黄河三角洲土壤及其红粘层的地球化学特征与环境意义

	黄河三角洲土壤及其红粘层的地球化学特征与环境意义
	李远
学位类型	博士
导师	骆永明
	2016-05-12
学位授予单位	中国科学院大学
学位授予地点	北京
学位专业	土壤环境地球化学
关键词	黄河三角洲红粘层土壤质量土壤地球化学陆海相互作用
其他摘要	黄河三角洲是受到黄河来水来沙、尾闾流路变迁、全球气候变化等自然因素和农业耕种熟化、城镇化、工业化等人类活动交互作用、叠加影响的区域。目前对气候变化、人类活动和陆海相互作用多重影响下黄河三角洲区域土壤环境质量、土壤发生发育过程和土壤沉积物物质链关系缺乏一个整体认识。本论文基于黄河三角洲地区的42个典型类型土壤剖面（182个土壤样品）和26个临近海域表层沉积物样品，分析了土壤基本理化性质、土壤重金属元素与稀土元素、有机氯农药和石油烃等有机污染物、土壤原状土和胶体的矿物组成、化学组成、磁学性质等地球化学特征、土壤和沉积物放射性铅同位素和稳定性碳、氮同位素，表征了黄河三角洲地区土壤由陆到海的土壤质量特征；探讨了无机元素和有机污染物的土壤环境地球化学行为及来源；揭示了黄河三角洲土壤剖面红粘层的时空分布、地球化学特征和陆海相互作用下的环境意义。这些研究成果可为高强度人类经济活动及强烈陆海交互作用下黄河三角洲区域生物地球化学循环与可持续发展提供基础数据和科学依据，具有重要的科学意义和现实的指导意义。本研究的主要结果包括以下几个方面：（1）黄河三角洲在滩涂、湿地、棉田、粮田、菜地由海到陆的利用方式和空间过渡下，土壤盐分逐渐降低，土壤结构和肥力水平逐渐提高。其中，滩涂土壤结构较差，肥力水平很低，代表了该地区自然成陆条件下的原始土壤理化性质特征。滩涂发育为湿地后，湿地淹水的环境及丰富的植被，使得在该利用方式下土壤粘粒、有机质、氮、磷等含量显著提高。湿地开垦为农田后，人为改良使得土壤脱盐脱碱显著，明显提高了土壤供氮、供磷强度，但人类活动加剧了土壤团聚体的破坏以及有机质的释放。（2）黄河三角洲土壤重金属、有机氯农药和石油烃的整体含量较低，目前环境生态风险不高。土壤重金属在黄河河岸和三角洲南部区域含量有升高趋势；有机氯农药中相对活跃组份（γ-HCH和o,p’-DDT）和相对稳定组份（β-HCH和p,p’-DDE）有沿海-内陆的两极分布趋势。土壤总石油烃呈现代黄河三角洲内部低、外部高的趋势，靠近孤东油田的区域土壤中总石油烃含量相对较高。土壤剖面中铁氧化物和粘土矿物对重金属有显著富集，土壤粘粒也是表层和剖面土壤中γ-HCH的重要载体，土壤石油烃则主要与土壤发育程度相关。黄河泥沙的搬运和沉积是多数污染物的主要来源，但随着调水调沙、石油开采、农业垦殖和海岸工程等人类活动的日益频繁，黄河三角洲污染物逐渐受到了当地人为过程的影响。（3）黄河三角洲土壤剖面中稀土丰度与物源的风化程度和成土程度有正相关趋势。土壤剖面不同层次之间稀土分馏情况是同步的，轻稀土相对重稀土富集，La-Eu曲线较陡，Eu-Ld曲线较平缓，Eu呈较为明显的负异常，Ce正异常不明显。通过稀土特征参数可以得出，黄河三角洲各层次土壤的源物质在黄河侵蚀、搬运、沉积过程中经历了充分的混匀过程。（4）黄河三角洲土壤剖面中的典型红粘层主要分布在1855年之后形成的现代黄河三角洲和1855年之前形成的古代三角洲区域，在黄河和弥河之间为红粘层过渡区，在弥河以东无红粘层分布。出现深度较浅的红粘层沉积相对较厚。对典型剖面的¹³⁷Cs和²¹⁰Pb定年可得，黄河三角洲剖面红粘层沉积的年代在1910s～1960s区间内，红粘层多出现于沉积速率发生较为剧烈变化的层次区间，与水动力变化有关。在形貌特征上，典型红粘层平均粒径为6.69±0.79φ、中值粒径为11.6±7.3 μm、红度（a^）值为7.5±0.4。（5）黄河三角洲土壤红粘层粘土矿物和方解石含量都显著高于其上下黄砂层，而原生矿物如石英和长石的含量则显著低于黄砂层。在常量元素组成上，典型红粘层SiO₂为55.6±3.7%、Al₂O₃为13.5±1.1%、CaO为8.18±1.03%、Fe₂O₃为5.49±0.83%、MgO为2.83±0.34%、K₂O为2.54±0.83%和Na₂O为1.34±0.32%。19种微量元素中，红粘层只有Zr和Hf含量显著低于黄砂层，其余微量元素都要显著高于黄砂层。红粘层相对黄砂层具有较高的风化程度，典型红粘层的硅铝率为6.71±1.06。磁学性质上，红粘层的磁学特征参数数值χ_fd%为8.3±1.7%、χ_arm为362.7±90.0×10^-8 m³/kg、χ_arm/SIRM为67.1±15.1×10^-5 m/A、SIRM/χ_lf为9.6±1.5×10³ A/m和χ_ARM/χ_lf为6.3±1.0，说明了红粘层中较细的成土性SP/SD颗粒含量较高，对该层磁性增强贡献较大。红粘层和黄砂层土壤胶体间色度和磁学特征差异较小，但粘土矿物和元素组成略有差异。黄河三角洲土壤红粘层是源区温湿气候条件下的高风化物质，经黄河由上游至下游搬运、混合、沉积，在三角洲地区水动力分选而形成。红粘层与黄砂层物源总体上较为相似，但又存在区别，主要是由于不同时期沉积造陆物源不同以及沉积时海相的影响和成陆之后的成壤过程导致不同土层间的地球化学特征差异。（6）黄河三角洲土壤红粘层重金属平均含量是黄砂层的约1.5倍，红粘层中铁锰结合易还原态Pb、Co以及弱酸溶态Cd比例要高于黄砂层，红粘层中重金属的潜在迁移性更强。红粘层是三角洲底层土壤中重要的有机碳、有机氮和无机碳库，红粘层中累积的无机碳可能主要以次生碳酸盐形式存在，具有固碳的能力。红粘层出现的深度和厚度结合黄河尾闾改道时间可推测现代三角洲形成期环境和人类活动变化。黄河三角洲土壤和沉积物的碳氮稳定性同位素分馏特征表明，滨海湿地土壤、菜地土壤、田地（棉田和粮田）土壤、河相沉积物、海湾和深海沉积物是影响区域碳氮循环的6组重要介质，由自然土壤向海洋沉积物过渡，对应了由源区较活跃有机质库向沉积区较稳定有机质库转移的过程。; The Yellow River Delta (YRD) is heavily influenced by natural processes (e.g., Yellow River flow-sediment variation, river course transition and global climate change) and human activities (e.g., cultivation, urbanization and industrialization). A systematic knowledge is still limited on the soil genesis and development process, soil environmental quality, and the material relationship between soil and sediment under the conditions of climatic change, human activities and land-ocean interaction. Forty-two representative soil profiles with 182 soil layer samples and 26 surface (0−20cm) sediment samples were collected from the YRD and its adjacent offshore areas. All these samples were measured for soil properties, trace elements and rare earth elements, organochlorine pesticides, total petroleum hydrocarbon, radioactive lead isotope and stable carbon and nitrogen isotopes. Soil colloids were extracted from some bulk soils and were analyzed for the geochemical characteristics. The measured results have been employed to characterize the soil environment quality from inland to the coastal area, to investigate the environmental geochemical behavior and possible sources of the inorganic elements and organic pollutants, to reveal the spatial and temporal distribution, geochemical characteristics and environmental implications of the red clay layer (RCL) occurring in the soil profiles of the YRD. These results are expected to be useful in understanding the biogeochemical cycles and sustainable development of the YRD under high pressure of human activities and strong land-ocean interactions. The main results were summarized as follows: (1) Change of the land-use types from coastal beach to inland area resulted to a change of the soil properties. The soil salinity, texture and fertility status generally showed an increasing trend in the order of tidal flat, wetland, cotton field, cereal field, and vegetable field. The lowest soil fertility in the tidal flat indicated the primitive characteristics of natural soil physicochemical properties. After the tidal flat developed into wetland, the contents of clay, organic matter, nitrogen and phosphorus were all significantly enhanced due to the flooded conditions and increased vegetation cover. Some of the tidal flat were reclaimed into farmland and the cultivation process facilitated soil desalination and dealkalization, and improved the input of nitrogen and phosphorus into the soils. However, the cultivation meanwhile destroyed soil aggregates and promoted the mineralization of soil organic matter. (2) The soils of the YRD were less contaminated by heavy metals, organochlorine pesticides and total petroleum hydrocarbon based on current measurements. The mean concentrations of the heavy metals were elevated along the Yellow River and in the southern part of the delta. The percentages of γ-HCH and o,p’-DDT as less recalcitrant components tended to distribute in the coastal area. However, the more recalcitrant components, β-HCH and p,p’-DDE, tended to distribute in the inland area. The contents of the total petroleum hydrocarbon in the soils exhibited high levels in the inside of the modern YRD (especially near the Gudong oilfield), and low levels in the outside of the modern YRD. The heavy metals accumulation in the soil profiles was related with the contents of iron oxide and clays. The clays were also important carriers of γ-HCH in the surface and subsurface soils. The distribution of total petroleum hydrocarbon was mainly related to the degree of soil development. Suspended sediments transported by the Yellow River were suggested to be one of the major sources for the pollutants accumulation in the YRD soils. However, the increased intensity of regional human activities, such as water and sediment regulation, oil exploitation, agricultural reclamation and coastal engineering, has also increasingly threatened the soil environment of the area. (3) The content of rare earth element (REE) in the soil profiles of the YRD was positively correlated with the degree of soil development. The chondrite-normalized REE distribution patterns of the different soil layers were similar in shape. All the patterns were characterized by steep La-Eu and fairly flat La-Eu profiles and the higher accumulation of the light REE compared with the heavy REE. The significant europium (Eu) depletion and slight cerium (Ce) enrichment occurred in all the soils. The patterns of soil REE implied that the original materials of the different soil layers must have undergone thorough sedimentary mixing processes during erosion, transportation and deposition. (4) The typical RCL occurred in the soil profiles of the YRD was mainly distributed in the modern YRD that formed after 1885 and in the old YRD that formed before 1855. The area between the Yellow River and Mi River was a transition zone for the RCL distribution, which was not observed in the east of the Mi River. The shallower occurring depth of the RCL generally showed a thicker deposit. According to the ¹³⁷Cs and ²¹⁰Pb dating records, the depositional time of the RCL was in the range of 1910s−1960s. The RCL was more likely to occur in the section with high variability of deposition rate due to the hydrodynamic change of the Yellow River. The morphology features of the typical RCL were characterized by grain size=6.69±0.79φ, median grain size=11.6±7.3 μm and redness (a^) value=7.5±0.4. (5) The contents of clay minerals and calcite in the RCL were significantly higher than that in its Upper and lower yellow silt layer (YSL), while the primary minerals contents in the RCL were significantly lower. As for the major mineral elements, the typical RCL had SiO₂=55.6±3.7%, Al₂O₃=13.5±1.1%, CaO=8.18±1.03%, Fe₂O₃=5.49±0.83%, MgO=2.83±0.34%, K₂O=2.54±0.83% and Na₂O=1.34±0.32%. As for the 19 trace elements, only Zr and Hf contents in the RCL were lower than that in the YSL, while other trace elements were all shown enrichment in the RCL. The RCL displayed higher weathering intensity with silica to alumina ratio=6.71±1.06. For the magnetic properties, the typical RCL had χ_fd%=8.3±1.7%, χ_arm=362.7±90.0×10^-8 m³/kg, χ_arm/SIRM=67.1±15.1×10^-5 m/A, SIRM/χ_lf=9.6±1.5×10³ A/m and χ_ARM/χ_lf=6.3±1.0, which indicated that the magnetic enhancement of the RCL was mainly due to its higher contents of fine pedogenic SP/SD particles. The chromaticity and magnetic properties in the soil colloids (<2 μm fraction) showed less difference between the RCL and YSL, while the compositions of clay minerals and elements were slightly different. The geochemical results suggested that formation of the RCL source materials was associated with a warmer and wetter climate in the source areas and deposition of the RCL in the YRD was combination of transportation, mixture and hydrodynamic sorting by the Yellow River. The provenance was similar between the RCL and the YSL. However, the sedimentary epeirogenic process under different stages, marine alteration and pedogensis after deposition could also lead to the geochemical differences in different soil layers. (6) The mean contents of the heavy metals in the RCL were about 1.5 times higher than that in the YSL. The Pb, Co and Cd exhibited higher proportions in reducible and exchangeable fraction respectively in the RCL than that in the YSL, indicating a higher mobility of heavy metals in the RCL. The RCL also acted as an important pool for carbon and nitrogen accumulation in subsoil. The RCL accumulated significant amount of inorganic carbon by forming carbonate under the pedogenic condition. The depth and thickness of the RCL-YSL sequence together with the course change provided information in relation to climate change and human activities such as soil and water conservation and dam constructions during the formation of the modern YRD. The stable carbon and nitrogen isotopes fractionation indicated that wetland soils, vegetable soils, cropland soils, river sediments, bay and deep-sea sediments were the six sub-systems controlling the cycling of the organic carbon and nitrogen in the YRD. A transition from natural soils to marine sediments corresponded to the flux of organic matter from a labile pool in the source regions to a more recalcitrant pool in the sink regions.
语种	中文
文献类型	学位论文
条目标识符	http://ir.yic.ac.cn/handle/133337/13909
专题	中国科学院烟台海岸带研究所知识产出_学位论文中国科学院海岸带环境过程与生态修复重点实验室_海岸带环境过程实验室
作者单位	中国科学院烟台海岸带研究所
第一作者单位	中国科学院烟台海岸带研究所
推荐引用方式 GB/T 7714	李远. 黄河三角洲土壤及其红粘层的地球化学特征与环境意义[D]. 北京. 中国科学院大学,2016.

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