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沙漠湖盆区地下水生态系统及植被生态演替机制研究

Study on Groundwater Dependent Ecosystem and Ecological Mechanisms of Vegetation Succession in Desert Lake-Basin Region

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【Author in Chinese】 宋国慧

【Supervisor】 李云峰

【Author's Information】 长安大学, 地下水科学与工程, 2012, 博士

【Abstract in Chinese】 水是地球上一切生物赖以生存的宝贵资源。地下水,作为水资源的重要组成部分,对于自然环境和人类社会经济活动的可持续发展具有不可替代的作用,特别是在降水稀少的干旱荒漠区,是维系荒漠区天然植被生态平衡的重要部分。因而,深入探讨地下水生态系统变化与天然植被生态演替之间的机制,具有重要意义。干旱荒漠区,气候干燥、降水稀少、蒸发量大,自然环境条件恶劣,植被生态环境退化,土地沙漠化加剧。究其原因,除了地质构造变动、全球气候条件变化外,与地下水系统变化密切相关。例如我国西北的干旱荒漠区,从地理空间格局看,具有山地和盆地相间分布的特殊地理空间格局。其中,大型内流盆地主要包括甘肃河西走廊、新疆准噶尔盆地、塔里木盆地、青海的柴达木盆地以及吉兰泰—河套盆地等。由于气候极端干旱,盆地内呈现出典型的荒漠景观,然而盆地周边都有高山峻岭分布,如著名的祁连山、天山、昆仑山、贺兰山、阴山等,这些山脉在区域上成为干旱地区大气中水分凝聚中心,降水量相对较大,为风沙覆盖的山前洪积平原和湖积盆地地下水提供了重来的补给来源。所以说,在沙漠湖盆区,尽管生态环境恶劣,但是在地下水浅埋的风沙覆盖盐湖附近仍然生长着许多天然植被,它们对于维护该地区生态环境起着重要的作用。本文选取沙漠湖盆区为研究对象,依托SEE生态协会资助项目:“乌兰布和沙漠地下水资源及其生态效应研究”,以乌兰布和沙漠覆盖的吉兰泰湖盆地区为例,综合运用理论分析、野外调查、室内试验的方法,通过对研究区地下水生态系统指标体系的构建,开展了沙漠湖盆区地下水生态系统及植被生态演替机制研究,本文的主要研究成果:1作者重新界定了地下水生态系统定义,认为地下水生态系统,是指地下水系统及与地下水有依赖关系的生态系统,包括地下水系统及地下水生植物系统。地下水系统主要包括地下水流系统、地下水结构系统以及地下水系统生物。地下水生植物系统是指直接或者间接依赖地下水生存的植物系统。2研究了在地下水位上升和下降条件下,地下水系统对沙漠植被生态系统的制约作用和沙漠植被生态系统对地下水系统变化的适应机制。3从水分垂直循环角度分析了地下水、毛细带水与土壤水转化关系及沙漠凝结水与地下水的联系及生态意义,认为在沙漠覆盖湖盆区地下水较为丰富,水位埋深浅,风沙土毛细作用强烈,潜水面之上普遍存在着毛细水带。毛细带水与大气水、植物水、土壤水和地下水一起构成沙漠湖盆区独特的沙漠水文生态系统,并在其中起着联结纽带作用,是干旱区水文循环的重要环节。地下水系统动态、毛细水上升特性等决定了西北沙漠湖盆区土壤水分补给状况,进而控制沙漠植被种群的分布格局,影响着所存在植被的稳定性及演替趋势。而温度场的动态是影响潜水、毛细水、土壤水分转化的关键因素。4明确了沙漠湖盆区地下水生态水位的概念,认为生态水位是指能够满足生态环境的要求、不致发生植被退化、土地沙漠化、土地盐渍化问题,能维持非地带性自然植被生长所需水分的浅层地下水埋藏深度。它是满足植物生态环境需要,受土壤毛细性质影响,具有时间、空间动态变化规律的一个区间。提出了适合于地下水生植物的最佳地下水生态环境的地下水位埋深。即:最佳地下水埋深=根系深度+毛细上升高度。5区域地下水位持续下降是植被衰退的主要原因。盆地潜水除了蒸发排泄外,吉兰泰镇工业、生活用水井的地下水开采,查哈尔滩农业灌溉井的地下水开采成为主要人工排泄方式。在乌兰布和沙漠吉兰泰盆地地下水系统中,由盆地边缘到湖盆内部潜水埋深逐渐变浅,变化范围为0.23-9.47m。从1984年到2010年,研究区内查哈尔滩绿洲灌区农业用水量持续增加,地下水位持续下降,地下水潜水位总共下降了6m到10m,平均每年下降0.27m到0.45m,承压水位年均降幅为0.20m,年变幅为1.50m-2.75m,吉兰泰盐湖以北现在水位已经下降到10-15m,自流泉消失,地下水生植被衰亡。6毛细水上升特性具有植被生态学意义。在植物生长阶段,如果植物根系能够探及毛细水带,则植物生长就能免受水分胁迫。地下水位下降,毛细带降低,植被获取水分减少,会导致水分胁迫。在研究区,风砂土下覆湖相红粘土毛细上升高度为3.1-4.2m。风沙土毛细上升理论最大高度为0.63-1.66m。7在乌兰布和沙漠吉兰泰湖盆区,天然植被群落可归纳为梭梭林、沙冬青灌丛、白刺灌丛、柠条灌丛、盐爪爪灌丛、红砂—珍珠灌丛和沙蒿灌丛等7种类型。典型依赖地下水生存的非地带性荒漠植物群落有天然梭梭次生林、沙冬青、白刺、盐爪爪、柠条等群落。它们对于维护该地区生态环境起着重要的作用。8从湖盆中心到外围的风成沙丘地,地下水生植物呈有规律的环带状分布。依次为水生芦苇,马蔺、盐爪爪、芨芨草,沙冬青、梭梭,白刺。在不同的地貌单元,植物生长状态和地下水位埋深的关系略有不同。在吉兰泰湖盆边缘地带,地下水埋深大于3m,植被覆盖度小于15%,梭梭群落覆盖度随着地下水埋深加大而减小;在吉兰泰湖盆内部,地下水埋深小于3m,植被覆盖度大于15%,梭梭群落覆盖度也随着地下水埋深加大而减小;而大于10m埋深,无梭梭出现;在沙丘间洼地,地下水埋深一般小于1.2m,梭梭分布稀少,覆盖度很小。9浅层地下水及毛细水是土壤湿层的主要水分来源,土壤湿层的存在,有利于植物在春季生长期内适应水分胁迫。通过研究区土壤剖面含水率测定结果分析认为,土壤剖面从地面往下40-80cm处为含水率相对较高的土壤湿层。根据吉兰泰气象站气温、地温的日变化与季节变化及季节冻土数据,进一步探讨了温度场及季节冻土作用下水汽运移对土壤水分补给机理,认为温度场的动态是影响地下潜水、毛细水、土壤水分转化的关键因素。10根据研究区地下水生植物梭梭与白刺这两种典型沙生植被生长区的毛细上升高度分析得到了研究区最佳地下水埋深为1.6-4.7m,在此地下水埋深范围内毛细水能为植物生长提供充足水分,植物生长良好,植物生态系统稳定。地下水位埋深下降至10m以下时,研究区以地下水为生的灌木退化、衰败,以降水为水分来源的超旱生灌木和草类植物种类占据群落主体。11在沙漠湖盆区,虽然生态环境恶劣,但是在地下水浅埋的风沙覆盖盐湖附近仍然生长着许多天然植被。针对沙漠湖盆区退化的植被生态系统,提出了基于重视恢复植物种类的选择,合理利用地下水资源,保护沙漠区生态环境的植被恢复和重建的具体措施与建议:1)以种植白刺、梭梭为主,生物和工程措施相结合,建立起较为完备的防风固沙的防护林体系;2)优化土地利用结构,实施退耕还草,发展生态畜牧业和节水农业;3)合理利用地下水资源,优先考虑沙漠区生态环境用水;4)建立地下水和植被生态的监测系统。预期研究成果将对乌兰布和沙漠生态保护和受损生态系统的恢复和重建具有重要的理论指导和实践意义,同时对其它沙漠湖盆地区水文生态研究具有重要的借鉴意义。

【Abstract】 Water is a valuable resource which all the living things on earth live on. As an importantpart of forming water resource—groundwater, which plays an irreplaceable role in naturalenvironment and human social activities’ sustainable development. Especially in the ariddesert area with scarce precipitation, it is an important part in maintaining ecological balanceof natural vegetation in desert region. Therefore, it is of great significance to deeply probe themechanism between the changes of groundwater ecosystem and natural vegetation’ secological successionThe vegetation’s ecological environment degenerated and land desertification intensifiedin arid desert region with dry climate, scarce precipitation, high evaporation and bad naturalenvironment. In addition to the tectonic and global climate condition changes, the reason isclosely related with the changes in groundwater system. For example, in the northwestern ariddesert region of our country, it takes on a special pattern of geographic space betweenmountains and basins from its geographic distribution characters. Among them the largeendorheic basins mainly include the Hexi Corridor of Gansu Province, Xinjiang Junggar basin,Tarim Basin, Qinghai Basin, Jilantai—Hetao Basin,ect..Due to the extremely dry climate,there appears typical desert landscape in basin’s heart. However, around the basin’s distributesome high ranges such as famous Qilian Mountains, Tianshan Mountains, Kunlun Mountains,Helan Mountains, Yinshan, and so on. And these mountains in the region become the moisturein atmosphere condensed centre in arid regions. With high precipitation providing importantrecharge sources for sand-covered alluvial plains and lacustrine basin groundwater. So,though the ecological environment is harsh in desert lake basin area, there grow many naturalvegetations in the sand–covered Salt Lake near the sand in shallow groundwater, which playan essential role in maintaining ecological environment of this area.This paper chose desert basin area as research object, relying on SEE(Society ofEntrepreneurs&Ecology)Ecological Association Fund Project-Study on the groundwaterresources and its ecological effects in Ulan Buh Desert, taking the area of Jilan Tai lake basin covered by Ulan Buh Desert as an example, carrying out the research on desert basingroundwater ecosystem and vegetation’s ecological succession mechanism throughintegratedly using theoretical analysis, field investigation, means of indoor test. The mainresearch results:1The author put forward the definition of groundwater ecosystem, which refers to thegroundwater and groundwater dependent ecosystem, including groundwater system andgroundwater aquatic plant system. And groundwater systems mainly consist of groundwaterflow system, groundwater formation system and groundwater system biology. Groundwateraquatic plant system means the plant system which lives directly or indirectly on groundwater.2The author studied the conditions of groundwater level rising and falling, the restrictivefunction of groundwater system to desert vegetation ecological system and the adaptationmechanism of desert vegetation’s ecological system to the change of groundwater system.3From the water vertical angle, the author analyzed the transformation relationshipamong groundwater, capillary water and soil water and the contact as well as ecologicalsignificance between desert condensation and groundwater. The author also considered thatthe groundwater in desert-covered lake basin is relatively rich and the groundwater table isshallow. Meanwhile, sandy soil capillary zones generally exist on water table. The uniquedesert hydrological ecosystem in desert basin area consists of capillary fringe together withatmosphere water, plant water, soil water and groundwater. And capillary fringe plays the roleof connection in hydrological ecosystem. At the same time, it is an important link ofhydrological circle in arid region. The characteristics of groundwater dynamic and capillarywater rising decide the conditions of soil water supply in northwestern desert lake basin area,controlling the distribution pattern of desert vegetation divided by species and influencing thestability of existing vegetation and succession trend. But the dynamic of temperature field isthe key factor affecting groundwater, capillary water and soil water’s transformation.4The author clarified the definition of ecological level of groundwater in desert lakebasin and believed that it could meet the requirements of ecological environment, prevent thedegradation of vegetation, land desertification, soil salinization problems and maintain theburied depth of groundwater for azonal natural vegetation growth needed water. And it is alsoa zone to satisfy the needs of plant ecological environment and influenced by the properties of capillary soil with dynamic variations in time and space. Here the author also put forward theamount of optimal groundwater eco-environment’s groundwater depth and capillary which arefit for groundwater aquatic plants to grow. That is-the best groundwater buried depth isequal to root depth plus capillary rising height. And the amount of capillary water rise is equalto the amount of root which carries water plus the amount of soil moisture evaporation.5The main reason for vegetation degeneration is that the regional groundwater leveldeclines continuously. Besides basin phreatic water’s evaporation, the exploration ofgroundwater for Jilan Tai town’ s industry, living water and agricultural irrigation wells inChahar beach have become the main way of artificial excretion. The depth of phreatic watergradually becomes shallow ranging from0.23-9.47metres from the basin edge to the basininterior in Jilai Tai basin’s groundwater system of Ulan Buh Desert. From1984to2010, inresearch area the amount of water used in agriculture in Chahar beach oasis irrigation region,and the groundwater level continued to decline in the range of6-10metres at an average of0.27-0.45metres per year. Meanwhile, confined groundwater level fell at an annual average of0.20meters varying from1.50-2.75metres. And now the water in the north of Jilan tai SalineLake has fallen10-15metres with the artesian spring disappearing and groundwater aquaticvegetation degenerating.6The height, velocity and water volume of capillary rise are three elements with greatsignificance in vegetation ecology. During the plant growing period, if the plant roots are ableto reach capillary fringe, plant growth can be free of water stress. On the contrary, if thegroundwater falls, capillary fringe decreases and the chances for vegetation to get waterreduce, then plant growth will lead to water stress. In the research area, the height of capillaryrise of sand-covered lake red clay is3.1-4.2metres. And the theoretical maximum height ofaeolian sand soil capillary rise is0.63-1.66metres.7In Jilan Tai lake basin area of Ulan Buh Desert, natural vegetations can be divided into7groups, including Haloxylon ammodendron forest, Ammopiptanthus mongolicus shrub,White thorn Scrub, Caragana shrub, Salt claw shrub, Red sand pearl Scrub and Artemisiasphaerocephala. And among them natural Haloxylon ammodendron forest, Ammopiptanthusmongolicus shrub, Nitraria tangutorum, Kalidium, Caragana microphylla and other speciesare plant communities that are typically groundwater-dependent and azonic desert plants, which also play an important role in maintaining ecological environment in this area.8Groundwater aquatic plants appear in regular ring-belt distributions in an order ofAquatic reeds, Iris lacteals, Kalidiums, Achnatherum splendens, Ammopiptanthus mongolicas,Haloxylon ammodendrons and Nitraria tangutorums from the lake basin center to the dunefield made by outside sand. The relationship between plant growth statement and groundwaterdepth is slightly different in various geomorphic features. At the edge of Jilan tai lake basin,groundwater depth is more than3metres, and the amount of vegetation coverage is less than15%. Here with the groundwater depth increasing, the coverage of Haloxylon ammodendrongradually decreases. At the same time, in the interior of Jilan tai lake basin, with thegroundwater depth increasing, the coverage of Haloxylon ammodendron also graduallydecreases between the groundwater depth which is less than3metres and the amount ofvegetation coverage which is more than15%. But there will be no Haloxylon ammodendronsif the groundwater depth is above10metres. In the dune depressions, here in general thegroundwater depth is less than1.2metres and Haloxylon ammodendrons scarcely distributewith small coverage.9Shallow groundwater and capillary water are the main source of water for wet layer insoil. The existence of wet layer in soil is beneficial to plants to adapt themselves to waterstress in plant growth period of spring. The analysis through studying the measurements ofcontent water in soil profiles show that the soil profile from the ground below40-80meters isthe wet layer in soil contains relatively high water content. According to the statistics of airtemperature and ground temperature’s diurnal and seasonal variations as well as seasonalfrozen soil from Jilan tai meteorological station, the paper probed the mechanism of rechargewhich the movement of moisture showed to soil moisture with the effect of temperature fieldand seasonal frozen soil, considering the dynamic of temperature field is the key factor ofinfluencing shallow groundwater, capillary water and soil water’s transformation.10According to the analysis that the height of capillary rise in these two kinds of typicaldesert vegetation land in research area where underground aquatic plants-Haloxylonammodendron and Nitraria grow, it was proved that optimal groundwater depth in researcharea is1.6-4.7metres. Within the range of this groundwater depth capillary water can offeradequate water to plant growth. And if the plants grow well, the plant ecosystem will be stable.But if the groundwater depth drops to less than10metres, the shrubs in the research areawhich live on water will degrade and decline and the super-xerophytic shrubs together withgrass plant species which depend on precipitation as water resource will dominate the principal part of community.11Though the environment in desert basin area is bad, many natural vegetations still growaround the shallow groundwater and sand-covered saline lakes. The author recommendedsome concrete measures and suggestions on paying more attention to recovery of plantspecies’ selection, reasonable utilization of groundwater resources and protection ofecological environment’s vegetation restoration and reconstruction in desert area according todegraded vegetation ecological system in desert lake basin area. Seventhly, in order to protectthe ecological environment in desert area and promote coordinate development amongregional economy, society and environment, four aspects of vegetation ecosystem restorationmeasures are proposed as the followings: First of all, to build perfect sand-fixation shelterbeltsystem with Nitrarias and Haloxylon ammodendrons widely planted as well as biological andengineering measures combined.Secondly, optimizing land utilization structure, implementingthe strategy of returning the grain plots to grass and developing ecological stock raising aswell as water-saving agriculture. Thirdly, making rational use of groundwater and givingpriority to eco-environment water consumption in desert area. Finally, establishinggroundwater and vegetation’s ecological monitoring system.The expected research results will be of great theoretical conduct and practical significancefor Ulan Buh Desert ecological protection and damaged ecosystem restoration andreconstruction. Meanwhile, the research results will offer important lessons forhydro-ecosystem study of other desert lake basin areas.

  • 【Contributor】 长安大学
  • 【Year of Internet Publish】201405
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