ISWC OpenIR  > 水保所知识产出(1956---)
黄土塬区深剖面土壤水分特征及其补给地下水过程研究
程 立 平
Subtype博士
Thesis Advisor刘 文 兆
2013-05
Degree Grantor中国科学院研究生院
Place of Conferral北京
Keyword土壤水分 氧-18 土地利用 土壤干层 水量平衡 地下水
Abstract

在黄土塬区,地下水资源是居民生活和农业灌溉的重要水源,然而降水如何穿过
深厚黄土层补给地下水的过程在学术上不确定;赋藏在黄土中的土壤水是该区水资源
的重要组成部分,但是深层土壤水资源的研究还不够充分。本文以探明黄土塬区深剖
面土壤水分特征(包括垂直分布及干燥化、时间动态、土壤水资源数量及水量平衡等)
及其补给地下水过程为目的,以长期定位监测和野外调查测定相结合测定不同土地利
用方式下深剖面土壤水分含量,以同位素示踪技术为手段研究黄土塬区降水—土壤水
—地下水之间的转换关系,主要研究结果如下:
1 土壤水分垂直分布规律
长武塬区 0~20 m 黄土剖面土质大多数为中壤,部分土层为重壤,剖面田间持水
量和萎蔫湿度分别为(21.39±0.13)%和(8.06±0.45)%。古土壤层物理粘粒含量较黄
土层高约 2%~6%,黏土化较强,同时古土壤层孔洞、孔隙发育较差。因此,与黄土
层相比,古土壤层具有较强的持水能力。
黄土深剖面水分垂直分布特征与黄土-古土壤序列有关,通常情况下黄土层内土
壤湿度向下递增,至古土壤层出现最大值,古土壤层内湿度向下递减,至下一层黄土
层出现最低值。这样一层黄土和一层古土壤构成一次湿度起伏,并有随剖面深度增加
湿度变大的趋势。
2 土壤水资源及干燥化
长期定位监测表明,土地利用方式能显著影响深层土壤含水量,且影响深度可达
10 m 深度以下。2009 年 10 月荒草地、18 年苹果园地、8 年和 23 年苜蓿草地 0~20 m
土层平均湿度分别为 18.89%、15.45%、14.77%和 10.59%,休闲地、高产农田、低产
农田和 4 年苜蓿草地 0~15 m土层平均湿度分别为 21.59%、18.67%、19.65%和 16.52%。
不同土地利用方式下,黄土深剖面土壤水资源量、土壤水分有效性不同,大小依次为
休闲地>低产农田>荒草地>高产农田>4 年苜蓿草地>18 年苹果林地>8 年苜蓿草地>23
年苜蓿草地。黄土塬区土壤干层可划分为两类:一类为发生在一年生作物地的暂时性干层,一
类为发生在多年生人工林草地的持久性干层。暂时性土壤干层土壤水分在丰水年可恢
复;持久性土壤干层的发展是一个由浅及深、由轻度到重度的渐进化过程,其土壤水
分只有在林草被移除后才能恢复。
3 土壤水分动态特征
研究区降水入渗深度与雨季降水量有显著的线性关系:D = a · P – b,不同土地
利用方式之间,系数 a、b 不同。一般情况下,不同土地利用方式之间降水入渗深度
大小依次为休闲地>低产农田> 苹果林地>高产农田>苜蓿草地。
土壤剖面上,浅层土壤含水量随时间变化剧烈,随深度增加,土壤水分随时间变
化逐渐减小。休闲地在 4 m 以上、低产农田在 5 m 以上、高产农田在 4 m 以上、苹果
林地在 4 m 以上、苜蓿草地在 2 m 以上土层含水量具有明显的时间变化,属土壤水分
可变层;但在这些深度以下土层土壤含水量动态变化较小,属土壤水分相对稳定层。
研究区土壤储水量季节变化分为 3 个阶段:土壤水分消耗期(3~7 月),土壤水
分恢复期(7~10 月)和土壤水分相对稳定期(10~翌年 3 月)。
与实验初期相比,休闲地 0~15 m 土层和低产农地下 0~8 m 土层土壤储水量均显
著增加,高产农地下土壤储水量无显著变化,苜蓿草地下土壤储水量显著减少。表明
四种土地利用方式下,只有休闲地和低产农地条件下深层土壤水分能够得到降水的补
给,而高产农地和苜蓿草地深层土壤水分将不能得到降水的补给。
4 土壤水量平衡中土体深度选择
土壤水量平衡计算中土层深度的确定非常重要,这不仅与土地利用方式相关,也
与林草植被的生长阶段相联。对于农田,土层深度选择不宜小于 4 m;对于苜蓿草地
和苹果林地,在其生长旺盛期土层深度选择不宜小于 15 m;因深层取样困难,一般
可取至 10 m 计算。苹果林地(1993 年栽植)取 10 m 深度时 ET 计算结果分别为取
15 m 计算结果的 94.9%(2010 年)和 99.0%(2011 年),苜蓿草地(2006 年种植)
取10 m深度时ET计算结果分别为取15 m计算结果的93.2%(2010年)和95.2%(2011
年)。对于休闲地,土层深度也应选取降水入渗深度。长武塬区降水入渗深度可由其
与雨季降水量关系式估算得出。
5 长武塬区大气降水、土壤水、地下水同位素组成特征
大气降水 δD 和 δ 18 O 的范围分别为−142.01 ‰ ~ −1.98 ‰和−19.62 ‰ ~ −1.17 ‰,
其平均值分别为−55.45 ‰和−8.09 ‰。大气降水线方程为 δD=7.39δ 18 O+4.34(R 2 =0.94,
n=71),研究区降水稳定同位素组成具有冬春高、夏秋低的季节变化特征,降水量较大或持续时间较长的降水事件的雨量效应显著,降水同位素值明显偏负。
土壤水中 δD 值变化范围为−126.47 ‰~−46.66 ‰,平均值为−75.13 ‰;δ 18 O 值变
化范围为−16.63 ‰~−4.30 ‰,平均值为−9.56 ‰。土壤水氢氧同位素值落于大气降水
线右下侧,表明降水在补给土壤水过程中,经历了强烈的非平衡蒸发过程,分馏明显。
土壤水同位素组成在浅层土层随时间变化剧烈,随深度增加,土壤水同位素组成
随时间变化逐渐减小,甚至无变化。
井水 δD 和 δ 18 O 的范围分别为−72.31 ‰ ~ −69.08 ‰和−10.53 ‰ ~ −10.08 ‰,其
平均值分别为−71.31 ‰和−10.31‰;泉水 δD 和 δ 18 O 的范围分别为−72.36 ‰ ~ −68.41
‰和−10.51 ‰ ~ −9.98 ‰,其平均值分别为−70.68 ‰和−10.24 ‰。井水和泉水氢氧同
位素组成变化范围较降水和土壤水明显都小,且无明显季节变化。
6 地下水补给
通过研究降水、土壤水、地下水氢氧同位素组成变化特征,土壤水同位素组成剖
面发现,降水入渗土壤过程中,具有自上而下活塞式下渗的特征,同时部分雨水可能
通过一些“快速通道”以优先流的方式快速到达深层土壤。地下水补给过程中,存在
着活塞流与优先流两种形式,其中优先流形式在补给过程中占据主导地位;地下水补
给具有季节性特点,7~10 月份地下水补给量大于年内其它时段。但是优先流在空间
上并不普遍发生,与土地利用方式下土壤剖面水分状况有关。在苹果林地、苜蓿草地
等土地利用方式下,土壤干层将减小优先流发生的可能性;而在荒草地、农田等土地
利用方式下土壤剖面水分含量较高,则容易发生优先流,从而对地下水形成补给。
本文研究结果表明,在黄土塬区大面积的农田转换为果园将减小地下水的补给
量,对区域水文循环产生深刻影响。
关键词:土壤水分;氧-18;氘;土地利用;土壤干层;水量平衡;地下水;深剖面;
黄土塬区

Other Abstract

Soil water is one of the most important water resources, deep soil water is crucial for
maintaining the function as “soil reservoir” in the Loess Plateau. Groundwater is usually
the important water resource for human livings; however, the recharge mechanism of
groundwater has not been well understood in the Loess Tableland region. Soil water stored
in thick loess soil is the link between precipitation and groundwater; therefore,
understanding the dynamics of soil water in deep loess profile is of great importance to
understand the groundwater recharge for the Loess Tableland. The main objectives of this
dissertation were: (1) to investigate the characteristics of soil water in deep loess profiles in
the Loess Tableland region, including characteristics of vertical distribution, soil water
resources, soil desiccation, soil water dynamics, and soil water balance; (2) to explore the
mechanism of groundwater recharge. In this dissertation, soil water content in deep loess
profiles under different land use patterns were measured by both field investigation and
long term observation in situ; the isotopic composition of hydrogen and oxygen in
precipitation, soil water and groundwater were analyzed. The main results are as follows:
1 Vertical distribution characteristic of soil water in deep loess profile
The soil texture in 0~20 m profile of Loess Tableland is mainly middle loam, except
some clayey profiles. The field capacity and wilting point is (21.39±0.13) % and
(8.06±0.45) %, respectively. The content of physical clay in paleosol layers is 2%~6%
higher than that in loess layers, and the porosity of paleosol layers are smaller than that of
loess layers, therefore, paleosol layers has a stronger water-holding capacity than loess
layers.
The vertical distribution characteristic of soil water in deep loess profile is related to
the loess-paleosol sequences. Generally, one paleosol layer and one loess layer constitute  an up-down humidity level and there is an increasing trend in soil water content with
increased profile depth.
2 Soil water resources and soil desiccation
Long term experiments in situ showed that land use patterns can significantly affect
soil water content in deep loess profiles, and the influence depth is deeper than the depth of
10 m. The amount of soil water resources and the soil water availability in deep loess
profile of different land use patterns were different. Generally, the sequence is fallow land
> low-yield cropland > natural grassland > high-yield cropland > 4-yr planted alfalfa
grassland > 18-yr apple orchard > 8-yr planted alfalfa grassland > 23-yr planted alfalfa
grassland.
The dried soil layer was divided into two types, one is temporary dried soil layer,
which is typically formed in soils for annual crop plants, the other is persistent dried soil
layer, which is typically formed in soils for perennial artificial vegetations. The temporary
dried soil layer usually disappears in the wet years, while the persistent dried soil layer is
more stable and persistent. It will take several decades to recover the soil water content of
the persistent dried soil layer after the perennial plants are removed.
3 Characteristics of soil water dynamics in deep loess profile
The rainfall infiltration depth is linearly related to the precipitation during the rainy
season, the relationship can be described with the equation D = a · P – b,the coefficients
(a, b) varied in different land use patterns. Generally, the sequence of rainfall infiltration
depth is fallow land > low-yield cropland > apple orchard > high-yield cropland > alfalfa
grassland.
The temporal variation of soil water content was obvious in the upper part of the soil
profile; however, it decreased gradually with the depth increasing. Therefore, the shallow
soil layer can be regarded as changeable layer in soil water content. The depths of such soil
layer differed with land use types, the layers in fallow land, high-yield cropland, low-yield
cropland, alfalfa grassland and apple orchard were 0 ~ 4, 0 ~ 4, 0 ~ 5, 0 ~ 2, and 0~4 m,
respectively. The soil layers below these depths were regarded as relatively stable layer and
had little changes in soil water content.
The seasonal variation of soil water storage can be divided in to three main periods,
i.e., decreasing period (March to July), increasing period (July to October), and relatively  stable period (October to March of next year).
The soil water storage in the 0~15 m soil layer was significantly increased in fallow
land and low-yield cropland but significantly decreased in the alfalfa grassland compared
with that in the initial experiment. No significant change in the soil water storage was
observed in the high-yield cropland. This result suggested that deep soil water and ground
water could be replenished in fallow land and low-yield cropland.
4 The selection of soil depths for soil water balance calculations
The selection of soil thickness is very important for the calculation of soil water
balance on the Loess Tableland, which is determined by both the land uses and the growth
stages of the vegetations. The calculated soil thickness should be at least the depth of
rainfall infiltration in fallow land. The calculated soil thicknesses should be at least 4 m in
cropland, and 15 m in alfalfa grassland and apple orchard during the vigorous growth stage
of planted woodland and grassland. Because of the difficulty in collecting samples in deep
soil layers, the calculated soil thicknesses should be at least 10 m under planted woodland
and grassland. The calculated evapotranspiration of 0~10 m soil layer account for 94.9%
(2010) and 99.0% (2011) of 0~15 m soil layer in apple orchard (planted in 1993),
respectively. The calculated evapotranspiration of 0~10 m soil layer account for 93.2%
(2010) and 95.2% (2011) of 0~15 m soil layer in alfalfa grassland (planted in 1993) ,
respectively. The depth of rainfall infiltration in the study region can be estimated by the
linearly relationship between the depth and rainfall during rainy season.
5 The isotope compositions of precipitation, soil water and groundwater
The δD values of precipitation range from −142.0 ‰ to −2.0 ‰, with the arithmetic
mean of −55.4‰. The δ 18 O values of precipitation range from −19.6 ‰ to −1.2 ‰, with
the arithmetic mean of −8.1‰. The equation of the Local Meteoric Water Line (LMWL)
for the tableland was δD = 7.39δ 18 O + 4.34 (R 2 =0.94,n=71). The seasonal variation of the
isotope compositions of precipitation was obvious, with high values in winter and spring
and low values in summer and autumn. The amount effect of isotopes in precipitation was
obvious, and the lighter isotopes values were observed in heavy rainfall events or after
long duration rainfall.
The δD values of soil water range from −126.5‰ to −46.7‰, with the arithmetic
mean of −75.1‰. The δ 18 O values of soil water range from−16.6‰ to −4.3‰, with the  arithmetic mean of −9.6‰. The values of stable isotopes in soil water fall in the right-side
of the LMWL, implying that soil water originates from precipitation, and evaporation
occurs during the rainfall infiltration. The isotope composition in soil water changes
greatly with time in shallow soil layers, with the increase of soil depth, the temporal
change in the isotope contents was decreased.
The δD values of well water range from −72.3‰ to −69.1‰, with the arithmetic
mean of −71.3‰. The δ 18 O values of well water range from−10.5‰ to −10.1‰, with the
arithmetic mean of −10.3‰. The δD values of spring water range from −72.4‰ to −68.4‰,
with the arithmetic mean of −70.7‰. The δ 18 O values of spring water range from−10.5 ‰
to −10.0 ‰, with the arithmetic mean of −10.2‰. The seasonal variation of the isotope
compositions in groundwater was not obvious, and the variation of isotopic compositions
in groundwater is much smaller than those of precipitation and soil water.
6 Recharge of groundwater
Through comparing the variations of isotopic composition in precipitation, soil water
and groundwater, it can be found that the piston-type flow occurred in soil layer in the
process of rainfall infiltration. Meanwhile, part of the rainwater can move to deeper soil
layers quickly by the preferential type flow. There was a seasonal groundwater recharge,
and the recharge rates during July to October should be greater than other time of the year
on the Loess tableland. The groundwater was likely recharged by piston flow and
preferential flow through the unsaturated zone, and the recharge was dominated by the
preferential flow. However, the occurrence of preferential flow is not a common
phenomenon spatially, and it has a certain relationship with land use patterns. Generally,
soil desiccation caused by negative water balance can reduce the probability of preferential
flow occurrence in apple orchard and alfalfa grassland, whereas preferential flow easily
occurs in farmland or nature grassland.
The result indicates that the conversion from a large area of farmland to apple orchard
can affect the natural mode of water cycle and reduce the recharge of groundwater on the
Loess Tableland.
Key words: soil water; oxygen-18; deuterium; land use; dried soil layer; water balance;
groundwater; deep loess profile; Loess Tableland

Language中文
Document Type学位论文
Identifierhttp://ir.iswc.ac.cn/handle/361005/8982
Collection水保所知识产出(1956---)
Recommended Citation
GB/T 7714
程 立 平. 黄土塬区深剖面土壤水分特征及其补给地下水过程研究[D]. 北京. 中国科学院研究生院,2013.
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