【摘要】：三江源地區(qū)地處青藏高原腹地,由于其獨特的地理位置,形成了我國特有的高寒草地生態(tài)系統(tǒng),在水源涵養(yǎng)方面具有極其重要的生態(tài)地位,是我國水資源供給的核心發(fā)源地,具有以草地生境為主的豐富的動植物多樣性。由于長期發(fā)生在這一地區(qū)的土壤侵蝕現(xiàn)象的不斷演變惡化,導致牧草質量下降、草地退化,以及土地荒漠化和“黑土灘”化等一系列問題,因此,對該地區(qū)土壤侵蝕監(jiān)測與評估方法的研究具有十分重要的意義。本研究以GIS為技術平臺,RUSEL模型為參考,結合多種機器學習方法。依據(jù)137Cs侵蝕模數(shù)測算法建立自定義土壤侵蝕模型,并根據(jù)其精度進行比對分析,在研究區(qū)取得相對精確的侵蝕估算量的同時,評價分析了相應的參數(shù)篩選、建模方法和RUSLE模型結果,最后依據(jù)侵蝕結果提出了相應的防治對策。主要取得了以下研究結果:1)應用多種基于機器學習的參數(shù)篩選和建模方法,獲取了精度較高的三江源侵蝕模數(shù)空間分布圖和相應的侵蝕量,精度最高的自定義模型是模擬退火參數(shù)篩選法和Cubist建模方法結合的模型。2)利用RUSLE和模擬退火-Cubist模型分別估算的三江源多年平均侵蝕量分別為3.1*109 t*a-1和2.3*109 t*a-1,且模擬退火-Cubist模型精度顯著大于RUSLE模型的精度。說明結合了實測侵蝕數(shù)據(jù)和GIS遙感大面積應用優(yōu)勢的自定義模型估算精度上明顯優(yōu)于RUSLE模型。3)通過侵蝕強度分級的重心轉移分析,兩種模型結果的侵蝕強度等級在空間上都符合由東南向西北逐步升高的分布規(guī)律。基于縣界分區(qū)的侵蝕程度比較表明,侵蝕程度最高的三個地區(qū)為格爾木市唐古拉鄉(xiāng)、治多縣和興�？h。4)三江源區(qū)不同植被群系合并類型下的土壤侵蝕程度由高到低依次為:農耕地稀疏植被/沼澤/荒漠草原林地草甸灌叢。除草原類侵蝕強度顯著偏高,大部分類型基本符合其他研究對各類下墊面土壤侵蝕難易程度的比較結果。結合人文因素分析,草原類植被群系中多以適口性良好的牧草為優(yōu)勢種,故過度放牧是引起草原類下墊面侵蝕現(xiàn)象嚴重的主要原因。5)通過參數(shù)篩選方法對參數(shù)重要性的評價,表明風蝕和凍融侵蝕是研究高寒草地生態(tài)系統(tǒng)土壤侵蝕時是不可忽略的兩種侵蝕動力,是有別于其他下墊面土壤侵蝕的主要特征,而RUSLE模型參數(shù)中多年平均風速和土壤凍融數(shù)據(jù)的應用缺失,是本研究自定義模型整體優(yōu)于RUSLE模型的主要因素。6)三江源區(qū)的土壤侵蝕程度總體偏高。由土壤流失量結合市場價值法,估算研究區(qū)多年平均有機質經(jīng)濟損失價值,模擬退火-Cubist模型估算的年均經(jīng)濟損失為299億元,并且低于用于參考的RUSLE模型估算結果。由此可知,整個研究區(qū)受土壤侵蝕現(xiàn)象所產(chǎn)生的經(jīng)濟損失數(shù)額巨大。最后,依據(jù)三江源侵蝕模數(shù)的空間分布的特征,提出了一些土壤侵蝕防治措施及政策建議。
[Abstract]:The Sanjiangyuan region is located in the hinterland of the Qinghai-Xizang Plateau. Because of its unique geographical position, it has formed a unique alpine grassland ecosystem in China and has an extremely important ecological status in water conservation. It is the core source of water resources supply in China. It has abundant animal and plant diversity, which is dominated by grassland habitat. As a result of the continuous evolution and deterioration of soil erosion, which has been occurring in this area for a long time, resulting in a series of problems, such as the decline in the quality of forage, the degradation of grassland, the desertification of land and the transformation of "black soil beaches", and so on, It is of great significance to study the methods of soil erosion monitoring and assessment in this area. This research takes GIS as the technical platform, RUSEL model as the reference, and combines various machine learning methods. According to the calculation method of 137Cs erosion modulus, the self-defined soil erosion model was established, and the precision of soil erosion model was compared and analyzed according to its precision. At the same time, the relative accurate erosion estimation was obtained in the study area, and the corresponding parameter selection was evaluated and analyzed. Modeling method and RUSLE model result. Finally, the corresponding control measures are put forward according to the erosion results. The main results are as follows: 1) by using a variety of parameter selection and modeling methods based on machine learning, the erosion modulus spatial distribution map and the corresponding erosion amount of the three rivers source are obtained. The highest precision of the custom model is the combination of simulated annealing parameter screening method and Cubist modeling method. 2) the annual average erosion amount estimated by RUSLE and simulated annealing Cubist model is 3.1 109t, respectively. * a-1 and 2.3 109t / a, The precision of simulated annealing-Cubist model is significantly higher than that of RUSLE model. It shows that the estimation accuracy of the self-defined model which combines the measured erosion data and the advantages of GIS remote sensing in large area application is obviously superior to that of the RUSLE model. 3) through the gravity center transfer analysis of erosion intensity classification, The erosion intensity grades of the two models are consistent with the distribution law of increasing gradually from southeast to northwest in space. Based on the comparison of erosion degree between county boundaries and subzones, the three areas with the highest erosion degree are Tanggula Township of Golmud City. 4) the degree of soil erosion from high to low under the combination of different vegetation formations in the source region of the three rivers is: sparse vegetation / swamp / desert steppe forest meadow shrub. The soil erosion intensity of steppe was significantly higher than that of steppe, and most of the types of soil erosion were basically consistent with the results of other studies on the soil erosion difficulty and ease of various underlying surfaces. Based on the analysis of human factors, the herbage with good palatability is the dominant species in grassland vegetation formation. Therefore, overgrazing is the main reason for the serious erosion of steppe subsurface. 5) the importance of parameters is evaluated by parameter selection method. The results show that wind erosion and freeze-thaw erosion are two kinds of erosion power which can not be ignored in the study of soil erosion in alpine grassland ecosystem, and are the main characteristics of soil erosion different from those of other underlying surfaces. However, the lack of annual mean wind speed and soil freeze-thaw data in the parameters of RUSLE model is the main factor that the self-defined model is better than the RUSLE model. 6) the soil erosion degree in the source region of the three Rivers is relatively high. Based on the soil loss and market value method, the average economic loss of organic matter in the study area is estimated. The average annual economic loss estimated by simulated annealing-Cubist model is 29.9 billion yuan per year, which is lower than that estimated by the RUSLE model used for reference. Therefore, the economic loss caused by soil erosion in the whole study area is huge. Finally, according to the spatial distribution characteristics of erosion modulus of the source of three rivers, some measures of soil erosion prevention and control and policy suggestions are put forward.
【學位授予單位】：蘭州大學
【學位級別】：博士
【學位授予年份】：2016
【分類號】：S812.2

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