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   

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   

Orbital control on cyclical organic matter accumulation in Early Silurian Longmaxi Formation shales     

Siding Jin  Hucheng Deng  Xing Zhu  Yan Liu  Sibing Liu  Meiyan Fu 《地学前缘(英文版)》2020,(2):533-545

High resolution(939 samples)total organic carbon content(TOC)analyses were conducted on the Shuanghe Section of^152.6 m in the Changning area,Sichuan Basin.The sampling section was divided into two units considering the distinct-different deposit environment and sediments accumulation rate.The lower part(Unit 1)and the peer part(Unit 2)with high resolution sample spacing(0.08–0.4 m)enables the identification of the precession cycle in two sedimentary sequences with distinct different sedimentary accumulation rate.MTM Power spectral analyses on untuned TOC series reveals significant peaks exceeding above the 95%confidence level and shows that both Unit 1 and Unit 2 have recorded Milankovitch cycles of 405 kyr long eccentricity,short eccentricity,obliquity and precession.The floating astronomical time scale(ATS)was constructed on the Shuanghe Section in the Early Silurian(~439.673–444.681 Ma),and which was calibrated by 405 kyr long eccentricity cycles.The total duration of the Wufeng and Longmaxi shales is 5.01 Myr.The floating ATS used for estimating the duration of the graptolite zones and each stage in the study interval.Finally,we postulated two models that could verify the linkage between orbital cycle and organic accumulation.To make sure whether productivity or preservation is the main factor that under long eccentricity control,the phase correlation between the obtained filtered signal and the theoretical orbital solution should be made clear in the further research.  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   

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   

鄂尔多斯地块周缘垂直形变场负位错反演与应变积累研究     

张希  刘立炜  郝明  白卓立 《大地测量与地球动力学》2019,39(6):551-556

利用鄂尔多斯地块及其周缘1970～2014年的垂直形变速率场资料，借助负位错反演研究该区域长期应变积累。结果表明，地块东北缘山西断陷带中北段年均能量积累增量、剪应力强度都较高，西南缘六盘山断裂与渭河断裂西段次之；山西断陷带中南段至晋陕交界处年均剪应力强度较高且显示一定程度的能量积累；西秦岭构造区尤其西秦岭北缘断裂西段、晋冀蒙交界区也反映一定程度的能量积累特性。  相似文献   

基于LAHARZ的泥石流堆积范围预测模型的建立及应用     

王常明  李桐  田书文  李硕 《吉林大学学报(地球科学版)》2019,49(6):1672-1679

为了探究泥石流的堆积范围，利用LAHARZ软件，对北京市密云县泥石流沟喇嘛栅子南沟进行了数值模拟。结合泥石流沟小流域1：10 000数字高程模型图，模拟了泥石流的堆积范围。首先利用中国部分地区泥石流体积和堆积范围的数据资料，获得了泥石流体体积与其堆积范围的新的统计模型B=11.42V^0.7156；然后通过模拟沟道与实际沟道的对比，确定了最佳沟道阈值为15 000；再结合现场调查统计和降雨历史资料，确定了10年、20年、50年和100年一遇暴雨条件的泥石流体积值，分别为56 500、72 900、94 200和113 100 m³；最后在此基础上对该条泥石流沟的堆积范围进行了预测。结果表明，100年一遇的暴雨条件下泥石流堆积面积为48 729 m²，到达最远距离约为490 m，已影响下游村庄。  相似文献   

2001-2015年间我国陆地植被覆盖度时空变化及驱动力分析          下载免费PDF全文

赵明伟  王妮  施慧慧  江岭  王春 《干旱区地理》2019,42(2):324-331

本文基于MODIS-NDVI遥感数据反演计算了我国陆地2001—2015年地表植被覆盖度的空间分布，讨论了植被覆盖度的时空变化规律，分析了影响植被覆盖度近十几年来动态变化的主要驱动因素。研究结果表明：我国陆地植被覆盖度从2001—2015年，植被覆盖度总体上呈增加趋势，其中淮河流域、华北平原地区、以及黄土高原地区增加趋势显著。根据植被覆盖度在时间序列上的变化特征，可将其变化类型分为持续增长型、先减小后增长等六种类型，其中农业种植区基本为一直增长型，而主要森林覆盖区，特别是西南地区的植被覆盖度在研究时段内表现出波动性的变化特征。降水是驱动华北平原北部，内蒙古，以及西北大部分区域植被覆盖度动态变化的重要因素，东北、青藏高原等地区植被覆盖度受温度的影响较大，而在中国东南沿海地区，光照条件是影响该区域植被覆盖度的主要因素。  相似文献