青海湖流域高寒草甸季节冻土土壤温湿变化特征

根据2018—2020年青海湖流域高寒草甸野外定点监测的温度、降水、土壤水热数据，分析了高寒草甸生态系统土壤冻融特征以及不同冻融阶段土壤温度、水分的日变化和季节动态过程。结果表明：(1)基于土壤温度变化特征分析，可将冻融循环过程划分为始冻期、完全冻结期、解冻期和完全融化期。各阶段持续的天数长短依次为：完全融化期>完全冻结期>解冻期>始冻期。从表层到深层土壤，完全融化天数持续增大，完全冻结天数趋于减小，0～180 cm土层完全融化期持续天数超过半年以上。(2)冻土表现出单向冻结、双向融化的规律，土壤融化速率(5.45 cm/d)快于土壤冻结速率(2 cm/d)。整个冻融过程，不同深度土壤水分的变化比温度的变化更复杂。(3)随着冻融循环过程，土壤温湿度呈现出周期性的季节变动特征。土壤温湿度日变化具有一致性，表层日较差大，随着深度的增加，日较差变小并趋于稳定。土壤剖面的结构特征对土壤水分异质性分布具有较强的解释性。

Characteristics of Seasonal Frozen Soil Temperature and Moisture Changes in Alpine Meadow in Qinghai Lake Watershed

Characterizing seasonal changes in temperature and moisture of frozen soil has important scientific significance for the efficient use of water and soil resources in cold regions and the protection of ecological environment. Based on the temperature, precipitation, and soil moisture and temperature data of the alpine meadows in the Qinghai Lake Watershed from 2018 to 2020, the characteristics of soil freezing and thawing in the alpine meadow ecosystem and the daily changes and seasonal dynamics of soil temperature and moisture in different freezing and thawing stages are analyzed. The results show that: (1) Based on the analysis of the characteristics of soil temperature changes, the freeze-thaw cycle process can be divided into the initial freezing period, the complete freezing period, the thawing period and the complete thawing period. The duration of each stage is as follows: complete thawing period>complete freezing period>thawing period>initial freezing period. From surface to deep soil, the number of days of complete melting continues to increase, and the number of days of complete freezing tends to decrease. The period of complete melting of 0~180cm soil layer lasts for more than half a year. (2) Frozen soil shows the law of one-way freezing and two-way melting. The soil melting rate (5.45 cm/d) is faster than the soil freezing rate (2 cm/d). Throughout the freeze-thaw process, the changes in soil moisture at different depths are more complex than changes in temperature. (3) With the freeze-thaw cycle process, the soil temperature and moisture show periodic seasonal changes. The diurnal variation of soil temperature and moisture is consistent, and the surface layer has a large diurnal range. As the depth increases, the diurnal range becomes smaller and tends to be stable. The structural characteristics of the soil profile have a strong explanatory effect on the heterogeneous distribution of soil moisture.