黄土丘陵区坝地沉积序列重构及来源定量示踪
文献类型：学位论文
| 作者 | 唐强 |
| 学位类别 | 博士后 |
| 答辩日期 | 2016-05 |
| 授予单位 | 中国科学院研究生院 |
| 授予地点 | 北京 |
| 导师 | 傅伯杰 |
| 关键词 | 黄土高原 Loess Plateau 土壤侵蚀 soil erosion 泥沙来源 sediment source 断代 dating 生态修复 ecological restoration 淤地坝 check dam |
| 学位专业 | 生态学 |
| 中文摘要 | 黄土高原位于我国北方干旱半干旱区，生态环境脆弱，人类活动强烈，生产力低下，土地利用粗放，是我国典型的水土流失区和黄河泥沙主要来源区。过去几十年来，黄土高原经历了复杂的人类活动过程，实施了一系列水土保持和生态修复措施，导致区域土地利用和覆被格局发生重大变化，驱动流域侵蚀产沙过程持续演变。黄土高原生态治理突出表现在治理模式简单粗放，措施实施范围局限在小区域尺度，治理效益缺乏稳定性和可持续性，治理成果可推广性差等方面。措施的设计和实施缺乏充分的理论认识支撑。因此，开展黄土高原侵蚀产沙过程对人类活动的响应研究，探明各项水土保持和生态修复措施的效益及潜在机理，为当前措施的优化调整提供理论支撑。本研究选取黄土丘陵区典型恢复小流域，通过坝地沉积序列重构及来源复合指纹示踪，揭示淤地坝泥沙沉积过程及基于土地利用类型的来源构成。取得的主要研究结论如下： （1）降雨是半干旱黄土丘陵区侵蚀产沙的主要驱动力，降雨特征（强度和频率）决定侵蚀产沙的时间动态过程和强度。侵蚀性降雨主要发生在雨季6～9月，侵蚀产沙和坝地淤积主要发生于频次低、历时短、强度大的次暴雨过程。因此，历史降雨资料能有效指示流域侵蚀产沙和坝地沉积事件，为坝地沉积反演提供重要前提。分析研究区临近的延安气象站 1951～2014年日降雨资料得出，年均降雨量为 520.1 mm，年均降雨日数为 78.2天。其中雨季6～9月，降雨日数占全年总降雨日数 58%，贡献了年总降雨量的 73%；>10 mm降雨日数占全年总降雨日数 15%，贡献了年总降雨量的 56%；>20 mm降雨日数占全年总降雨日数7%，贡献了年总降雨量的 38%。研究区所在的延河流域出口甘谷驿水文站 1953～2012年，年均径流量 1.98亿 m3，雨季 6～9月径流量占年总径流量 65%，47%的年径流量发生在 7～8月；年均输沙量为 0.37亿 t，雨季 6～9月输沙量占年输沙量98.7%，86%的年输沙量发生在 7～8 月。径流和泥沙输出更加集中，主要发生在高强度降雨集中的 7～8月。 （2）坝地沉积物和流域内来源土壤的粒度、有机质和 137Cs 比活度存在差异，反映了侵蚀产沙过程的差异和土地利用/覆被类型的影响。坝地沉积物颗粒组成以砂粒为主。颗粒组成较流域内表土（沟间地）颗粒细，比冲沟土壤（沟谷地）的颗粒粗，反映侵蚀类型差异对颗粒的分选机制，即沟间地以雨滴溅蚀、面蚀和细沟侵蚀为主，地表土壤中细颗粒组分优先被剥蚀和搬运，而沟谷地以崩塌等重力侵蚀为主，在一次侵蚀事件中，所有颗粒组分都脱离原位而运移。沉积物137Cs 浓度明显高于流域内耕地和冲沟土壤的 137Cs 浓度，一方面可能是由于颗粒差异的影响，即 137Cs在表面积较大的细颗粒上的富集特性决定了经历颗粒筛选后的沉积物 137Cs浓度高于耕地；另一方面，冲沟侵蚀速率快，采集到的沟壁土壤为亚表层土壤137Cs 浓度低。沉积物有机质含量低于流域内沟间地坡面表层土壤，与沟壁土壤有机质含量接近。林地和灌丛有机质含量明显高于草地和耕地，表明植被恢复有利于黄土高原土壤有机碳库的积累。 （3）通过沉积剖面粒度和 137Cs 的分布，辨识出沉积旋回层结构，结合建坝历史和降雨资料，筛选出有效的暴雨事件，作为反演沉积旋回的年代标记，重构出坝地泥沙淤积时间序列过程。坝地沉积序列未受到溃坝和人为干扰，旋回层结构得到了较好地保存。根据沉积剖面的粒径变化，辨识出了 11个明显的旋回结构，代表次暴雨过程侵蚀产沙的产物。结合坝地建设和历史次暴雨资料，将辨识出的坝地沉积物旋回层与历史侵蚀产沙事件相对应，甄别出 1981～1983年间11次侵蚀沉积事件，估算出次暴雨过程淤地坝沉积速率介于 20～135cm。 （4）基于泥沙来源复合示踪框架，根据地形分异和土地利用划分出五类来源类型，筛选出 9种具有诊断识别能力的指纹因子，估算了各来源对坝地沉积物的相对贡献。流域泥沙来源按地形分异划分为沟间地和沟谷地（冲沟），再根据土地利用将沟间地进一步划分为林地、灌丛、草地、耕地 4大类。基于坝地沉积物旋回分层，将沉积剖面分层样品合并为 12个混合泥沙样，代表流域产沙。利用统计分析筛选出具有诊断能力的九种指纹因子（ Na，Fe，Sr， Co，Cu，Li，V，Be，C/N），运用混合模型估算了各物源单元对坝地沉积物的相对贡献。结果表明，耕地和冲沟为坝地沉积物的主要贡献来源，但在 12个旋回层中其相对贡献大小存在波动，反映次暴雨过程侵蚀产沙过程的差异。 |
| 英文摘要 | The Loess Plateau in the arid and semiarid region of northern China is a fragile landscape with occurrence of intense human activities, irrational land use. It represents a typical soil erosion region in China and constitutes a principal source area for sediment yield in the Yellow River. Over the past several decades, complex human activities have taken place in this region, as well as numerous soil conservation and ecological restoration measures have been implemented, which consequently led to dramatic changes in regional land use and land cover pattern, and constant evolution of catchment soil erosion and sediment yield processes. Some shortages regarding these measures has emerged, including relatively simple and crude measures, small scale of implementation, instability and unsustainability of practices efficacy, and unfeasibility of large scale promotion. The design and implementation of conservation measures lack sufficient theoretical support. Therefore, it is necessary to realize the response of soil erosion and sediment yield to human intervention, and reveal the potential effectiveness and underlying mechanisms of numerous conservation practices, which finally will support contemporary strategy adjustment and optimization. In this study, a typical small catchment in the loess hilly region was selected. Historical sedimentation processes in a controlling check dam were interpreted and reconstructed by stratigraphy differentiation and its land use-based source compositions were quantified using fingerprinting technique. Major conclusions obtained are as follows: (1) Rainfall is a major driving force for soil erosion and sediment yield in the semiarid loess hilly region, rainfall pattern (intensity and frequency) determines the timing and magnitude of sediment yield. Erosive rainfalls mainly occur in the rainy season from June to September, while sediment yield and sedimentation in check dams mains occur in association with low frequency, low duration and large magnitude summer storm events. Therefore, historical precipitation data is an effective indicator of the occurrence of sediment yield and sediment accumulation in check dams, which affords an important premise for sedimentary reinterpretation. Analyzing daily rainfall data of 1951～2014 observed at a nearby meteorological station (Yan’an), it was found that mean annual rainfall is 520.1 mm, and average annual rainfall days are 78.2 d. During the rainy season from June to September, cumulative rainfall days account for 58% of annual total, but contribute to 73% of annual precipitation. Rainfall days with intensity larger than 10 mm account for 15% of annual total, and contribute to 56% of annual precipitation. Rainfall days with magnitude larger than 20 mm account for 7% of annual total, but contribute to 38% of annual precipitation. Mean annual runoff observed at the controlling hydrological station (Ganguyi) of Yanhe during 1953～2012 is 0.198 billion m3, 65% of which occurs during June to September and 47% of which occurs during July and August. Mean annual sediment load is 0.037 billion t, 98.7% of which occurs from June to September and 86% occurs in July and August. Runoff and sediment yield behaved a much more concentrated pattern than regional rainfall, which mainly takes place during July and August. (2) Difference in particle size, organic matter and 137Cs content exists between check dam infilling sediments and upland source materials, reflecting the influence of contrasting sediment yielding processes and land use and vegetation cover. Check dam infilling sediments is dominated by sandy fractions. Its particle size is relatively finer than upland source materials (inter-gully slope), but coarser than soils collected from gully wall, respecting particle selectivity associated with different erosion processes. Soil erosion on inter-gully slopes is mainly conducted through raindrop detachment, sheetwashing, and rilling. Fine fractions of bulk surface soils are preferentially eroded and moved away, while all fractions of gull soils are transported during a signal event such as mass failure. 137Cs content of check dam sediments is obvious higher than that of source materials from arable land and gully wall, which may be attributed to particle difference between sediments and farmland soils, on account of that 137Cs is preferentially adsorbed on fine particles with relatively large specific surface area. It may also be ascribed to that gully wall soils is subsurface material with low level of 137Cs content, due to atmospheric-input fallout 137 Cs content is enriched in surface land. Organic matter of sediments is lower than source materials from inter-gully slopes, but get close to that of gully wall soils. Surface soils from forestland and shrubs have higher levels of organic matter than grassland and arable land, reflecting the effect of vegetation restoration on soil carbon stock. (3) According to depth distribution of particle size and 137Cs content of the core profile, sedimentary stratigraphic units were differentiated. Effective storm events were selected based on the operation history of the check dam and historical daily rainfall data, which were used as time marker for the identified stratigraphy units, and finally, sedimentary processes were reconstructed. The sedimentary archives of the check dam has not been disturbed by past dam failure and human interruption, and the original sedimentary laminations have been well preserved. According to depth distribution of absolute particle size, 11 stratigraphic units were obviously differentiated. Each one represents the product of one storm event. Based on operation history of the check dam and historical rainfall data, the identified units were ascribed to storm events, and the sedimentation time was marked during 1981～1983. The sedimentation rate ranges from 20 to 135 cm. (4) Applying the sediment source fingerprinting technique, five potential sources were identified based on landform and land use. Nine diagnostic fingerprints were selected and were used in mixing model to calculate the relative importance. Within the source classification framework, the catchment was preliminarily divided as gully area and inter-gully area according to landform property. Inter-gully slopes were further classified into four categories of forestland, shrubs, grassland and arable land based on land use. The sectioned sediment samples were mixed to form 12 composite samples according to the stratigraphic differentiation. Nine diagnostic properties were selected using statistical analysis, and the relative contributions were estimated using mixing model. Result indicated that of the 12 mixing sediment samples, arable land and gully are the two most important sources, but their relative importance differs among the 12 events, reflecting effect of varying rainfall property. |
| 源URL | [http://ir.rcees.ac.cn/handle/311016/36962]  |
| 专题 | 生态环境研究中心_城市与区域生态国家重点实验室 |
| 推荐引用方式 GB/T 7714 | 唐强. 黄土丘陵区坝地沉积序列重构及来源定量示踪[D]. 北京. 中国科学院研究生院. 2016. |
入库方式： OAI收割
来源：生态环境研究中心
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