新疆克里雅河流域平原区地下水“三氮”的空间分布特征及影响因素

新疆克里雅河流域绿洲区地下水作为农业生产和生活饮用主要水源之一,研究地下水中"三氮"分布特征和影响因素对该地区地下水保护具有重要意义。通过数理统计方法、空间插值法等对研究区41组地下水水样检测结果进行分析。结果表明:克里雅河流域平原区地下水中NH₄⁺-N、NO₂^--N和NO₃^--N含量随着时间呈增加趋势,其中NO₂^--N达到地下水质量标准Ⅲ类水标准,2017年和2021年NH₄⁺-N都存在超标点,超标率分别为6.7%和41.7%,2021年NO₃^--N存在超标点,超标率为25.0%;空间上,地下水中"三氮"含量较高地区分布在克里雅河流域中游沿岸的绿洲带上,呈零星分布,该区域受到人类活动影响较大;研究区内地下水"三氮"含量受到自然因素和人为因素共同影响,人为因素占主导地位,氮肥的施用、人畜粪便、生活污水是地下水中氮的主要来源。     

汾河流域土地利用变化及生态环境效应

选取汾河流域为研究区，采用土地利用动态度、地学信息图谱、生态价值指数和植被覆盖度综合分析研究区2000年、2005年、2010年、2015年及2018年土地利用变化及生态环境影响效应问题。结果表明：（1）2000—2018年，流域建设用地、林地呈现增长趋势，增长面积分别为1350.90 km²、85.50 km²，增长率分别为92.83%、0.96%；耕地、草地出现小幅下降趋势，缩减面积分别为729 km²、674.10 km²，缩减率分别为-5.02%、-7.63%；水域及未利用土地维持多年平均水平，平均面积为297 km²、7.92 km²。空间格局呈现建设用地、耕地集中于流域核心区，草地、林地集中于边缘区的分异特征。（2）各时序综合土地利用动态度、土地转移图谱、土地利用涨落势变化近似，显著变化区主要位于流域盆地及其与山地过渡区，多年综合土地利用动态度为4.34%，单一土地利用动态度及土地利用涨势幅度最高的是建设用地及林地。（3）基于不同的主导土地利用...     

铵态氮和硝态氮对香蕉枯萎病发生的比较研究

 为寻找降低香蕉枯萎病发生的防治措施,通过室内盆栽接种试验,研究了铵态氮(NH₄⁺-N)和硝态氮(NO₃^--N)对香蕉枯萎病发生及其植株叶绿素含量、气体交换参数、病原菌在植物体内的数量分布和植物钙(Ca)、镁(Mg)、铁(Fe)、钼(Mo)、可溶性糖和木质素含量的效应。结果表明:不接种病原菌的条件下,不同氮素处理对香蕉幼苗生长影响无差异;接菌情况下,与NH₄⁺-N处理相比,NO₃^--N处理显著降低植株各器官的病原菌数量、发病率和发病严重程度。病原菌侵染后,不同氮素处理下植株光合作用均显著下降:NO₃^--N处理香蕉苗保持比NH₄⁺-N处理更高的光合速率;病原菌侵染后NH₄⁺-N处理的植株Ca、Mg、Fe和Mo含量相对于侵染前没有显著差异,但NO₃^--N处理下此4种元素含量均显著升高。病原菌侵染后的植株叶片可溶性糖含量在不同氮素处理中都没有显著变化,但在根系中,NO₃^--N处理的侵染植株可溶性糖含量显著降低。与此同时,病原菌侵染后,木质素含量在NH₄⁺-N处理植株中变化不显著,但其含量在NO₃^--N处理侵染后显著上升。综上所述,NO₃^--N处理可增加植株抗病相关矿质元素的吸收,诱导香蕉苗木质素形成,使其木质化程度增加,从而维持较高的光合作用,保持较高的抗病水平。     

伊犁河谷西北部地下水化学特征及成因分析

为探究新疆伊犁河谷西北部地下水化学特征及成因,运用数理统计以及Piper三线图、Gibbs图、离子比图等方法,对2018年伊犁河谷西北部地下水取样监测数据进行分析。结果表明:(1)研究区地下水属于总硬度偏高的弱碱性水,地下水化学组分含量整体变异性不大,主要阳离子为Ca²⁺,主要阴离子为HCO₃^-。(2)地下水水化学类型以HCO₃-Ca、HCO₃·SO₄-Ca、HCO₃·SO₄-Ca·Mg、HCO₃·SO₄-Ca·Na和HCO₃^-Ca·Mg型为主。(3)研究区地下水化学组分主要受岩石溶滤作用控制,蒸发-浓缩作用及阳离子交换作用对地下水化学组分有一定的贡献,个别地下水水样点可能受到人为活动的影响。(4)地下水中的Na⁺、Cl^-和SO₄^2-主要来自岩盐、石膏等蒸发岩的溶解,Ca²⁺和Mg²⁺主要来自方解石、白云石和石膏等矿物溶解。     

乌鲁木齐大气总悬浮颗粒物（TSP）离子化学组分及影响因素

利用2009年乌鲁木齐4个大气总悬浮颗粒物（TSP）观测站点资料,采用离子色谱仪分析了TSP中水溶性离子成分。结果表明：① 2009年乌鲁木齐市区3站总离子浓度为151.28 μg/m³,白杨沟为40.83 μg/m³。4站NO₃^-/SO4^2-比值较小,表明乌鲁木齐大气污染主要来自于固定污染源。② 2009年乌鲁木齐4站TSP中SO₄^2-、Ca²⁺、NO₃^-和NH₄⁺的浓度高于其他各离子,各站离子浓度有明显的季节变化特征,采暖期各离子浓度明显增加,SO₄^2-、NO₃^-增幅最大。③ 对各主要离子进行相关性分析,得到NH₄⁺与SO₄^2-的相关系数为0.828,与NO₃^-的相关系数为0.659,说明铵盐化合物主要以硫酸铵和硝酸铵的形式存在;SO₄^2-与NO₃^-的相关性很大,相关系数为0.973,表明二者主要来自二氧化硫和氮氧化物,排放方式与在大气中的传输途径较一致;地壳元素Ca²⁺和Mg²⁺有很好的相关性,相关系数是0.914,表明二者来源相似,可能主要来自风沙土壤尘、道路尘和建筑尘。     

新疆昌吉州东部平原区地下水水文地球化学演化分析

为探究新疆昌吉州东部平原区地下水水质演化过程，采用数理统计、Piper三线图、Gibbs图和离子比法对昌吉州东部平原区2016年63组地下水水质取样点及54组2012—2015年地下水水质监测数据进行分析。结果表明：昌吉州东部平原区2012年地下水阳离子平均含量总体为Ca²⁺>K⁺+Na⁺>Mg²⁺，阴离子平均含量总体为HCO^3->SO₄^2->Cl^-；从2013年开始，SO₄^2-逐渐增大，Ca²⁺逐渐减小；到2016年阳离子平均含量总体为Ca²⁺>K⁺+Na⁺>Mg²⁺，阴离子平均含量总体为HCO₃^->SO₄^2->Cl^-。水化学类型由2012年HCO₃—Ca·Mg（Ca·Na、Ca·Na·Mg）型向2016年HCO₃·SO₄—Ca·Na·Mg（Ca·Mg、Ca·Na）演化，这主要与含水介质的风化作用和蒸发浓缩作用有关，而蒸发浓缩作用更加体现在承压水区的上部潜水中。地下水中Na⁺、K⁺、Cl^-主要来自岩盐的溶解；Ca²⁺、Mg²⁺主要来自蒸发岩溶解；SO₄^2-主要来自石膏（CaSO₄·2H₂O）和芒硝（Na₂SO₄·10H₂O）的溶解。Cl^-、SO₄^2-除来自岩盐的溶解外，还受到人类活动的影响。     

西藏易贡湖流域地表水水化学特征及其控制因素

为探究易贡湖流域地表水水化学特征及其控制因素,以藏东南易贡湖流域为研究对象,采集了26组地表水样,绘制了水样点主要离子线性变化趋势图、Gibbs图及Piper三线图等,运用相关分析、线性趋势分析、数理统计和离子比等方法。分析了研究区地表水主要离子特征及其控制因素,揭示了研究区地表水水中的主要物质来源。结果显示：易贡湖流域地表水阳离子主要为Ca²⁺、Mg²⁺,K⁺和Na⁺含量较低,4种阳离子的含量关系为：Ca²⁺>Mg²⁺>Na⁺>K⁺,阴离子主要为HCO₃^-、SO₄^2-和Cl^-,NO₃^-和F^-含量较低,阴离子含量关系为：HCO₃^->SO₄^2-...     

博尔塔拉河上游河谷地区水化学特征及水质评价

为了解博尔塔拉河上游河谷地区地下水和地表水水化学特征及水质状况,以36组水样数据为基础,运用Piper图、相关性分析、Gibbs图和离子比值等方法研究水化学特征及其影响因素,采用熵权-贝叶斯水质评价模型、Wilcox图和USSL图等方法进行水质评价。水化学分析结果显示：（1）研究区机井水、泉水和河水均为弱碱性淡水,总硬度（TH）、溶解性总固体（TDS）、F^-和NO₃^-整体表现为：机井水>泉水>河水,HCO₃^-和Ca²⁺分别为优势阴、阳离子,博尔塔拉河上游水中各组分含量沿程呈增加趋势;（2）区内机井水和泉水水化学类型以HCO₃-Ca型为主,河水水化学类型主要为HCO₃-Ca型和HCO₃·SO₄-Ca·Na型,水化学特征主要受控于岩石风化作用,水化学组分主要来源碳酸盐岩风化,且存在蒸发盐岩溶解,同时也受阳离子交换作用和人类活动的影响。饮用水水质评价显示,82.6...     

淮河流域高碘地下水环境健康风险评估

淮河流域是我国高碘地下水的主要分布区之一，高碘已成为继高砷、高氟后淮河流域又一饮水安全问题。文中应用指示克里格法对在淮河流域采集的地下水样品4997组开展健康风险评估，研究高碘地下水的空间分布，给出碘含量超过阈值的概率风险图。结果显示：碘是影响流域地下水质量的主要原生劣质指标，表现出明显的空间变异性，高碘地下水在淮河流域呈3个明显的风险区域分带，浅层(≤50m)地下水高碘风险区(F>0.9)面积22780.60km²,面积占比12.18%;深层(>50m)地下水高碘风险区(F>0.9)面积13686.88km²,面积占比7.32%。淮河流域高碘地下水系原生成因，影响与控制地下水中碘形态的重要因素是氧化还原环境、天然有机质含量，此外人类活动农业灌溉也促进了碘的迁移。应用指示克里格法从健康风险评估角度划分淮河流域高碘地下水风险区，对有效预防与控制地下水高碘问题，实行加碘盐分区供给以防碘摄入过量，保障安全饮水提供了科学的参考依据。     

灌溉水矿化度对棉田土壤呼吸速率的影响

为探究不同灌溉水矿化度对棉田土壤呼吸速率的影响,设置了4个灌溉水矿化度,分别为0.85 g·L^-1(CK,当地灌溉水矿化度)、3 g·L^-1(S1)、5 g·L^-1(S2)和8 g·L^-1(S3),在新疆进行了膜下滴灌棉花大田试验。在棉花生育期,每月采集两次土壤呼吸速率值(R_s),并同时监测土壤温度(ST)、含水率(SWC)、电导率(EC)、硝态氮含量(NO₃^--N)、铵态氮含量(NH₄⁺-N),运用通径分析研究了灌溉水矿化度下土壤参数对土壤呼吸速率的影响。结果表明：微咸水灌溉(S1和S2)在一定程度上提高了土壤含水率、电导率和铵态氮含量;咸水灌溉(S3)显著增加了土壤水分和盐分,并降低了土壤硝态氮含量;灌溉水矿化度的增加会减弱土壤呼吸速率。土壤的水分和温度与呼吸速率的相关性,随灌溉水矿化度的增加而呈减弱趋势。通过运用二次函数式来表示0～10 cm的土层温度对土壤呼吸速率的响应(R^...     

Source identification of nitrate in the upper aquifer system of the Wadi Shueib catchment area in Jordan based on stable isotope composition

Groundwater forms the main freshwater supply in arid and semi-arid areas,and contamination of this precious resource is complicated by the slow rate of recharge in these areas.Nitrate contamination of groundwater is a global water quality problem,as it entails threat to human health as well as aquatic ecosystems.Source identification of contamination is the cornerstone and a prerequisite for any effective management program of water quality.Stable isotope composition of the dissolved nitrate(δ¹⁵N-NO₃-andδ¹⁸O-NO₃-)has been applied to identify NO₃-sources and the main transformation processes in the upper aquifer system(A1/2,A4,and B2/A7 aquifers)in the Wadi Shueib catchment area,Jordan.Moreover,the stable isotope compositions of the groundwater(δ²H-H₂O andδ¹⁸O-H₂O)in conjunction with the groundwater hydrochemistry were integrated to investigate the origin and evolution of the groundwater.Results revealed that groundwater in the study area is fresh and hard-very hard water,and mainly a Ca-Mg-Cl type.NO₃-concentration was in the range of 7.0-74.0 mg/L with an average of 37.0 mg/L.Most of the samples showed concentration higher than the natural background concentration of NO₃-(5.0-10.0 mg/L).Theδ²H-H₂O andδ¹⁸O-H₂O values indicated that the groundwater is meteoric,and of Mediterranean origin,with a strong evaporation effect.Theδ¹⁵N-NO₃-values ranged between 6.0‰and 11.3‰with an average of 8.7‰,and theδ¹⁸O-NO₃-values ranged between 1.6‰and 5.9‰with an average of 3.4‰.These values are in conformity with the stable isotope composition of nitrate derived the nitrification of wastewater/manure,and soil NH4.Nitrification and denitrification are the main transformation processes affecting nitrogen species.Statistical analysis revealed no significant differences in theδ²H-H₂O andδ¹⁸OH₂O values,andδ¹⁵N-NO₃-andδ¹⁸O-NO₃-values for the three aquifers(A1/2,A4,and B2/A7),indicating that the groundwater of these aquifers has the same origin,and a common source of pollution.     

Atmospheric deposition of inorganic nitrogen in a semi-arid grassland of Inner Mongolia,China

Due to increasing global demand for crop production and energy use, more and more reactive nitrogen(Nr) has been generated and emitted to the environment. As a result, global atmospheric nitrogen(N) deposition has tripled since the industrial revolution and the ecological environment and human health have been harmed. In this study, we measured dry and wet/bulk N deposition from July 2013 to December 2015 in a semi-arid grassland of Duolun County, Inner Mongolia, China. The samples of dry and wet/bulk N deposition were collected monthly with a DELTA(DEnuder for Long Term Atmospheric sampling) system and with Gradko passive samplers and a precipitation gauge. The measured results show that the annual mean concentrations of NH_3, NO_2, HNO_3, particulate NH_4~+(pNH_4~+) and particulate NO_3~-(pNO_3~-) in atmosphere were 2.33, 1.90, 0.18, 1.42 and 0.42 μg N/m3, respectively, and that the annual mean volume-weighted concentrations of NH_4~+-N and NO_3~--N in precipitation were 2.71 and 1.99 mg N/L, respectively. The concentrations of Nr components(including NH_3, NO_2, HNO_3, p NH_4~+, pNO_3~-, NH_4~+-N and NO_3~--N) exhibited different seasonal variations. Specifically, NO_2 and HNO_3 exhibited higher concentrations in autumn than in summer, while the other Nr components(NH_3, pNH_4~+, pNO_3~-, NH_4~+-N and NO_3~--N) showed the highest values in summer. Based on measured concentrations of Nr components and their deposition velocities estimated using the GEOS-Chem global atmospheric chemical transport model, the calculated annual mean dry deposition fluxes were 3.17, 1.13, 0.63, 0.91 and 0.36 kg N/(hm~2·a) for NH_3, NO_2, HNO_3, p NH_4~+ and pNO_3~-, respectively, and the calculated annual mean wet/bulk deposition fluxes were 5.37 and 3.15 kg N/(hm~2·a) for NH_4~+-N and NO_3~--N, respectively. The estimated annual N deposition(including dry N deposition and wet/bulk N deposition) reached 14.7 kg N/(hm~2·a) in grassland of Duolun County, approaching to the upper limit of the N critical load(10–15 kg N/(hm~2·a)). Dry and wet/bulk deposition fluxes of all Nr components(with an exception of HNO_3) showed similar seasonal variations with the maximum deposition flux in summer and the minimum in winter. Reduced Nr components(e.g., gaseous NH_3 and p NH_4~+ in atmosphere and NH_4~+-N in precipitation) dominated the total N deposition at the sampling site(accounted for 64% of the total N deposition), suggesting that the deposited atmospheric Nr mainly originated from agricultural activities. Considering the projected future increases in crop and livestock production in Inner Mongolia, the ecological and human risks to the negative effects of increased N deposition could be increased if no mitigation measures are taken.     

Land use/land cover change responses to ecological water conveyance in the lower reaches of Tarim River,China

The Tarim River is the longest inland river in China and is considered as an important river to protect the oasis economy and environment of the Tarim Basin. However, excessive exploitation and over-utilization of natural resources, particularly water resources, have triggered a series of ecological and environmental problems, such as the reduction in the volume of water in the main river, deterioration of water quality, drying up of downstream rivers, degradation of vegetation, and land desertification. In this study, the land use/land cover change (LUCC) responses to ecological water conveyance in the lower reaches of the Tarim River were investigated using ENVI (Environment for Visualizing Images) and GIS (Geographic Information System) data analysis software for the period of 1990-2018. Multi-temporal remote sensing images and ecological water conveyance data from 1990 to 2018 were used. The results indicate that LUCC covered an area of 2644.34 km² during this period, accounting for 15.79% of the total study area. From 1990 to 2018, wetland, farmland, forestland, and artificial surfaces increased by 533.42 km² (216.77%), 446.68 km² (123.66%), 284.55 km² (5.67%), and 57.51 km² (217.96%), respectively, whereas areas covered by grassland and other land use/land cover types, such as Gobi, bare soil, and deserts, decreased by 103.34 km² (14.31%) and 1218.83 km² (11.75%), respectively. Vegetation area decreased first and then increased, with the order of 2010<2000<1990<2018. LUCC in the overflow and stagnant areas in the lower reaches of the Tarim River was mainly characterized by fragmentation, irregularity, and complexity. By analyzing the LUCC responses to 19 rounds of ecological water conveyance in the lower reaches of the Tarim River from 2000 to the end of 2018, we proposed guidelines for the rational development and utilization of water and soil resources and formulation of strategies for the sustainable development of the lower reaches of the Tarim River. This study provides scientific guidance for optimal scheduling of water resources in the region.     

沙地樟子松人工林土壤氮矿化特征

土壤氮(N)的有效性是沙地林生态系统生产力和稳定性的关键限制因子。本研究以科尔沁沙地樟子松人工林为研究对象，分析测定了10~60 a林龄土壤NH₄⁺-N、NO₃^--N和矿质N含量、氨化速率、硝化速率和N矿化速率的变化规律。结果表明：樟子松人工林土壤NH₄⁺-N、NO₃^--N和矿质N含量，随着不同林龄在10~60 a内表现出增加的趋势，其中10~30 a增幅较小，40~60 a显著提高；随着土层深度增加而减小，主要集中在0~20 cm，呈现出表聚性。不同林龄樟子松人工林土壤氨化速率、硝化速率和矿化速率均随林龄增加而增加，随土层深度的增加而降低，其中0~40 cm土层明显大于40~100 cm。通过双因素方差分析，得出林龄与土层对各矿化指标影响显著。土壤矿化指标与人工林地上樟子松株高、胸径、冠幅以及土壤有机碳、全氮、碱解氮有显著的正相关关系。通过冗余分析(RDA)表明，影响不同林龄土壤矿化指标的主要环境因子为全氮、全磷、有机碳；影响不同土层土壤矿化指标的主要环境因子为全氮、碱解氮、有机碳。因此，樟子松人工林能够改善沙地土壤N的有效性，幼龄林和中龄林改善效果较小，近成熟林和成熟林改善效果明显；对表层土的改善效果优于深层土；土壤肥力是影响土壤矿化指标的主要环境因子。     

Chemical characteristics of precipitation and the indicative significance for sand dust events in the northern and southern slopes of Wushaoling Mountain,northwestern China

Precipitation chemistry analysis is essential to evaluate the atmospheric environmental quality and identify the sources of atmospheric pollutants. In this study, we collected a total of 480 precipitation samples at 6 sampling sites in the northern and southern slopes of Wushaoling Mountain from May 2013 to July 2014 to analyze the chemical characteristics of precipitation and to identify the main sources of ions in precipitation. Furthermore, we also explored the indicative significance for sand dust events in the northern and southern slopes of Wushaoling Mountain based on the precipitation chemistry analysis.During the sampling period(from May 2013 to July 2014), the p H values, EC(electrical conductivity)values and concentrations of cations(Ca~(2+), Mg~(2+), Na~+, K~+ and NH_4~+) and anions(SO_4~(2–), NO_3~–, Cl~–, NO_2~– and F~–) in precipitation were different in the northern and southern slopes at daily and seasonal time scales, with most of the values being higher in the northern slope than in the southern slope. The chemical type of precipitation in the southern and northern slopes was the same, i.e.,SO_4~(2–)-Ca~(2+)-NO_3~–-Na~+. The concentrations of ions in precipitation were mainly controlled by terrigenous material and anthropogenic activities(with an exception of Cl~–). The concentration of Cl~– in precipitation was mainly controlled by the sea salt fraction. The concentrations of Na+ and Cl~– showed an increasing trend after the occurrence of sand dust events both in the northern and southern slopes. In addition, after the occurrence of sand dust events, the concentrations of K~+, Mg~(2+), SO_4~(2–), NO_3~– and Ca~(2+) showed an increasing trend in the southern slope and a decreasing trend in the northern slope. It is our hope that the results may be helpful to further understand the atmospheric pollution caused by sand dust events in the Wushaoling Mountain and can also provide a scientific basis for the effective prevention of atmospheric pollution.     

Impact of land use/land cover types on surface humidity in northern China in the early 21st century

In the context of global change, it is essential to promote the rational development and utilization of land resources, improve the quality of regional ecological environment, and promote the harmonious development of human and nature for the regional sustainability. We identified land use/land cover types in northern China from 2001 to 2018 with ENVI images and ArcGIS software. Meteorological data were selected from 292 stations in northern China, the potential evapotranspiration was calculated with the Penman-Monteith formula, and reanalysis humidity and observed humidity data were obtained. The reanalysis minus observation (RMO, i.e., the difference between reanalysis humidity and observed humidity) can effectively characterize the impact of different land use/land cover types (forestland, grassland, cultivated land, construction land, water body and unused land) on surface humidity in northern China in the early 21^st century. The results showed that from 2001 to 2018, the area of forestland expanded (increasing by approximately 1.80×10⁴ km²), while that of unused land reduced (decreasing by approximately 5.15×10⁴ km²), and the regional ecological environment was improved. Consequently, land surface in most areas of northern China tended to be wetter. The contributions of land use/land cover types to surface humidity changes were related to the quality of the regional ecological environment. The contributions of the six land use/land cover types to surface humidity were the highest in northeastern region of northern China, with a better ecological environment, and the lowest in northwestern region, with a fragile ecological environment. Surface humidity was closely related to the variation in regional vegetation coverage; when the regional vegetation coverage with positive (negative) contributions expanded (reduced), the land surface became wetter. The positive contributions of forestland and water body to surface humidity were the greatest. Unused land and construction land were associated with the most serious negative contributions to surface humidity. Affected by the regional distribution pattern of vegetation, surface humidity in different seasons decreased from east to west in northern China. The seasonal variation in surface humidity was closely related to the growth of vegetation: surface humidity was the highest in summer, followed by autumn and spring, and the lowest in winter. According to the results, surface humidity is expected to increase in northeastern region of northern China, decrease in northern region, and likely increase in northwestern region.     

Isotope implications of groundwater recharge,residence time and hydrogeochemical evolution of the Longdong Loess Basin,Northwest China

Groundwater plays a dominant role in the eco-environmental protection of arid and semi-arid regions.Understanding the sources and mechanisms of groundwater recharge,the interactions between groundwater and surface water and the hydrogeochemical evolution and transport processes of groundwater in the Longdong Loess Basin,Northwest China,is of importance for water resources management in this ecologically sensitive area.In this study,71 groundwater samples(mainly distributed at the Dongzhi Tableland and along the Malian River)and 8 surface water samples from the Malian River were collected,and analysis of the aquifer system and hydrological conditions,together with hydrogeochemical and isotopic techniques were used to investigate groundwater sources,residence time and their associated recharge processes.Results show that the middle and lower reaches of the Malian River receive water mainly from groundwater discharge on both sides of valley,while the source of the Malian River mainly comes from local precipitation.Groundwater of the Dongzhi Tableland is of a HCO3-Ca-Na type with low salinity.The reverse hydrogeochemical simulation suggests that the dissolution of carbonate minerals and cation exchange between Ca²⁺,Mg²⁺and Na+are the main water-rock interactions in the groundwater system of the Dongzhi Tableland.Theδ¹⁸O(from-11.70‰to-8.52‰)andδ2H(from-86.15‰to-65.75‰)values of groundwater are lower than the annual weighted average value of precipitation but closer to summer-autumn precipitation and soil water in the unsaturated zone,suggesting that possible recharge comes from the summer-autumn monsoonal heavy precipitation in the recent past(≤220 a).The corrected 14C ages of groundwater range from 3,000 to 25,000 a old,indicating that groundwater was mainly from precipitation during the humid and cold Late Pleistocene and Holocene periods.Groundwater flows deeper from the groundwater table and from the center to the east,south and west of the Dongzhi Tableland with estimated migration rate of 1.29-1.43 m/a.The oldest groundwater in the Quaternary Loess Aquifer in the Dongzhi Tableland is approximately 32,000 a old with poor renewability.Based on theδ¹⁸O temperature indicator of groundwater,we speculate that temperature of the Last Glacial Maximum in the Longdong Loess Basin was 2.4℃-6.0℃ colder than the present.The results could provide us the valuable information on groundwater recharge and evolution under thick loess layer,which would be significative for the scientific water resources management in semi-arid regions.     

Quantification of groundwater recharge and evapotranspiration along a semi-arid wetland transect using diurnal water table fluctuations

Groundwater is a vital water resource in arid and semi-arid areas. Diurnal groundwater table fluctuations are widely used to quantify rainfall recharge and groundwater evapotranspiration(ET_g). To assess groundwater resources for sustainable use, we estimated groundwater recharge and ET_g using the diurnal water table fluctuations at three sites along a section with different depths to water table(DWT) within a wetland of the Mukai Lake in the Ordos Plateau, Northwest China. The water table level was monitored at an hourly resolution using a Keller DCX-22 A data logger that measured both the total pressure and barometric pressure, so that the effect of barometric pressure could be removed. At this study site, a rapid water table response to rainfall was observed in two shallow wells(i.e., Obs1 and Obs2), at which diurnal water table fluctuations were also observed over the study period during rainless days, indicating that the main factors influencing water table variation are rainfall and ET_g. However, at the deep-water table site(Obs3), the groundwater level only reacted to the heaviest rainfalls and showed no diurnal variations. Groundwater recharge and ET_g were quantified for the entire hydrological year(June 2017–June 2018) using the water table fluctuation method and the Loheide method, respectively, with depth-dependent specific yields. The results show that the total annual groundwater recharge was approximately 207 mm, accounting for 52% of rainfall at Obs1, while groundwater recharge was approximately 250 and 21 mm at Obs2 and Obs3, accounting for 63% and 5% of rainfall, respectively. In addition, the rates of groundwater recharge were mainly determined by rainfall intensity and DWT. The daily mean ET_g at Obs1 and Obs2 over the study period was 4.3 and 2.5 mm, respectively, and the main determining factors were DWT and net radiation.