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黄土高原水蚀风蚀交错带 土壤侵蚀速率的7Be和137Cs示踪研究
孙喜军
Subtype硕士
2012-05
Degree Grantor中国科学院研究生院
Place of Conferral北京
Keyword水蚀速率 风蚀速率 7be 137cs
Abstract

黄土高原水蚀风蚀交错带由于水力和风力两相侵蚀的耦合作用,土壤侵蚀强烈,成为黄土高原强烈的侵蚀中心。定量研究两相侵蚀中水蚀、风蚀速率对此区水土流失防治具有重要的指导意义。本项研究以位于黄土高原水蚀风蚀交错带的典型流域陕西省神木县六道沟流域为研究区域,首先通过室内风洞实验建立包含风蚀分选性因子的7Be示踪估算土壤风蚀速率的模型,把7Be示踪技术拓展到野外坡面风蚀研究中,并结合137Cs示踪技术定量区分该流域峁坡水蚀、风蚀速率;同时结合室内风洞实验与接着的降雨模拟实验,来初步分析风蚀对降雨侵蚀的影响。研究得到以下主要结果:
(1)以黄土高原水蚀风蚀交错带砂黄土为研究对象,利用室内风洞模拟实验对7Be示踪估算土壤风蚀速率的可行性进行了探讨。由于风蚀过程易带走土壤细颗粒,且7Be在土壤细颗粒中含量较高,所以利用7Be水蚀模型计算的土壤风蚀速率高于实测值。实验中发现样点风蚀后和风蚀前土壤颗粒比表面积之比与样点风蚀后7Be含量之间存在幂函数关系,基于此,提出了颗粒分选校正系数P的计算式,并建立了包含颗粒分选校正系数P的7Be示踪风蚀速率模型。计算分析发现,和实测值相比,利用建立的7Be示踪风蚀速率模型计算的土壤风蚀速率误差均不超过5%,这说明建立的7Be示踪风蚀速率模型能较准确地估算土壤风蚀速率,利用7Be示踪技术估算土壤风蚀速率是可行的。
(2)通过7Be示踪技术,利用提出的包含风蚀分选因子的7Be示踪估算土壤风蚀速率的模型定量计算了神木县六道沟流域旱期内两个坡面的土壤风蚀速率,结果表明:随坡长的不断增加,7Be含量逐渐增加,坡面上部7Be含量最小,且北向砂性土壤坡面A的7Be含量(137.53 Bq/m2)低于西北向粘性土壤坡面B的7Be含量(212.58Bq/m2)。风蚀速率从坡底到坡顶呈现出增大—减小—增大的趋势,且砂性土壤坡面A的土壤风蚀速率(1425.57 t/km2)高于粘性土壤坡面B的土壤风蚀速率(880.98 t/km2),证明土壤质地对风蚀有重要影响。
(3)在黄土高原水蚀风蚀交错带的典型流域陕西省神木县六道沟流域,选择了峁顶海拔高度相近,坡度近乎相同,距离峁顶坡长相同的八个不同坡向的峁坡坡面,利用137Cs示踪技术,定量分析了不同坡向的土壤侵蚀状况,结果表明,不同坡向峁坡坡面最上部采样点的颗粒组成及有机质含量差异明显,其中颗粒西北坡最粗,南坡最细,有机质含量西北坡最低,东南坡最高,表明此区风蚀具有明显的坡向分异特点;以东坡平均侵蚀速率8609 t/(km2·a)为基准,计算了其它7个坡向坡面的风蚀(风积)速率,结果表明东南坡和南坡的风积速率为299 t/(km2·a)和207 t/(km2·a),其他各个坡向风蚀占总侵蚀量的比例为16.36%~22.07%,其中西北向坡面风蚀速率最高,为2439 t/(km2·a)。此区峁坡坡面平均土壤风蚀速率为1455 t/(km2·a)。 (4)以黄土高原水蚀风蚀交错带陕西神木县六道沟流域的砂黄土为研究对象,通过室内风洞实验与接着的降雨模拟实验,探讨了小区坡面风蚀对水蚀的影响,实验条件下的结果表明:风蚀会对降雨实验的初始产流时间、坡面平均水流速度、侵蚀量、坡面径流量产生影响。同一坡度和雨强条件下风蚀后接着的降雨实验的初始产流时间、坡面平均水流速度、侵蚀量均小于单独降雨实验的相应值;而坡面径流量却大于单独降雨实验的相应值。且同一坡度和雨强条件下随着风洞实验风速的增大,降雨实验的初始产流时间、坡面平均水流速度、降雨侵蚀量均逐渐减小;而径流量逐渐增大。定义△f为水风复合侵蚀作用强度,其值等于风蚀后接着的降雨实验侵蚀量与单独降雨侵蚀量的差值。实验中风速和雨强越大,△f越小,即水风复合侵蚀作用强度越大。
关键词:水蚀速率;风蚀速率;7Be;137Cs;

Other Abstract

The Wind-Water Erosion Crisscross Region on the Loess Plateau of China experiences intense soil erosion due to the dual action of wind and water. Quantifying the rate of water and wind erosion in the Loess Plateau is significant for soil and water conservation programs. In this paper, the Liudaogou watershed in the Wind-Water Erosion Crisscross Region was selected for the study area. In order to exactly calculate the wind erosion rate using the 7Be technique, firstly a particle size correction factor P was incorporated into the 7Be-based water erosion model through the wind tunnel test. Then combined with the 137Cs technique and 7Be technique, the rate of water erosion and wind erosion in the Liudaogou watershed were estimated quantitatively. At last, continues simulated experiment of erosion by wind and rainfall were conducted in order to identify the role of wind erosion on water erosion. The main results were as follows:
(1) Sandy loess from the wind-water erosion crisscross region on the Loess Plateau of China was used in wind tunnel to test the feasibility of using the 7Be technique to estimate wind erosion rate. Since wind erosion selectively removes finer particles of soil, the direct use of the 7Be-based water erosion model tends to overestimate wind erosion rate as 7Be is preferentially associated with the fine particles. The results showed an exponential function relationship between Se/So and the concentration of 7Be at the eroded site (Se and So are the specific surface areas of eroded soil and the original soil, respectively). Thus, a particle size correction factor P was incorporated into the 7Be-based water erosion model. The wind erosion rates calculated by the 7Be-based wind erosion model were within 5% error compared with the measured values, indicating that the corrected model estimates wind  erosion rate fairly accurately and that the 7Be technique could be used to estimate wind erosion rate. (2) Using the 7Be-based wind erosion model we estimated the wind erosion rate of the two slopes in the Liudaogou watershed during the drought period, the results showed that the content of 7Be increased from the top of slope to the slope toe. The 7Be content for A slope (137.53 Bq/m2) is lower than that of B slope (212.58 Bq/m2). With the decrease of slope length, the rate of wind erosion increased firstly and then decreased and again increased at last. The wind erosion rate for A slope (1425.57 t/km2) was higher than that of B slope (880.98 t/km2), which proved that the soil texture had a significant influence on the wind erosion. (3) Eight hillslopes with different aspects but similar slope inclination, length, and height were selected in the Liudaogou watershed in the Wind-Water Erosion Crisscross Region. Total soil loss on different slopes was analyzed quantitatively using 137Cs. Meanwhile particle size distribution and soil organic matter of surface soil at different slope sites were analyzed. The results showed that soil particle size distribution and organic matter content at the uppermost site of different hillsides were significantly different, which demonstrated a great difference in the intensity of wind erosion on different hillside aspects. Using the erosion rate of the east facing hillside (8609 t/(km2·a)) as the benchmark we calculated the wind erosion rates (or wind deposition rates) of the other slopes. The wind deposition rate for the southeast and south facing hillsides were 299 t/(km2·a) and 207 t/(km2·a), respectively, and the percentage of wind erosion on different hillsides ranged from 16.36% to 22.07%. Wind erosion on the northwest facing hillside was highest (2439 t/(km2·a)). The average wind erosion rate of slope in this region was 1455 t/(km2·a)).
(4) Sandy loess from the wind-water erosion crisscross region on the Loess Plateau of China was selected for continues simulated experiment of erosion by wind and rainfall. The results showed that the wind erosion had an impact on the runoff duration, the average flow velocity along the slope, the amount of soil erosion in rainfall experiment and the amount of runoff. The runoff duration, the average flow velocity along the slope and the amount of soil erosion in rainfall experiment after wind tunnel test were all lower than that of the single rainfall experiment, but the amount of runoff were higher. With the increasing  of wind speed in experiments, the runoff duration, the average flow velocity along the slope and the amount of soil erosion in rainfall experiment after wind tunnel test were gradually decreasing, but the amount of runoff was gradually increasing. We defined the △f was the coupling intensity of water and wind erosion and its value was the difference between the amount of rainfall erosion after wind erosion and the amount of single water erosion. The higher the wind speed and the rainfall intensity were, the lower the value of △f was.
Keywords: Water erosion rate; Wind erosion rate; 7Be; 137Cs

Language中文
Document Type学位论文
Identifierhttp://ir.iswc.ac.cn/handle/361005/8910
Collection水保所知识产出(1956---)
Recommended Citation
GB/T 7714
孙喜军. 黄土高原水蚀风蚀交错带 土壤侵蚀速率的7Be和137Cs示踪研究[D]. 北京. 中国科学院研究生院,2012.
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