Occurrence of soluble salts and moisture in the unsaturated zone and groundwater hydrochemistry along the middle and lower reaches of the Heihe River in northwest China

Deforestation, over-development of water resources and population growth have contributed to degeneration of vegetation in the Heihe River Basin in northwest China. Salts and water contents are the most important factors affecting the growth of vegetation in this arid area. This study was conducted to determine soluble salt levels of soils in the unsaturated zone and the hydrochemistry of groundwater at 14 sites in this region. Concentrations of soluble ions in the soils deceased with depth. Soil ion contents increased at depths below the root system of native plants. Sulfate was the dominant anion in both the unsaturated zone and the groundwater. Total dissolved solids (TDS) in groundwater ranged from less than 1 g/L in the middle reaches of the watershed to about 10 g/L in the arid lower reaches. In the middle and upper reaches of the watershed, salinity in soil and groundwater decreased. Groundwater was highly variable in hydrochemistry. The lower reaches was predominated by SO₄–Na•Mg and SO₄–Mg•Na type water, whereas in the middle reaches groundwater is characterized by lower TDS and HCO₃-dominated type water. Evapotranspiration is responsible for occurrence of the soluble salts in the soil profiles. Dissolution is the dominant chemical process in the middle reaches, whereas evapotranspiration prevails in the lower reaches of the Heihe River.     

西北地区额济纳绿洲非饱和带水分和盐分分布

在西北地区黑河流域下游的额济纳绿洲选择3个土壤剖面采集不同深度土壤样品和潜水样品进行测试,并在野外观测非饱和带不同深度的水土势变化。结果表明,SO4^2-是非饱和带土壤和地下水中的主要离子成分,土壤和地下水呈偏碱性。土壤易溶离子含量随深度大体上呈减少趋势。绿洲非饱和带发育有收敛型和发散型零通量面,自夏季至冬季,零通量面变得不清晰直至消失。在非饱和带中,土壤易溶盐含量、含水量和总水土势随深度的变化趋势基本相同,植物根系的吸收对水分和盐分的垂直分布有着重要的影响。     

Movement of water through the thick unsaturated zone underlying Oro Grande and Sheep Creek Washes in the western Mojave Desert,USA

Previous studies indicate that a small quantity of recharge occurs from infiltration of streamflow in intermittent streams in the upper Mojave River basin, in the western Mojave Desert, near Victorville, California. Chloride, tritium, and stable isotope data collected in the unsaturated zone between 1994 and 1998 from boreholes drilled in Oro Grande and Sheep Creek Washes indicate that infiltration of streamflow occurs to depths below the root zone, and presumably to the water table, along much of Oro Grande Wash and near the mountain front along Sheep Creek Wash. Differences in infiltration at sites along each wash are the result of hydrologic variables such as proximity to the mountain front, quantity of streamflow, and texture of the subsurface deposits. Differences in infiltration between the washes are the result of large-scale geomorphic processes. For example, Oro Grande wash is incised into the Victorville fan and infiltration has occurred at approximately the same location over recent geologic time. In contrast, Sheep Creek Wash overlies an active alluvial fan and the stream channel can move across the fan surface through time. Infiltration does not occur to depths below the root zone at control sites outside of the washes. Electronic Publication     

基于流动电位正演模型的非饱和带水流过程监测

为了获取非饱和带水流过程的信息,借助流动电位正演模型,通过数值实验探讨非降雨和降雨两种条件下非饱和带流动电位和水流过程的关系,然后用南京中山植物园试验场地野外观测的流动电位和张力数据加以对比和验证。野外试验表明:流动电位可以有效地反映非饱和带水流过程。在夏季无降雨入渗的条件下,日周期变化的地表地下温度差导致水分的运动,流动电位准确地指示了非饱和带含水量和毛细压力的变化情况,从而指示出了水分运移的方向;在夏季有降雨入渗的条件下,降雨锋面推进之处,含水量和流动电位同时有明显的响应,进而根据不同位置的流动电位对降雨入渗响应的时刻差,直接求出入渗锋面的推进速度。     

The combined effect of clay and moisture content on the behavior of remolded unsaturated soils

The behavior of unsaturated clayey soil is highly influenced by the coupled interaction between water and clay content. Various aspects of the behavior of artificial clay–sand mixtures with variable water content were experimentally studied. Laboratory tests were utilized for the determination of consistency limits, the stress–strain relationship, strength parameters, hydraulic conductivity, and volume change characteristics for various combinations of water and clay content in soil mixtures.

Results presented for various clay–sand mixtures include: new normalized consistency limits; the combined effect of clay content and water content on the stress–strain relationship and on the strength parameters (c and φ); and the effect of clay content on hydraulic conductivity and swelling potential. The cohesion of clayey sand is found to increase with increasing water content to a certain limit, above which it decreases. The angle of internal friction for clayey sand is found generally to decrease with increasing water content. The degree of saturation is found to be better than the water content in explaining the strength behavior. The hydraulic conductivity sharply decreases with increasing clay content up to 40% beyond which the reduction becomes less significant. Simple empirical equations are proposed for predicting the swelling potential of clayey soils as a function of either the clay content or plasticity index.     

包气带中温度变化对水分分布影响的实验研究

笔者在高180cm、宽50cm的砂槽中,做了温度对水分运移影响的模拟试验。试验结果表明,在包气带一定深度以下,孔隙相对封闭,孔隙内液态水与气态水处于动态平衡,相对湿度接近或达到饱和状态。在此条件下,砂柱内温度场的任何微小变化都会导致孔隙系统内的水分发生蒸发或凝结。当包气带内温度场发生变化时,气态水在温度梯度作用下,向最低温度界面运移,蒸发或是凝结取决于最低温度界面的性质。在不发生聚集的开放性界面上出现蒸散,消耗包气带内水分。在聚集性封闭界面上则出现凝结,使包气带内水分增加。在温度场控制下,包气带中气态水凝结或蒸发是水分运移的另一重要形式,它在一定程度上决定着水分的分布状态,尤其在温差巨大的地区,这种作用显得十分重要。     

Trends of water resource development and utilization in arid north-west China

 From an analysis of the current water resources and their development and utilization in arid north-west China, the authors conclude the extent of channelled water accounts for only 56.0% of the total, exploitable surface-water resources of arid north-west China. The utilization ratio of canal systems is 42%, and farmland use is 0.8. When the ground and surface waters of river basins in the region are comprehensively developed, the channelled water will reach its climax, accounting for 80% of the total, exploitable surface-water resources, which would constitute a 91% increase over current levels in surface-water resource development. In the future, the utilization ratio of canal system as well as the utilization ratio of farmland water will reach 0.9 with the help of scientific and technological advancements. The channelled water is the same as the comprehensive development and utilization stages, but the total water use will be increased by 247×10⁸ m³, and will reach 756.8×10⁸ m³, accounting for 88.2% of the total, exploitable surface-water resources in arid north-west China. Also, the authors suggest that the scientific and technological measures to increase the water-use ratio include improving management, strengthening protection of water resources and the environment, and increasing studies of water saving techniques. Received: 11 January 1999 · Accepted: 6 July 1999     

Re-evaluating the impacts of human activity and environmental change on desertification in the Minqin Oasis, China

The Minqin Oasis and its adjacent regions in northern China experienced significant desertification beginning 2,000 years ago and continuing to the present, and numerous studies have claimed that human activities, especially the flourishing of agriculture, have played a major role in environmental change in this region. Our analysis suggests that the observed desertification was mainly controlled by changes in the water component of the ecosystem and the arid climate. The impacts of cultivation on desertification from 2,000 years ago to the mid-1900s appear to have been relatively minor compared to the impacts of the area’s arid climate and its native geomorphological processes. Although human activity has increased from the late-1940s to the present, and the areas of the oasis reclaimed for agriculture have reached a maximum, desertification over the past 50 years appears to be a continuing process that began thousands of years ago, and is mainly controlled by decreasing water levels caused by the arid climate, local geomorphological processes and overuse of water in the upstream. Although both human activities and climate variation are important drivers of the desertification process, and it is not possible to completely separate the human influence from the climate impact, key factors on controlling desertification should be investigated before we place the blame solely on the flourishing of agriculture in this region.     

The characteristics of water resources and the changes of the hydrological process and environment in the arid zone of northwest China

 Water resources in the arid zones of northwest China mainly come from mountain areas and then flow to and disappear in the piedmont plains. These water resources, with inland river basins as the geographic unit, form relatively independent ecosystems and the surface runoff flowing out of the mountain mouth becomes the only water source available for the middle and lower reaches of these basins. Both the ecosystem stability and sustainable development depend on the surface water and groundwater resources of these inland river basins. Over the last 50 years, exploitation of water and land resources in the arid northwest regions of China has been expanding, forming 390.07×10⁴ ha of irrigation oases, with construction of 622 reservoirs of different sizes with a total storage capacity of 65.5×10⁸ m³ ensuring the sustainable development of industrial and agricultural production. In the meantime it has also caused a series of environmental changes. Discharge of the majority of rivers has been drastically reduced (even dried up), river courses have been shortened, and terminal lakes contracted or dried up. Land desertification and soil salinization has developed rapidly. Vegetation is degrading and biodiversity is decreasing, as compared with the early 1950s; the natural grassland area is decreasing by 16–75.4%. Economical and high-effective use of water resources and harmonization of eco-environment benefits with economic benefits are the fundamental ways to achieve sustainable development of arid northwest China. Received: 20 January 1999 · Accepted: 4 May 1999     

The impact of the development of water resources on environment in arid inland river basins of Hexi region, Northwestern China

Water resources use is a key parameter in the hydrological cycle, especially in arid inland of Northwest China, groundwater movement and circulation processes are closely related to the surface water, while recoverable and renewable groundwater mainly comes from the conversion of surface river water, and there is extensive transfer among rainfall, surface water and groundwater. Human activity, in particular, large-scale water resources exploitation and development associated with dramatic population growth in the last decades, has led to tremendous changes in the water regime. There are misuse and wastage of surface water with traditional multi-channel irrigation for most rivers, which in turn leads to over-exploitation of groundwater to augment supplies. This situation has been exacerbated by rapid population growth and socio-economic development, with decreased irrigational systems return to groundwater due to the irrigation system in the middle reaches of rivers in the Hexi region becoming better. The investigations of this study revealed that over the last decades, man-made oases have developed rapidly in various inland river basins. With the increasing human demand for water, the contradiction between water demand and water supply is becoming increasingly acute and the amount of groundwater usage significantly increased. Notwithstanding the annual surface water from mountains is relatively stable in the Hexi region, the recharges of groundwater have been reduced by 11.1%, with a maximum reduction of 50% in the Shiyang River basin. Groundwater abstraction increased by approximately six times, particularly in the Shiyang River basin, groundwater abstraction exceeds recharge by 4.1×10⁸ m³ year⁻¹ in recent decades. Consequently, the groundwater level has declined widely by 3–16 m, with a maximum decline of 45 m in several groundwater observation wells in the Minqin basin on the lower reaches of the Shiyang River basin. These cause serious human activity-induced environmental problems, such as water-quality deterioration, vegetation degradation, soil salinization and land desert desertification, etc. It is suggested that modernized irrigation technology and new regulation to cover water resources management and allocation with the river basins are urgently needed to achieve a sustainable development. The aim of this study is to analyze the impact of the development of water resources on the environment in arid inland river basins in Northwestern China, which were analyzed by comparing the three main river basins (i.e., the Shuilei, the Heihe and the Shiyang River basins) with different water resources development cases.     

冻融和非冻融条件下包气带土壤墒情垂向变化的试验与分析

冻结层的存在使得寒区有着与非寒区差别明显的水文循环过程,土壤冻融规律、水热盐运移、融雪水入渗等已成为众多学者的研究对象. 寒区低温条件下冻融土壤持水性质与非冻融土壤不同,其包气带冻结层往往具有弱透水性、蓄水保墒和隔热减渗的作用,使得寒区春季冻结层土壤的墒情较高. 以冻融土壤和非冻融土壤墒情对比监测为基础,选取地表以下100 cm的土壤为研究对象,在黑龙江大学呼兰校区设置冻融和非冻融对比监测试验场,同时段、同频率、同埋深（间隔 20 cm土层）进行土壤结构、水热及环境参数监测. 通过对比分析了不同埋深不同冻融阶段的墒情参数,量化了低温冻融条件下土壤墒情较非冻融土壤的高出部分,最后对冻土保墒的机理进行探讨与分析. 结果表明：冻结条件下土壤水分重新分布,在土水势的作用下由非冻结区向冻结区迁移. 初冻期地表土壤墒情达到最大,冻结期土壤最大墒情值随冻结锋面迁移分别在20、40、60 cm处达到最大,稳定冻结期和融化初期在80 cm处达到最大;土壤最大墒情值一般在冻结锋面前沿的10～20 cm处,较好地保持了土壤水分. 无论是从空间（不同埋深）还是时间（不同冻融阶段）角度分析,冻融土壤含水率均大于非冻融土壤,二者含水率的差值随埋深和冻融阶段的推移而加大,在稳定冻结期80 cm处达到最大,差值量可达6.4%～7.8%.     

Soil water movement and deep drainage through thick vadose zones on the northern slope of the Tianshan Mountain: Croplands vs. natural lands

Regional aridity is increasing under global climate change, and therefore the sustainable use of water resources has drawn attention from scientists and the public. Land-use changes can have a significant impact on groundwater recharge in arid regions, and quantitative assessment of the impact is key to sustainable groundwater resources management. In this study, the changes of groundwater recharge after the conversion of natural lands to croplands were investigated and compared in inland and arid region, i.e., the northern slope of the Tianshan Mountain. Stable isotopes suggest that soil water in topsoil (< 2 m) has experienced stronger evaporation under natural lands than croplands, and then moves downward as a piston flow. Recharge was estimated by the tracer-based mass balance method, i.e., chloride and sulfate. Recharge rates under natural conditions estimated by the chloride mass balance (CMB) method were estimated to be 0.07 mm/a in deserts and 0.4 mm/a in oases. In contrast, the estimated groundwater recharge ranged from 61.2 mm/a to 44.8 mm/a in croplands, indicating that groundwater recharge would increase significantly after land changes from natural lands to irrigated croplands in arid regions. Recharge estimated by the sulfate mass balance method is consistent with that from the CMB method, indicating that sulfate is also a good tracer capable of estimating groundwater recharge.     

1960-2013年艾比湖绿洲湿地潜在蒸散量及地表湿润度变化特征分析

基于阿拉山口、精河、博乐、温泉4个气象站点1960-2013年地面观测气象数据,采用Penman-Monteith公式、Mann-Kendall检验、小波分析、主成分相关分析等方法分析艾比湖绿洲湿地年及季节潜在蒸散量及地表湿润度的特征变化及定量化成因,以期为艾比湖绿洲湿地区域的水资源科学配置提供科学依据。结果表明：（1）1960-2013年,艾比湖绿洲湿地年平均潜在蒸散量为1 063.52mm,夏季值最大为552.3 mm,冬季最小为25.3 mm,年平均潜在蒸散量以12.68 mm·（10a）^-1的速率递减,各季节潜在蒸散变化趋势与年变化一致,夏季表现最明显;（2）Mann-Kendall检验表明,年均和春、夏、秋潜在蒸散量显著性突变时间分别是1991年、1994年、1994年和1993年,冬季不存在突变,显著性突变均发生在21世纪90年代,地表湿润度年突变时间为1985年;（3）艾比湖绿洲湿地潜在蒸散量及地表湿润度存在明显的周期变化,主震荡周期分别为29 a和21 a,以多、少交替发生,具有全域性;（4）风速是年及季节潜在蒸散量的主导因素,地表湿润度变化的主导因素是降水量和相对湿度。     

Responses of phreatophyte transpiration to falling water table in hyper-arid and arid regions,Northwest China

Quantitative assessment of the impact of groundwater depletion on phreatophytes in (hyper-) arid regions is key to sustainable groundwater management. However, a parsimonious model for predicting the response of phreatophytes to a decrease of the water table is lacking. A variable saturated flow model, HYDRUS-1D, was used to numerically assess the influences of depth to the water table (DWT) and mean annual precipitation (MAP) on transpiration of groundwater-dependent vegetation in (hyper-) arid regions of northwest China. An exponential relationship is found for the normalized transpiration (a ratio of transpiration at a certain DWT to transpiration at 1 m depth, T_a*) with increasing DWT, while a positive linear relationship is identified between T_a* and annual precipitation. Sensitivity analysis shows that the model is insensitive to parameters, such as saturated soil hydraulic conductivity and water stress parameters, indicated by an insignificant variation (less than 20% in most cases) under ± 50% changes of these parameters. Based on these two relationships, a universal model has been developed to predict the response of phreatophyte transpiration to groundwater drawdown for (hyper-) arid regions using MAP only. The estimated T_a* from the model is reasonable by comparing with published measured values.© 2021 China Geology Editorial Office.     

基于土壤水势变化的灌溉节水机理与调控阈值

大量试验结果表明,在农田灌溉过程中,土壤含水率及水势变化具有入渗排气、渗吸增能、吸脱水减能和缓慢脱水减能的阶段性特征。当土壤处于水分亏缺状态急需补充水分(土壤吸水)时,土壤水势梯度大于1.0 cmH2O/cm;当土壤水分得到充分补给达到过水(土壤含水率不变,且水通量不为零)状态时,土壤水势梯度等于1.0 cmH2O/cm;当土壤中水分过剩而处于脱水(流出大于流入水量)状态时,土壤水势梯度小于1 cmH2O/cm。由此,根据上述特征指导农田灌溉调控节水,其中土壤层下部(深度15~60 cm)的水势梯度等于或小于1.0 cmH2O/cm可作为监测及预警节水灌溉的阈值。     

中亚热带典型植物群落下表土植硅体组合及其保存特征

现生植被与植被代用指标的对应关系是准确复原历史时期植被面貌的基础,本研究系统分析了中亚热带地区隶属于森林（常绿阔叶林、常绿/落叶阔叶混交林和落叶阔叶林）、灌丛和草本群落的39个样点的植物群落及其对应表土植硅体的组合特征和保存特性,共鉴定出32种植硅体类型。结果表明,森林、灌丛、草本群落及其相应表土间的植硅体组合特征均具有明显差异。其中,森林群落以短细胞植硅体、扁平状和硅化气孔为主,灌丛群落中短细胞植硅体、扁平状和棒型较多,而草本群落则以短细胞植硅体、棒型和尖型为主。同时,不同植物群落下表土植硅体组合表现出与其地上植物群落相似的特征,且依据表土植硅体组合可以在一定程度上定量区分不同植物群落。此外,基于保存指数（R值）,发现不同植物群落下表土植硅体的保存明显不同,其中,森林群落保存最好、灌丛群落其次、草本群落最差;且森林群落中常绿阔叶林中植硅体的保存好于落叶阔叶林、常绿/落叶阔叶混交林与落叶阔叶林相近。表土中不同类型植硅体的保存也具有明显差别,扇型、块状和尖型在土壤中保存较好,短细胞植硅体、棒型和扁平状保存适中,硅化气孔、表皮植硅体和毛发状保存较差。因此,本研究不仅有助于理解表土中植硅体的埋藏机制,也可为中亚热带地区基于植硅体的古植被重建精度的提高提供重要依据。

     

西北旱区潜在蒸散发的气候敏感性及其干旱特征研究

潜在蒸散量（PET）是干旱监测评价的重要指标,分析影响潜在蒸散发的气候敏感因子对揭示气候变化的水文响应机理尤为重要。常采用的局部敏感性方法不适用于非线性模型且难以评估各气象因子间的相互作用。对此,基于1964—2018年西北旱区内163个气象站的监测数据,通过Penman-Monteith公式,采用Sobol全局敏感性方法分析了西北旱区潜在蒸散发的气候敏感因子,计算得到了自校准帕默尔干旱指数（scPDSI）,进而分析了区域干旱的时空演变特征。结果表明：1964—2018年西北旱区年均潜在蒸散量为1157.8 mm,高值出现在新疆东部与内蒙古西部地区,低值出现在青海南部地区。1993年为转折点,西北旱区潜在蒸散发受气温、日照时数、风速、相对湿度等多种因素综合影响由显著下降的趋势转变为显著上升,且在夏季最为明显。在1964—1993年,净辐射、风速与相对湿度的变化对潜在蒸散发的影响较大;在1994—2018年,风速与相对湿度的变化对潜在蒸散发的影响较大。scPDSI的时空分布表明新疆北部、青海中部以及甘肃境内的干旱有缓解的趋势;而黄河流域西南部干旱呈现加重趋势,将加剧区域水资源紧张,威胁生态安全。     

西北地区沙丘凝结水形成机制及对生态环境影响初步探讨

西北地区沙漠及荒漠化地区，包气带的水分来源除来自大气降水外，还来自凝结水，凝结水对包气带中水分的保存、运移及荒漠植被生态起到至关重要的作用。作者在甘肃省河西走廊高台县西的流动沙漠边缘的半固定沙丘上，采用TSCⅡ智能化土壤水分快速测试仪，SN2202数字温度计、CENTER1300相对湿度仪进行了凝结水观测试验。对沙丘表层0～30cm范围内的气温、地表温度、地温和含水量进行连续观测，每2h观测一次，试验历时5d。试验结果表明，在西北沙漠、荒漠化地区有凝结水存在，它的形成不仅对包气带中水分的保存及分布起着重要的作用，并且对维系荒漠化地区的植被生态系统的稳定至关重要。并对凝结水形成机制进行了初步探索；初步确定，日气候变化造成的地表温度与地温温差是凝结水形成的主控因素，包气带中的含水量分布则控制着凝结水的多寡，凝结水主要出现在干沙层与湿润砂层界面上。     

中国南方2008年与2016年两次低温雨雪冰冻天气过程对比分析

利用2.5°×2.5° NCEP/NCAR月平均资料、1°×1° FNL再分析资料、国家气候中心1951年至2016年1月西太平洋副热带高压脊线和西伸脊点两项环流指数,从事件实况（降水、气温和冰冻灾害）、环流条件、能量条件、水汽条件和动力条件几个方面出发,对2008年1月10日至2月2日和2016年1月20至25日发生在中国南方的两次低温雨雪冰冻天气过程做了对比分析。研究表明：（1）"0801南方雪灾"的主要特征表现为降水范围大、过程持续时间长、灾害重;2016年1月低温雨雪冰冻过程的主要特征表现为降水范围小、过程持续时间短、灾害轻。"0801南方雪灾"冷空气强度不如2016年1月强。（2）造成"0801南方雪灾"的亚欧大环流背景为"北脊南槽"型,2016年1月低温雨雪冰冻的亚欧环流形势中低纬同位相,从西伯利亚到伊朗为脊,中蒙由低涡控制。（3）与"0801南方雪灾"相比,2016年1月低温雨雪冰冻期间我国南方对流层中下部10°~20° N的温差较强。（4）"0801南方雪灾"水汽输送偏北（到达34° N）且更高（到达300 hPa）,2016年1月低温雨雪冰冻期间水汽输送偏南（到达28° N）且较低（到达400 hPa）。（5）"0801南方雪灾"水汽输送轨迹在5 000 m、3 000 m和1 500 m高度均以西南路径为主,2016年1月低温雨雪冰冻期间水汽输送轨迹在5 000 m、3 000 m和1 500 m高度均以西北路径为主,冷空气沿着低压底部从西北移至南方变性增湿。（6）2008年1月26至28日整层垂直运动弱,但向上扩展高（至200 hPa）;2016年1月22日至24日垂直运动强,但扩展高度低（500 hPa以下）。     

Analysis of the exchange of groundwater and river water by using Radon-222 in the middle Heihe Basin of northwestern China

In arid regions of western China, water resources come from mountain watersheds and disappear in the desert plain. The exchange of surface water and groundwater takes place two or three times in a basin. It is essential to analyze the interaction of groundwater with surface water to use water resources effectively and predict the change in the water environment. The conventional method of analysis, however, measures only the flow of a stream and cannot determine groundwater seepage accurately. As the concentration of Radon-222 (²²²Rn) in groundwater is much higher than in surface water, the use of ²²²Rn was examined as an indicator for the analysis of the interaction between surface water and groundwater. Measurement of the ²²²Rn concentration in surface water was conducted to detect groundwater seepage into a stream in the middle Heihe Basin of northwestern China. Furthermore, the simultaneous groundwater flow into and out of a stream from the aquifers was quantified by solving the ²²²Rn mass balance equation, in which the losses of gas exchange and radioactive decay of ²²²Rn are considered. Meanwhile, river runoff was gauged to determine the exchange rates between surface water and groundwater. The result shows that ²²²Rn isotope can be used as a good environmental tracer with high sensitivity for the interaction between surface water and groundwater, especially in the fractured aquifer system, karst aquifer system and discharge basins.