Partition of soil moisture profiles based on sequential clustering method

【目的】研究有序聚类法在土壤水分剖面划分中的应用。【方法】在黄土高原丘陵区陕西省安塞县,以乔木林地、灌木林地、果园用地和天然草地等4种土地利用类型为研究对象,测定4种用地类型0~500 cm土层(每20 cm为1层,共25层)的土壤水分含量,然后采用有序聚类法对4种土地利用类型土壤水分剖面进行分层。【结果】从专业角度无法确定最优分类数K时,可以利用碎石图来确定,对全部样本进行分类并作碎石图可知,当K=4时,有序分割达到最优;对土地利用类型而言,土壤水分剖面总体可划分为水分弱利用层、根系集中层、强烈耗水层、水分调节层等4层,中间2层又可简单地归结为土壤水分利用层。【结论】基于有序聚类法划分的土壤水分剖面分层结果符合黄土高原丘陵沟壑区的土壤水分垂直分布实际,表明了该分层方法的合理性。【Objective】 The research was conducted to study the application of sequential clustering method in the vertical profiles of soil moisture classification.【Method】 In the hilly Loess Plateau of Ansai Shaanxi,the research object was 4 land-use types such as tree land,shrub land,orchard and grassland land use types.The soil water profile of 4 land-use types was classified by the orderly clustering method according to the water content of 0-500 cm(every 20 cm for 1 layer,altogether 25 layer).【Result】 When K valu..

Relationships between soil moisture and environmental factors at different spatial scales

以延河流域为例,利用典范对应分析方法对坡面、小流域、区域3个尺度的土壤水分与环境因素关系进行研究。结果表明:坡位、土地利用类型是坡面尺度影响土壤水分变化的主控因素;坡度、土地利用类型是小流域尺度影响土壤水分变化的主控因素;蒸散、降水、土地利用类型是区域尺度影响土壤水分变化的主控因素。可见,随着研究尺度的增加,坡向、坡位、坡度等地形承担的信息量逐渐流向蒸散、降水等气象因子,土地利用类型承载的信息量基本未变。结果对土壤水分与水文模型及其尺度外推有重要的意义。Taking Yanhe basin as a case，this paper studied the relationships between soil moistureand environmental factors at slope surface，small watershed，and regional scales by usingcanonical correspondence analysis ( CCA) ． In the basin，slope position and land use type werethe main factors controlling soil moisture change at slope surface scale，slope and land use typewere the dominating factors at small watershed scale，while evapotranspiration，precipitation，andland use type were the key factors at regional scale，which suggested that with the enlargement ofstudied spatial scale，the information contained by topographic factors ( slope direction，slope position，and slope) gradually converted to climatic factors ( evapotranspiration and precipitation) ，but the information contained by land use type was almost invariant． This study could have significancein studying soil moisture model and hydrological model and their extrapolation

Differences of above-ground biomass and comparisons of its effect on soil moisture between natural vegetation and artificial vegetation in Yanhe basin

【目的】针对延河流域人工植被建造存在植被退化的问题,比较了自然植被与人工植被地上生物量的差异及其土壤水分效应,探寻人工植被退化的原因,为延河流域植被恢复重建提供理论支持。【方法】共采集57个气象站点1980-2000年的气候数据,并根据降雨和温度变化,将延河流域划分为17个环境梯度单元,测定了自然植被地上生物量及0～500cm土层土壤含水量,分析自然植被的空间变化及其影响因素,对自然植被与人工植被地上生物量及相应的土壤水分变化进行比较分析。【结果】延河流域自然植被地上生物量在空间上存在明显差异,从西北向东南呈现逐渐递增的变化趋势。自然植被地上生物量与年均总降雨量呈正相关关系,与年均生长季温度呈负相关关系;相同气候区的自然植被地上生物量随坡位和坡向的变化差异均很大。以自然植被为参照,人工植被地上生物量最大超载可达30 425.83g/m2,最小超载为118.93g/m2,平均为6 668.00g/m2,说明人工植被地上生物量明显超出了自然状态下所能承载的范围。与自然植被相比,人工植被土壤水分最大亏缺量可达80.5g/kg,说明人工植被地上生物量的超载引起平均土壤含水量显著低于自然植被,出现了不同程度的土壤干层,...【Objective】 Above-ground biomass and soil moisture between natural and artificial vegetation,were compared to explore the reason of artificial vegetation degeneration,vegetation restoration planning and decision support in Yanhe basin.【Method】 We collected climate data of 57 meteorological stations from the year 1980-2000,and divided the Yanhe basin into 17 environmental gradient units according to rainfall and temperature changes.Above-ground biomass of the natural vegetation and 0-500 cm soil moisture con..