【作者】 田风霞；

【导师】 冯兆东； 赵传燕；

【作者基本信息】 兰州大学 ， 自然地理学， 2011， 博士

【摘要】 位于我国西北干旱区的祁连山,地处青藏高原、黄土高原和蒙新荒漠的交会地带,其生态环境不仅受区域条件的限制,而且对全球变化响应敏感。长期以来,祁连山区人口为了维持自身的生存,对该区生态系统产生了各种干扰,不仅导致草场退化、土壤侵蚀加剧而且对森林造成了严重破坏。祁连山森林生态系统与整个山区生态过程和水文过程的相互作用和耦合关系十分密切,它一方面通过调控物质循环和能量流捍卫着冰源水库(冰川和积雪)的安全,另一方面通过对山区水文路径的调节担当着涵养水源、净化水质、保持水土资源和维护生物多样性的重任。但是,森林和水的相互作用受多种因素影响,使得森林植被生态过程和水文过程的作用机理尚不明确。因此,本研究以祁连山区青海云杉林为研究对象,通过对该植被系统生态过程、水文过程及其相互作用过程的研究,定量的揭示青海云杉林植被系统的水文循环机理及其对山区水文路径的调节机制,深入理解祁连山区各种水文现象的发生规律及其内在联系,为建立合理的区域水资源管理模式提供科学依据。本研究取得的主要结论如下：(1)试验区日均气温和日最高气温具有明显的季节变化；林内空气相对湿度基本维持在60%左右；林内风速总体上小于0.5 m·s-1；林内太阳辐射强度最高仅为86.6 W·m-2。试验区降水具有明显的季节分布特征,2008年整个生长季(5-9月)的降雨量占年降水量的78.7%,且主要以低降雨量和低降雨强度的降雨事件为主。林内土壤温度和土壤体积含水量的垂直分布在不同月份呈现不同的变化特征,且不同深度土壤的温度和体积含水量的年内变化总体上呈先增大后减小趋势。(2)实验观测期间内(2008年6月12日至2008年10月8日),青海云杉林的穿透雨量、截留量和干流量分别为212.6mm、64.5mm和3.4mm,分别占大气降雨量的75.8%、23.0%和1.2%。林内穿透雨随大气降雨量的增大而增大,且在空间分配上具有异质性；在没有前日降雨的情况下,当降雨量达到5.6mm时青海云杉林才开始产生树干茎流,且干流量随降雨量的增大而增大,34场降雨的平均干流率为0.58%；林冠截留率随降雨量的增大先急剧减小后逐渐趋于稳定,实验观测期间的平均截留率为33.9%。(3)采用改进的Penman-Monteith修正式估算的青海云杉林2008年整个生长季的蒸腾耗水量为160.8 mm,平均日蒸腾量为1.05 mm,且日蒸腾量从5月开始逐渐增大,在7月中上旬达最大值,随后其值逐渐减小。单变量敏感性分析法对模拟蒸腾量的分析表明,林冠层接收的净辐射和林地叶面积指数对模拟结果的影响最大,其次是气温和风速,而空气相对湿度的影响最小；当模型输入参数在±10%变动时,模拟蒸腾量的变化幅度均<10%,说明该模型的模拟结果比较稳定,有很大的可信性。(4)采用改进的Penman-Monteith修正式估算的青海云杉林2008年整个生长季的林地土壤蒸发量为51.9mm,平均日土壤蒸发量为0.34mm,且模拟的日土壤蒸发量没有明显的季节变化。利用自制小型桶式蒸渗仪观测的青海云杉林非雨天的林地土壤蒸发平均为1.25 mm·d-1,最大可达2.82 mm·d-1。在试验观测期间内的38个非雨天,蒸渗仪实测的土壤蒸发量明显高于Penman-Monteith修正式的估算值,但两者的变化趋势基本一致。(5)基于改进的Penman-Monteith修正式估算的青海云杉林2008年整个生长季的蒸散量为313.6 mm。其中,林冠截留蒸发量、冠层蒸腾量和林地土壤蒸发量依次为100.9 mm、160.8mm和51.9mm,分别占总蒸散量的32.2%、51.3%和16.5%。采用Penman-Monteith修正式估算的青海云杉林的蒸散量与涡动相关系统实测的蒸散量相差不大,尤其是在连续晴天期间,两者吻合得很好,且月蒸散量变化呈先增大后减小趋势。(6)研究区大部分降雨以林内雨的形式进入林下并贮存于土壤中,同时季节性冻土随气温的升高逐渐融化,也使得土壤含水量剧增,最终导致土壤储水量在2008年整个生长季内可增加191.5mm。未考虑冻土的存在和考虑其存在,根据水量平衡方程推算的青海云杉林2008年整个生长季的总蒸散量分别为187.5mm和306.7mm,分别比基于改进的Penman-Monteith修正式估算的蒸散量低126.1mm和6.9mm。更多还原

【Abstract】 The Qilian Mountains is located at the intersection of the Tibetan Plateau, the Loess Plateau and the Mongolia-Xinjiang Desert, northwestern China. Its ecological environment is not only restricted by regional conditions but also sensitive to global change. In order to address the subsistence needs, local residents have exerted all kinds of serious interferences to regional ecosystem of the Qilian Mountains for a long time, which lead to grassland degradation, soil erosion intensification, and severe forest destruction. There are close interactions and coupling relationships between forest ecosystem and the ecological and hydrological processes in the whole Qilian Mountains. On the one hand, forest ecosystem defends the safety of permanent snow and glaciers by controlling the energy balance and the water cycle; on the other hand, it plays the role of water conservation, purifying water, protecting soil and water resources, and maintaining biological diversity by regulating hydrological paths (e.g., intercepting and regulating the mountainous precipitation and melt-water). However, the mechanism of the ecological and hydrological processes in the forest ecosystem has not been well understood due to the complex influences on the interaction between forest and water resouces. Therefore, this study aims to investigate the ecological and hydrological processes of Qinghai spruce (Picea crassifolia) forests. Based on the analysis of ecological processes and hydrological processes and their interactions, the mechanism of hydrological cycle in the Qinghai spruce forests and its regulation on the whole mountainous hydrological processes could be quantitatively revealed. Furthermore, the occurrence rules and internal relationships of various hydrological phenomena in the Qilian Mountains can be thoroughly understood, which can provide scientific basis for establishing a rational management pattern on water resources. The main results are as follows:(1) The daily maximum and average air temperature in the study area have obvious seasonal variations. In the Qinghai spruce forest, the relative humidity is basically around 60%, wind speed is less than 0.5 m-s-1, and the highest understory solar radiation intensity is only 86.6 W-m-2. Precipitation in the study area also has a significant seasonal distribution. Rainfall during the growing season (from May to September) of 2008 accounts for 78.7% of annual precipitation, and the rainfall events mainly occur as low rainfall amount and intensity. The vertical distribution of soil temperature and soil moisture in different months show different variation trends, while soil temperature and volume water content of different soil depths during the whole year increase firstly and then decrease.(2) During the observation period (from June 12 to October 8 in 2008), the total throughfall, rainfall interception and stemflow of the Qinghai spruce forest were 212.6 mm,64.5 mm and 3.4 mm, and accounted for 75.8%,23.0% and 1.2% of the total precipitation, respectively. Throughfall increased with the increase of rainfall and had a great spatial variability. Under the conditions of no rainfall before a rain event, stemflow in the Qinghai spruce forest began to yield when rainfall amount reached 5.6 mm. The stemflow amount increased with the increase of rainfall and stemflow rate of 34 rain events averaged 0.58%. Canopy interception rate gradually decreased and finally stabilized with the increase of rainfall, and the averaged proportion of canopy interception was 33.9%.(3) This study simulated canopy transpiration of the Qinghai spruce forest during the growing season of 2008 using an improved Penman-Monteith equation and the univariate sensitivity analysis was performed to test the sensitivity of variables affecting the canopy transpiration. The total transpiration of the Qinghai spruce forest in the whole growing season of 2008 is 160.8 mm and the daily canopy transpiration rate averages 1.05 mm. The modeled daily canopy transpiration starts to increase at the beginning of May, reaches its maximum in the middle of July, and returns to its minimal value towards the end of the growing season. Our sensitivity test shows that among the factors affecting the canopy transpiration, the sequential order of the importance is as follows:net radiation received by canopy> leaf area index> daily air temperature> wind speed>relative humidity. We consider that less than±10% change in the estimated daily canopy transpiration resulted from about±10% change in any of the contributing factors is acceptable and thus the model-based estimation of the daily canopy transpiration is acceptable.(4) The total soil evaporation (estimated by using an improved Penman-Monteith equation) of the Qinghai spruce forest in the whole growing season of 2008 is 51.9 mm and the daily soil evaporation rate averages 0.34 mm. Meanwhile, the daily soil evaporation rates of non-rainy days, observed by small man-made lysimeters, average 1.25 mm and the daily maximum of soil evaporation is 2.82 mm. During the observation period, the measured soil evaporation by lysimeters on 38 non-rainy days was higher than that estimated by the improved Penman-Monteith, but the variation trends were consistent with each other.(5) Based on the improved Penman-Monteith equation, the estimated total evapotranspiration of the Qinghai spruce forest throughout the entire 2008 growing season was 313.6 mm. Canopy interception evaporation, canopy transpiration, and soil evaporation were 100.9 mm,160.8 mm and 51.9 mm, and accounted for 32.2%, 51.3% and 16.5% of the total evapotranspiration, respectively. The estimated evapotranspiration of the Qinghai spruce forest during the whole growing season was not obviously higher or lower than that observed by the eddy correlation system in the study area, and the differences between them were much smaller on sunny days. Specially, the modeled monthly evapotranspiration starts to increase at May, reaches its maximum in July, and decrease towards September.(6) In the study area, most of the rainfall reaches the Qinghai spruce forest floor via forest canopy and is stored in the soil. Meanwhile, seasonal frozen soil melts gradually with the increase of air temperature, which also results in sharply increase in soil moisture. Therefore, the storage of soil water during the whole growing season of 2008 increased 191.5 mm. Furthermore, the evapotranspiration deduced from water balance equation was 187.5 mm and 306.7 mm without and with the consideration of the seasonal frozen soil, respectively. They were lower than that estimated based on the improved Penman-Monteith equation as much as 126.1 mm and 6.9 mm, respectively.更多还原