In recent years, steppe degradation in North China has become a serious environmental problem. Most research on steppe degradation is conducted at the level of communities or at the scale of small regions. To better understand the spatio-temporal variation and driving factors of grassland degradation, monitoring and analysis at broad regional scales are needed. This paper systematically describes the state and characteristics of steppe degradation at the Xilinhot plateau, makes an in-depth empirical analysis of the natural and man-made causes leading to degradation, and analyzes what driving factors have influenced degradation in this typical steppe region over the last 20?years. Ten biophysical and socio-economic variables, including altitude, slope, precipitation, temperature, soil conditions, distance to river, distance to highway, population density, sheep unit density, and fencing policy, were evaluated on their impact on observed patterns of degradation. The results indicate that all of these factors had a significant influence on the process of steppe degradation. During the first 10?years, from 1991 to 2000, steppe degradation increased, but after 2000, the degradation trend has, to some extent, reversed. The analysis indicates that the measures taken by the government, such as fencing vulnerable areas, played an important role in this change. The results advance the understanding of grassland degradation and contribute to constructing an empirical and theoretical base for grassland management and planning. 相似文献
The wide use of polyacrylamide (PAM) in enhanced oil recovery generates a large amount of polymer-bearing wastewater featuring high viscosity and difficult viscosity reduction, making the treatment of wastewater increasingly difficult. In this paper, the experimental study on reducing the viscosity of wastewater containing polyacrylamide by using the plasma generated by dielectric barrier discharge (DBD) and the synergistic effect of catalyst γ-Al2O3 is carried out. The law of plasma reducing the viscosity of wastewater containing polyacrylamide is studied under the different conditions of amounts of γ-Al2O3 catalyst, discharge voltages, and initial concentrations of polyacrylamide-containing wastewater. The mechanism of viscosity reduction of polyacrylamide is studied through environmental scanning electron microscope (ESEM), Fourier transform infrared (FTIR) spectrometer, and X-ray photoelectron spectroscopy (XPS). The results show that the catalytic viscosity reduction is the best when the discharge voltage is 18 kV and the discharge time is 15 min. With the increase in the input of the γ-Al2O3 catalyst, the viscosity of the PAM solution decreases gradually. When the amount of γ-Al2O3 is 375 mg, the shear rate changes from 0.5 1/sec to 28 1/sec, and the viscosity of the solution containing polyacrylamide changes from 434.5 mPa·s to 40.2 mPa·s. The viscosity reduction rate of the PAM solution is 90.7%. After the catalytic viscosity reduction, the functional groups of polyacrylamide do not change much. The elemental composition of the catalyst has not changed, which is still Al, C, and O.
Abstract Miyun County, located in the northeast of Chinese capital Beijing, was underwent remarkable variations in land use in recent years. This paper aimed to detect changes in land use of Miyun from 1997 to 2005, and to qualify the response of ecosystem to LUCC based on ecosystem services valuation. With two-periods TM images, we got land use change data, and then ecosystem services values were calculated using ecosystem services valuation coefficients proposed by Chinese scholar Xie Gaodi. Results showed that water area, farm land and unused land decreased while residential land, forest land, grassland and orchard land increased during the study period. The loss of ESV was RMB 206 million and the main reason was the decrease of water area and farm land area. As for spatial variation, there were most dramatically land use change and ESV decline in reservoir ecological protection region. The coefficient sensitivity analysis indicates that valuation coefficients used in the study are suitable and results are reasonable. The driving forces of ESV loss were rapid population growth and economic development. More work should be done to make eco-environment stay healthy. 相似文献