【作者】 徐存东；

【导师】 冯起；

【作者基本信息】 兰州大学 ， 自然地理学， 2010， 博士

【摘要】 我国西北干旱区土地资源丰富,光热条件充足,受水资源短缺和干旱少雨的气候制约,大片适宜耕种的土地长期荒芜。随着我国人口的快速增长,西北干旱区的水土资源得以快速地开发利用,特别是随着电力提水设备和引水灌溉技术的发展,在我国西北地区建成了许多高扬程的扬水灌区,这些灌区的出现和发展,从生态景观角度来看,是在原有的天然荒漠上建起了大面积的人工绿洲,在创造了巨大的经济效益、生态效益和社会效益的同时,由于灌区粗放灌溉,有灌无排致使局地出现了一些不良生态环境问题,如土壤次生盐渍化、天然植被衰败、地下水质恶化等,这种人工灌溉造成的局域水土环境演化和变迁,在一定程度上制约着灌区经济的持续、稳定、健康发展。所以,研究扬水灌区的灌溉水转化规律,及时掌握灌区土壤水盐的运移动态,同时研究灌区的水盐运移与局域水土环境变迁的耦合关系对指导灌区可持续发展和科学管理具有重要现实意义。本文以甘肃省景泰川电力提水灌区为研究区域,通过对灌区发展40年来局域水土资源变迁过程的现场调查和环境监测资料分析,将地表水的转化模型和地下水盐的运移模型结合起来,采用理论研究、现场试验、数值模拟等综合研究方法,深入研究了灌区的水盐运移规律、模拟了灌区不同水文地质单元的地下水动态、分析计算了灌区的水盐平衡状况,研究了人工扬水灌溉对区域水土环境变迁的影响,得出了如下结论：(1)甘肃省景电灌区地处我国西北内陆干旱区,灌区内士地资源丰富、光热条件充足,气候干旱少雨,水资源极度匮乏,特殊的地理位置和气候条件决定／了水资源是该地区工农业生产的决定性要素,而灌区内最大的水资源量来自于灌区引水灌溉,长期的人工灌溉引起了区域水土资源的变迁和水环境的演化,研究该区域的水盐运移对局域水土资源的影响具有很好的代表性。(2)干旱区扬水灌溉对局域水土资源变迁的影响同时具有正面效应和负面效应。扬水灌区在通过电力扬水人工灌溉建起大面积的人工绿洲,改善了局地的生态环境和生产生活环境的同时,局域水盐的演化和迁移同时伴随着部分的土地次生盐碱化和水土资源的退化等负面效应。(3)景电灌区的地表水和地下水的转化具有明显的特点,灌区水循环系统经过了跨区域引水—灌溉入渗—地下水—潜流运移或消散这样大面积的集中转化过程。灌溉水的入渗是地下水的主要补给源,占地下水补给量的75.9%,大气降水补给仅占地下水总补给量的5.38%,潜流补给量占地下水补给量的15.3%；径流补给量占地下水补给量的3.42%。(4)灌区实际的土壤水盐在运移过程中,主要受灌溉入渗和土壤水蒸发两种条件的影响,本文以入渗和蒸发条件下的非饱和渗流理论为基础,建立了饱和—非饱和土壤水的运动模型,同时建立了土壤溶质运移的饱和—非饱和带中水动力弥散方程以及灌区土壤溶质弥散的水质模型。(5)灌溉水在土壤入渗过程中受土壤结构、灌水次数、灌水量等多个因素的影响,入渗过程复杂多变、土壤盐分以灌溉入渗水为载体运移。在常年多次灌溉入渗的情况下,灌区表层耕地均出现脱盐的趋势和动态,这些盐分随灌溉水的入渗被逐渐转化为潜水含盐,并随地下水的运动而不断转移。(6)灌区内封闭型的水文地质单元水盐运移具有径流滞缓、水盐积累的特点。一般从外围向盆地中心逐渐形成了潜水交替相对流畅的灌溉入渗带、溶质迁移带,并逐渐转化为潜水交替迟缓的汇水聚盐带；各运移带内的地下水位变化随灌溉阶段不同呈规律性变化,灌溉入渗带地下水位年内的变化与灌溉高峰期(5-10月)一致,最大的变幅达3.6m,溶质迁移带变化趋势与灌溉入渗带呈滞后性的相似变化,年内变化幅度为0.6-1.8m,汇水聚盐带的地下水位年内变化不大。1994-2008年的地下水监测表明,在封闭型的水文地质单元内,各水盐运移带年际地下水位均呈逐年上升趋势,汇水聚盐带的年际变化最明显,灌区内最大的地下水位上升高达22.6m,溶质迁移带地下水位的累计上升为5-8m。(7)灌区内开敞型的水文地质单元水盐运移呈地下潜水径流通畅、溶质迁移滞缓的特点。开敞型的水文地质单元也形成入渗径流带、溶质迁移带并逐渐向潜水排泄带运移,其流向与地势变化吻合,多年地下水位累计上升幅度为1.2-4.6m,年内地下水位随灌溉水入渗量变化,变幅为0.5-2.6m。(8)开敞型水文地质单元和封闭型水文地质单元的地下水化学类型转化演变过程有所不同。在灌溉水入渗带和溶质迁移带的地下水水质均从低矿化度的重硫酸钙型水过渡到矿化度为2.1-5.2g／L的SO42-—Cl-—(K++Na+)—Ca2+或SO42-—Cl-—(K++Na+)—Mg2+型水,在封闭型水文地质单元的汇水聚盐区,地下水矿化度最高达273.15g／L,水化学类型为Cl-—SO42-—(K++Na+)—Ca2+型水；开敞型的水文地质单元的潜水排泄带,地下水含盐量受深层潜水水质和灌溉入渗水含盐量控制,其化学类型以为SO42-—Cl-—Ca2+—(K++Na+)型水为主。(9)灌区的水盐均衡计算表明,1994-2008年灌区年均引黄灌溉水量为3.89亿m3,带入灌区的年均总盐量为1.556万t；灌区内的排水沟排出的水量由1978年的0.07亿m3至2008年增高至0.237亿m3,年均带走盐量为1.68万t,其排放量比引入量高出0.12万t,灌区处于脱盐进程。从外向型转化的水量构成来看,渠道引水是灌区水量的主要来源,约占76.3%,其次为降雨带来的水量,约占18.6%,其余仅占5.1%；在排除和消耗的水量中,农林耗水所占的份额最大,约64.31%,次为荒地蒸发,占15.37%,排水沟和地下排水量,占13.37%,其余的仅占6.95%。(10)景电灌区的水盐演化使灌区地下水储存量每年约增加0.357亿m3,地下水水质随区域不同变化剧烈；灌区的水盐运移同时影响着灌区内的土地利用类型的时空转化,其中水浇地与沙漠土地的相互变迁的比例为71.72%。另外,水盐运移已造成次生盐碱化土地0.67万hm2,另有1.2万hm2耕地存在着盐碱化的威胁。区域景观格局由原来的荒漠景观逐步变迁为荒漠绿洲的景观格局。以上研究成果有望为灌区的综合治理规划、土地资源的合理配置、水资源高效利用与保护、灌区可持续发展提供科学依据,为灌区管理部门制定有关政策和决策提供可供参考的对策措施,以便更好地为扬水灌区经济建设与可持续发展服务。更多还原

【Abstract】 China’s northwest arid area has abundant land, adequate light and heat resources, while subject to long-term draught and water shortages, large tracts of arable land are desolate. Along with rapid growth of Chinese population, land resources in northwest arid area are exploited in a fast way, especially with the development of electric water pumping equipment and irrigation technology, many high-pumping irrigation zones are built in Northwest China. From the ecological perspective, the emergence and development of these irrigation zones are large area of artificial oasis building over the natural desert, creating huge economic, ecological and environmental benefits. In the meanwhile, due to extensive irrigation without appropriate discharge, adverse ecological and environmental problems arise consequently, such as soil salinization, natural vegetation decay, and deterioration of groundwater quality. These consequent environment evolution and changes have constrained the irrigation district’s economy sustainability, stability and healthy development to certain extent. Therefore, it is of great significance to study the law of irrigation water transport in pumping area, grasp the dynamic migration of water and salt in soil, and also research the coupling between water-salt transport and irrigation water changes. These researches would play an important role in sustainably developing and scientifically managing irrigation area.The project, which focused on JingDian Electricity Pumping Irrigation District(hereafter JEPI) in Gansu Province, analyzed field investigation and environment monitoring data of the soil changes in this area within 40 years. Afterwards, I intensively studied the law of water-salt transport in irrigation area, simulated dynamic of ground water in different hydrogeological units, calculated the situation of water-salt balance, and studied the impact of artificial pumping irrigation on environmental changes. In the research, I combined the transform model of surface water with transport model of ground water, introducing several methods, such as theoretical research, field test and numerical simulation and so on. The conclusion reached from this project is as following:(1) JEPI is located in arid inland of Northwest China, where it is rich in land resources, sunlight and heat, and lack of rainfall and water resource. The unique geographical and climate conditions make the water resources, mainly irrigation water, the most critical factor of agriculture industry. Long-term irrigation caused regional changes in soli and water resources and environment, which is a typical case for researching the impact of water-salt transport on soil resources.(2) Pumping irrigation in arid areas has both positive and negative effects on transformation of local soil and water resources. On one hand, it improves local ecological environment and living environment, by building a large plateau area of oasis through electronic pumping irrigation in drought land. On the other hand, inappropriate irrigation system and long-term irrigation without reasonable drainage process leads to regional water-salt evolution and migration, accompanied part of secondary land salinization and soil degradation.(3) The transformation between surface water and groundwater in JEPI has remarkable features, with the water cycling system in irrigation area experiencing the concentrated transformation process of cross-regional water-irrigation infiltration-groundwater-subsurface transport or dissipate. Infiltration of irrigation water is the main recharge source of groundwater, accounting for 75.9%of groundwater recharge, while meteoric accounts 5.38%of total recharge, subsurface flow account for 15.3%; runoff recharge accounted for 3.42%.(4) The actual level of water and salt in the migration process is mainly affected by water infiltration, and evaporation from soil. The thesis established water movement model in saturated soil-non-saturated soil conditions, based on the unsaturated flow theory under infiltration and evaporation conditions. In the meanwhile, it established hydrodynamic dispersion equation of soil solute transport in saturated-unsaturated zone, and water quality model of soil solute dispersion.(5) Infiltration process of irrigation water in soil is quite complex, affected by soil structure, irrigation frequency, irrigation capacity and other factors, with soil salinity transport in the process of irrigation water infiltration. In case of perennial irrigation infiltration, the land surface are tends to be desalinated, the salinity is gradually transformed into deep water salt during the infiltration of irrigation water, and continually moving with the groundwater transport.(6) Water-salt transport in closed-type of hydrogeological unit shows the feature of water run-off stagnant and water-salt accumulation. In general, it gradually forms a relatively smooth irrigation infiltration zone, solute migration zone from the periphery to the center of basin, and gradually turns into a lagging irrigation infiltration zone with accumulative water and salt. Level of groundwater in migration zones changes regularly with stages of irrigation, and the changes within one year is the same with that during the irrigation peak period (May-October), the largest amplitude is up to 3.6m. The trend of changes in solute transport zone is similar to lagging change of irrigation infiltration zone, in the range of 0.6-1.8m, but change of groundwater level in water catchment-poly salt zone is small. According to the monitoring data of groundwater during 1994-2008, in closed-type of hydro geological unit, groundwater level showed an upward trend year by year in the water-salt transport zone, especially significant in the water catchment-poly salt zone, with largest increasing level by 22.6m. In the solute transport zone, the monitoring cumulative increase of groundwater level is 5-8m.(7) Water-salt transport in open-type of hydrogeological unit is smooth with groundwater flow,.but stagnant with solute transport. The open-type unit has also formed infiltration runoff zone, solute transport zone which gradually moving to drainage zone, with its flows coinciding with the terrain changes. For years, the cumulative rise in groundwater level ranges from 1.2-4.6m, the groundwater level changes with infiltration of irrigation water, ranged from 0.5-2.6m last year.(8) The process of groundwater chemical evolution differs between open-type hydrogeologicaunits and closed hydrogeological unit. In the area of irrigation water infiltration and solute transport, calcium carbonate type of groundwater with low salinity is transiting to type of 2.1-5.2g/ L of SO42-—Cl-(K++Na+)—Ca2+or SO42-—Cl-(K++Na+)—Mg2+. While in the salt-congregating drainage district of closed unit, groundwater salinity is up to 273.15g/L, with head water chemistry type of SO42-—Cl-—Ca2+—(K++Na+).(9) The data of water-salt balance in irrigation district shows that average annual irrigation water from Yellow River is 389 million m3 from 1994 to 2008, bringing to the area extra 15,560 tons of salt annually. The water discharged from the drain rises from 700 million m3 in year 1978 to 23.7 million m3, with average 16,800 tons of salt taking away annually, which means the irrigation is in the condition of desalination. From the perspective of export-oriented water composition, irrigation from channel is the main source of water, accounting for 76.3%, followed by rain water brought about 18.6%, and 5.1%from other process. Among the way of water exclusion and consumption, agriculture and forest take the largest share of 64.31%, followed by 15.37%from wasteland evaporation,13.37 from gutters and underground discharge, and the remaining 6.95%of others.(10) Due to water-salt evolution in the JEPI, the storage of groundwater increases by about 035.7 million m3 per year, with dramatic differences of groundwater quality among regions. The water-salt transport also affects the spatiotemporal transformation among different land types, e.g. the transformation ratio between irrigated land and desert is 71.72%. In addition, water-salt transport has resulted in 6,700 hm2 of secondary salinizated land, and another 12,000 hm2 arable land under threat of salinization. The previous desert landscape before introduction of irrigation gradually switches to oasis land.The results above are expected to provide science basis for the integrated management of irrigation, rational allocation of land resources, utilization and protection of water resources, and sustainable development model for irrigation area. Besides, it advanced several alternative references for administration departments to formulate relative policy or decision, in order to better serve economic construction and sustainable development in Pumping Irrigation District.更多还原