| Ninghua City, locating in the area of "the source of three rivers", suffers the most serious soil erosion in Fujian Province. It is one of typical representatives of purple soil erosion region in South China, and its history of soil erosion has been more than a century. Study and investigation on the status quo of purple soil erosion and degradation, on changes in the law for many years, the establishment of a database concerning related data on soil erosion, proposals on prevention and control measures, all of those mentioned above can effectively guide local treatment on soil erosion and lay good foundation for better integrated soil erosion control under the government's macro-control foundation.With in-depth developments on remote sensing, geographic information systems technology and spatial analysis model, remote sensing and geographic information systems have become one of the most rapid and reliable means to study soil erosion and its changes in the typical regional. Ninghua City has launched a large-scale and comprehensive treatment on soil erosion since 2000. With the social, economic and other factors, great changes for both soil erosion and landscape have taken place in the western part of the city. In this paper, on the basis of the relevant theories on soil and water conservation, ecology, setting the most serious purple soil erosion area, the western part in Ninghua City, as research region, with help of topographic maps, ALOS and other remote sensing data, "3S" technologies and ArcView, ArcGIS, Erdasimagine and so on, data in the five fields including topography (mainly using DEM to extract data of elevation, slope, aspect and other terrain factors), land-use types, vegetation, soil erosion and soil conservation measures have been acquired, and then large-scale, high-precision regional geo-spatial data sets on soil erosion have been established as well as the the status quo of soil erosion that based on the verification and expert advice in the open field. In addition, reasons for soil erosion evolution and changes of both intensity and quantity structure in time and space have been analyzed in west Ninghua during the period from 2000 to 20007. Finally, treatment and control strategies have been proposed according to integrated treatment and related experience in Ninghua county. Main conclusions are come up as follows:1. Soil erosion situation in 2007. In 2007, the total soil erosion area in the western region of Ninghua county, Fujian Province, is 13123.82 hm2, 27.04% of the total land area. And the extent of soil erosion is slight and mild-oriented. With the increase of erosion intensity, soil erosion area becomes downward. From soil erosion status chart of Ninghua county generated in 2007, the soil erosion region mainly locates in central hilly areas around Shibi. The land area of Shibi and Huaitu only accounts for 45.2% of total regional land area, however the soil erosion area is about 4 / 5 (that is 79.73%) of the total erosion area.2. Dynamic changes law of soil erosion quantity and intensity during 2000-2007. Based on statistical results of soil erosion classification, from overall changes trend, the soil erosion area in western NingHua is declining since 2000. By comparing the erosion area in 2007 with that in 2000, soil erosion area reduced 1509.86 hm2 in total with the rate of 3.11% and annual change rate of 1.47%. From changes trend of erosion intensity, slight and moderate degree erosion increased obviously, other types of erosion declined, with the biggest area change at moderate and slight erosion, and the most obvious annual changes rate at moderate and extreme strong erosion. Aforesaid results have proved early fruits in soil erosion treatment on purple soil erosion in west Ninghua in past seven years.3. From transfers of various erosion types and new erosion sources, there are about 15462.98hm2 area that suffered changes of different degrees erosion in past 7 years, accounting for 31.85% of the total regional area. Among erosion changes, slight erosion manly turned into mild erosion; slight, moderate and extreme strong erosions all turned into moderate erosion, extreme strong erosion turned into moderate erosion mainly locating in the central region areas where banned and strengthened protection measurements have been taken. Slight and moderate erosions mainly conversed from mild and strong erosions; mild and strong erosions mainly from slight erosions; extreme strong erosions mainly from mild and slight erosions locating sporadically and mainly in regions inferred seriously by human activities such as fully-cultivated land developing, mountains burining, project development and construction.4. Using the soil erosion distribution model to analyse spatial locations of the different erosion types, it is concluded that the center of soil erosion distribution in the west Ninghua has moved to the northwest, with an overall movement of 1945.813m in past 7 years. From erosion types, the shift direction for slight and mild erosion centers were southeast and northwest respectively, for both moderate and extreme strong erosion centers are southwest, for extreme strong erosion southeast. Among them, most intensive erosion is extreme strong erosion with an overall deviation distance of about 8066.912m.5.Through the analysis for different terrains on regional soil erosion dynamic changes based on SEIC and SEII indicators, it indicates that different terrain factors such as elevation, slope angle and slope direction brought about great discrepancies in severity and structure types of soil erosion. Through the comparison of related data between 2000 and 2007, it is found that indicators in 2007 on most the vast majority of elevation, slope grading, slope direction types for both SEIC and SEII are less than those in 2000, which means the role of human intervention overrun the impact of natural factors. In the west Ninghua in past 7 years, through comprehensive measures such as closure, fertilization, forest and grassland protection, economic orchard, sloping land transformation, shallow gully treatment, the surface vegetation cover has significantly increased. As a result soil erosion alleviates continuously. |
PDF Full Text Request