Knowledge Resource Center for Ecological Environment in Arid Area
| 祁连山青海云杉林水文过程观测与模拟研究 | |
| 其他题名 | Observation and Simulation on Hydrological Processes of QinghaiSpruce (Picea Crassifolia) Forest in the Qilian Mountains |
| 杨军军 | |
| 出版年 | 2016 |
| 学位类型 | 博士 |
| 导师 | 何志斌 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 森林是地球表面最重要的地表覆被类型之一，是全球水量平衡和水分传输过程的重要环节，关于森林的水文过程及其对流域径流的影响一直存在争议。目前该领域主要针对湿润地区的森林开展了大量研究工作，干旱区山地由于降雨量小、观测难度大且区域间差异显著，森林水文过程研究相对较少。近年来，随着全球气候变暖，极端天气事件增多，气候变化引起的流域水资源和水文过程变化已经成为当前研究热点。干旱区水资源紧缺，任何水文过程或水资源量的变化都会引起显著的生态系统反馈，进而影响干旱区生态系统稳定和用水安全，因此量化干旱区山地森林水文传输过程和森林水文组分，以及阐明森林对流域水文过程的影响机制是干旱区生态水文学关注的热点问题。本研究以典型干旱区山地祁连山排露沟流域为主要研究区域，以青海云杉林作为研究对象，基于长期野外观测和样地调查数据，定量分析青海云杉林一维水分传输过程，即大气降水、林冠截留、地表覆被物吸收、地表蒸发、土壤入渗、植被蒸腾和土壤存储等七个过程，最后通过水量平衡法和生态水文模型将各过程进行整合，阐明森林水文组分及相互间反馈机制，主要结论陈述如下：（1）在样地尺度上，实验利用60个截留桶，开展了2个生长季青海云杉林冠截留观测，并建立了林冠截留率与降水特征、林冠结构参数间的回归关系。结果表明，郁闭度为0.68的青海云杉林，最大冠层截留容量为1.16 mm，青海云杉林冠截留率取值范围在-8.8% ~ 84.1%之间（平均值为35.1%），林冠截留率存在较大的空间异质性。结合林冠结构参数分析发现植物面积指数（PAI）是导致林冠截留率出现空间异质性的主要因素之一，而叶面积指数（LAI）与林冠截留率的相关性较差，因此，本研究认为PAI更适合应用在林冠截留模型中。同时，本研究提出了依据PAI空间格局布设林冠截留桶位置的方法，该方法不仅减少了截留桶数量，并且缩短了观测时间。 （2）基于SFM1型号的液流仪对不同胸径青海云杉树干液流进行测定，确定了青海云杉胸径与边材面积间的函数关系，并以胸径为关键参数，构建了单株、林分到流域耗水的尺度转换模型。基于2013至2015年的观测数据，青海云杉林年均蒸腾耗水量为157 mm，占年降水量的34.2%。对比夜间蒸腾量和日蒸腾量，青海云杉夜间蒸腾量占日蒸腾量约24%。在生长季，青海云杉蒸腾量大小与树干径向变化量存在良好相关性，即蒸腾量变化是导致青海云杉径向变化的主要因素。（3）青海云杉地被物以苔藓为主，基于野外调查和室内对比实验，研究流域苔藓分布特征、截持能力及其对林地地表蒸发的保湿功能。研究区林地苔藓平均厚度为14.3 cm，苔藓底部有腐殖质层，其中苔藓质量占苔腐（苔藓-腐殖质）总质量约33.6%。根据室内吸水实验，林地苔藓平均单位面积最大持水量为2.29 kg?m-2，单位质量持水量为20.71 kg?kg-1，苔藓是林地降雨的第二截留层，截持容量较大。晴朗条件下，厚度为2.5 cm ~ 3 cm的苔藓层能够降低约21.9%的土壤蒸发，因此，林下苔藓层具有重要的保湿功能。林下苔藓层在降雨事件中的快速、高储水能力和非降雨时期的地表保湿功能，使其在森林拦蓄洪水、调节径流、蓄水和保持地面植被多样性等方面作用显著。（4）林地土壤的水文作用主要体现在透水和蓄水两个方面。本研究利用Guelph 2800K1渗透仪测定林地原状土壤水分传导率，确定林地透水能力。同时，以ECH2O土壤水分监测仪基于样点测定不同海拔林地土壤水分变化过程，研究土壤水分蓄水能力及影响因素。结果表明，青海云杉林地饱和导水率在0.01 cm?min-1 ~ 0.14 cm?min-1之间，其中10 cm深度平均饱和导水率为0.09 cm?min-1，20 cm至70 cm深度平均为0.04 cm?min-1。对不同海拔样地多年土壤水分动态分析发现，生长季（6至9月）土壤含水量变化主要受降水事件影响，单次或多次降雨事件后土壤含水量迅速升高，且随无降雨时间的增加而迅速降低；非生长季土壤含水量主要受土壤冻融过程影响，冻结过程中土壤含水量迅速下降，相反消融时逐渐升高。同时，对2014和2015年深度40 cm以内土壤含水量数据统计发现，海拔3200 m生长季和非生长季土壤含水量分别为26.9%和13.7%，2700 m分别为17%和11.8%，生长季高海拔土壤含水量显著高于低海拔，不同海拔间差异显著。研究认为高海拔土壤水分除受垂向更多降雨补给外，高海拔林分郁闭度较低穿透雨量大和冻土消融产生的壤中流也是影响因素之一。（5）在样地尺度上，通过水量平衡法量化林地水文组分，评价林地水分收支状况，并以CoupModel生态水文模型模拟林地一维水热传输过程。水量平衡分析结果表明，年降雨量为451 mm时，林冠截留量为152 mm（占33.7%），蒸腾量为154 mm（占34.2%），地表蒸发量为138 mm（占30.7%），林地蓄水量为9mm占降水量1.5%。在林地一维水热过程模拟中，CoupModel模型对土壤温度模拟效果较好，但土壤含水量模拟结果与观测记录差异较大，研究认为主要原因可能来自模型自身结构的不完善和林地土壤水分的高度空间异质性，因此，干旱区林地生态水文模型的建模和应用仍然存在较大挑战。 |
| 英文摘要 | Forest is one of the most important land cover types on earth, and the key link in global water-budget and transport processes. The role of forests in hydrological processes and their effects on runoff remain strongly contested because of the complicated hydrologic feedbacks in watersheds. Most studies addressing hydrological processes were conducted in humid regions; arid regions received much less attention on the account of infrequent precipitation, lack of field observations, and dramatic differences in the ecological environment among arid regions. Recently, however, water resources and process-changes in arid regions have become subject of much debate because of climate warming and an increase in the frequency of extreme weather events. Water availability in arid areas is the most important natural resource. Even small fluctuations in water yields have critical effects on the drinking-water security and on the stability of ecosystems. Therefore, quantification of water-transfer processes, definition of the components of the water balance, and clarification of the role of forests in hydrological processes in arid mountain regions are critical scientific questions in ecohydrology today.This study was conducted in the Qilian Mountains, located in the upper Heihe River Basin, in pure stands of P. crassifolia growing on a bench at an elevation between 2700 m and 3200 m in the Pailugou catchment. Using long-term field records over an extensive area, we quantified hydrological processes in the vertical direction. Specifically, we analyzed precipitation, canopy interception, absorption by land cover, evaporation from the land surface, transpiration by vegetation, soil infiltration, and soil water storage. The quantified processes were integrated using a water-balance method and an ecohydrological model to determine feedback mechanisms among the forest components. Our main findings are outlined as follows:(1) At the patch-scale, extensive data (from 60 collectors) were used to determine accurate canopy interception of Qinghai spruce, and regression relationships between canopy interception and precipitation, and interception and canopy structure. Results showed that at canopy density of Qinghai spruce of 0.68, canopy storage capacity was 1.16 mm, and canopy interception losses ranged from -8.8 to 84.1%, and with a mean value of 35.1%, and a significant spatial variation. Analysis of spatial patterns of canopy interception, plant area index (PAI), and leaf area index (LAI) showed that PAI was more appropriate than LAI for use in the canopy interception model. Based on the relationship between canopy interception loss and PAI, a more efficient method was found for the arrangement of collectors, and it not only reduced the number of collectors, but also decreased the required observation time.(2) Based on SFM1 sap flow meters for various tree diameters at breast height (DBH), we determined the relationship between DBH and sapwood area, and used DBH as the key parameter to scale water consumption by transpiration from individual-tree to stand basis. Statistical analysis of empirical data showed that annual water consumption by transpiration was 157 mm, and it comprised 34.2% of the mean annual precipitation. The magnitude of the nocturnal water losses was up to 24% of daily water losses for Qinghai spruce. In the growing season, transpiration and radial variation exhibited a complementary relationship, that is, water loss by transpiration was the main factor in radial variation of Qinghai spruce.(3) Moss was the major vegetative cover in the Qinghai spruce forest, and we used field observations and laboratory experiments to study the distribution characteristics of moss, its water-holding capacity, and water-retention capacity of land-surface. The mean thickness of moss in the study forest was 14.3 cm, and the weight constituted 33.6% of the gross weight of the moss-humus complex. Our water-sorption experiments in the laboratory showed that the maximum water holding capacity of the average forest land was 2.29 kg?m-2 per area, and 20.71 kg?kg-1 per mass. In the non-rainfall period, moss with a thickness of 2.5 to 3 cm can reduce land evaporation by 21.9% compared with bare soil, indicating that moss was the second most important interception layer for precipitation. Moss, with its fast-absorption, high water-conservation, and excellent water-retention capacity had remarkable effects on the ability of forests to store flood waters, regulate flow, and maintain biodiversity of the forest system.(4) The major hydrological functions of forest soil were infiltration and storage. In-situ hydraulic conductivity of forest soil was determined with Guelph 2800K1 permeameter. ECH2O was used for measuring changes in water content and temperature at different soil depths to define water conservation capacity and control factors. Experimental results showed that field saturated hydraulic conductivity in the soil of Qinghai spruce forest ranged from 0.01 to 0.14 cm?min-1, with mean value at 10 cm depth at 0.09 cm?min-1, and at 20 to 70 cm at about 0.04 cm?min-1. Soil water dynamics at different altitudes indicated that soil water content was mainly influenced by rainfall events in the growing season; soil water content increased rapidly with one or several rainfall events, and sharply decreased during extended periods of no rainfall. While soil water content was controlled by the freezing and thawing processes of soil during the non-growing season, soil water content rapidly decreased with freezing and increased slowly during thawing. Soil water contents during the growing and non-growing seasons were 26.9% and 13.7%, respectively, at the elevation of 3200 m, and 17% and 11.8% at 2700 m. The significant differences in soil water contents between the high- and the low-altitude areas can be interpreted not only as more precipitation, but also smaller LAI and interflow from the thawing of frozen soil at the high altitude region.(5) At the plot-scale, we quantified components of the water budget using the water-budget method, and simulated the vertical water-transport processes with the ecohydrological model – the CoupModel. In the water budget, if precipitation was 451 mm, canopy interception consumed 152 mm, transpiration consumed 154 mm, and evaporation of the land surface consumed 138 mm, resulting in storage of the forest land was only 7 mm. Soil temperature simulation in the CoupModel was satisfactory, but there was a large difference between the simulation results and empirical data for soil water content; one possible explanation was a measurement deviation due to the significant spatial variation of the canopy structure and soil water content in the forest. We concluded that important challenges still exist for modeling of hydrological processes in forests, and in the application of an ecohydrology model. |
| 中文关键词 | 祁连山 ; 青海云杉 ; 林冠截留 ; 土壤水分 ; 林地蒸散 |
| 英文关键词 | Qilian Mountains Qinghai spruce Canopy interception Soil moisture Forest Evapotranspiration |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 自然地理学 |
| 来源机构 | 中国科学院西北生态环境资源研究院 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/287716 |
| 推荐引用方式 GB/T 7714 | 杨军军. 祁连山青海云杉林水文过程观测与模拟研究[D]. 中国科学院大学,2016. |
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