桂江流域土壤侵蚀估算及其时空特征分析

Estimating soil erosion and analyzing its spatio-temporal characteristics in Guijiang river basin,Guangxi

桂江流域的水土流失现状研究对珠江三角洲的水生态安全有重要的现实意义。采用修正的通用土壤流失方程（RUSLE）估算了桂江流域的土壤侵蚀模数与年侵蚀总量,分析流域内土壤侵蚀的时空分布特征,探讨了影响该区域土壤侵蚀强度的自然与人文因素。结果表明,桂江流域51.8%的地表都在发生不同程度的土壤侵蚀。从全流域平均土壤侵蚀强度来看,属于中度侵蚀。从土壤侵蚀面积来看,约85%的地表处于微度、轻度与中度侵蚀。4-6月的全流域平均土壤侵蚀强度最大,侵蚀总量也是最大的。流域的土壤侵蚀主要发生在高程在30~600m的低山丘陵-高地地貌区内的林地与耕地中。流域内岩溶区的土壤侵蚀强度随着石漠化程度从无到中度逐渐增加,轻、中度石漠化区的土壤侵蚀强度达到强度侵蚀等级。

The Guijiang river basin is situated in China＇s southwest karst area.It is well-known for the Lijiang river,which has the most scenic karst landforms in the upper reaches of the basin.The Guijiang river is a major tributary of Xijiang river in the Pearl river basin.Research on soil erosion in the Guijiang river basin,hence,has practical significance for conservation of the aquatic ecology and security of the Pearl River Delta.In addition,the soil erosion model developed for this study is fundamental to research on the carbon budget of this karst area.The Revised Universal Soil Loss Equation（RUSLE）was utilized to calculate the soil loss rate and soil loss amount in the Guijiang river basin,Guangxi.The spatial distribution of soil erosion was analyzed,and the natural and human factors associated with soil erosion discussed.It was shown that about51.8% of the land area of the Guijiang river basin underwent soil loss to differing degrees.The Guijiang river basin had an average-annual soil loss of up to 2.95×106 tons and the average soil erosion rate was 153.5t/km2,identified as medium erosion.85%of the total area of the study basin had micro-slight and medium soil erosion.Strong or greater soil erosion was found in 15% of the study area,mainly in the north of the basin,the high-elevation south and northwest mountain areas of the Gongcheng river.The seasonal distribution of rainfall in the basin determined similar temporal distribution of soil erosion.Soil erosion intensity and total soil loss peaked in the second quarter,because the ratio of rainfall erosivity from April to June is highest in a whole year.This is followed by the third quarter,which accounted for one third of the total annual soil loss.Soil loss reached a maximum in the hilly and mountainous areas with elevations ranging from 30 mto 600m.Soil loss in the karst areas was nearly all derived from areas of no or slight karst rocky desertification.The intensity of soil erosion was enhanced following increases in the degree of karst rocky desertification from no to medium,and the soil erosion in areas of slight or medium karst rocky desertification reach strong degree.Soil losses calculated by the RUSLE model developed for the Guijiang river basin were basically in accord with sediment discharge data from past literature,indicating that RUSLE can be properly used to estimate soil erosion intensity and soil loss in karst river basins.