Seasonal connections between meteoric water and streamflow generation along a mountain headwater stream     

Sam J. Leuthold  Stephanie A. Ewing  Robert A. Payn  Florence R. Miller  Stephan G. Custer 《水文研究》2021,35(2):e14029

In snowmelt-driven mountain watersheds, the hydrologic connectivity between meteoric waters and stream flow generation varies strongly with the season, reflecting variable connection to soil and groundwater storage within the watershed. This variable connectivity regulates how streamflow generation mechanisms transform the seasonal and elevational variation in oxygen and hydrogen isotopic composition (δ¹⁸O and δD) of meteoric precipitation. Thus, water isotopes in stream flow can signal immediate connectivity or more prolonged mixing, especially in high-relief mountainous catchments. We characterized δ¹⁸O and δD values in stream water along an elevational gradient in a mountain headwater catchment in southwestern Montana. Stream water isotopic compositions related most strongly to elevation between February and March, exhibiting higher δ¹⁸O and δD values with decreasing elevation. These elevational isotopic lapse rates likely reflect increased connection between stream flow and proximal snow-derived water sources heavily subject to elevational isotopic effects. These patterns disappeared during summer sampling, when consistently lower δ¹⁸O and δD values of stream water reflected contributions from snowmelt or colder rainfall, despite much higher δ¹⁸O and δD values expected in warmer seasonal rainfall. The consistently low isotopic values and absence of a trend with elevation during summer suggest lower connectivity between summer precipitation and stream flow generation as a consequence of drier soils and greater transpiration. As further evidence of intermittent seasonal connectivity between the stream and adjacent groundwaters, we observed a late-winter flush of nitrate into the stream at higher elevations, consistent with increased connection to accumulating mineralized nitrogen in riparian wetlands. This pattern was distinct from mid-summer patterns of nitrate loading at lower elevations that suggested heightened human recreational activity along the stream corridor. These observations provide insights linking stream flow generation and seasonal water storage in high elevation mountainous watersheds. Greater understanding of the connections between surface water, soil water and groundwater in these environments will help predict how the quality and quantity of mountain runoff will respond to changing climate and allow better informed water management decisions.  相似文献   

Origin of sulphate in the unsaturated zone and groundwater of a loess aquifer     

Yin Long  Tianming Huang  Fen Zhang  Zhenbin Li  Baoqiang Ma  Yiman Li  Zhonghe Pang 《水文研究》2021,35(4):e14166

The use of the sulphate mass balance (SMB) between precipitation and soil water as a supplementary method to estimate the diffuse recharge rate assumes that the sulphate in soil water originated entirely from atmospheric deposition; however, the origin of sulphate in soil and groundwater is often unclear, especially in loess aquifers. This study analysed the sulphur (δ³⁴S-SO₄) and oxygen (δ¹⁸O-SO₄) isotopes of sulphate in precipitation, water-extractable soil water, and shallow groundwater samples and used these data along with hydrochemical data to determine the sources of sulphate in the thick unsaturated zone and groundwater of a loess aquifer. The results suggest that sulphate in groundwater mainly originated from old precipitation. When precipitation percolates through the unsaturated zone to recharge groundwater, sulphates were rarely dissolved due to the formation of CaCO₃ film on the surface of sulphate minerals. The water-extractable sulphate in the deep unsaturated zone (>10 m) was mainly derived from the dissolution of evaporite minerals and there was no oxidation of sulphide minerals during the extraction of soil water by elutriating soil samples with deionized water. The water-extractable concentration of SO₄ was not representative of the actual SO₄ concentration in mobile soil water. Therefore, the recharge rate cannot be estimated by the SMB method using the water-extractable concentration of SO₄ in the loess areas. This study is important for identifying sulphate sources and clarifying the proper method for estimating the recharge rate in loess aquifers.  相似文献   

黄土洞室掘进深度与围岩位移变化规律研究     

时卫民  王鹏  赵尚毅 《岩土工程技术》2020,(2):70-75

应用PLAXIS 2D/3D有限元分析软件,对某黄土洞室进行了二维、三维分步掘进、三维一次掘进等工况的弹塑性有限元分析,研究分析了不同工况下洞室围岩位移的变化规律,并对掌子面的空间效应进行了分析。分析结果表明,二维与三维分步计算的最终位移基本一致,可以用二维的计算结果来估算洞室开挖的最终位移。三维分步掘进的分析表明,不同埋深的洞室其位移比的变化规律基本一致,当L/B<1时(L为掘进深度,B为洞室跨度),位移比呈线性增加;当L/B>1时,位移比呈非线性增加;当L/B>3时,其最大位移接近最终位移。掌子面的空间效应分析表明,在掌子面处的位移约为最终位移的1/3,距掌子面0.5倍跨度处的位移约为最终位移的2/3,距掌子面2.5倍跨度处的位移基本达到了最终位移。  相似文献   

Temporal and Spatial Dynamics Analysis of Grassland Ecosystem Pressure in Kazakhstan     

WEN Xin  YAN Huimin  XIE Xiaoping  DU Wengpeng  LAI Chenxi  ZHEN Lin 《资源与生态学报(英文版)》2019,10(6):667-675

Affected by climate change and policy factors, Kazakhstan is the country with the most severe ecological degradation and grassland conflicts in Central Asia. Therefore, studying the state of grassland carrying resources in Kazakhstan is particularly important for understanding the responses of grassland ecosystems to climate change and human activities. Based on Kazakhstan's remote sensing data and animal husbandry statistics, this study analyzes the patterns of changes in grassland ecosystems in Kazakhstan based on the supply and consumption of these ecosystems. The results show that: 1) From 2003 to 2017, the number of livestock raised in Kazakhstan showed a trend of sustained and steady growth. Due to freezing damage, the scale of livestock farming decreased in 2011, but a spatial difference in the livestock farming structure was not obvious. 2) The fluctuation of grassland supply in Kazakhstan has increased, while the consumption due to animal husbandry has also continued to increase, resulting in an increasing pressure on the grassland carrying capacity. 3) Between 2003 and 2017, the overall grassland carrying status of Kazakhstan have been abundant, but the grassland carrying pressure index has shown a steadily increasing trend, the grassland carrying pressure is growing, and it is mainly determined by grassland productivity. The greater pressure in lower Kyzylorda state, the southern Kazakhstan state of the cultivated land and the northern Kazakhstan state has gradually expanded to include the agro-pastoral zone and the semi-desert zone.  相似文献   

花岗岩残积土动态冲击性能的SHPB试验研究     

刘新宇  张先伟  岳好真  孔令伟  徐超 《岩土力学》2020,41(6):2001-2008

为研究花岗岩残积土的动态冲击性能，开展了高速冲击下的分离式霍普金森压杆（SHPB）试验，与常规应变率下的试验结果比较，分析了高应变率对花岗岩残积土的应力?应变特性和强度的影响。结果表明：低、高应变率下的花岗岩残积土的?-?a（轴向应力?轴向应变）曲线均呈现出软化型。随着应变率 增加，?-?a曲线向?a增大的方向移动，破坏应变?af增加。但高应变率下?af增加的程度更加明显。花岗岩残积土的峰值强度普遍具有应变率依赖性，二者可用直线关系拟合，但低、高应变率下的拟合关系并不一致。提出了率敏性因子m定量评价依赖性强弱。研究发现，随着应变率的提高，强度的应变率依赖性减弱，低应变率下的m为26.694，而高应变率下仅为0.013。相关试验结果指出，高速冲击荷载对土体总体有害。工程中应该采取合理措施控制冲击荷载的危害。该研究有助于深化花岗岩残积土动态冲击性能的理解，为相关工程的施工与设计提供技术参考。  相似文献   

Study on multiple induced polarization parameters in groundwater exploration in Bashang poverty alleviation area of Heibei Province,China          下载免费PDF全文

LIU Zhi-yuan  TAN Ding  CHEN Zhi-bin  WEI Yun-fei  CHAI Quan  CHEN Xiao-hang 《地下水科学与工程》2020,8(3):274-280

The study examines a water exploration and poverty alleviation project in Guyuan county. The study analyzes correlations between aquifers and multiple induced polarization (IP) parameters, including resistivity, polarizability, deviation, half decay time, water-bearing factors, and Kc, a new parameter refined in this study. Based on the study, the well was placed accurately, and its maximum water inflow reached 30 m³/h. Kc value highlights the rate of change at early stages of IP secondary field. Kc value served as a quick indicator in this groundwater prospecting and is validated in practice. Progress has been made in finding new parameters in exploring water with IP method. Thanks to the project, local people have access to water and poverty alleviation has scored some achievements.  相似文献   

Interplay of S and As in Mekong Delta sediments during redox oscillations   总被引：1，自引：1，他引：0  

Van T.H.Phan  Fabrizio Bardelli  Pierre Le Pape  Raoul-Marie Couture  Alejandro Fernandez-Martinez  Delphine Tisserand  Rizlan Bernier-Latmani  Laurent Charlet 《地学前缘(英文版)》2019,10(5):1715-1729

The cumulative effects of periodic redox cycling on the mobility of As,Fe,and S from alluvial sediment to groundwater were investigated in bioreactor experiments.Two particular sediments from the alluvial floodplain of the Mekong Delta River were investigated:Matrix A(14 m deep)had a higher pyrite concentration than matrix B(7 m deep)sediments.Gypsum was present in matrix B but absent in matrix A.In the reactors,the sediment suspensions were supplemented with As(Ⅲ)and SO_4~(2-),and were subjected to three full-redox cycles entailing phases of nitrogen/CO_2,compressed air sparging,and cellobiose addition.Major differences in As concentration and speciation were observed upon redox cycling.Evidences support the fact that initial sediment composition is the main factor controlling arsenic release and its speciation during the redox cycles.Indeed,a high pyrite content associated with a low SO_4~(2-)content resulted in an increase in dissolved As concentrations,mainly in the form of As(Ⅲ),after anoxic half-cycles;whereas a decrease in As concentrations mainly in the form of As(Ⅴ),was instead observed after oxic half-cycles.In addition,oxic conditions were found to be responsible for pyrite and arsenian pyrite oxidation,increasing the As pool available for mobilization.The same processes seem to occur in sediment with the presence of gypsum,but,in this case,dissolved As were sequestered by biotic or abiotic redox reactions occurring in the Fe—S system,and by specific physico-chemical condition(e.g.pH).The contrasting results obtained for two sediments sampled from the same core show that many complexes and entangled factors are at work,and further refinement is needed to explain the spatial and temporal variability of As release to groundwater of the Mekong River Delta(Vietnam).  相似文献   

喀喇昆仑断裂北段晚第四纪活动特征及其构造意义     

赵一霖  刘健  姜科庆  祝明伟 《地球学报》2019,40(4):601-613

右旋走滑的喀喇昆仑断裂(KK F)作为青藏高原的西部边界, 在印度板块与欧亚板块碰撞引起的陆内变形过程中扮演了重要的角色。近年来KK F北段全新世以来的活动特征存在争议。通过遥感解译和野外观测, 在喀喇昆仑断裂(KK F)的北段——新疆卡拉苏地区, 对KK F及其两条分支断裂的几何学、运动学进行了研究, 获得了现今发育的冰水扇被右旋错断和冰水扇上分布羽列式T张破裂等指示KK F右旋走滑的证据。采集了KK F控制的浅冰水湖相沉积中贝壳的AMS 14C样品, 获得年龄分别为(5.20±0.03) ka、(5.61±0.03) ka 和(9.95±0.04) ka。表明KK F北段晚全新世以来仍在活动, 其右旋走滑速率约为3.7 mm/a, 累计垂向滑移速率约为1.7 mm/a。据前人在KK F中部的研究成果, 推测KK F北段在卡拉苏地区由南东往北西右旋走滑速率有增大的趋势。  相似文献   

青藏高原东部雀儿山地区新近纪隆升速率探讨——来自雀儿山花岗岩体磷灰石裂变径迹证据   总被引：2，自引：2，他引：0       下载免费PDF全文

曾强  徐天德 《沉积与特提斯地质》2019,39(3):92-100

通过青藏高原东部川西地区雀儿山花岗岩体磷灰石裂变径迹分析,新获得了4个磷灰石裂变径迹年龄值,分别为4. 9±0. 3Ma、6. 2±0. 5 Ma、7. 2±0. 4 Ma和7. 3±0. 7 Ma。运用径迹年龄-地形高差法计算出雀儿山花岗岩体新近纪的隆升速率,为0. 15～2 mm/a,平均隆升速率为0. 78mm/a。隆升速率在每个阶段有所不同,但呈现出一种快速隆升→缓慢隆升的过程,为整个青藏高原东缘的隆升过程提供了约束条件。  相似文献   

四川米易海塔地区混合岩型铀矿流体包裹体特征     

郭锐  陈友良  刘凯鹏  郑玉文  胡漾 《矿物学报》2020,40(2):137-148

混合岩型铀矿是康滇地轴上最有希望取得找矿突破的铀矿类型,海塔地区的铀矿化即是该类型铀矿的典型代表。本文针对区内的长英质脉矿石、富晶质铀矿石英脉矿石和含矿热液石英脉中的石英流体包裹体进行了研究。结果表明,海塔地区混合岩型铀矿的成矿作用可分为2个阶段:早期混合岩化热液成矿阶段为高温、中低盐度流体,流体包裹体均一温度集中在380~540℃,盐度变化范围为16.15%~23.18%NaCl eqv,是区内铀成矿的主要阶段;晚期热液叠加改造成矿阶段为中低温、低盐度流体,流体包裹体均一温度集中在140~220℃,盐度变化范围为5.56%~23.18%NaCleqv,是区内富铀矿的形成阶段。流体包裹体的气相成分测试表明,长英质脉矿石石英包裹体中以CH4、CO2为主,其次为H2O和N2;而富晶质铀矿石英脉及含矿热液石英脉石英包裹体中以H2为主,部分含有CO2、CH4、H2O。氢、氧同位素研究表明,早期混合岩化成矿阶段的成矿流体可能为岩浆水与变质水的混合,而晚期热液叠加改造成矿阶段成矿流体中可能有大气降水的加入。  相似文献