祁连山天涝池流域亚高山草甸冻融期土壤水热变化特征

Characteristics of soil water-heat at a subalpine meadow during the freezing and thawing periods in Tianlaochi catchment of the Qilian Mountains

祁连山是我国重要的生态安全屏障,其高寒生态环境和水源涵养能力广泛受到近地表冻融过程的复杂影响。为了解土壤水热在冻融期的变化情况,以祁连山中部天涝池流域亚高山草甸为研究对象,分析2014—2019年冻融期大气温度、土壤温度及未冻水体积含水量(USWC)变化特征,通过统计分析法对亚高山草甸土壤冻融期土壤温度对大气温度的响应及土壤水热拟合进行了探讨。研究结果表明:冻融期亚高山草甸土壤呈单向冻结双向融化特征,观测时段内冻结深度在100~140 cm,土壤温度与大气温度的相关性较好,其中0~40 cm深度土壤温度与大气温度显著正相关(P<0.01),120~180 cm土壤温度与大气温度显著负相关(P<0.05);冻融过程中土壤USWC变化趋势呈“U”形,40~60 cm深度土壤层和表层分别在冻结期和融化期出现水分高值区;土壤USWC与负温绝对值之间具有较好的幂函数相关关系(y=axb),其中经验参数a始终为正值,b始终为负值且逐年增大;观测期间(2014—2019年)的土壤冻结时长、冻结速率和冻结深度等都在减小。本研究可为祁连山亚高山草甸土壤冻融作用对径流形成的影响研究奠定基础,对进一步探讨祁连山区季节性冻土对气候变化的响应提供科学参考。

The Qilian Mountains is an important ecological security barrier in our country,and its alpine ecologi⁃cal environment and water conservation capacity are widely affected by the process of freezing and thawing of near-surface.In order to understand the changes in soil water and heat during the freezing and thawing periods,we selected the subalpine meadow in the Tianlaochi catchment of the Qilian Mountains as the study object.The near-surface air temperature,soil temperature,and unfrozen soil water content(USWC)from 2014 to 2019 were measured during freezing and thawing periods when the soil water and heat change characteristics were ana⁃lyzed.The relationship between the soil temperature and the atmospheric temperature was statistically explored.In addition,the power function was used to fit the soil temperature and USWC.Results showed that the soil ex⁃pressed unidirectional freezing and bidirectional thawing,and the frozen depth was 100~140 cm in the study peri⁃od.The soil temperature at each depth was well correlated with the near-surface air temperature.The soil tem⁃perature at 0~40 cm depth was significantly positive correlation with the near-surface air temperature(P<0.01),and lagged behind the near-surface air temperature.However,the soil temperature at 120~180 cm depth was sig⁃nificantly negative correlation with the near-surface air temperature(P<0.05).The changing trend of USWC displayed a U-shape during the freezing and thawing periods.The soil depth with high water content appeared at the depth of 40~60 cm and surface soil,respectively.There was a power function correlation between the abso⁃lute value of the negative soil temperature and USWC(y=axb),where the empirical parameter“a”was positive,and“b”was negative and increased year by year.In addition,the freezing duration,freezing rate,and freezing depth of subalpine meadows in the study area all decreased during the study period.This study can lay a founda⁃tion for studying the effect of soil freezing and thawing on the formation of runoff in the subalpine meadows and provide a scientific reference for discussing the response of seasonally frozen soil to climate change in the Qilian Mountains.