青藏高原多年冻土区高寒草甸土壤水分入渗变化研究

A study on the changes of soil water infiltration in alpine meadow of permafrost regions in the Tibetan Plateau

在多年冻土区典型坡面上,将坡面划分为坡下(L)、坡中(M)和坡顶(H)三个坡位,每个坡位上各选取92%、60%和30%植被盖度为研究对象,用双环入渗仪测定土壤水分入渗过程,对影响土壤入渗过程的环境因子进行了分析,并基于土壤物理特性及土壤水分的测定进行模型模拟。结果表明:研究区不同植被盖度下土壤水分入渗性能在活动层冻融过程中差异明显,初始含水量和初始入渗率具有较好的负相关关系;稳定入渗率大小为:活动层融化期,92%(0.61 mm·min^(-1))>60%(0.50 mm·min^(-1))>30%(0.29 mm·min^(-1));活动层开始冻结期,60%(0.56 mm·min^(-1))>30%(0.39 mm·min^(-1))>92%(0.26 mm·min^(-1))。土壤水分入渗速率具有显著的坡位差异并与冻土的冻融循环过程关系紧密。主要表现为,稳定入渗速率随坡位高度的降低依次递减;同一坡位下,开始冻结期入渗速率小于融化期。在整个入渗阶段,坡顶的累积入渗量是最大的,体现了较好的入渗性能。影响高寒草甸土壤水分入渗的环境因子主要有容重,有机质含量及粒径<0.1 mm微粒。通过比较研究得出,在长江源地区,活动层融化期通用经验模型f(t)=a+bt^(-n)更适用于该研究区域高寒草甸土壤水分入渗过程的研究,而在开始冻结期Horton模型f(t)=i_c+(i_0-i_c)e^(-kt)则具有更好的适用性。

A typical slope of the permafrost regions was divided into three slope positions： the low（ L）,middle（ M） and high（ H） parts. The vegetation coverage of 92%,60% and 30% for each slope position were selected as study objects to determine the soil water infiltration process by double ring infiltration apparatus. The environmental factors,which impact the process of soil infiltration,were analyzed and model simulation had done based on soil physical properties and soil water. The results showed that the soil water infiltration of different vegetation coverage in the study area had obvious difference during the freezing and thawing process of the active layer,and the initial soil water content had a good negative correlation with the initial infiltration rate. The stable infiltration rate was： vegetation coverage of 92%（ 0. 61 mm·min^（-1）） vegetation coverage of 60%（ 0. 50 mm·min^（-1）） vegetation coverage of 30%（ 0. 29 mm·min^（-1）） during the period of active layer thawing,and vegetation coverage of 60%（ 0. 56 mm·min^（-1）） vegetation coverage of 30%（ 0. 39 mm·min^（-1）） vegetation coverage of 92%（ 0. 26 mm·min^（-1）） during the beginning period of active layer freezing. The soil water infiltration rate had a significant difference among slope positions and was closely related to the freezing-thaw cycle,mainly reflected in that the infiltration rate decreased with the slope position downwards; the infiltration rate during the beginning period of freezing was less than that during the thawing period on the same slope position. During the whole infiltration stage,the cumulative infiltration at the slope top was the maximum,showing a better infiltration performance.The environmental factors influencing the infiltration of alpine meadow soil were bulk density,organic matter content and particle size. It was concluded that in the source regions of the Yangtze River the general empirical model f（ t） = a ＋ bt^（-n） is more suitable for the period of active layer thawing to study soil water infiltration in alpine meadow in the study area,while the Horton model f（ t） = i_c ＋（ i_0-i_c） e^（-kt） is more suitable for the beginning period of active layer freezing.