【作者】 刘刚；

【导师】 刘普灵； 杨明义；

【作者基本信息】 中国科学院研究生院（教育部水土保持与生态环境研究中心） ， 土壤学， 2009， 博士

【摘要】 陕北黄土高原是世界上水土流失最严重的地区之一,该地区的黄土沉积速率是确定容许土壤流失量的基础。全新世以来气候波动变化,对黄土的沉积和发育造成一定影响,而该时期形成的土壤与人类关系最为密切,因此需要探讨全新世气候影响下的黄土沉积速率。可为容许土壤流失量的确定以及进行黄土高原土壤侵蚀危险度评价提供理论基础及数据支撑。本研究在陕北黄土高原南部洛川县、中部延长县、北部横山县分别设置A、B、C、D共4个土壤剖面,通过分层采集土壤样品,利用¹⁴C测年技术,对全新世以来各剖面不同气候影响下的黄土沉积速率进行了研究。其主要研究结果如下:（1）通过对塬面剖面A、B、D的土壤颗粒组成、土壤有机质含量、土壤pH值以及土壤CaCO₃含量进行分析,发现土壤颗粒组成和土壤CaCO₃含量随土壤年龄变化,反映出地质时期的气候变化对成土作用产生影响;而土壤有机质含量和土壤pH值随纬度的变化均表明成土作用由南向北逐渐减弱。该结果为进一步进行全新世气候变化以及黄土沉积速率时空变异的研究奠定了基础。（2）分别计算各种气候替代指标的Hurst指数和分形维数,并对各气候指标进行相关分析,探讨了各气候替代指标对各气候要素的指示关系。选取磁化率、碳酸钙含量、总有机碳含量和0.01⁰.05 mm粗粉粒含量作为气候替代指标,利用小波分析方法研究了A、B、D三个剖面全新世以来气候变化情况。结果表明,总体上,A和B剖面10000 a B.P.⁸500 a B.P.为变暖期;8500 a B.P.³000 a B.P.温湿大暖期;3000 a B.P.以来为变冷干期;而D剖面表现为,8000 a B.P.⁴000 a B.P.为温湿大暖期,4000 a B.P.以来为变冷干期,其时间差异可能是由于D剖面比A、B剖面相同时期的埋藏土壤年龄偏老而造成的。（3）运用土壤深度-年龄曲线法,得到各剖面全新世以来不同气候条件下黄土沉积速率,A、B、D剖面全新世平均黄土沉积速率为0.0179 cm/a、0.0153 cm/a、0.0213 cm/a。该研究区黄土沉积速率分布图表明,黄土沉积速率由西北向东南逐渐减小,并且在中部出现了极低值点。利用磁化率重建历史时期降雨量变化状况,并根据降雨量与土壤侵蚀强度的关系分析了地质时期土壤侵蚀情况,详细讨论了土壤侵蚀对各气候时期的沉积速率的影响,发现此极低值是由该地区地质时期土壤侵蚀造成的。因此,黄土沉积速率受到土壤侵蚀作用的影响。土壤深度-年龄曲线法得到的黄土沉积速率可以对这一综合结果进行精确地定量表达。（4）首次通过塬面和坡面对比研究,利用土壤年龄、黄土沉积速率以及气候替代指标,复原了12000 a B.P.以前C剖面所处坡面的地貌,并且发现该坡面12000 a B.P.以来由于受到自然侵蚀和人为加速侵蚀的共同作用,导致土壤侵蚀速率大于沉积速率,为定量研究地质时期土壤侵蚀及地貌提供了新的思路和方法。（5）通过计算土壤流失量与黄土沉积量的比值,定量探索了区域及流域土壤侵蚀危险度。结果表明,洛川县、延长县和横山县土壤侵蚀危险度分别为14.1、43.3和24.8,均远远大于1,因此该地区为水土流失重点防治区域。随着对燕沟流域治理度的增加,土壤侵蚀危险度Vdan值由1997年的28.8逐渐降低到2007年的0.2,土壤侵蚀已不具危险性,因此治理效果较好。本论文研究为确定土壤容许流失量以及明确土壤的发生、发育规律提供了理论基础;为定量研究地质时期地貌提供了新的思路和方法;黄土沉积速率在土壤侵蚀危险度评价方面的应用可以为环境治理决策提供理论依据。更多还原

【Abstract】 Soil loss in loess plateau in northern Shaanxi is the most serious all over the world. The loess deposition rate in this region is the base for determination of soil loss tolerance. Unstable climate in the Holocene affects on loess deposition and formation. Meanwhile, the loess formed in this period has the closest relationship with human. Thus, it is necessary to research the loess deposition rate under influence of climate in the Holocene. This study could provide theoretical basis and data supporting for determination of soil loss tolerance and assessment of soil erosion risk.Four soil profiles A, B, C and D were located in three locations in north, middle and south of loess plateau in northern Shaanxi. The loess deposition rates were researched by analysis of soil ¹⁴C age in every layer of the profiles. The main results were that: （1） Particle size distribution, TOC, pH and CaCO₃ content of A, B, D profiles on tableland were analyzed. The variation of particle size distribution and CaCO₃ content showed that the climate affected on soil formation. The changing of TOC and pH with latitude indicated that the degree of pedogenesis decreased from south to north in this region. These results laid a foundation for researches on climate changes and tempo-spatial variations of loess deposition rate.（2） The Hurst index and fractal dimension of seven climatic indexes were calculated, and correlation analysis was done between all the climatic indexes. The indexical relation between the climatic indexes and climatic elements was discussed. Finally, four indexes （χIf, CaCO₃ content, TOC and the content of 0.01⁰.05 mm particles） were selected, and wavelet analysis was used to analyze variations of paleoclimate. In total, in A and B profile, 10000 a B.P.⁸500 a B.P. was warming period, 8500 a B.P.³000 a B.P. was warm period, 3000 a B.P. present was cooling period; in D profile, 8000 a B.P.⁴000 a B.P. was warm period, 4000 a B.P. present was cooling period. The differences between them may be caused by the older age of the soil deposited at the same period in D profile than in A and B profile.（3） The loess deposition rate in different climate period was calculated by depth and age of soil in every layer. The average loess deposition rate of A, B and D profile in the Holocene was 0.0179 cm/a、0.0153 cm/a、0.0213 cm/a, respectively. The distribution of loess depostion rate in this region showed that, it decreased from northwest to southeast, and the minimum was in the middle of region. The soil erosion in the Holocene was analyzed by the annual rainfall which was calculated by magnetic susceptibility. The influences of soil erosion on soil deposition rate were discussed. The minimum in the middle of region was caused by soil erosion. Therefore, the loess deposition rate was comprehensive results of deposition, erosion and other pedogenesis. The loess depotition rate derived from soil depth and age could show the comprehensive result quantitatively.（4） Soil age, loess accumulation rate and climate indexes of B and C profile were used to reconstruct the landforms on the slope where the C profile on before 12000 a B.P.. The soil eosion rate was lager than loess deposition rate, and it was proved that this method could be used to research on soil erosion and reconstruct the landforms in geological period.（5） Soil erosion risk of the research region and a watershed was assessed by the ratio of soil loss to soil deposition. The soil erosion risk in Luochuan, Yanchang and Heangshan was 14.1、43.3 and 24.8, much larger than critical value 1, so this region should be an important protection and control area. With the growth of management degree, the soil erosion risk dropped from 28.8 in 1997 to 0.2 in 2007 in Yan’gou watershed. The soil erosion was under control.This study could provide theoretical basis for determination of soil loss tolerance, soil genesis and development. It would provide new idea and method for quantificationally research on reconstruct the landforms in geological period. The application of loess deposition rate on assessment of soil erosion risk could provide theoretical basis for environmental treatment decision.更多还原