Mineral-magnetic characteristics of sediments from Maigang Reservoir,Guizhou Province and their implications on soil erosion
贵州麦岗水库沉积物的矿物磁性特征及其土壤侵蚀意义

Soil erosion is one of the most serious environmental problems in the world. In Southwest China dominated with carbonate-rocks and karst landscapes, soil erosion and its resultant 'rocky desertification' are also very serious. Studies of sediments of lakes and reservoirs have been used to obtain information on changes in soil erosion through time of catchment by sampling and dating sediment cores, and calculating sediment deposition rates and analyzing them for proxy data such as mineral-magnetics. Mineral magnetism techniques have been widely used in analyses of lake and reservoir sediments to research soil-erosion changes. It has been proved to be a valuable method to investigations on soil erosion occurring in the catchments of lakes and reservoirs. Maigang Reservoir (26°00'50.3″N, 106°17'38.4″E) was built in Ziyun County of Guizhou Province, Southwest China in 1956. It has sub-tropical monsoon humid climate and is located in a carbonate-rock-dominated catchment of 7.5 km2. A 19-cm long sediment-core (MG1-1) was sampled from the reservoir in April, 2008. Some mineral-magnetic parameters including SIRM, ARM, lf, hf, IRM20mT and IRM-100mT were measured and ARM/SIRM, HIRM, IRM-100m T/SIRM and fd were calculated. We inferred soil erosion that occurred during 1960~2007 (47 years) in the drainage basin based on these mineral-magnetic characteristics in combination with the results from analyses of 137Cs, grain-size, TOC and C/N for these sediment samples. Soil erosion generally has some sub-order fluctuations in its changes which presents a pattern "intensive-weak-intensive-weak" in this period. According to the precipitation and land use/land cover change (LUCC) data, the primary causes of soil erosion are deduced. Precipitation has small impact on the changes of soil erosion, but human activities, especially the land use and land cover changes are the main causes for soil erosion in the catchment of Maigang Reservoir.