青藏高原含砂砾石土壤导热率实验研究

土壤导热率是土壤的基本物理参数之一,也是陆面模式的重要输入量,对研究土壤热传输、水热耦合运移有重要意义。青藏高原由于独特的地理环境备受学者关注,但目前常用的土壤水、热属性参数化方案仅仅考虑了沙土、粉土和黏土,就砂砾石重要性的认识还不足,很少有模式模拟砾石对青藏高原多年冻土和高寒草地的影响。采用便携式热导仪(KD2 Pro,DECAGON,美国)测量了青藏高原玛多和北麓河两地典型土壤在冻结和未冻结状态下不同水分条件时的土壤导热率,分析了砂砾石含量对土壤孔隙度的影响及冻结和未冻结状态下,不同水分条件下砂砾石含量对土壤导热率的影响。结果表明:当含水量高于某一阈值时,含水土壤冻结状态下的导热率高于未冻结状态下的导热率;土壤含水量对土壤导热率影响显著,导热率随着含水量的增加而增大,在含水量较小时变化更明显;砂砾石含量比重多的土壤孔隙度较小,且砂砾石含量越大的土壤在冻结状态下导热率高。以上结果表明,砂砾石对土壤导热率有显著影响,在将来的模式模拟研究中必须考虑砂砾石对土壤热属性的影响,进而提高土壤水热过程模拟的精度。

Experimental study on thermal conductivity of soil with gravel on the Qinghai-Tibet Plateau

Soil thermal conductivity is one of the important soil physical parameters and important input parameters of land surface model,which has important implications for the study of soil heat transfer and hydro-thermal coupling movement.Widely used parameterization schemes of soil water and thermal properties only considered the sandy soil,silt and clay.However,soils of the Qinghai-Tibet Plateau (QTP) contain large amount of gravel,which may have different thermal properties.At the current stage,few models simulate the effect of gravel on permafrost dynamcis and alpine grassland on the QTP.In this study,we used the thermal conductivity meter (KD2 Pro,DECAGON,USA) measured soil thermal conductivity of soil samples from the Maduo and Beiluhe on the QTP under different combination of water conditions and thermal states,and analyzed the effects of gravel content on soil porosity and thermal conductivity.Results showed:(1) when moisture content was above a certain threshold value,thermal conductivity in the frozen state is higher than that of unfrozen state;(2) soil moisture content had great influence on soil thermal conductivity;thermal conductivity increased with the increase of water content,as well as it had a sharp increase in the range of less water content;(3) when gravel content in soil sample was larger,soil porosity was smaller and soil thermal conductivity was higher in the frozen state.The results suggested that gravel has a remarkable influence on soil thermal conductivity,and it is necessary to consider the impact of gravel on the soil thermal properties,so as to improve the accuracy of hydrothermal condition simulation in the future.