贵州麦岗水库沉积物的矿物磁性特征及其土壤侵蚀意义

Mineral-magnetic characteristics of sediments from Maigang Reservoir,Guizhou Province and their implications on soil erosion

对取自贵州西南部紫云县麦岗水库的沉积物柱芯MG1-1进行了包括SIRM、ARM、χlf、χfd、IRM-20mT和IRM-100mT等磁性参数的矿物磁性测量,并计算了ARM/SIRM、HIRM和IRM-100mT/SIRM。根据沉积物的这些矿物磁性特征,并结合137Cs、粒度、TOC、C/N分析结果,推测了麦岗水库流域在1960～2007年(47年)间的土壤侵蚀变化情况。研究表明:麦岗水库流域的土壤侵蚀强度变化虽然存在一些波动,但整体上呈现由强到弱到强再到弱的变化过程。结合降水资料和土地利用/土地覆被变化情况,探讨了影响土壤侵蚀变化的主要原因。结果表明,降水量对流域土壤侵蚀变化的影响不大,而人类活动,特别是土地利用的变化可能是引起流域土壤侵蚀变化的主要原因。

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.