共查询到20条相似文献，搜索用时 15 毫秒
1.
Zihuan Fu Yunqiang Wang Zhisheng An Wei Hu Khan M.G. Mostofa Xuezhang Li Bingxia Liu 《水文研究》2018,32(16):2557-2569
Dynamic relationships among rainfall patterns, soil water distribution, and plant growth are crucial for sustainable conservation of soil and water resources in water‐limited ecosystems. Spatial and temporal variation in deep soil water content at a watershed scale have not yet been characterized adequately due to the lack of deep soil water data. Deep soil–water storage (SWS) up to a depth of 5 m (n = 73) was measured at 19 sampling occasions at the LaoYeManQu watershed on the Chinese Loess Plateau (CLP). At a depth of 0–1.5 m, the annual mean SWS was highly correlated with rain intensity, and the correlation decreased with depth, but within the layers at 1.5–5.0 m, the changes in SWS indicated a lag between precipitation and the replenishment of soil water. Geostatistical parameters of SWS were also highly dependent on depth, and the mean SWS presented similar spatial structures in two adjacent layers. Temporal stability of SWS as indicated by mean relative difference, standard deviation of the relative difference (SDRD), and mean absolute bias error (MABE) was significantly weaker at the shallow than at deeper layers. Soil separates and organic carbon content controlled the spatial pattern of SWS at the watershed scale. One representative location (Site 57) was identified to estimate the mean SWS in the 1‐ to 5‐m layer of the watershed. Semivariograms of the SDRD and MABE were best fitted by an isotropic spherical model, and their spatial distributions were depth‐dependent. Both temporal stability and spatial variability of SWS increased over depth. This study is helpful for deep SWS estimation and sustainable management of soil and water on the CLP, and for other similar regions around the world. 相似文献
2.
新安江水库(千岛湖)热力学状况及热力分层研究 总被引：6，自引：3，他引：3
利用2012年1-12月在新安江水库(千岛湖)6个点位的每月一次的水温及其他环境因子的周年观测资料,分析了水库水温逐月变化、季节变化、垂直分布及温跃层的形成与变化,探讨了温跃层特征量(温跃层深度、厚度、强度)与表层水温、水体透明度的关系.新安江水库表层和中层水温与气温存在显著的线性相关,又以表层水温线性关系最好,而下层水温与气温没有显著相关性,说明下层水温受气温的影响很小,全年处于相对恒温状态.水库表层和中层水温逐月变化明显,呈现夏季最高、春秋季次之、冬季最低的变化趋势,其中中层水温最高值出现的季节较表层水温明显后延,下层水温没有明显的逐月变化和季节变化.水温垂直分布显示,4个季节均存在不同程度的温跃层和温度分层现象,其中水深最深的大坝前水温分层最明显.小金山、三潭岛和大坝前3个典型点位从春季的4月份到冬季的2月份温跃层深度由1.61±0.47 m逐渐增加至39.37±5.35 m,而温跃层厚度和强度则在夏季最高、冬季最低,温跃层随着季节的变化呈现增强稳定减弱消失的周期变化.温跃层深度与水体透明度存在显著正相关,与表层水温存在显著负相关,并基于透明度和表层水温建立温跃层深度的多元线性回归模型. 相似文献
3.
The study of water masses is important as they transport water properties affecting the biosphere and ocean dynamics. In this study, we revisit water masses in the Caribbean Sea using climatology and 11 months of observations at different depths from 3 moorings placed in the Guajira upwelling region, providing some new findings. The Caribbean Surface Water (CSW) seasonal variability is studied at the mixed layer depth. Salinity differences between CSW and the saltier North Atlantic Subtropical Underwater (SUW) determine static stability spatial and temporal variations, with implications for regional ocean dynamics. Besides, we assess the climatologic distribution of water masses below the salinity maximum using the optimum multiparameter analysis and the Thermodynamic Equation of Seawater 2010, defining their source water indices when entering the Caribbean Sea. The SUW, with its core at ~ 150 m depth, occupies 16% of the Caribbean Sea volume, complemented by 38% of Antarctic Intermediate Water, with its core at ~ 700 m depth and North Atlantic Deep Water, which as bottom water occupies 46% of the volume. Hydrographic observations do not differ from climatology, regardless of their large sub-annual variations decreasing with depth. Daily time series of dominant water fractions at different depths correlate at each mooring, indicating a common forcing. Besides, rotated wind stress, which is an indicator of the Guajira upwelling, correlates regularly with water mass fractions down to 700 m depth. However, during strong wind shifts, upwelling seems to affect them down to 1450 m depth.
相似文献4.
水深与水体的多个环境要素(如光照、温度等)密切关联.因而水深会影响沉水植物的生长、繁殖和生理生化特征,包括叶片的光合色素组成和C、N、P化学计量特征.本研究通过对洱海4种沉水植物苦草(Vallisneria natans)、微齿眼子菜(Potamogeton maackianus)、光叶眼子菜(Potamogeton lucens)和篦齿眼子菜(Potamogeton pectinatus)在不同水深梯度的叶片色素组成和C、N、P化学计量特征进行分析,以阐明水深对这些指标的影响规律和机制.结果表明:水深对4种沉水植物叶片光合色素组成和C、N、P化学计量特征的影响具有种间差异性;苦草、微齿眼子菜和光叶眼子菜叶片N含量,苦草和光叶眼子菜叶片P含量都与叶片叶绿素含量呈显著正相关;苦草叶片N含量随水深增加而增加,可能是由苦草为应对深水弱光胁迫而加强光合色素和蛋白的合成导致的,而磷含量的增加可能还受其他因素的影响. 相似文献
5.
Water uptake by saltcedar (Tamarix ramosissima) in a desert riparian forest: responses to intra‐annual water table fluctuation 
下载免费PDF全文
下载免费PDF全文 There is considerable interest in naturalizing flow regime on managed rivers to slow the spread of saltcedar (Tamarix ramosissima) invasion in southwestern USA or to preserve riparian forests dominated by saltcedar and other species in northwestern China. However, little is known about the responses of established saltcedar in water sources to frequent intra‐annual fluctuation of water table resulting from this new, more dynamic flow regime. This study investigates how saltcedar at a riparian site in the middle reaches of the Heihe River, northwest China, responds in water sources use to intra‐annual water table fluctuations. Stable oxygen isotope was employed to determine accurate depth at which saltcedar obtains its water supply, and soil moisture monitoring was used to determine sources of plant‐available soil water. We found that the primary zone of water uptake by saltcedar were stable at 25–60 cm depth, but the water sources used by saltcedar switched between groundwater and soil moisture with the water table fluctuations. Saltcedar derived its water from groundwater when water table was at depth less than 60 cm but switched to soil moisture at 25–60 cm depth when water table declined. It is supposed that the well‐developed clay layer at 60–80 cm depth constrained lateral roots of saltcedar to the soil layers above 60 cm, while the fine‐textured soils at this site, which were periodically resaturated by rising groundwater before the stored soil moisture had become depleted, provided an important water reservoir for saltcedar when groundwater dropped below the primary zone of fine roots. The root distribution of saltcedar may also be related to local groundwater history. The quick decline in water table in the early 1980s when the riparian saltcedar had established may strand its roots in the shallow unsaturated zone. We suggested that raising the water table periodically instead of maintaining it invariably above the rooting depth could sustain desired facultative phreatophytes while maximizing water deliveries. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
6.
根据2008—2016年苏06井400 m和800 m深度的水温观测数据,分析不同深度的水温年变速率及日变曲线形态,并运用差值、水温梯度的小波变换方法,对2个不同深度的水温变化特征进行分析,发现:苏06井不同深度水温的长期变化与水位变化具有一定同步性,事实上水位变化起主导作用,构造引起水位变化使不同深度水温的表现不同,对周围近距离显著地震发生有一定意义;从短期变化看,不同深度水温之间很少出现同步变化;400 m深度水温异常信号频度及强度高于800 m深度水温异常信号。 相似文献
7.
Water flow in the soil–root–stem system was studied in a flooded riparian hardwood forest in the upper Rhine floodplain. The study was undertaken to identify the vertical distribution of water uptake by trees in a system where the groundwater is at a depth of less than 1 m. The three dominant ligneous species (Quercus robur, Fraxinus excelsior and Populus alba) were investigated for root structure (vertical extension of root systems), leaf and soil water potential (Ψm), isotopic signal (18O) of soil water and xylem sap. The root density of oak and poplar was maximal at a depth of 20 to 60 cm, whereas the roots of the ash explored the surface horizon between 0 and 30 cm, which suggests a complementary tree root distribution in the hardwood forest. The flow density of oak and poplar was much lower than that of the ash. However, in the three cases the depth of soil explored by the roots reached 1·2 m, i.e. just above a bed of gravel. The oak roots had a large lateral distribution up to a distance of 15 m from the trunk. The water potential of the soil measured at 1 m from the trunk showed a zone of strong water potential between 20 and 60 cm deep. The vertical profile of soil water content varied from 0·40 to 0·50 cm3 cm?3 close to the water table, and 0·20 to 0·30 cm3 cm?3 in the rooting zone. The isotopic signal of stem water was constant over the whole 24‐h cycle, which suggested that the uptake of water by trees occurred at a relatively constant depth. By comparing the isotopic composition of water between soil and plant, it was concluded that the water uptake occurred at a depth of 20 to 60 cm, which was in good agreement with the root and soil water potential distributions. The riparian forest therefore did not take water directly from the water table but from the unsaturated zone through the effect of capillarity. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
8.
This study is undertaken to understand how calcite precipitation and dissolution contributes to depth-related changes in porosity and permeability of gas-bearing sandstone reservoirs in the Kela 2 gas field of the Tarim Basin, Northwestern China. Sandstone samples and pore water samples are col-lected from well KL201 in the Tarim Basin. Vertical profiles of porosity, permeability, pore water chem-istry, and the relative volume abundance of calcite/dolomite are constructed from 3600 to 4000 m below the ground surface within major oil and gas reservoir rocks. Porosity and permeability values are in-versely correlated with the calcite abundance, indicating that calcite dissolution and precipitation may be controlling porosity and permeability of the reservoir rocks. Pore water chemistry exhibits a sys-tematic variation from the Na2SO4 type at the shallow depth (3600-3630 m), to the NaHCO3 type at the intermediate depth (3630―3695 m),and to the CaCl2 type at the greater depth (3728―3938 m). The geochemical factors that control the calcite solubility include pH, temperature, pressure, Ca2 concen-tration, the total inorganic carbon concentration (ΣCO2), and the type of pore water. Thermodynamic phase equilibrium and mass conservation laws are applied to calculate the calcite saturation state as a function of a few key parameters. The model calculation illustrates that the calcite solubility is strongly dependent on the chemical composition of pore water, mainly the concentration difference between the total dissolved inorganic carbon and dissolved calcium concentration (i.e., [ΣCO2] -[Ca2 ]). In the Na2SO4 water at the shallow depth, this index is close to 0, pore water is near the calcite solubility. Calcite does not dissolve or precipitate in significant quantities. In the NaHCO3 water at the intermedi-ate depth, this index is greater than 0, and pore water is supersaturated with respect to calcite. Massive calcite precipitation was observed at this depth interval and this intensive cementation is responsible for decreased porosity and permeability. In the CaCl2 water at the greater depth, pore water is un-der-saturated with respect to calcite, resulting in dissolution of calcite cements, as consistent with microscopic dissolution features of the samples from this depth interval. Calcite dissolution results in formation of high secondary porosity and permeability, and is responsible for the superior quality of the reservoir rocks at this depth interval. These results illustrate the importance of pore water chemis-try in controlling carbonate precipitation/dissolution, which in turn controls porosity and permeability of oil and gas reservoir rocks in major sedimentary basins. 相似文献
9.
Peter Kokelaar 《Bulletin of Volcanology》1986,48(5):275-289
In the subaqueous growth and emergence of a basaltic volcano clasts are formed by one or a combination of (1) explosive release of magmatic volatiles; (2) explosive expansion and collapse of steam formed at magma-water contact surfaces; (3) explosive expansion of steam following enclosure of water in magma, or entrapment of water close to magma; and (4) cooling-contraction. These processes, named respectivelymagmatic explosivity, contact-surface steam explosivity, bulk interaction steam explosivity, andcooling-contraction granulation, can be enhanced by mutual interaction and feedback. The first three (explosive) processes are limited at certain water depths (hydrostatic pressures) and become increasingly vigorous at shallower levels. The depth of onset of magmatic explosivity depends largely on juvenile volatile content; it is up to 200 m for tholeiitic magmas and up to 1 km for alkalic magmas. At the depth where formation of clastic deposits becomes predominant over effusion of lavas, magmatic explosivity is subordinate to steam explosivity as a clast-forming process. The upward transition to accumulation of dominantly clastic deposits is not simply related to the onset of substantial exsolution of magmatic volatiles and can occur without it. Contact-surface explosivity commonly requires initiation by a vigorous impact between magma and water and, although no certain depth limit is known, likelihood of such explosivity decreases rapidly with depth. Clast generation by bulk interaction explosivity appears to be restricted to depths much shallower than that of the critical pressure of water, which in sea water is at about 3 km. Cooling-contraction granulation can occur in any depth of water, but at shallow levels may be replaced by contact-surface explosivity. During continuous eruption under water, tephra can be ejected and deposited within a cupola of steam such that rapid quenching does not occur. Emergent volcanoes are characterized by distinctive steam-explosive activity that results primarily from a bulk interaction between rapidly ascending magma and a highly mobile slurry of clastic material, water, and steam. The water gets into the vent by flooding across or through the top of the tephra pile, and violent explosions cease when this access is sealed. The eruptions during emergence of Surtsey and Capelinhos typify the distinctive explosive activity, the style and controls of which are different from those of maar volcanoes. 相似文献
10.
Ben Roudnew Justin R. Seymour Thomas C. Jeffries Trish J. Lavery Renee J. Smith James G. Mitchell 《Ground Water Monitoring & Remediation》2012,32(4):72-77
Bacteria and viruses are ubiquitous in subterranean aquatic habitats. Bacterial abundance is known to vary with depth in aquifers; however, whether viral abundance varies with depth is less well known. Here we use flow cytometry (FCM) to enumerate bacteria and virus‐like particles (VLP) from groundwater depth profiles. Groundwater samples were obtained from a set of nested piezometers from depths of 15, 30, 45, 60, 80, and 90 m and bacteria and VLP abundances were determined in purged aquifer water and unpurged water at each slot depth. Mean bacterial abundance (cells / mL) was not significantly different in unpurged water (3.2 × 105) compared to purged water (1.4 × 105); however, mean VLP abundance (particles / mL) was significantly greater in unpurged water (4.4 × 105) compared to purged water (2.3 × 105). Purged water was used to investigate the aquifer depth profile and bacterial and VLP abundances were observed to vary significantly between depths. The virus‐bacteria ratio was determined and was observed to steadily increase with depth. Overall, our data indicate the dynamic nature of bacterial and viral abundances in subsurface environments which should be considered when designing groundwater microbial sampling methodologies. 相似文献
11.
Zygmunt Meyer 《Acta Geophysica》2011,59(2):317-333
The wind set-up of water level in a river is of great importance in many practical cases, notably in the river mouth section
where the slope of the free water table is very small (sometimes 10−5) and the wind shear stress acting at the water surface generates significant changes in the vertical velocity profile. If
the wind is blowing opposite to the main flow, an increase of water depth is observed. In the outlet area, the increase of
water depth can reach up to 0.5 m (Lower Odra River). The paper presents an analysis of wind set-up of water level based on
hydrodynamic principles. 相似文献
12.
The simultaneous transfer of pore fluid and vapour was studied in the unsaturated shallow subsurface of a Plio-Pleistocene marine mudstone badland slope in southwestern Taiwan during the dry season using field monitoring data and numerical simulations. Data from field monitoring show mass-basis water contents of ~0.05 to ~0.10 that decrease towards the unsaturated ground surface and were invariant during the middle part of the dry season, except for daily fluctuations. In addition, the observed daily fluctuations in water content correlate with fluctuations in bedrock temperature, especially at depths of 2.5–5.0 cm. Periodic increases in water content occurred most notably during the day, when the bedrock temperature showed the greatest increase. Water contents then decreased to the previous state as bedrock temperature decreased during the night. Calculated vapour fluxes within the mudstone during the day increased up to 6 × 10−6–1 × 10−5 kg m−2 s−1, deriving a 0.01–0.02 increase in mass-basis water content at 2.5 cm depth for a 12-h period. This agrees with field monitoring data, suggesting that increases in water content occurred due to vapour intrusions into the bedrock. Pore water electrical conductivity (EC) showed periodic variations due to vapour intrusion, and gradually increased between the ground surface and depths of 2.5–5.0 cm. In contrast, pore water EC gradually decreased between 15 and 40 cm depth. Calculated water fluxes at depths of 2.5–40.0 cm varied from −4 × 10−6 to −2 × 10−9 kg m−2 s−1. These fluxes generated an increase in solute concentrations at the ground surface, with negative values of water flux indicating an upwards movement of water towards the surface. We show that the increase in solute content due to solute transfer from depth is highly dependent on variations in water flux with depth. © 2020 John Wiley & Sons, Ltd. 相似文献
13.
水深梯度对苦草(Vallisneria natans)克隆生长与觅食行为的影响 总被引：1，自引：1，他引：0
为了解水深梯度对苦草克隆生长与觅食行为的影响,通过大型原位浮台实验,将苦草幼苗盆栽后悬挂在不同水深(1.0、2.5、4.0、5.5、7.0 m)下培养,比较其生物量、无性系分株数、出芽数、株高、最大根长和匍匐茎总长的变化,并且评估了植株生物量对这些性状的影响.研究结果表明,随水深的增加苦草的生物量、无性系分株数、出芽数、最大根长、匍匐茎总长均显著降低,而株高随水深梯度呈先增加后降低的趋势.植株生物量仅对出芽数没有显著影响.水深梯度与植株生物量的交互作用仅对无性系分株数和匍匐茎总长有显著影响,而对其他性状没有显著影响,说明这两个性状对水深的响应受到个体发育的影响. 相似文献
14.
Rafael Matias Feltrin João Batista Dias de Paiva Eloiza Maria Cauduro Dias de Paiva Fábio Alex Beling 《水文研究》2011,25(15):2321-2328
This study aims at monitoring the behaviour of the rainfall, runoff, drainage, soil water storage, and evapotranspiration variables involved in the water balance measured by lysimeter data. The evaluation of the water balance considered different time scales, where the components were monitored daily and in 10‐day accumulated period intervals. The results demonstrated that in wet periods the soil water content was greater at a depth of 10 cm, whereas in the dry periods a greater concentration was observed at 70 cm depth. At the depth of 30 cm, the lowest values of soil water content were observed for both wet and dry periods. The results, obtained through the use of tensiometers and time domain reflectometry installed internally and externally to the lysimeter, were very close, which was more noticeable during the periods of lower water loss by the soil. The water balance, calculated from the lysimeter data, demonstrated that 70% of the total rainfall was lost by the process of evapotranspiration. The drainage accounted for 27·5% of the precipitated water, highlighting the fact that this component should not be disregarded in the water balance calculation. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
15.
水温传感器置深不同,所反映的固体潮效应不同。基于非自流井水温传感器深度,从与井底深度和含水层顶板埋深的相对位置关系,探讨水温传感器不同置深对固体潮体应变响应的影响,明确其最佳观测条件,分析认为:非自流井中水温记录固体潮效应的前提条件依次为:水位能记录到固体潮效应,水温传感器投放在观测含水层上方,传感器投放在地温梯度相对较大位置及井半径较小位置。 相似文献
16.
Travis G. Gerwing Kieran Cox Alyssa M. Allen Gerwing Charmaine N. Carr-Harris Sarah E. Dudas Francis Juanes 《国际泥沙研究》2018,33(2):149-156
The usefulness of the apparent redox potential discontinuity (aRPD) in assessments of marine benthic habitat quality was explored at two intertidal mudflats along the north Pacific coast of Canada. Two transects were established at each intertidal site, with three sediment biogeochemistry cores collected from each transect four times over the summer of 2016. Measurements of the sediment pore water dissolved oxygen (DO) content and redox (Eh) conditions were taken at the surface of the core (measured vertically), as well as at increasing depths (1 cm between readings) into the sediment (measured horizontally through predrilled holes in the biogeochemistry corer). While oxic, anoxic, oxidized, and reduced sediment pore water was observed above and below the aRPD, in general, sediment above the aRPD had higher DO content, and higher Eh values than sediment below the aRPD. Therefore, the aRPD depth can be used as a relative indicator of sediment pore water DO and Eh conditions: sediment with a deeper aRPD depth has more available DO, and the pore water has higher Eh values (more oxidized or less reduced) than sediment with a shallower aRPD depth. As such, the aRPD depth is a useful parameter to include in models that assess the quality of marine benthic habitats. 相似文献
17.
三峡水库香溪河库湾拟多甲藻(Peridiniopsis)的昼夜垂直迁移行为对碳磷分布的响应 总被引：1，自引：0，他引：1
于2015年2月26-27日在香溪河库湾高岚河段拟多甲藻(Peridiniopsis)水华发生地昼夜监测其在水体中的垂直迁移,分别在6个时间段(8:00、12:00、16:00、20:00、0:00、4:00)分层取样分析拟多甲藻在水中的叶绿素a浓度、细胞密度、碳酸酐酶(CA)与碱性磷酸酶(AP)活性;分析总磷(TP)、溶解性总磷(DTP)、溶解性反应磷(SRP)与溶解性有机磷(DOP)浓度在水中的垂直分布.结果显示,水华发生期拟多甲藻为绝对优势种,监测的6个时段中,拟多甲藻呈显著的昼夜垂直迁移规律,正午12:00,表层细胞密度最大,可达5.2×10~6cells/L,凌晨0:00表层细胞密度最低,仅为0.4×10~6cells/L;TP与DTP浓度无垂直分布规律,但SRP与DOP浓度呈现显著的垂直分布规律,SRP浓度随水深增加而减小,DOP浓度随水深增加而增加;CA活性日间高于夜间,日间CA活性呈垂直分布规律,随水深增加而减小,但夜间无垂直分布规律;AP活性在水中昼夜呈极其显著的垂直分布规律,随着水深增加逐渐增加.相关性分析结果表明,拟多甲藻细胞密度与水深、DOP浓度呈极显著负相关,水深与CA和AP活性分别呈极其显著负相关与正相关,拟多甲藻细胞密度与CA和AP浓度分别呈极其显著正相关与负相关.因此,拟多甲藻的垂直迁移行为可能是对日间迁移至表层获取光能和无机碳来源、夜间迁移至水下获取磷源的一种适应. 相似文献
18.
Given the continuing concern about rising concentrations of dissolved organic carbon (DOC) in stream water leaving peat‐covered catchments, this study has considered the impact of managed burning or cutting of Calluna vulgaris, a dominant vegetation cover in many UK peatlands. Pristine mature Calluna stands were compared with those that had been subject to cutting and or managed burning up to 5 years after intervention. The study measured the DOC concentration of both soil and surface runoff water over a period of 12 months in comparison with water table depth, conductivity, and pH. The results show the following:
- 相似文献
19.
在河北赤城井井下30 m、53 m、58 m处分别安装了3个温度传感器,进行水温微动态观测。通过对2004年12月以来全球发生的22次M_S≥8.0地震时赤城井不同深度水温观测数据的变化进行研究发现,井下30 m处水温均无明显同震变化;而7次大震时53 m、58 m处水温有明显的同震变化,53 m处水温同震初始变化形态均为上升,58 m处均为下降。同时,对水温变化机理进行探讨发现,井下30 m处水温日变幅度偏大是记录不到地震的主要原因;水温同震初始变化是由井孔水体对流引起的,53 m处水温同震初始变化形态均为上升是由于该处位于负温度梯度带,井孔中水体受震荡激发而加速对流与掺混是导致58 m处水温同震初始下降的主要原因,赤城井水温同震初始变化的后效恢复过程为热传导作用的结果。 相似文献
20.
Nitrate fluctuations at the water table: implications for recharge processes and solute transport in the Chalk aquifer 下载免费PDF全文
下载免费PDF全文 James P. R. Sorensen Andrew S. Butcher Marianne E. Stuart Barry R. Townsend 《水文研究》2015,29(15):3355-3367
This study investigates fluctuations in nitrate concentration at the water table to improve understanding of unsaturated zone processes in the Chalk aquifer. Sampling was conducted using a novel multi‐level sampler during periods of water table rise over 5 years at a vertical resolution of 0.05 m. Nitrate concentration increased as the water table seasonally recovered, with similar inter‐annual trends with depth. The rising water table activated horizontal fractures facilitating the delivery of water elevated by up to 10 mg/l of nitrate with respect to the adjacent groundwater below. These fractures are considered to activate via piston displacement of water from the adjoining matrix. Hydrograph analysis identified 16 events which significantly perturbed the water table within 24–48 h of rainfall. Consistent nitrate concentrations indicate recharge through persistent fracture flow from the surface was not generally the primary driver of the rapid water table response during these events. Instead, the response was attributed to the piston displacement of porewater immediately above the water table. However, a single event in November 2012 delivered relatively dilute recharge indicating rapid persistent fracture flow following rainfall was possible to a depth of 14–15 m. Decreases in porewater nitrate concentration around fracture horizons and the dilution of many groundwater samples with respect to porewaters indicate a fresher source of water at depth. This was considered most likely to be a result of near surface water bypassing the matrix because of widespread mineralization on fracture surfaces, which retard water and solute exchange. Therefore, persistent fracture flow maybe considered a frequent process, operating independently of the matrix, and is not necessarily event driven. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献