| Karst area in Southwestern China is regarded as one of the most vulnerable ecological zone with serious soil erosion. For restoring the degraded ecosystems, it's important to understanding the characters of land use and land cover change (LUCC), as well as to trace back the historical situation of soil erosion in catchment scale.In this paper, Kechou catchment, located in middle Guizhou Province, is selected for case study. According to LUCC study based on remote sense images, the historical land use and land cover change is getting clear. Experimental studies on soil profiles and reservoir sediment cores are carried out. Dating by isotope and grain size, the intensity and mode of soil erosion around past 40 years are recognized from environmental magnetic properties and other features, such as cumulative mass depth. An ORDB hierarchy model is used for simulating soil erosion process. Finally, some stratagems are proposed for better regional development based on eco-evolution and regionalization.Following are some conclusions from this study:(1) Land use and cover change of small catchmentBy the technique of RS and GIS, LUCC statuses in the year 1973, 1990, 1991, 1994, 1998, 2000 and 2002 are achieved from TM/MSS images and DEM data. In general, grassland (with shrub) is the main type of land cover, and bare land also occupies certain proportion. As a farm zone, paddy field and dry land are two main types of arable land.In the period from 1973 to 2002, Woodland decrease generally; grassland increase slightly first and decrease rapid after a short term fluctuate; dry land decrease after increase, as well as paddy field but more slightly; bare land increase significantly in later period despite decrease in previous stage.Land covers type in different slope range shows that land use intensity is increasing. According to land cover change matrixes, it is markedly for woodland changes to grassland, and grassland to dry land or bare land. In the other hand, it is likely for bare land turns to grassland. While grassland (with shrub) hardly turns back to woodland.(2) Magnetic properties of soil profilesIn most soil profiles, amounts of Ferromagnetic, Ferrimagnet and Canted Antiferromagnet (CA) exist more in surface layer and decrease less and less from shallow layer to deeper layer. CA shows an extreme larger amount in surface layer. Super Paramagnetic Grain (SP) shows the largest amount in shallow layer. Multi-Domain Grain (MD) exist less in surface than shallow and slightly decrease in deep layer. In the surface layer, CA leads the main contribution to SIRM, while in deep layer Ferrimagnet does, although it is not so much. Among Ferrimagner, surface layer contains more MD and PSD, while deep layer contains more SSD. Arable land contains less magnetic metter than physical profiles.(3) Dating analysis of sediment coresFacing the problem of the traditional 137Cs dating method which only relied on the position of peak in profile, an imporved dating method is devised. As the absolute values of 137Cs in small catchments often appear in the low level, soil erosion, which was caused by precipitation and other reasons, should intensively affect the amount of 137Cs depositing from soil to sediment in reservoir. It should be the main reason that 137Cs shows different distribution pattern in the sediment-core. More details are obtained with ten key time point dating by 137Cs and grain size changes. A co-adjusting way of magnetic properties is carried out for asserting sediment cores sampled from different point to certain years.(4) Soil erosion messages according to sediment core analysisErosion intensity can be expressed by cumulative mass depth. Erosion intensity is stronger in the phases 60~63,71~75,82~83,89~92 and 97~99 than the phases 64~70,76~81,84~88,93~96 and 00~04. Rainfall is the main influential factor of erision intensity.Erosion mode can be expressed by magnetic properties. In general, 1984 is an important time point, surface layer erosion mainly occurs before 1984, while shallow layer and deep layer erosion occurs more and more after 1984. For more detail: Strong surface layer erosion with some shallow layer erosion occurs during 1960~1963; Slightly surface layer erosion occurs during 1964~1970; Erosion turns to deeper layer during 1971~1974; Strong surface layer erosion with some shallow layer erosion occurs again during 1975~1979; Gently surface layer erosion and shallow layer erosion occurs during 1980~1984; Erosion during 1985~1988 is not steadily; Shallow layer and deep layer erosion occurs during 1989~1993; Erosion decrease during 1994~2000; Deep layer erosion occurs during 2001~2004. Both rainfall and LUCC status are influential factors of erosion mode, woodland and grassland show their positive effects, while dry land and bare land are negative ones.(5) Erosion simulate modelThe hierarchy model M-L-E(S, A) is imporved by using entities based on objects, it is used to simulate soil erosion with data of land cover pattern, topography situation and daily rain fall record. After comparing the simulation result and experimental data, the erosion explanation from sediment core is assured.(6) Regionalization of small catchmentConsiding regional situation, Kechou catchment is regionalized to three regions and eight sub-regions. The important area of soil ersion is recognized. Regional development stratagems of developing tourism and improving land use efficiency are pointed out.
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