基于同位素和水化学示踪剂的黄土高原小流域径流来源和地下水补给

发布时间：2018-03-31 03:32

本文选题：黄土高原　切入点：地下水补给　出处：《西北农林科技大学》2017年硕士论文

【摘要】：丘陵沟壑区为高土高原主要的地形地貌单元。土层深厚、地下水埋深大以及严重的坡面侵蚀等特点为黄土高原创造了特殊的水文过程。坡地在黄土高原乃至全世界的分布都非常广泛,其地下水研究以及降雨径流过程既复杂、难以理解,也极其重要,对理解地下水的补给以及河流沟道的排泄重要的作用。在黄土高原,坡地将降雨分为侧向的坡面径流和垂直的土壤水入渗。穿过植物根层的降水将补给到地下水;而坡面径流、流域储存的地下水以及土壤水在流域出口处汇合,进而达到对沟道溪水的补给。地下水补给关系到区域水资源的可持续发展以及水资源的可更新能力,同时也关系到人类的用水安全。了解黄土高原坡地的地下水补给通量以及补给方式,有助于我们更好的评估深层土壤水的运移方式以及区域地下水水资源量,从而为黄土高原的生态水文和土壤水文提供理论支撑。我们猜想:在研究区黄土高原丘陵沟壑区坡地,非饱和带的地下水主要补给方式为活塞流,同时其补给量很微小,但是却很重要。为了印证这个猜想,在2014年和2015年半干旱和半湿润流域的坡地上,我们共进行了7个深剖面土壤取样(15~20 m不等)。通过核爆后黄土高原土层中显著的的氚坡面来示踪坡地地下水补给及其控制因素。结果表明:每一个土层中都呈现良好的铃形氚剖面,显示出土壤水运移主要以活塞流的方式。氚峰值在半干旱的清涧园则沟流域位于9.3~11 m,在半湿润长武王东沟流域为6.3~7.2 m。7个剖面补给速率变化为22.9~31.9 mm yr~(-1),达到长期降水量的4%~7%,约为典型平地的54%。地下水补给主要是受土壤质地以及土地利用方式的影响,受到区域气候的影响较为微弱。在全世界,对土层深厚、植被覆盖度较低的流域径流来源的研究较少。国内外的研究表明流域储存的老水对沟道径流有着重要的贡献,在土层浅薄区域地下径流占有主导优势。我们选取黄土高原丘陵沟壑区作为研究对象,通过同位素(~2H)和水化学示踪剂(Cl~-、SO_4~(2-))来探究降水以及流域储存的深层土壤水或者地下水对沟道溪水的贡献。通过6场不等强度的降水、溪水的连续取样,及流域降雨前泉水和基流水取样分析,结果表明溪水的主要成分为降水,示踪剂的计算结果表明降水对溪水的最大贡献可以高达100%(~2H)以及75%(Cl~-和SO_4~(2-))。溪水的同位素随着降水有明显的波动,这表明了坡面的超渗产流过程主导研究区流域的径流过程。水化学示踪剂的研究表明沟道溪水多余的Cl~-来源于降水对土壤的表层矿物质溶解等过程。相对于同位素示踪剂,水化学示踪剂的结果会低估降水对径流水的贡献。本文的研究为黄土高原丘陵沟壑区径流的形成机制以及退耕还林还草对于流域水文过程的影响提供一定的参考价值。
[Abstract]:The hilly and gully region is the main topographic and geomorphologic unit in the high soil plateau.The characteristics of deep soil layer, deep groundwater and serious slope erosion have created special hydrological process for the Loess Plateau.Slope land is widely distributed on the Loess Plateau and all over the world. The study of groundwater and the process of rainfall runoff are complicated, difficult to understand, and extremely important, which plays an important role in understanding the recharge of groundwater and the discharge of rivers and ditches.On the Loess Plateau, rainfall is divided into lateral runoff and vertical infiltration of soil water.The precipitation through the plant root layer will recharge to the groundwater, while the runoff on the slope, the groundwater stored in the basin and the soil water will converge at the outlet of the basin to recharge the channel stream water.Groundwater recharge is related to the sustainable development of regional water resources, the renewable ability of water resources, and the water security of human beings.Understanding the groundwater recharge flux and recharge mode of sloping land on the Loess Plateau is helpful for us to better evaluate the migration mode of deep soil water and the amount of regional groundwater resources.Therefore, it provides theoretical support for ecological hydrology and soil hydrology in the Loess Plateau.We conjecture that in the slope of hilly and gully region of the Loess Plateau the main recharge mode of groundwater in unsaturated zone is piston flow and its recharge is very small but very important.In order to verify this conjecture, in 2014 and 2015, on the slopes of semi-arid and sub-humid watersheds, we have carried out seven soil samples of 15 ~ 20 m in deep profile.The significant tritium slope in the soil layer of loess plateau after nuclear explosion was used to trace groundwater recharge of slope land and its controlling factors.The results show that there is a good bell-shaped tritium profile in each soil layer, which shows that the water transport of the soil is mainly in the form of piston flow.The peak value of tritium in Qingjianzigou watershed is 9.310m, and in the sub-humid Wangdonggou basin of Changwu, the supply rate of 7.7mm ~ 31.9 mm ~ (-1) ~ (-1) is 22.9m ~ 31.9 mm ~ (-1) ~ (-1), which is about 54.45% of the long-term precipitation, which is about the same as that in typical flat land.Groundwater recharge is mainly affected by soil texture and land use patterns, but by regional climate.In the world, there are few researches on the runoff sources with deep soil layer and low vegetation coverage.Studies at home and abroad show that the old water stored in the watershed plays an important role in channel runoff and dominates the underground runoff in shallow soil areas.We select the hilly and gully region of the Loess Plateau as the research object and explore the contribution of precipitation and the deep soil water or groundwater stored in the basin to the gully stream by means of the isotopic isotope (2H) and the hydrochemical tracer (ClCl-so _ 4).The main components of stream water are precipitation, the continuous sampling of stream water, and the sampling analysis of spring water and Ji income before rainfall, the results show that the main component of stream water is precipitation.The results of tracer calculation show that the maximum contribution of precipitation to stream water can be as high as 100 ~ 2H) and 75 ~ (-) Cln- and so _ (4) ~ (-) ~ (2).The isotopes of stream water fluctuate obviously with precipitation, which indicates that the process of overosmotic runoff on the slope dominates the runoff process in the study area.The study of hydrochemical tracer shows that the excess Cl- in channel stream water originates from the process of precipitation dissolution of surface minerals in soil.Compared with isotopic tracers, the results of hydrochemical tracers underestimate the contribution of precipitation to runoff water.The research in this paper provides a certain reference value for the formation mechanism of runoff in the hilly and gully region of the Loess Plateau and the effect of returning cropland to forest and grass on the hydrological process of the watershed.
【学位授予单位】：西北农林科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P333;P641

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