祁连山中段林草交错带土壤水热特征及其对气象要素的响应

利用综合环境观测仪(ENVIS)的长期监测数据,分析了2002-06-01—2008-05-31期间祁连山阴坡林草交错带土壤水热特征及其与气象要素的统计关系,结果表明:1)土壤温度与空气温度年内变化格局相似,但存在滞后期,滞后时间随土壤深度增加而增加;土壤温度年际变化与气温一致,呈逐渐降低趋势。2)土壤水分表现为20—80 cm土壤水分易受外界降水过程影响,120 cm和160 cm深度土壤水分变化相对平缓;土壤水分季节性冻融过程中的主要控制因子为温度,但20—80 cm冻土的融化还受上层土壤水分融化和降雨下渗影响。3)月尺度上土壤水分和温度与气象要素的统计关系优于日尺度。利用气象要素在月尺度上建立的经验模型上对20—60 cm深度土壤温度的估算效果相对较好。

Soil moisture and temperature characteristics of forest-grassland ecotone in middle Qilian Mountains and the responses to meteorological factors

Land surface processes and land-atmosphere interactions are hot research focuses of the earth science,and the coupling soil heat and water dynamics in the near surface is the critical link between these processes and interactions.Analysis of the soil heat and water dynamics in Qilian Mountains was quite limited,primarily because there was no enough long-term monitoring data.This situation has been moderated,more or less,with a lot of automatic recording field station been established over the past decade.Pailugou forest station is among the stations with the longest periods of observations(10 years) in this region.By using the long-term field monitoring dataset(measured via ENVIS system from Jun 1,2002 to May 31,2008),we analyzed the relationships between soil temperature,soil moisture dynamics and other meteorological factors in the forest-grassland ecotone of Qilian Mountains.The results were shown as follows: 1) the changing patterns and trends of the soil temperature are largely consistent with the air temperature at different temporal scale,while a lag phase between them was observed which increase with soil depth.2) Soil moisture dynamics is much more complex compared with the temperature dynamics,and strongly affected by the precipitation / evaporation and melting / freezing processes.Generally,the variability of soil moisture is relatively more intense at the depths of 20—80 cm and less intense at the depths of 80—160 cm in the soil profile.Moreover,small differences exist between the evolution trends in the soil moisture dynamics at the different depths,for example,soil moisture slightly decreased at the 40 cm and 80 cm,while increased at the other depths of the soil profile during the study period.3) Energy budget at the soil surface significantly controlled the seasonal melting of the top-layer frozen soil(0—20 cm),while the liquid water infiltrated from the precipitation and melting water in the top-layers also contributed a lot to the melting processes of low-layer frozen soil(20—80 cm).4) At the daily time scale,soil temperature is highly related with the air temperature,while the soil moisture is also highly related with the net solar radiation beside the air temperature.At the monthly time scale,soil temperature is mainly controlled by the air temperature and relative air humidity,and soil moisture dynamics is controlled by the air temperature,saturated vapor pressure differences(VPD),and net solar radiation.Better statistical relationships between soil temperature and meteorological factors was observed at month-scale rather than a daily time scale,and as a result,the relationships built at monthly time scale can be used to get a better prediction of temperature in the top soil layers,i.e.20 cm,40 cm and 60 cm.The results derived from this study clearly indicate that precipitation and air temperature are among the most important environmental factors that affect soil heat and water dynamics in Qilian Mountains.More modeling efforts are needed to quantify and qualify these effects for the fragile alpine ecosystem in the arid northwest China,especially under future climate scenarios and under regional disturbance regimes.