Synthesis Analysis of Soil Erosion for Three-River Headwater Region Based on GIS

In this paper,based on the common soil erosion model,the Three-River Headwaters region was select for study object. GIS methods are applied to conduct Semi-quantitative assessment for different types of soil erosion,and some results are concluded. The water erosion occurs in High Mountain and extra-high mountain of Yushu,Nangqian,Banma and Jiuzhi County in the southeast and south of the Three-River Headwaters region. The degree of erosion is prone to topography,precipitation,river and human activity. The freeze-thaw erosion mainly distributes in the northwest of the Three-River Headwaters region. The area of middle and above middle erosion degree accounts for roughly 50%.

Quantitative Remote Sensing Study on Regional Soil Erosion——Bin County of Heilongjiang as an Example

Based on Chinese soil loss equation （CSLE） model, this paper utilized technical advantages of RS and geographic information system （GIS） on data access and erosion factors database building to study prediction methods of regional soil erosion. The spatial analysis module of ARCGIS platform was applied to study the spatial distribution of erosion and the inter-relations of the factors influencing regional soil erosion in the research area. As a result, the mean soil erosion modulus of Bin County is 3 555.42 t/（km^2.a）, which suggests moderate degree erosion. The mean soil erosion modulus of clayey meadow soil is higher than those of dark brown soil and black soil. Vegetation factor values are between 0.1-0.2. The mean slope gradient and slope length values are respectively 1.335 and 6.061 which shows slope length is a dominant factor. And soil type, vegetation coverage and topographic factors have remarkable relevance to each other. Therefore, RS, GIS and CSLE are applicable in regional scale to disclose spatial distribution characteristics of soil erosion and to analyze the characteristics of dominant soil erosion factor quantitatively.

Gully Erosion Regionalization of Black Soil Area in Northeastern China

Gully erosion is the frequent and main form of soil erosion in the black soil area of the northeastern China, which is one of the most important commodity grain production bases in China. It is encroaching upon the fertile farmland there. Regionalization of gully erosion can reveal the spatial distribution and regularity of the development of gully erosion. Based on the eco-geographical regional background features of the black soil area, this study combined the regionalization with influencing factors of the development of gully erosion. GIS spatial analysis, geostatistical analysis, spatial statistics, reclassification, debris polygon processing and map algebra methods were employed. As a result, the black soil area was divided into 12 subregions. The field survey data on type, length, volume and other characteristics indicators of gully erosion were used to calibrate the results. Then the features of every subregion, such as where the gully erosion is, how serious it is, and why it happens and develops, were expounded. The result is not only an essential prerequisite for gully erosion surveys and monitoring, but also an important basis for gully erosion prevention.

Comparison and quantitative assessment of two regional soil erosion survey approaches

Regional soil erosion surveys are the first step of soil conservation planning.Grid and sampling ap-proaches are commonly used for soil erosion surveys at the regional scale.With the grid approach,the region is divided into grids(e.g.,1 km × 1 km),and the soil erosion rate of each grid was calculated.With the sampling approach,a small portion of the area(typically 4%or less)was taken and then the soil erosion rate was calculated.Based on the above calculation,both approaches evaluated the soil erosion area(which is the area where the soil erosion rate is greater than the soil loss tolerance(t))and its distribution in the whole region.The purpose of this paper is to compare the assessment results of the two approaches and analyse their practicality using Yunyang County,Chongqing,China(area is 3636 km^(2)).The soil erosion rate,percentage of soil erosion area(PSEA,which is the ratio of the area where the soil erosion rate is greater than the soil loss tolerance(t)to the area of the total study region)and its spatial distribution were compared between the two approaches.The results showed that the grid approach overestimated the average soil erosion rate and PSEA overall for all 33 sample units and the whole region in comparison to the sampling approach.The sampling approach can yield a reasonable spatial distribution of the soil erosion rate in the whole region.In addition,the soil erosion regions were more clustered than those using the grid approach,which can be more suitable for soil conservation planning.Therefore,the sampling approach is an efficient and practical approach in regional soil erosion surveys.The results can provide insights into regional soil erosion surveys.

Spatial Distribution and Temporal Dynamics of Soil Carbon Removal Caused by Water Erosion in China

Using water erosion data from three national soil erosion remote-sensing surveys （the first：1985-1986; the second：1995-1996; the third： 2000-2001） and carbon density data from the second national soil survey （1979-1992）, we computed soil carbon removal caused by water erosion, and analyzed its spatial distribution and temporal dynamics in China. Results revealed that the total removal of soil carbon caused by water erosion was about 74.61 Tg C y^-1 , of which 51.49 Tg C y^-1 was organic carbon, and 23.12 Tg C y^-1 was inorganic carbon. The main erosion level of the whole is moderate erosion. Among the seven erosion regions, the Southwest Karst Region had the most significant removal of soil organic carbon, which was 26.48% of the total and mainly due to its moderate erosion. In contrast, about 67.62% of the soil inorganic carbon removal occurred in the Loess Plateau Region, which mainly due to its highly intense and intense erosion. As a whole, the removals of soil carbon caused by water erosion represented a decreasing trend among the three national soil erosion remote-sensing surveys. Between the first and the second survey, soil carbon removal decreased by 11.66 Tg C y^-1 , of which 81.93% was organic carbon. Compared with that in the second survey, soil carbon removal decreased by 1.65 Tg C y^-1 in the third survey, of which 1.514 Tg C y^-1 was organic carbon, and 0.134 Tg C y^-1 was inorganic carbon.

侵蚀地形对马尾松林下土壤特性的影响

土壤是植被生长的重要物质基础,其分布和发育受土壤侵蚀的影响。红壤丘陵区马尾松林下土壤侵蚀严重,生态环境脆弱,探清该区马尾松林下土壤侵蚀对土壤分布及其特性的影响,对该地区的植被重建和生态恢复具有重要意义。基于调查取样和分析测试获取的数据,采用统计和灰色关联度分析法分析侵蚀地形对红壤丘陵区马尾松林下土壤特性的影响。结果表明:不同侵蚀地形的土壤特性差异显著,相对于山脊坡和鞍部坡,切沟土壤理化性质的大部分指标含量最高,微生物数量最多,土壤酶活性最大;不同侵蚀地形的土壤特性指标间的相关性差异较大,与山脊坡和鞍部坡相比,切沟的土壤理化性质指标与土壤酶及微生物指标的显著正相关明显增多,土壤特性与切沟的关联度也最高;切沟形成的微环境提升了土壤特性,为植被恢复提供了有利的条件。因此,加大侵蚀沟的环境研究可为快速恢复该地区的土壤与植被提供科学依据。