Study The Impact On Its Downstream Soil By The Fukang 500 Reservoir Built On

Fukang 500 reservoir is a reservoir formed by t he construction of embankments and control gates and other buildings by plain area of low- lying land, lakes and channels. The construction of the reservoir can effectively solve the problem of regional water shortage, so it has been an important part of the construction of water conservancy projects. The dam is an earth rock dam, which is simple in structure and convenient in management. In the arid and semi arid area, the irrigation of the lower reaches of the plain reservoir, although the reservoir provides the water needed for crop growth, but at the same time, the degree of salinization of the soil is increasing. The early construction of the reservoir can have been raised its downstream water level due to water seepage. Therefore, later built the reservoir(Fukang 500) using anti-seepage measures, on the one hand can reduce the moisture loss due to leakage at the bottom, on the other hand can avoid greatly raise the groundwater level caused by soil salinization downstream from a reservoir.Human activity is a ubiquitous phenomenon in nature. Under conditions of relatively uniform habitat, human disturbance is an important reason for the changing properties of the soil such as: soil moisture, salt content, organic matter, ph value and other indicators. It is a major cause of soil physical properties change. The manner, the extent, the duration of human activities have a significant impact on the heterogeneity of soils.Soil salinization is one of the land degradation in the most common natural phenomenon. In the arid and semi-arid regions, the soil salinization has formed by water will quickly evaporate, and the lower part of the soil salt up to the surface. The natural factors is one reason that has caused by soil salinization, including scarce rainfall, sustained high temperatures, strong soil evaporation, high water table, the unreasonable land use of human activity is another.The reflectance of saline soil in the downstream of No. 500 reservoir in Fukang, Xinjiang province was investigated. Through filed sampling and spectral test, using the method of spectral transform, correlation analysis, a quantitative analysis was conducted on the salt and water content of the soil under different disturbance degree. A multiple linear regression model was establis hed between the soil reflectance and soil salinity content.The main findings and conclusions are as follows.First, the human disturbance has a significantly positive correlation with the soil content while has an extremely negative correlation with the water content. The correlation coefficients are respectively 0.961 and-0.929.Secondly, the analysis of the correlation is between the soil and its water-soluble ionic spectral reflectance of different interference. It’s found that these ions(Mg2+, K+, SO42-, Clˉå'Œ Ca2+)for the spectral reflectance of soil influence is relatively weak. Among them, the correlation coefficient of Na+ ions at 550 nm after HCO3ˉ beyond SO42- and become the largest of all the ions. The correlation coefficient HCO3ˉ greater than 0.36, the correlation coefficient has become second only to Na+ ions in the second position. The correlation between Na+ and HCO3ˉ and soil spectra are increasing with degree of interference. This indicates that the influence of human disturbance, soil salinization of Na + and HCO3ˉ with water and salt to the surface migration has gathered phenomenon.Thirdly, it shows that those most heavily disturbed soil reflectance higher than the slightly disturbed about 10%, while the slightly disturbed soil reflectance higher than the undisturbed soil about 17%. The reason is that it have been destroyed that the soil surface of barren land with a small amount of vegetation, the biological creature and soil surface crust. The more the disturbance, the greater chance the surface layer would be destroyed. Meanwhile, the surface layer of soil will be lack of the crust protective, the soil salinity of the bottom rises to the surface associated with the soil moisture will quickly evaporate. The salt is concentrated to the surface layer due to both little precipitation and a lack of protection of soil crust.Fourthly, the peak wavelength location of the spectrum is increased(999, 876-979, 1182-1370, 1900 nm) while the soil is taken from undisturbed to heavily disturbed conditions, which means that with the increase of disturbance, the soil becomes more sensitive in the near infrared region.Fifthly, the three different prediction models were established though the reflectance R, the reflectivity of the first derivative R’, the reflectance R + water. According to the R2 and the RMSE to comprehensive judge the accuracy of the model. It is found that among those established prediction models of the same soil salinity in the different levels of disturbance, the smaller the degree of human disturbance, the higher the accuracy of model. It is found that among all of those established prediction models, the one based on the derivative of R works the best, of which R2 is larger than 0.983, model accuracy is improved by 5% — 10%,which means that through a derivative transformation, the linear noises in the original spectrum can be removed.Sixthly, the original spectral reflectance(In the wavelength range of 350 ~ 2500 nm) was negatively correlated with the soil organic matter content, and the strongest correlation bands were in the visible light band. After the first derivative transformation, the most sensitive area is concentrated near the near infrared band.Seventhly, the original spectrum is processed by the first order derivative, the inverse of the logarithm of the number of different degrees to improve the sensitivity of the content of organic matter, especially in the first derivative transformation is the most sensitive. This is because the spectrum is not only able to eliminate the influence of part of the atmosphere, but also the effect of partial linear or near linear background, noise spectrum and so on.What’s more, in three kinds of different levels of interference using spectral reflectance first-order derivative of soil organic matter content prediction model prediction is better than the reflectance R and the reciprocal of log(1 / R) model, the model accuracy increased approximately 15%- 32%. This fully shows that the original spectra by first derivative transformation processing, can remove the interference of the linear part of the background and noise spectrum, the model can more accurately reflect the different disturbance degree of soil organic matter content and its change information. It has important significance for the study of soil information and dynamic monitoring in the future.