闽西南崩岗土壤理化性质及可蚀性分异特征

Variation of soil physical-chemical property and erodibility in the area of collapse mound of southwestern Fujian

崩岗是南方红壤区侵蚀沟在水力和重力交互作用下沟头遭受坍塌、陷蚀作用而形成的围椅状地貌,是该区域土壤侵蚀及生态系统退化的最高表现形式之一。为揭示崩岗侵蚀对土壤理化特性及可蚀性的影响,以福建省长汀县濯田镇黄泥坑崩岗群内植被盖度分别为2%,20%,95%的3个典型崩岗为研究对象,分别对崩岗系统内的集水坡面、崩壁、崩积体和沟口进行采样和理化特性的测定,并运用EPIC模型测算土壤可蚀性(K)。结果表明:1)从集水坡面到崩壁、崩积体至沟口,3个崩岗的土壤砂粒质量分数、p H值和土壤密度呈升高趋势,粉粒、砂粒的质量分数和含水量呈下降趋势。2)1号和2号崩岗,集水坡面的土壤有机质质量分数最高,在崩壁最低;3号崩岗土壤有机质质量分数在崩壁处急剧下降,在崩积体中又明显上升。3)各崩岗中集水坡面、崩壁和崩积体的土壤颗粒组成、土壤密度和含水量差异较小,各土壤理化特性指标在沟口与集水坡面、崩壁和崩积体之间存在显著差异。4)崩岗系统内的集水坡面、崩壁、崩积体和沟口4个子系统的K值差异显著,1、2号崩岗呈现崩壁>崩积体>沟口>集水坡面的变化规律,而3号崩岗则表现为沟口>崩积体>崩壁>集水坡面的趋势。5)崩岗系统内的黏粒质量分数、p H值和有机质质量分数与土壤可蚀性关系密切,可以作为表征崩岗土壤可蚀性的有效指标。崩岗侵蚀造成土壤理化特性不断恶化,砂化严重,研究崩岗系统的土壤理化特性与可蚀性空间变化规律,对指导崩岗的恢复与重建具有重要意义。

Background Collapsing mound, called ＂Benggang＂ by local residents which originated from Chinese geomorphic pictograph, has been known to describe an erosion phenomenon in hilly area in subtropical and some tropical climatic zone of southeast China where the edge of gully source collapses and develops a deep-seated shape landform with deep-cut concave. Under the pressure of loose and barren surface soil with high acidity, as well as low vegetation coverage by deforestation, a collapsing hill is vulnerable to degenerate into eroded badland. I Methods ] To reveal the effect of soil physical-chemical property and erodibility from collapsing mound, three typical collapse mounds （No. 1, No. 2 and No. 3 representing the vegetation coverage in the range of 2% , 20% and 95% , respectively ） being selected within Huangnikeng collapse mound group of Zhuotian Town, Changting County in southwestern Fujian Province, basic soil physical property from the system of collapse mound including upper catchment, collapsing wall, colluvial deposit and channel outlet were investigated and measured, and erodibility K value were also calculated applying the model of Erosion Productivity Impact Calculator （EPIC）. [ Results] 1 ） For these three collapse mounds with different vegetation coverage, soil sand content, pH and bulk density had an increasing trend from upper catchment, collapsing wall, colluvial deposit till channel outlet, however, soil silt content, clay content and moisture content were descended. 2） Soil organic matter content of collapse mound No. 1 and No. 2 were the highest at upper catchment, and the lowest at collapsing wall; soil organic matter content of collapse mound No. 3 declined sharply at collapsing wall and increased significantly at colluvial deposit. 3 ） Little variation of soil particle composition, bulk density and content existed in upper catchment, collapsing wall and colluvial deposit among three collapse mounds, and all indicators of soil physical properties existed obvious difference between channel outlet and upper catchment, collapsing wall, colluvial deposit. 4 ） There were significant differences of K value among upper catchment, collapsing wall, colluvial deposit, channel outlet, and the K value of collapse mound No. 1 and collapse mound No. 2 declined in order of collapsing wall 〉 colluvial deposit 〉 channel outlet 〉 upper catchment, but collapse mound No. 3 declined in order of channel outlet 〉 colluvial deposit 〉 collapsing wall 〉 upper catchment. 5） The clay content, pH value, and organic matter content could be cited as the valid index to determine the intensity of soil erosion in the area of collapse mound, since they were close correlation with K value. [ Conclusions] In summary, collapse mound erosion caused deterioration of soil physical properties and severe sandy associated with relative high magnitude of erodibility K value; studying the spatial differentiation on soil physical properties and erodibility in the eroded area of collapse mound erosion system presented important significance in the restoration and reconstruction in the degraded ecosystem of eroded red soil region.