【作者】 王贤；

【导师】 张洪江；

【作者基本信息】 北京林业大学 ， 水土保持与荒漠化防治， 2014， 博士

【摘要】 本研究选取位于长江三峡库区库尾的重庆四面山为试验区,利用CoupModel模拟了不同土地利用方式,即阔叶林(木荷×石栎)、针叶林(杉木×马尾松)和农地(玉米)2008—2009年土壤—植被—大气系统的水分和热量差异,可为三峡库区植树造林和生态重建等提供科学依据。(1)对CoupModel土壤参数,包括土壤颗粒组成、密度、孔隙度、水分特征曲线、饱和导水率、土壤水分和土壤温度等物理性质研究表明,农地土壤质地较细,孔隙度低,而林地土壤具有相对疏松、通透性好的结构,提高了水分的入渗能力。森林植被对土壤物理性质的改善和提高具有重要作用。试验地土壤水分和温度均具有明显的季节变化特征,土壤水分平均值大小依次为农地(12.57%)>针叶林(10.86%)>阔叶林(10.47%),农地土壤水分含量更高、变异性更小。土壤温度平均值大小依次为农地(19.41℃)>针叶林(18.95℃)>阔叶林(18.87℃)。冠层生长状况更好、郁闭度更大的森林植被对土壤表面的遮蔽作用更大,因而生长季期间林地土壤温度更低,且变化趋势更为缓和,振幅更小。(2)土壤水分、土壤温度和冠层截留量模拟值与实测值拟合度较高(决定系数R2为0.69-0.99),CoupModel在三峡库区四面山地区具有较好的适用性。采用OAT方法(即每次只改变一个参数的方法)对模型参数进行了敏感性分析,结果表明,对土壤水分模拟结果影响较大的参数有孔隙分布参数、进气吸力、残留含水量、饱和含水量、饱和导水率和蒸发阻力系数。而对土壤温度模拟结果敏感性较大的参数有土壤热传导系数、有机质层厚度、植被反照率、消光系数、水汽压亏缺、蒸发阻力系数。(3) CoupModel对农林地水量平衡模拟结果表明,2008-2009年3种植被覆盖类型SPAC系统水分输入均为2214mm,阔叶林水分支出(2224mm)高于收入,这是引起阔叶林地土壤储水而呈现负补偿现象的主要原因。蒸散是水量平衡中最主要的支出项,其比例高达61%,大小依次为阔叶林(720mm/a)>针叶林(700mm/a)>农地(601mm/a)；其季节变化规律主要由叶面积指数(LAI)的变化规律来决定(R2为0.61-0.77),而在日时间尺度上,植被蒸散量主要受气象和土壤因素的影响。农地年均深层渗透量为452mm/a,分别比阔叶、针叶林高60mm、47mm,且在降水较多的年份表现更加明显。研究区农林地水分条件具有较大差异,水分盈余是农地水量平衡的主要特征,而林地却发生了春旱和秋旱。造林对水量平衡具有重要影响,森林在提高系统蒸散量的同时,也减小了土壤水分的深层渗透以及对地下水的补给,使水分分配过程变得更加复杂。树种对水量平衡亦有影响,在以提高地下水补给为目标的造林地区应注意树种的选择。(4) CoupModel对农林地热量交换模拟结果表明,2008—2009年样地接收太阳辐射量实测值为7096MJ·m-2,与农地相比,林地能够接收到更大的净辐射量,这主要与地表反射率有关。潜热是热量耗散的主要支出项,其值从大到小依次为阔叶林(1702MJ·m-2)>针叶林(1642MJ·m-2)>农地(1415MJ·m-2),分别占净辐射的83%、81%和73%。感热通量的大小决定于乱流交换系数和温度的垂直梯度,农地感热通量大于林地,这主要是农地乱流作用更强、表层土壤气温更高的缘故。试验期间农地土壤热通量为正值(2MJ·m-2),处于热汇阶段,土壤吸收环境中的热量,阔叶林和针叶林分别为-35MJ·m-2和-28MJ·m-2。模拟结果表明,阔叶林、针叶林和农地植被层每蒸散1kg水分所消耗的能量分别为2.33MJ、2.30MJ和2.28MJ能量。林地系统获得的能量约60%用于植被蒸散耗能,农地则同时以植被蒸散和土壤蒸发耗能为主。水分条件决定了热量的分配形式和影响潜热通量、感热通量占净辐射的比例,同时热量供给的多少也决定了水分可以蒸散出去的量,土壤—植被—大气系统呈现一种水热相互制约的局面。森林植被恢复后,通过其反射率、蒸散等的变化对水分和热量具有调节作用,森林能够提高水分和热量的利用效率。更多还原

【Abstract】 Based on field measurement, the CoupModel (Coupled heat and mass transfer model for soil-plant-atmosphere system) was applied to simulate water balance and heat transfer in three kinds of vegetation types, including broadleaved forest (Schima superba and Lithocarpus glaber), coniferous forest (Cunninghamia lanceolata and Pinus massoniana) and farmland(Zea mays) in Simian Mountain, which located in the terminal Three Gorges Reservoir Area of China. This study can provide foundation for the management afforestation and ecological reconstruction.(1) Soil particle composition, bulk density, porosity, water characteristic curve, saturated hydraulic conductivity, soil moisture and temperature among different vegetation types were studied. The results showed that the farmland had finer soil texture with lower porosity, while forest had a porous soil structure, which can increase water infiltration capacity. Forest played an important role on improving soil physical properties. Soil moisture and temperature had obvious seasonal variation characteristics, the average values of soil moisture were as follows:broad-leaved forest (10.47%)<coniferous forests (10.86%)<farmland (12.57%), soil moisture from the farmland was higher with less variability. Because of the better growth status of huge canopy, the soil surface always covered by forest, soil temperature from forestland was lower during the growing season, and its fluctuation was also much more moderate.(2) Simulated soil moisture, soil temperature and canopy capacity were fairly consistent with measured ones and the determination coefficient (R2) was0.69to0.99. It meant that the model had a good applicability in this region. And then, the OAT method (one factor at a time) was adopted to analyze sensitivities of the model parameters. The results of the sensitivity analysis indicated that, many parameters had great influence on the simulation of soil moisture, they were lambda, air entry, residual water, saturation, matrix conductivity and PsiRs-lp. While scaling coefficient, organic layer thick, plant albedo, light extinction coefficient, cond VPD and PsiRs-lp impacted on simulation of soil temperature.(3) Water balance simulation showed that water input/precipitation was2214mm for all the plots during the experimental period, but the water consumption (2224mm) was more than income in the broad-leaved forestland, this was the main reason causing soil water deficit. Evapotranspiration was main output of water balance with the percentage up to61%, and the figures were ranked as follows:broad-leaved forest (720mm/a)> coniferous forest (700mm/a)> farmland (601mm/a). In the growing season, leaf area index (LAI) determined the seasonal variation of ET, while weather condition determined its variation at a much smaller time scale such as one day. Annual simulated deep percolation decreased by60mm for broad-leaved forest and47mm for coniferous forest compared with that for farmland (452mm/a), and it was even greater in wet year. There was obvious difference between forestland and farmland for water conditions, the water balance of farmland was characterized by moisture surplus, while spring and autumn drought occurred in forestlands. This study indicated that a shift from cropland to forest would lead to an increase in evapotranspiration while a reduction in deep percolation or groundwater recharge, afforestation made the water balance process more complicated. Model results also indicated that vegetation species significantly influence the magnitude of water balance components, which call for further attention to the selection of tree-species when planning future afforestation projects.(4) Simulations of heat transfer showed that the plots received the amount of solar radiation was7096MJ-m-2during the experimental period of2008and2009. Compared with cropland, forestland received lardger amount of net radiation, this is mainly related with the surface reflectance. Latent heat was the main output in thermal dissipation, it ranged as follows:broadleaved forest (1702MJ·m-2)> coniferous forests (1642MJ-m’2)> farmland (1415MJ·m-2), respectively, and they accounted for83%,81%and73%of the net radiation. The sensible heat flux was higher in the the farmland than the forestland, for the bigger turbulent exchange and the higher vertical gradient of temperature in the farmland plot. During the experimental period, the soil heat flux was above zero for the farmland plot, it meant thatthe farmland soil needed to absorb heat from the environment. But the values of soil heat flux for the broad-leaved and coniferous forestland were only-35MJ·m-2and-28MJ·m-2. Simulation results also implied that it required2.33MJ energy for broadleaf-conifer forest and2.30MJ and energy for coniferous forest to evapotranspire1kg water, while for farmland, this value was2.28MJ. Forest consumed approximately60%of energy on transpiration, but for farmland, energy was consumed by plant transpiration and soil evaporation. Soil moisture conditions determined the distribution of heat flux, and in turn heat supply also impacted the amount of evapotranspiration, water and heat are interdependent in the soil-vegetation-atmosphere transfer system. After afforestation, water and heat balance was regulated by reflectivity or evapotranspiration of forest. Forest can improve the utilization efficiency of water and heat.更多还原