而增加，随降雨量的增加而减少，表明气候因子是影响（类）黄土母质发育的土壤CaCO3含量分异的主要因素。（2）代表性剖面不同土层土壤碳酸盐的主量元素含量，Ca最高，Mg次之，Si、Al较低；微量元素含量，Sr最高，Ba次之，Pb极低。碳酸钙淋失的土层土壤碳酸盐Ca、Mg含量低，钙积层（钙磐）土壤碳酸盐Ca、Mg含量高。整体上，土壤碳酸盐Ca与Si呈极显著负相关关系，表明碳酸盐积累越强（气候越干旱），硅酸盐风化越弱；土壤碳酸盐Ca与Sr的相关性检验不显著，反映了这些土壤碳酸盐的来源不尽相同。9个剖面的土壤碳酸盐锶同位素组成具有较大差异，可以近似指示土壤碳酸盐来源不同。灌溉影响的HCO01和HCO02剖面土壤碳酸盐87Sr/86Sr比值通体较高。干盐湖PL01的钙积层和PL02的钙磐土壤碳酸盐87Sr/86Sr比值在其剖面中最高；（类）黄土母质发育的MF01、MG01、TS01、DS01和DS02剖面土壤碳酸盐87Sr/86Sr比值整体随深度降低（MF01除外），此外，土体碳酸盐87Sr/86Sr比值随降雨量的增加而增加。因此，土壤碳酸盐87Sr/86Sr比值受碳酸盐来源和成土作用的双重影响，其比值可以指示（类）黄土风化成壤强度。（3）（类）黄土母质发育的土壤，不同土层土壤次生碳酸钙（PC）含量为2.1~137.9 g kg-1，1米土体中PC的形成速率为0.3~9.2 g CaCO3 m-2 yr-1。不同土层PC含量与CaCO3含量呈显著正相关关系，PC/CaCO3与原生碳酸钙（LC）含量呈极显著的负相关关系，表明随着LC的溶解、迁移，增加了土壤中PC/CaCO3比例。土体PC/CaCO3与MAP呈显著正相关关系，而PC含量与MAP呈显著负相关关系，表明较高的降雨量可以促进PC的形成，同时也会加强CaCO3的淋溶强度。淤灌土壤HCO01剖面不同土层土壤PC含量为80.9~98.2 g kg-1，PC/CaCO3接近100%，1米土体PC形成速率为55.5 g CaCO3 m-2 yr-1，表明灌溉促进了土壤次生碳酸钙的形成。干盐湖PL01和PL02剖面不同土层土壤PC含量为5.1~300.4 g kg-1，湖积物（PL01-C层）和钙磐土壤PC含量超过250 g kg-1，湖积物和钙磐PC的形成速率分别为30.8和9.7 g CaCO3 m-2 yr-1，上升成因模式是钙磐形成的主要机制。（4）沙尘源汇关系表明，高山景观（上游祁连山）主要扮演沙尘汇的角色，接受来自阿尔泰戈壁－阿拉善干旱区和塔克拉玛干沙漠的降尘输入；绿洲景观（中游河西走廊）既是沙尘的汇又是沙尘的源，降尘来自阿尔泰戈壁－阿拉善干旱区；荒漠景观（下游阿拉善）是沙尘源区。此外，河西走廊绿洲灌溉水和灌於物的Ca通量分别为36.0~43.2和421~1404 kg ha-1 yr-1，古日乃干盐湖地下水Ca含量高达560 mg L-1。祁连山区的山地森林、山地草原、干草原和荒漠化草原景观土壤发育于（类）黄土母质，为“加积型”成土模式。祁连山黄土沉积和现代降尘监测一致表明这些景观土壤碳酸钙主要来自大气降尘。河西走廊绿洲土壤发育于富含碳酸钙的灌於物和细土冲积物，是土壤碳酸钙的主要来源；另外，灌溉和降尘也是其重要来源。阿拉善戈壁、沙漠和干盐湖景观位于流域下游，来自内陆河流搬运的冲洪积物作为成土母质是土壤碳酸钙的主要来源；干盐湖钙磐的形成模式表明地下水也是其碳酸钙的重要来源。此外，降尘监测结果表明阿拉善荒漠景观土壤受风蚀影响，丢失碳酸钙。 |
| 英文摘要 | Carbonate, predominately calcium carbonate (CaCO3), is an important soil component, which has a significant impact on multiple soil physical, chemical and biological properties. The elluviation and illuviation of CaCO3 in soils is a key pedogenic process in arid and semiarid regions. The morphological features and vertical distribution of CaCO3 in soils has been widely used in evaluating the degree of soil development and in classifying soils. As a product and record of pedogenic process, pedogenic CaCO3 (PC) has been used as a proxy for dating soils and for reconstructing paleoenvironment. Thus, to trace the sources of CaCO3 in soils and to identify the mechanisms and influences of PC are important research topics in pedology. Besides, soil carbonate plays a key role in global biogeochemical cycling of carbon by regulating CO2 exchange with the atmosphere during its dissolution/weathering and reprecipitation.The Heihe River Basin is the second largest inland river basin in arid region of northwestern China, where detailed information on the composition and the distribution patterns of soil carbonate is still scarce. It is an ideal region to study the geochemical variations of soil carbonate considering its contrasting landscapes and diverse soil forming factors. To identify the variation patterns of soil carbonate between different landscapes is of great theoretical significance in understanding formation and development of soil in this (semi-)arid region. On the other hand, the identification of pedogenic carbonates, especially the differentiation between lithologic CaCO3 and PC is of urgent and practical significance to the precise estimation of soil inorganic carbon (SIC) pool as well as the evaluation of soil carbon sequestration potential. Based on similarity combination of soil forming factors, we classified 10 landscape units in three major landscape settings along mountains, oases, and deserts across the Heihe River Basin. Variations of soil CaCO3 contents, SIC density and their vertical distribution patterns in different landscapes were examined. Further, we selected 9 representative soil profiles based on the vertical distribution patterns of soil CaCO3. Elemental and isotopic characteristics of soil carbonate as well as the forming processes and formation rates of PC of these soils were studied. Also, the sources of soil CaCO3 in different landscapes were explored by taking account of both potential soil CaCO3 sources and evolution modes of soils in contrasting settings. Results showed that:(1) Soil CaCO3 contents and SIC intensities varied significantly among different landscapes with contrasting soil-forming environments. The order of average contents of CaCO3 in soil profile is desert steppe > typical steppe > Hexi Corridor oasis > mountain grassland > playa > Alxa Gobi desert > sand desert > mountain forest > subalpine shrub and meadow > alpine meadow. Accordingly, SIC density in the top meter of soils among different landscapes differed from 0.22 kg C m-2 to 20.22 kg C m-2. Vertical variations of CaCO3 in soil profiles showed three major distribution patterns: uniform throughout the profile, form a calcic horizon at some depth, and increase downward with depth. Moreover, the contribution of CaCO3 to soil carbon pool increased with depth, showing that carbonate is mainly distributed in deep soils.The influencing factors of soil CaCO3 varied greatly at the watershed scale. In arid regions (MAP＜200 mm), CaCO3 content was mainly determined by parent materials while climate factors played a negligible role. For loess-derived soils, however, CaCO3 content increased with temperature and decreased with precipitation, indicating that climate is the primary driver of CaCO3 variation in soils derived from loess.(2) For the selected nine soils, Ca was the most abundant element in soil carbonate followed by Mg; Si and Al had relatively low concentrations. For trace elements, Sr had the highest concentration followed by Ba, Pb appeared in tiny amount. Ca and Mg in carbonates showed low concentration in carbonate-depleted horizons, while concentrated in calcic horizons and calcipan. Overall, Ca showed significant negative correlation with Si, suggesting that the climate conditions favor the accumulation of carbonates inhibit the weathering of silicate. No significant correlation was observed between Ca and Sr in carbonate of the selected nine soils, reflecting the multiple sources of soil carbonate in these soils.To a large extent, the large variations in 87Sr/86Sr of soil carbonates among the nine soil profiles indicated the diverse sources of soil carbonates. Irrigated soils, HCO01 and HCO02 showed the highest 87Sr/86Sr values. In playa, the calcic horizon of PL01 and the calcipan of PL02 had the highest level of 87Sr/86Sr in their respective profiles. For loess-derived soils (MF01, MG01, TS01, DS01 and DS02), 87Sr/86Sr of soil carbonates showed an overall decrease with depths. On the other hand, 87Sr/86Sr of soil carbonates in these soils exhibited an increasing trend with precipitation. Taken together, the 87Sr/86Sr of carbonates was controlled by both parent materials and pedogenic processes, and its value could indicate chemical weathering intensities for loess-derived soils.(3) In the five loess-derived soils, PC contents ranged from 2.1 to 137.9 g kg-1, and formation rates of PC in the top meter of soils varied from 0.3 to 9.2 g CaCO3 m-2 yr-1. PC was positively correlated with CaCO3 while PC/CaCO3 was negatively correlated with LC, indicating that PC/CaCO3 increase with the dissolution and leaching of LC. PC/CaCO3 showed a positive relationship with MAP while PC in whole profile showed a negative relationship with MAP, suggesting that precipitation enhances the leaching density of PC on one hand, and promotes the formation of PC by dissolving more LC on the other hand.For the irrigated soil HCO01, PC contents in different horizons varied from 80.9 to 98.2 g kg-1, taking a proportion nearly 100% of total CaCO3; formation rate of PC within top meter soil reached 55.5 g CaCO3 m-2 yr-1. This indicates that irrigation with silt-rich water greatly promotes the formation of soil PC. In playa, PC contents of PL01 and PL02 had a high variability between 5.1 and 300.4 g kg-1. PC contents of lacustrine deposit in C horizon of PL01 and in calcipan of PL02 even exceeded 250 g kg-1. PC formed at rates of 30.8 and 9.7 g CaCO3 m-2 yr-1 in lacustrine deposit and calcipan, respectively. The formation of calcipan can be explained with the Perascendum model.(4) The source-sink relationships of aeolian sediments revealed that mountains zone (Qilian Mountains) acted as a huge sink of dust that sourced in the Altai Gobi-Alxa desert and the Taklamakan desert; oases zone (Hexi Corridor) served as both sink and source of aeolian sediments, it received dusts from Altai Gobi-Alxa desert; deserts zone (Alxa Plateau) was a source of aeolian sediments. In addition, irrigation water and sediments induced by siltigation supplies 36.0~43.2 kg Ca ha-1 yr-1 and 421~1404 kg Ca ha-1 yr-1 to oases soils, respectively. And the contents of Ca2+ in groundwater of Gurinai Playa can reach up to 560 mg L-1.Soils of mountain forest, mountain grassland, typical steppe and desert steppe in the Qilian Mountains were mainly developed from loess deposits in an accretional mode. Records from loess archives and modern dusts along the Qilian Mountains suggested that soil CaCO3 in these landscapes were primarily derived from aeolian sediments. Soils on the Hexi Corridor were mainly developed from irrigation-induced silts and fluvial sediments, which were main sources of soil CaCO3; irrigation water and aeolian dust were also important sources of soil CaCO3. For soils on deserts and playa landscapes, soil CaCO3 came from diluvial and alluvial materials, while groundwater was another important source of CaCO3 for soils in playa. Besides, monitoring data of aeolian sediments suggested that Alxa desert zone is losing carbonates due to wind erosion. |
| 中文关键词 | 次生碳酸钙 ; 土壤发生 ; 地球化学 ; 土壤无机碳 ; 大气降尘 |
| 英文关键词 | Pedogenic CaCO3 Pedogenesis Geochemistry Soil inorganic carbon Aeolian dust |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 土壤学 |
| 来源机构 | 中国科学院南京土壤研究所 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/288102 |
| 推荐引用方式 GB/T 7714 | 杨帆. 黑河流域土壤碳酸盐地球化学特征及其发生学意义[D]. 中国科学院大学,2018. |
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