recharge of the upper chalk aquifer at a site in hampshire england 2 solute movement abstract this paper describes a field experiment to study the movement of solutes through the unsaturated zone of the chalk using soil physical techniques to calculate water fluxes and sequential soil coring to measure solute concentrations with depth and time deuterium oxide was used as a tracer to follow water movement nitrate leaching beneath spring barley was calculated below the root zone approximately 40 kg ha 1 yr 1 of nitrate nitrogen were leached beyond root depth 1 m in the two study years at concentrations of between 20 and 75 mg l 1 and at a downward velocity of 0 85 m yr 1

the effects of biological and hydrodynamic processes on physical and acoustic properties of sediments off the eel river california abstract the spatial trends in surficial sediment macro and microstructure and the resultant values of sediment physical and geoacoustic properties are controlled by the water depth dependent interplay of biological depositional and hydrodynamic processes along shore normal 25 100 m water depth and shore parallel 70 m contour transects north of the eel river northern california values of sediment compressional and shear wave speed porosity bulk density mean grain size and shear strength cluster within reasonably well defined surficial sediment facies inshore sands 21 42 m water depth offshore muds 90 100 m flood deposits 57 80 m and transition sediments between flood deposits and inshore sands 47 57 m statistical relationships among seafloor impedance calculated from in situ and laboratory measurements or measured remotely by acoustic methods sediment physical properties and geoacoustic properties are sufficiently robust to allow prediction with confidence the high local spatial variability in values of sediment physical and geoacoustic properties reflects the variability in macro and microstructure exhibited in x radiographs and ct imagery large scale distribution of sedimentary facies is controlled by flood deposition from the eel river and subsequent remobilization by hydrodynamic processes high local variability in sediment properties occurs where no single process is consistently dominant transition sediments the high variability of seafloor properties in flood deposits reflects the high structural heterogeneity associated with the interaction among numerous flood deposits resuspension and redeposition of flood deposits by surface gravity waves and mixing by bioturbation faunal reworking of sediments rapidly

distributions and vertical variation patterns of sound speed of surface sediments in south china sea the distributions of sound speed show different characteristics in continental shelf continental slope and nansha trough the differences have closely related to the distributions of sediment physical properties in the southern south china sea according to the analysis of sound speeds and physical properties variation characteristics with buried depth the vertical variations of sound speed are closely related to sediment texture sedimentary environment transport erosion compaction consolidation etc the comparison results indicate 3 vertical variation patterns of sound speed increasing model invariant model and complicate variation model the above 3 variation models represent the vertical distribution characteristics of sound speed in different depositional environments different variation patterns have different key factors which generally contain porosity or grain size the calculated sound speeds with buckingham s theory of compressional waves in fluid like marine sediments follows the trend of measured speeds accurately c 2014 elsevier ltd all rights reserved

mechanisms of groundwater recharge and pesticide penetration to a chalk aquifer in southern england abstract in order to assess the potential for enhanced agrochemical contamination of shallow groundwaters a field study was established on the upper chalk in hampshire uk two instrumented sites 380 m apart were established on a hillslope one on the interfluve with a deep water table 18 m depth the other on the dry valley bottom where the groundwater was close to the surface 4 m depth hourly measurements of water potentials in the unsaturated zone to 3 0 m depth identified very different groundwater recharge processes between the two sites in response to the same storm event on the interfluve site with the deep water table only matrix flow through the chalk unsaturated zone at 3 m depth was identified in contrast at the dry valley bottom with a shallow water table both rapid preferential flow and matrix flow processes were observed at a 3 m depth the correlation between groundwater depth measurements and unsaturated profile moisture content measurements demonstrated the importance of the capillary fringe in sustaining a higher moisture content in the unsaturated zone at the shallow groundwater site the resulting reduced water storage capacity for vertical drainage fluxes meant that little water was required to wet the shallow profile before rapid preferential flow events demonstrated by rapid water potential responses occurred however where the groundwater was deeper intermediate storage sites located on chalk surfaces and at chalk ped block contact points remained empty and unsaturated water potential profiles showed that rainfall pulses were attenuated as these sites absorbed the downward water fluxes consequently preferential events at these deep groundwater sites are rare the importance of these intermediate storage sites in controlling recharge processes is highlighted the potential mass load of pesticide transported to the shallow groundwater in preferential events during 1996 7 was determined using bromide tracer studies water balance calculations and measured groundwater pesticide concentrations an estimated 0 1 of the applied pesticide reached the shallow groundwater along preferential pathways in 1996 7 calculations under a worst case scenario showed that this value did not increase beyond 0 2 of pesticide applied

abstract structural and paleogeographic elements of the nanpanjiang basin guizhou guangxi and yunnan provinces south china a compilation from satellite images regional geologic maps and ground observations

approximate boundaries between different flow regimes in fractured rocks recent studies have shown how water films at near zero matric potentials on fracture surfaces could permit fast flow in unsaturated fractures the present work is aimed at delineating the ranges of conditions necessary to permit film flow the approximate matric potential needed to permit thickening of water films on fracture surfaces was estimated through correlating air entry matric potentials and permeabilities for a wide range of porous media an upper matric potential limit associated with saturating the fracture was related to the fracture aperture these two limits one dependent on matrix permeability and the other on fracture aperture delineate the matric potential range within which thick water films develop on fracture surfaces rocks with matrix permeabilities less than 10 14 m2 and fractures with apertures greater than 30 m permit some matric potential range over which thick water films can form highly transmissive films can develop on fracture surfaces only under near zero matric and pressure potentials

modelling flow and heat transfer through unsaturated chalk validation with experimental data from the ground surface to the aquifer abstract during the winter and spring of 2000 2001 large floods occurred in northern france somme river basin and southern england patcham area of brighton in valleys that are developed on chalk outcrops the floods durations were particularly long more than 3 months in the somme basin and caused significant damage in both countries to improve the understanding of groundwater flooding in chalk catchments an experimental site was set up in the hallue basin which is located in the somme river basin france unsaturated fractured chalk formation overlying the chalk aquifer was monitored to understand its reaction to long and heavy rainfall events when it reaches a near saturation state the water content and soil temperature were monitored to a depth of 8 m and the matrix pressure was monitored down to the water table 26 5 m below ground level the monitoring extended over a 2 5 year period 2006 2008 under natural conditions and during two periods when heavy artificial infiltration was induced the objective of the paper is to describe a vertical numerical flow model based on richards equation using these data that was developed to simulate infiltrating rainwater flow from the ground surface to the saturated aquifer the marthe computer code which models the unsaturated saturated continuum was adapted to reproduce the monitored high saturation periods composite constitutive functions hydraulic conductivity saturation and pressure saturation that integrate the increase in hydraulic conductivity near saturation and extra available porosity resulting from fractures were introduced into the code using these composite constitutive functions the model was able to accurately simulate the water contents and pressures at all depths over the entire monitored period including the infiltration tests the soil temperature was also accurately simulated at all depths except during the infiltrations tests which contributes to the model validation the model was used to calculate the aquifer recharge over a long period that included droughts and floods the calculated recharge is realistic as it makes it possible to simulate the corresponding monitored groundwater level data which increases confidence in the modelling approach

recharge of the upper chalk aquifer at a site in hampshire england 1 water balance and unsaturated flow abstract measurements of the annual cycle of changes in water content and potential in the 40 m thick unsaturated zone of upper chalk at a site in southern england are described measured evaporation continued at the penman potential rate until the soil moisture deficit reached 175 mm this suggested that a root constant of 200 mm would be more appropriate than the much lower values generally used the field capacity concept could not be reconciled with the timing of renewed water recharge and the reasons for this are discussed the mechanisms of water flow through the unsaturated zone of the chalk are examined and it is shown that at this upper chalk site matrix flow is the dominant recharge mechanism

the significance of flow in the matrix of the chalk unsaturated zone the significance of flow in the matrix of the chalk unsaturated zone in comparison with flow in fractures has been the subject of much debate in this article important elements of the literature are discussed in detail and several simple modelling analyses based on steady state flow are presented a study of the sensitivity of solute spreading to fracture spacing in models that ignore matrix flow shows that this latter assumption is generally incompatible with observed solute profiles unless unrealistically small fracture spacings are assumed the effect of air phase continuities e g bedding planes on matrix flow has also been examined these discontinuities are frequently interrupted by points of connectivity between matrix blocks an issue therefore is the relationship between connectivity and its effect on inter block conductance a simple analysis of the laplace equation shows that just 1 connectivity represents an effective pathway equivalent to 18 of the local rock hydraulic conductivity obviously when there is no fracture flow solute spreading is significantly reduced however dual permeability model simulations show that matrix flow reduces solute spreading in the presence of persistent fracture flow all of the above studies suggest that flow in the matrix of the chalk unsaturated zone is significant and that ignoring it may result in a serious misunderstanding of the system

acoustic impedance properties of seafloor sediments off the coast of southeastern hainan south china sea geoacoustic parameters are essential inputs to sediment wave propagation theories and are vital to underwater acoustic environment and explorations of the sea bottom in this study 21 seafloor sediment samples were collected off the coast of southeastern hainan in the south china sea the sound speed was measured using a portable wsd 3 digital sonic instrument and the coaxial differential distance measurement method based on the measured sound speed and physical properties the acoustic impedance and the pore water independent index of impedance ioi were calculated in this study similar to the sound speed the ioi values are closely related to the sediment physical properties and change gradually from the northwest to the southeast the relations between ioi and physical properties were studied and compared to the relations between the sound speed and physical properties ioi is better correlated to physical properties than sound speed this study also uses an error norm method to analyze the sensitivity of ioi to the physical parameters in the double parameter equations and finds that the most influential physical parameters are as follows wet bulk density porosity clay content mean particle size

correlations between the in situ acoustic properties and geotechnical parameters of sediments in the yellow sea china knowledge about the marine sediment acoustic properties is a key to understanding wave propagation in sediments and is very important for military oceanography and ocean engineering we developed a hydraulic drived self contained in situ sediment acoustic measurement system and measured for the first time the in situ acoustic properties of sediments on 78 stations in the yellow sea china by employing this system the relationships between the in situ measured acoustic properties and the onboard or laboratory determined geotechnical parameters were analyzed porosity was found to be the dominant factor in reducing velocity in a quadratic fashion velocity showed an increment with bulk density and a decrement with mean grain size and clay content both with a nonlinear dependence acoustic attenuation showed a bell shaped correlation with porosity and mean grain size but reduced with clay content of the sediments the attenuation results indicate that intergrain friction rather than viscous interactions between pore fluid and solid grains is the dominant loss mechanism in our marine sediments the relationships established would be used to predict the geotechnical parameters from in situ measured acoustic properties and vice versa as well as being an indicator of the seafloor processes potential gas bubbles hazard and gas hydrates resources or other suitable targets of acoustic surveys

mechanisms of water storage and flow in the unsaturated zone of the chalk aquifer abstract it is known that the volumes of water draining from some chalk catchments in recessions are significantly greater than can be explained by gravity drainage from fissure porosity the most likely source of this water is slow drainage from the matric porosity above the water table this paper suggests that the location of this storage is in the irregularities on the fissure surfaces studies of resin impregnated blocks of chalk failed to reveal the presence of hydrologically significant microfissures or macropores that could be the source of additional drainage ultrasonic measurements at varying values of effective stress show no indication of changes in the acoustic transmission properties that could be attributed to closure of microfissures drainage and mercury intrusion measurements indicate that there is significant storage on block surfaces the drainage measurements confirm that the storage is of the order of magnitude about 0 3 needed to explain the slow drainage this additional storage explains why the water table is slow to respond after recharge events and why the chalk is resilient to drought the presence of storage in the unsaturated zone implies that the position of the water table may not be an accurate indicator of groundwater resources the concept of filling and draining of irregularities on fissure surfaces also leads to a new model for the generation of fissure flow in the unsaturated zone of the chalk this suggests that fissure flow can be generated at any depth in the profile and in a sequence of uniform vertical permeability is likely to originate near the water table rather than high in the unsaturated zone

geo acoustic modelling of late and postglacial sedimentary units in the baltic sea and their acoustic visibility abstract acoustic profiling methods are commonly used in the geosciences to obtain knowledge about the sedimentary structures of marine deposits however their interpretation and the correlation of acoustic reflectors with sedimentological boundaries remain difficult the gradient in acoustic impedance determines the intensity of acoustic reflectors which are not necessarily sedimentary boundaries suitable geo acoustic models that cover a wide range of sediment types have not yet been developed for the baltic sea based on comprehensive investigations of sediment cores from mecklenburg bay and the arkona basin we developed geo acoustic models that enable the transfer of laboratory p wave velocity measurements to in situ conditions while considering changes in pressure salinity temperature and the frequency dependence of the p wave velocity i e acoustic dispersion this modelling allows the calculation of the wet bulk density and in situ p wave velocity from which the acoustic impedance is calculated from core logging and selected sedimentological data such as the water content loss on ignition and grain size precise plotting of core data into the acoustic profiles is now possible and represents a crucial step towards the interpretation of these profiles modelled p wave velocities are used to convert two way travel time to depth the average sedimentological parameters for the different development phases of the baltic sea are calculated using geo statistical methods and may allow for rough p wave estimations if core logging data are not available

evidence for rapid groundwater flow and karst type behaviour in the chalk of southern england with the growing importance of groundwater protection there is increasing concern about the possibility of rapid groundwater flow in the chalk of southern england and therefore in the frequency and distribution of karstic features pumping test data although useful in quantifying groundwater resources and regional flow give little information on groundwater flow at a local scale evidence for rapid groundwater flow is gathered from other less quantifiable methods nine different strands of evidence are drawn together tracer tests observations from chalk caves chalk boreholes that pump sand descriptions of adits the nature of water level fluctuations the chichester flood the nature of the surface drainage geomorphological features and the presence of indicator bacteria in chalk boreholes although the evidence does not prove the widespread existence of karstic features it does suggest that rapid groundwater flow should be considered seriously throughout the chalk rapid groundwater flow is generally more frequent close to palaeogene cover and may also be associated with other forms of cover and valley bottoms

unsaturated flow and solute transport through the chalk tracer test and dual permeability modelling a tracer test was carried out in the unsaturated chalk at the fleam dyke research site in cambridgeshire uk to investigate the role of the chalk fractures and matrix in unsaturated flow and solute transport the experiment under natural rainfall conditions involved distributing deuterated water on a grass covered lysimeter a cube of volume 125 m3 and on an adjacent 4 m 4 m field plot tracer migration was monitored through regular core sampling and collection of lysimeter drainage water the presence of occasional secondary peaks in sampling of the vertical tracer profile suggested the occurrence of fracture flow allowing some tracer to bypass the chalk matrix however in the 15 months following application none of the tracer was detected in the lysimeter drainage at 5 m depth modelling of the tracer results was undertaken with the 1 d numerical transient dual permeability model macro 5 0 initially developed for macroporous soils modelling results showed that macro 5 0 could reliably simulate transient recharge through the chalk the simulations suggested that fracture flow is important at the site but that it is only initiated at 1 m depth or deeper the extent of fracture flow appeared to be highly variable in different layers of the profile varying between 40 and 85 of the cumulative flux mainly depending on the saturated hydraulic conductivity of the matrix diffusion between the fractures and the matrix tended to equalize solute concentrations in both flow domains although solute bypass through the fractures occurred in some chalk strata besides diffusive exchange the modelling stressed the importance of advective exchange of solutes the results suggest that the chalk aquifer at the fleam dyke site is only moderately vulnerable to pollution even though for moderate rainfall conditions some bypass flow was possible

transient simulations of flow and transport in the chalk unsaturated zone chalk is a fractured porous medium composed of matrix blocks bounded by interconnected fractures furthermore there are a number of commonly observed and apparently contradictory phenomena these include a fast water table response slow solute migration and very little solute dispersion to the authors knowledge no unified physically based numerical model has been able to reconcile all of these points in this paper these issues were addressed through the development of a transient dual permeability model of flow and transport the behaviour of the model was explored through a hypothetical scenario the one dimensional model featured a fixed water table at 10 m depth a recharge time series derived using the penman grindley model in conjunction with daily precipitation and monthly potential evaporation data from the kennet valley berkshire was applied at the top of the model a conservative solute that could be tritium chloride or nitrate was applied to the recharge for 1 year subsequent years involved the input of clean water the simulations suggested that although transient effects have been previously neglected overlying soil and gravelly chalk layers are likely to cause significant attenuating effects on flow such that most flow occurs through the matrix fracture flow was found to be episodic and infrequent and represented between 17 and 30 of the annual recharge

stable carbon isotope stratigraphy across the permian triassic boundary in shallow marine carbonate platforms nanpanjiang basin south china a distinct negative 13c excursion is documented in two permian triassic sections heping and taiping in shallow marine carbonate platform deposits in the nanpanjiang basin south china these sections span from the changhsingian to the dienerian and are characterized by a distinct marine boundary facies change from massive skeletal lime packstone in the changhsingian to distinctive calcimicrobial framestone in the griesbachian hindeodus parvus zone the 13corg and 13ccarb excursions occur directly after the onset of the calcimicrobial framestone herein termed the permian triassic boundary event and before the first occurrence of h parvus the isotope shifts are associated with a sharp drop in species abundance and diversity and coincide with a decrease in total organic carbon toc content the shift towards depleted values in 13corg and 13ccarb at the permian triassic boundary event together with low toc contents persists throughout the griesbachian h parvus zone these data document a corresponding negative shift of 13corg and 13ccarb values and low toc contents with the onset of growth of calcified microbial framestones a postextinction disaster facies immediately below the base of the griesbachian h parvus zone based on paleontological evidence the first occurrence of the disaster facies follows the extinction event which implies that the 13c depleted values above this facies postdate the event this suggests that two separate events had to account for the initiation of the extinction and the 13c excursion however the consequences that led to the negative isotopic shift might be linked to the intriguing recovery lag of early triassic ecosystems based on data from ptb sections worldwide of a greater 13c offset in high compared with low latitudes we propose that methane eruptions from thermal destabilization of high latitude clathrate deposits may have led to the negative 13c shift and may have caused long term adverse ecological conditions

impact of differential tectonic subsidence on isolated carbonate platform evolution triassic of the nanpanjiang basin south china the nanpanjiang basin of south china contains four exceptionally well exposed isolated triassic carbonate platforms detailed mapping of two dimensional transects and description of stratigraphic sections allow the reconstruction of facies architecture sequence stratigraphy and evolution of the platforms biostratigraphy magnetic susceptibility profiles and volcanic ash horizons allow chronostratigraphic correlation and thus a basinwide evaluation of mechanisms controlling platform evolution a comparison of platform architecture demonstrates that southerly platforms have substantially greater thickness backstepping geometry pinnacle development and earlier drowning that resulted from greater tectonic subsidence proximal to a probable convergent margin along the southern perimeter of the basin felsic volcanics thicken southward and contributed to the termination of the southernmost platform indicating the development of a volcanic arc along the southern margin of the south china tectonic block the northernmost isolated platform had greater longevity and lesser accumulation and lacks backstepping and pinnacle phases of development basin margin intertonguing relationships or lack thereof demonstrate that earlier siliciclastic influx into the basin to the south and concurrent starved basin conditions to the north impacted the evolution of platform margin geometries comparative analysis of platform evolution shows that the timing and rates of tectonic subsidence controlled the timing of platform termination by drowning backstep geometries pinnacle development and overall platform thickness the timing of siliciclastic basin fill dictated differences in platform margin geometries such as slope angle relief above basin floor and the presence or absence of basinward platform progradation despite the dramatic differences in platform architecture eustatic sea level fluctuations imparted a basinwide sequence stratigraphic signal

a stable isotope study of recharge processes in the english chalk the 2h and 18o values of water contained in unsaturated chalk have been measured in drillcore profiles taken over a period of 28 months on arable land in cambridgeshire eastern england the isotopic composition of rainfall and lysimeter drainage on the same site has also been monitored over a period of four years the distribution of isotope values in the upper few metres of soil and unsaturated chalk shows that the mechanism of infiltration is not simple piston like downward displacement since the scale of vertical fluctuations is incompatible with estimated annual infiltration and the apparent rates of movement of matrix water derived from thermonuclear tritium studies lysimeter drainage is not isotopically identical to matrix water at the same depth suggesting that different routes to water table are associated with consistently different isotopic content although there is an apparent difference between matrix water beneath arable and permanent grassland these differences appear to cancel out in the composition of bulk recharge beneath these land types the regional aquifer has a uniform isotopic composition similar in value to weighted average rainfall and lysimeter drainage suggesting that the recharge abstraction system has been in isotopic equilibrium for many years despite changes in pumping rates and land use two other chalk sites in southern england have been investigated in less detail but indicate clear difference in infiltration behaviour from that seen in cambridgeshire this seems to be related to a higher matrix conductivity and annual rainfall amount