黄土关键带深层土壤水分动态模拟与主控因素

地球关键带是维系地球生态系统功能和人类生存的关键区域，土壤水分是黄土高原关键带植被恢复与生态环境重建的关键因子之一。为探明黄土关键带深剖面土壤水分变化过程并进行模型模拟，对黄土高原长武塬区苹果地和小麦地的深层土壤水分（0~18m）进行监测（2011~2013年，共选择11个不同日期进行深剖面土壤水分监测），在此基础上，采用Hydrus-1D进行模型模拟，分析了深剖面土壤水分动态及其模拟效果的主控因素。结果表明：1）苹果地（6~18m）、小麦地（3~18m）的深层土壤含水量随时间变化很小；0~1m的土壤含水量随时间变化较大；不同土地利用类型会产生不同的土壤水分过程及运动机制；在根系及近根系区，土壤含水量变化受根系分布格局及土壤质地共同影响，接近地表时还同时受降雨、蒸发等上边界条件影响；在非根系区，土壤含水量的主要影响因素为土壤质地；2）利用前6次的实测数据进行调参和校正，后5次实测数据进行预测效果检验，取得了较好的深剖面土壤水分模拟效果——苹果地的决定系数、相对误差绝对值、均方根误差分别介于0.5923~0.7637、3.33%~5.20%、0.0149~0.0168cm³/cm³ 之间，小麦地分别介于0.2414~0.6822、2.64%~4.58%、0.0177~0.0247cm³/cm³ 之间；3）叶面积指数、根系深度与分布是影响深剖面土壤水分动态模拟效果的主控因素。相关结果可为黄土关键带深剖面土壤水分模拟与调控提供参考。

Simulation and controlling factors of deep soil moisture dynamics in the critical zone in the Chinese Loess Plateau

Soil water process is one of the important processes and plays a key role in vegetation restoration and ecological environment reconstruction in the critical zone (CZ). To ascertain and simulate the change of soil water content (SWC)in the CZ on the Chinese Loess Plateau, we selected two sampling points in the center of wheat field (35°14'27.6"N, 107°40'56.8"E; altitude in 1225m)and apple orchard (35°14'34"N, 107°41'5.2"E; altitude in 1256m)respectively. Sampling point was located at a distance of 1m from the representative apple tree trunk in apple orchard. After that, we monitored the dynamics of SWC to the depth of 18m in 11 different dates from 2011 to 2013 at Wangdonggou watershed, Changwu County. Then, we simulated the changes of SWC along the 0~18m soil profile by using Hydrus-1D. Results showed that:(1)The soil water content in the deep layer varied from 0.09 cm3/cm3 to 0.29 cm3/cm3. In apple orchard (6~18m)and wheat field (3~18m), deep SWC changed slightly with time, while in surface 0~1m layer, SWC varied greatly with high coefficient of variation; Different land use types caused the discrepancy between coverage of aboveground vegetation, the distribution pattern of underground plants, evapotranspiration ability and crop water consumption characteristics, and then produced different soil water processes and movement mechanism; In root zone, the change of SWC was highly affected by root distribution pattern and soil texture, although the upper boundary conditions (i.e., rainfall, evaporation)also may to some extent affect the pattern; below the root zone, soil texture became the main influencing factor; (2)The simulation and prediction of deep SWC in the two sites were acceptable:the coefficient of determination, the absolute value of the relative error and the root mean square error were 0.5923~0.7637, 3.33%~5.20% and 0.0149~0.0168 cm3/cm3 under apple orchard, and were 0.2414~0.6822, 2.64%~4.58% and 0.0177~0.0247 cm3/cm3 under wheat field, respectively; (3) The controlling factors of SWC dynamics and simulations were leaf area index and the distribution of root system. With increasing of simulation period, the simulation performance decreased due to the influence of the varied root distribution pattern and soil structure. Therefore, it is advisable to recalibrate the model parameters by using the re-measured data when the simulation period is long and the root distribution is deep. Understanding this information is helpful for deep SWC simulation and regulation within the CZ of the Loess Plateau and may provide a scientific reference for soil water management under different land uses in the water-limited ecosystem.