旱涝急转期红壤坡地水土流失响应机制研究

The frequent occurrence of seasonal drought and the following rainstorm leads to drought-flood abrupt alternation, accompanying by severe water loss and soil erosion in red soil areas of south China. The topsoil moisture content is in extreme low level in the early stage of soil drought which generates the changes of soil property like the hardened and cracked topsoil. Then, soil swells after absorbing water in the heavy rainstorm. As a result, the cracks disappear and the crusts develop, increasing the surface runoff and sediment yield of soil erosion. This study was designed to study the typical Quaternary red soil in Jiangxi science and technology eco-park of soil and water conservation. The experiment was conducted by rainfall simulation experiment with three different levels of rainfall intensity under five different drought degrees (normal condition, light drought, moderate drought, severe drought and excessive drought) controlled by potable soil tank. The method of multivariate statistical analysis was employed in the study with the help of long-term observations from the field runoff plots to analyze such impacts like hydrological characteristics of near surface soil and soil anti-erosion features posed by prior drought. The features of runoff and sediment production were analyzed in the case of drought-flood abrupt alternation. Meanwhile, the quantitative relations among hydrological characteristics of near-surface soil, soil anti-erosion features affectd by prior drought, rainfall intensity of late period and the production of runoff and sediment were estabilished in the study. Finally, the responding mechanisms of water and soil erosion on the red soil slope to sudden turn of droughts and floods was revealed in the study. The results would contribute to expand the comprehension of soil erosion mechanisms under the extreme weather conditions and be practically significant for the comprehensive control for soil and water conservation.

南方红壤区季节性干旱频发，随后往往出现大暴雨事件，形成红壤区特定的旱涝急转气象，引发严重水土流失。前期土壤干旱导致表层土壤含水量极低，引起表土板结、干裂等土壤性质改变，遇到后期暴雨土壤吸水膨胀，导致土壤裂缝消失，形成表土结皮，增加地表径流和侵蚀产沙。本项目选择江西水土保持生态科技园的典型第四纪红壤作为研究对象，采用可移动试验土槽设定无旱、轻旱、中旱、重旱、特旱5个干旱等级，通过3个不同雨强模拟降雨试验，并结合野外径流小区观测资料，采用多元统计研究分析前期干旱对近地表土壤水文特征、土壤抗蚀特征等的影响，分析旱涝急转下坡面产流、产沙特征，建立前期干旱影响下近地表土壤水文特征、抗蚀特征、后期雨强与产流产沙的定量关系，揭示红壤坡地水土流失对旱涝急转的响应机制。研究结果将有助于加深旱涝急转下水土流失机制的理解，对于水土保持综合治理具有现实意义。

南方红壤区旱涝急转极端事件频发，前期干旱影响地表土壤干缩裂缝、土壤硬度、抗剪强度，干旱土壤遇到后期暴雨，土壤裂缝、土壤硬度等性质随着土壤含水量的增大而变化，造成旱涝急转事情下水土流失规律有其特殊性。本项目以江西省各市气象站点50年以上气象数据位基础，分析表明江西省旱涝急转事情主要发生在夏季，年际上旱情、涝情上下波动，整体上呈现涝情加重、旱情减轻的趋势。选择江西省典型第四纪红壤为研究对象，通过对不同干旱下模拟试验表明土壤硬度、抗剪强度从无旱到重旱随着干旱等级的增大而增大，重旱以后趋于稳定；土壤干缩裂缝总长度、长度密度、宽度、面积随着干旱等级增而增大。通过旱涝急转模拟试验和野外定位观测试验，结果表明前期土壤从无旱到重旱遇到暴雨后，坡面产流随着旱情等级增大先增大后减小，重旱后产流低于无旱，前期干旱坡面产沙均大于无旱土壤，并且随着干旱等级增大先增大后减小，轻旱土壤侵蚀产沙强度最大；土壤干旱形成的干缩裂缝为优先流发育提供了通道，从轻旱到重旱壤中流不断增大，地表下土壤含水量开始上升时间提前，以壤中流形式流失氮、磷比例不断增大。相关成果发表论文6篇，其中EI论文3篇，授权国家专利1项，获水利部大禹水利科学技术奖二等奖1项，培养硕士1人。