子午岭地区林地破坏加速侵蚀对土壤养分流失和微生物的影响研究

以浅沟集水区为研究对象，分析了子午岭地区林地被开垦破坏15年后裸露地在不同侵蚀强度和侵蚀方式下的土壤养分流失和土壤微生物数量的变化。结果表明，林地开垦破坏后，土壤侵蚀加剧发展，侵蚀强度达159．7t／（hm^2·a），是林地土壤侵蚀量的上千倍。开垦破坏15年后，裸露地浅沟集水区不同地形部位表层土壤全氮、有机碳、速效磷和土壤微生物总数显著减少，同林地相比，依次分别减少37．9％～82．6％、42．7％～86．4％、24．2％～80．3％和31．8％～92．0％。在裸露地浅沟集水区梁坡随坡长的增加，表层土壤有机碳、全氮和速效磷含量及微生物总数呈显著的下降趋势，且沟槽的土壤各养分含量及微生物总数明显低于沟间。裸露地浅沟集水区土壤养分流失强度及微生物数量减少幅度在浅沟集水区的空间分布与土壤侵蚀方式和侵蚀强度相对应。林地开垦破坏15年后，土壤养分以有机碳流失最严重，其次分别为速效磷、全氮；微生物中的真菌减少幅度最大，细菌次之，放线菌减少幅度最小。

近100年植被破坏加速侵蚀下土壤养分和酶活性动态变化研究

选取不同开垦年限的阳坡梁坡农地为研究对象,研究子午岭地区近100年植被破坏加速侵蚀下土壤养分和酶活性动态变化。结果表明,林地被开垦近100年来,阳坡梁坡农地0—20和20—40 cm土层中土壤的有机碳、全氮含量,碱性磷酸酶和蔗糖酶活性皆随开垦年限的延长呈明显的下降趋势。与对照林地相比,不同开垦年限的农地土壤剖面0—20 cm土层的土壤有机碳、全氮含量,碱性磷酸酶和蔗糖酶活性分别下降了26.6%-84.4%、17.6%-76.9%,15.7%-73.8%和37.6%-68.6%;20—40 cm土层分别下降了30.7%-81.0%、8.3%-71.9%,17.3%-96.9%和51.1%-92.6%。土壤有机碳、全氮含量和碱性磷酸酶、蔗糖酶活性在开垦初期（4 a）年均下降速率最大;而后,随开垦年限延长年均下降速率减少。土壤有机碳和全氮含量在0—20和20—40 cm土层之间差异随着开垦年限的延长呈减少趋势。土壤脲酶活性随开垦年限的延长呈先上升后下降的趋势,开垦9 a农地的土壤脲酶活性最高。受施用磷肥的影响,土壤速效磷含量随开垦年限延长,在0—20 cm土层呈波动变化,在20—40 cm土层呈微弱下降趋势。

Principal Denudation Processes and Their Contribution to Fluvial Suspended Sediment Yields in the Upper Yangtze River Basin and Volga River Basin

This paper synthesized the principal land denudation processes and their role in determining riverine suspended sediment yields(SSY) in two typical geographical environments of the Upper Yangtze River Basin in China and the Volga River Basin in Eastern Europe. In the Upper Yangtze River Basin, natural factors including topography, climate,lithology and tectonic activity are responsible for the spatial variation in the magnitude of denudation rates.Human disturbances have contributed to the temporal changes of soil erosion and fluvial SSY during the past decades. On one hand, land use change caused by deforestation and land reclamation has played an important role in the acceleration of sediment production from the central hilly area and lower Jinsha catchment; On the other hand, diverse soil conservation practices(e.g., reforestation,terracing) have contributed to a reduction of soil erosion and sediment production since the late 1980 s.It was difficult to explicitly decouple the effect of mitigation measures in the Lower Jinsha River Basindue to the complexity associated with sediment redistribution within river channels(active channel migration and significant sedimentation). The whole basin can be subdivided into seven sub-regions according to the different proportional inputs of principal denudation processes to riverine SSY. In the Volga River Basin, anthropogenic sheet, rill and gully erosion are the predominant denudation processes in the southern region, while channel bank and bed erosion constitutes the main source of riverine suspended sediment flux in the northern part of the basin. Distribution of cultivated lands significantly determined the intensity of denudation processes.Local relief characteristics also considerably influence soil erosion rates and SSY in the southern Volga River Basin. Lithology, soil cover and climate conditions determined the spatial distribution of sheet, rill and gully erosion intensity, but they play a secondary role in SSY spatial variation.