| The system of natural vegetation in arid areas is an important part of ecological and geological environment system; especially it is fragile in region ecological and geological environment of the northwest of China. For recent decades, ecological geological environment problems in relation to groundwater resource had been increasingly prominent happened in the areas of natural vegetation system and wetland degradation. As a typical inland arid area of the Hexi corridor, Dunhuang basin has been seriously affected by degradation of natural vegetation system. And the natural ecological restoration of vegetation system has become a primary goal by the engineering of guide water from Ha er teng river into the Dang river.The thesis focused on the relationship the groundwater and soil-vegetation and to determine the groundwater effect on the control of natural vegetation structure and its expression form by means of analyzing the surface of0-100cm different depth of soil salinity, soil water content, organic matter and the occurrence features of groundwater and salt, also through using remote sensing quantitative inversion of the distribution characteristics of vegetation coverage and plant community in Dunhuang basin. It would provide scientific support for ecological environment protection, vegetation restoration and guide water from Ha’erteng river into the Dang River through studying the influence of the groundwater system of natural vegetation growth, as well would offer scientific mind for research of dependent groundwater ecosystems.This paper get the following conclusions through the above-mentioned-research:(1) Using Rapideye images technology of the normalized difference vegetation index (NDVI) has extracted the natural vegetation information about the reed community, alhagi community, Philippine community, lam wood community in iminqak community, salt, white communities, and the spatial location of black Chinese wolfberry community distribution and their average vegetation coverage is respectively:13.1%,8.6%,8.2%,4.2%,8.2%,3.4%and2.8%, respectively, based on a large scale in the dunhuang basin in2010. (2)The research of surface of soil salinization, the distribution characteristics and salinization type. Through analying the vertical and horizontal distribution characteristics of five different depth (0-20cm、20-40cm、40-60cm、60-80cm and80-100cm) and soil salinization (soil salinity, K+, Na+, Ca2+, Mg2+, Cl-, SO42-, NO3-) to determine the type of soil salinization in the study area and its spatial distribution features, to clarify the workspace salt has a relatively strong cohesion and also certify the soil salinity decrease size is top-down according to its content of the rule of vertical differentiation. Area of soil organic matter content is low and the highest value in20-40cm, high organic content areas are mainly distributed in the Mamitu of west lake to Yumen pass, and most of east lake and north lake have low organic content in the study area. Characteristics of soil water content distribution in the study area:the average depth of soil water content from high to low is (40-60cm,60-80cm,80-100cm,20-40cm,0-20cm), water content has increased with the increase of depth from0to60cm deep.(3)The classification of soil salinization in the study area:the types of salinization are main of chloride, chloride-sulfate and sulfate-chloride by the Cl-/SO42-equivalent weight in the study area. The performances are the chloride content from top to bottom gradually decreases, and showed a strong surface concentration, the sulfate showed a trend of increased from top to bottom, the chloride basic remains the same, the sulfate and sulfate-chloride has a tendency to increase from top to bottom, and showed a strong bottom concentration. In addition, the soil salt salinization results of under the different depth of soil salinity of the principal component analysis show that the study area is the main NaCl and Na2SO4.(4)The correlation analysis of soil base cation and soil salinity under different depth in study area:the soil base cations of Cl-, Na+and SO42-have higher positive correlation with the soil salinity. It shows that the organic content and soil salinity has certain relevance in the0-20cm and it becomes weaken with the increase of depth. There have well positive correlation about Cl-, SO42-,Na+from0to60cm, while there has low relationship Cl-and SO42-in the60-100cm.(5)The soil salinity and the vegetation fraction have a certain relationship under different depth of the study area. The vegetation fraction decrease with the soil salinity increase in the0-80cm, especially in the0-40cm has a significant impact on natural vegetation. The vegetation fraction increase with decrease of organic content that shows the relationship between organic matter and natural vegetation fraction.(6)The research of relationship between the soil salinity and vegetation fraction under type of different soil salinization according to the Cl-/SO42-equivalent weight ratio shows average vegetation fraction of the sulfate, sulfate-chloride and chloride-sulfate, chloride were10.4%,9.7%and7.1%. The general trend is salinity increase with the decrease of vegetation fraction within the sulfate area but there is no clearly trend in the sulfate-chloride, chloride-sulfate and chloride area.(7)The research of relationship between the groundwater buried depth and vegetation fraction under type of different soil salinization according to the Cl-/SO42-equivalent weight ratio shows the different groundwater buried depth has various impact on the natural vegetation growth. The suitable for natural vegetation growth groundwater buried depth are1.82m,2.17m and3.3m in the sulfate area, chloride-sulfate area, chloride area.(8)The research of relationship between the TDS and the vegetation fraction in different type of salinization indicate that the natural vegetation fraction and TDS has a good corresponding relation. It suitable for vegetation development order for sulfate> sulfate-chloride> chloride. When the TDS is greater than10g/L, the natural vegetation fraction has the trend of decrease.(9)The research of relationship between the soil water content and the vegetation fraction shows the vegetation fraction increase first and then decrease with increase the soil water content in0-100cm and the soil water content affect on the natural plant growth in0-60cm. When the soil water content is25%the vegetation fraction up to the highest value, but when the soil water content continue increase the vegetation fraction rapidly reduced.(10)Study on the relationship between the plant community’s distribution and groundwater recharge, runoff and discharge shows the plant communities distribution different under different conditions of groundwater. The drought resistance plant absorbs the water from the phreatic surface or the capillary rise. And the hydrophile plant uses the water after the groundwater reach to surface.(11)The study on groundwater effect on the control of natural vegetation structure come up with three vegetation systems are the effect by groundwater system of natural vegetation, part of the groundwater system of natural vegetation and non-groundwater system of natural vegetation according to extent of natural plant dependence on groundwater, the natural vegetation use of groundwater and the way of groundwater discharge, also according to each characteristic of GDEs divide the area and calculate the vegetation area in the Dunhuang basin.(12) Groundwater flow system has a macro control influence on natural vegetation community pattern. There have different vegetation community in the groundwater recharge area, runoff area, and drainage area. And buried depth of underground water level, the soil salt content and water content play a very important role to the evolution of the local vegetation pattern, in the drainage area. |
PDF Full Text Request