Study On Water And Soil Loss Mechanism Of The Ecological Rehabilitation Based On Small Watershed Scale In Guizhou Karst Region

Water and soil loss in Karst areas is the focus of research in the field of water and soil loss in China, in-depth study of natural karst eco-environment and social conditions of water and soil loss mechanism portfolio characteristics, and probing into water and soil loss mechanism of the temporal and spatial distribution, which can help making macro decision for water and soil loss prevention and provide a theoretical basis and foundation of information.Because Guizhou Karst areas are of fragile ecological environment, severe water and soil loss and its huge devastating effect make studying on water and soil loss mechanism in Guizhou karst areas great realistically significant.Choosing several Guizhou Karst curing areas to study ,such as Qingzhen Wangjiazhai- Yangchang dong small drainage basin, the top Zhenfeng Dingtan small drainage basin, Bijie Shiqiao small drainage basin, Zunyi Longba small drainage basin and Yanhe small drainage basin, prefering to the analysis methods of soil physical and chemical properties of Nanjing Soil Research Institute Chinese Academy of Sciences, while water and soil loss survey methodology according to Water Conservancy Section criterion . There are 64 sample points in the Study Areas. From April 2006 to December 2007, to collect the basic data, field sampling and monitoring have been done six times in April, August, December of the two years, and using SPSS, EXCEL, MAPGIS, PHOTOSHOP etc. data analysis software for the maps and data analysis. Studying the following aspects: Water and soil loss mechanism in Karst areas on geology, geomorphic, soil, vegetation and climate; Water and soil loss mechanism spacial differences in differrent geomorphic karst environmental structure, different karst river background, different karst ecological environment; Water and soil loss mechanism dynamic changes in different grades Desertification, different land use patterns, different governance model; Ultimately, the model of water and soil loss mechanism in the Karst region has been built. To realize innovation, the paper takes two sides for consideration. On the one hand, it combines both macro and micro sides to analyze geomorphic factor of water and soil loss. On the other hand, it divides the small watersheds into different units to study the law of water and soil loss in Guizhou karst region. The research results obtained are as following:â‘ The soil micro-structure of different soil texture is the important indicator of soil erosion wear resistance. The maximum difference among various types of soil particles is the size of <0.01 mm, a difference to 26%. Clay(<0.001 mm) is in larger amount, more than 20 per cent, will directly decrease soil infiltration capacity; Karst soil, the stable infiltration rate differentiate significantly, the average upper stable infiltration rate is 3.13 times faster than the lower layer's; The soil moisture diversifies significantly with different vegetation types; Soil moisture has close relation with the growth situation of vegetation, and field hold capacity is related with capillary water capacity significantly, which illustrates the soil moisture is easy to lose in karst areas; The average upper soil stable infiltration rate increases with the increasing of the amount of > 0.25 mm micro-aggregrates; The soil disintegration rate is close to land use patterns as well as the growth situation of vegetation.â‘¡Vegetation is the most important dynamic change direction factor; Under the circumstances that other conditions are basically the same, the water and soil protection effect shows as following: forestry, shrub, lawn> shrub, lawn> the economic fruit forests, grasslands> natural grassland> purple Alfalfa > young bamboo turf> maize, the water conservation effect of portfolio configuration is obviously better than a single vegetation, especially tree, shrub and grassland vegetation combining configuration is more ideal; The relationship between vegetation cover rate and soil erosion modulus is: y = 31.998-0.0027x² - 0.1413x, y is soil erosion modulus, x is the vegetation cover rate, and the correlation coefficient r is 0.793, 47.07% confidence level; Litter layer thickness, litter layer water-holding amount and its rate have direct impact on water and soil loss, maximum water retention rate is associated with the maximum effective rate of water significantly, and the correlation coefficient is 0.875.â‘¢The evolution sequence of karst geomorphic types is , plateau mountain→plateau basin→plateau canyon, from the plateau mountain ,plateau basin to the plateau canyon, which is actually composed of a lag stage with the landscape is not yet affected by the erosion of origin and a vigorous down cut erosion stage, geomorphology of the surface caused the difference secondary material (product of weathering, slope, flood, etc.), the intensity of the camp, undulating terrain size, topography characteristics, river conditions and even the soil, vegetation, light, heat, water, gas changes ,which lead to change of land type and land use, as a result , the natural and human factors of water and soil loss change. Soil, vegetation, these dynamic factors of water and soil loss show spacial differences in different entironment structures. Size of the combined effects of water and soil loss mechanism displays as: karst mountain plateau> karst plateau valleys> karst plateau basin, karst upper river reaches> karst lower river reaches> karst middle river reaches. Field investigation of water and soil loss factors showes that the average karst mountain sloping grades as following , plateau mountain (20.917°)> plateau valley (19.167°)> plateau basin (15.947°),and average sloping grade significantly controls water and soil loss.â‘£There is a significant difference of the water and soil loss in the upper, middle and lower reaches of the Wujiang river, upstream> downstream> midstream. Contrasting geology, topography, climate ,from the upper reaches, middle reaches to lower reaches of the Wujiang river valley, the weathering crust thickness were decreased, lithology distribution as the upper reaches of carbonate rocks, purple rocks, basalt, the middle reaches of carbonate rocks, shale area and downstream of carbonate rocks, erosion datum plane is reduced, the bending of the river is reduced, the largest valley density downstream, midstream artificially project of slope changed into terrace works best, an average annual rainfall, downstream> midstream> upstream , comparative analysing different reach background of water and soil loss factors that rainfall factor was not the major factors leading to water and soil loss differences in karst area, according to the contribution rate of water and soil loss, the sequence is human engineering measures, weathering crust thickness, lithologic, erosion datum plane, valley density , the river bending rate. ⑤Water and soil loss mechanism shows a dynamic change, the dynamic factors such as, soil, vegetation, microclimate show different change breadth as, intensive rocky desertification < moderate rocky desertification water conservation forest> the fruit forest> stairs level ground > wasteland> slope land, ecological agriculture> ecological animal husbandry. The dynamic factors of water and soil loss mechanism such as, soil temperature, vegetation, the vegetation coverage rate, plant biomass, illuminate intensity, air temperature and relative humidity of micro-climate factors show a significantly dynamic change. The seasonal change of water and soil loss is significant, the field monitoring data indicate that the rainy season from April to October end of the rainy season, water and soil loss during this period is noticeably strengthened, accounting for more than 90 per cent. From December in winter to April in the spring of the next year, water and soil loss is very weak; The results of the comparison of vegetation cover and soil erosion modulus in different karst ecological rehabilitation small watershed are, Qingzhen Wangjiazhai small watershed, Qingzhen Yangchangdong small watershed, Zhenfeng Dingtan small watershed, Bijie Shiqiao small watershed, Zunyi Longba small watershed, Yanhe Lizishui small watershed, vegetation covering rate from 2006 to 2007 to increase by 25.6%, 18.1%, 9.8%, 15.2%, 4.5%, 1.2%, decreasing rate of soil erosion modulus is 12.6%, 6.2%, 20.1%, 12.8 %, 8.7%, 5.7%.â‘¥The model of water and soil loss mechanism shows that vegetation factor indicators (Zx), the surface material factor indicators (Wx), the topographical factors indicators (Dmx), the precipitation factor indicators (Px), the human factor indicators (Rx) are the closest factors. Respectively choosing vegetation coverage rate of vegetation factor, the soil thickness and uncovered rock rates of the surface material factor, the average slope gradient of different terrain factor, annual rainfall, the rainy season precipitation volume in June, July, August, the heaviest thity-day and one-day rainfall of the rainfall factor, the proportion of slope to terrace of human factor to analyze, and ultimately establish macroeconomic estimation model as following: A_x=2.29+7.18/(9/Z_x+5/W_x+7/(1/3×(S₁+S₂+S₃)/100)+3/ (log(1+1.5G_r×(1-Mr)/100))+4/(log(1+1.5G_r×M_r/100))+3/ (ln((P_y+P₆+P₇+P₈+P₃₀+10P_d)/6)))...