a kinetic model for the methane hydrate precipitated from venting gas at cold seep sites at hydrate ridge cascadia margin oregon we develop a kinetic model for hydrate crystallization from methane gas venting through shallow sediments at hydrate ridge on the cascadia margin of oregon that predicts how pore water chlorinity temperature and crystallized hydrate evolve after the onset of steady venting predictions are compared to observations at ocean drilling program site 1249 in the preferred model calculated gas hydrate saturation and chloride concentrations reach those observed at depths less than 20m below seafloor bsf under the southern summit of hydrate ridge in similar to 650years and the vertical water flux must be less than 50kg m 2 yr hydrate accumulates more slowly between 20m bsf and the base of the hydrate stability zone where there is no free gas accumulating to observed levels of a few volume percent of hydrate in 10 5 to 10 6 years depending on the water flux that is assumed through this zone this dichotomy means that the presently observed gas venting must have been diverted to this area similar to 650years ago or be episodic and infrequent if the gas venting for the last 650years has been as observed today the latent heat of hydrate precipitation in the upper 20m of sediments would have caused the temperature to increase similar to 0 8 degrees c at similar to 20m bsf and similar to 0 2 degrees c at similar to 100m bsf this would have caused a similar to 5m rise in the elevation of the base of hydrate stability zone and decreased the rate of hydrate crystallization from 1 5kg ch4 m 2 yr 650years ago to 0 7kg ch4 m 2 yr today

macropore flow on a reclaimed surface mine infiltration and hillslope hydrology abstract surface coal mining in central pennsylvania alters the physical and hydrological properties of soil from its undisturbed state and changes the surface hydrologic response to precipitation newly reclaimed minesoils exhibit low steady state rates of infiltration 1 2 cm h and produce runoff dominated by infiltration excess overland flow within 4 years after reclamation rates of infiltration on some minesoil surfaces approach pre mined rates 8 cm h as a greater percentage of rainfall infiltrates these reclaimed minesoils little change occurs in the total volume of surface storm runoff on an event basis this indicates that infiltrated water contributes to storm runoff by the processes of throughflow and return flow as the rate of infiltration increases with time the hydrologic response of the minesoil is controlled by rapid macropore throughflow within the unsaturated minesoil application of fluorescent dyes on the reclaimed surface reveals preferred flowpaths through macropores surrounding the numerous large rock fragments in the minesoil development and integration of a macropore network on a reclaimed surface mined watershed has a significant direct effect on the contributions to surface storm runoff from infiltration excess overland flow throughflow and return flow as rates of infiltration increase through time and slightly delayed macropore return flow increases the peak rate of surface storm runoff is reduced therefore reducing the potential for severe gully erosion on the reclaimed site in addition throughflow moves predominantly within the minesoil horizon and has limited contact with potentially acid producing backfill better understanding of the process of macropore flow in reclaimed minesoils will help investigators evaluate past strategies and develop new reclamation techniques that will optimize the long term effluent and ground water quality while minimizing the short term surface erosional effects of mining and reclamation

sulfide oxidation in brown coal overburden and chemical modeling of reactions in aquifers influenced by sulfide oxidation surface mining of brown coal in the rhineland brown coal mining area germany causes acidification of pyritic sandy overburden sediments convective transport of air indicated by an enrichment of nitrogen gas in oxidized overburden is in addition to diffusion of oxygen the driving mechanism for sulfide oxidation products of sulfide oxidation 2so42 2h fe2 stored in acidic material in the overburden dump are leached by groundwater filling the dump and react with the carbonate phases of nonacidic material the resulting hydrochemical composition up to 6000 mg l 1 so42 3000 mg l 1 fe2 ph 4 5 in groundwaters is controlled by simultaneous solubility equilibria with caso4 2h2o s fe oh 3 s fe0 9ca0 1co3 s and co2 g calculated equilibrium concentrations of major components and ph in groundwater partial pressure of co2 g in soil gas and coupled mass transfer match observed conditions

sediment surface effects on methane hydrate formation and dissociation abstract the effects of sediment surfaces on methane hydrate formation and dissociation were investigated using colloidal suspensions and new experimental methods developed for a large volume 72 liters temperature controlled pressure vessel hydrates were formed by bubbling methane gas through test solutions at temperatures and pressures within the hydrate stability field hydrate formation was visually detected by the accumulation of hydrate encrusted gas bubbles to measure hydrate dissociation conditions the pressure vessel was warmed while temperature was monitored within a zone of previously formed hydrate encrusted gas bubbles hydrate dissociation was indicated by a distinct plateau in the hydrate zone temperature while temperatures of the gas and liquid phases within the vessel continued to rise the dissociation plateau appears to be a phenomenon that is unique to the large volume of the pressure vessel used for the experiments in experiments where hydrates were formed in pure water temperature and corresponding pressure conditions measured during the temperature plateau matched model predicted values for hydrate stability in water thus confirming the validity of this new method for measuring hydrate dissociation conditions formation and dissociation conditions were measured for methane hydrates in colloidal suspensions containing bentonite hydrate formation experiments indicated that the presence of bentonite in water at 200 mg l significantly decreased pressures required for hydrate formation relative to formation in pure water alone on the other hand hydrate dissociation conditions measured in bentonite and silica suspensions with solids concentrations of 34 g l did not differ significantly from that of water these results are relevant to the origin and stability of natural gas hydrate deposits known to exist in deep permafrost and marine sediments where the effects of sediment surfaces are largely unknown

characterization of in situ elastic properties of gas hydrate bearing sediments on the blake ridge during ocean drilling program leg 164 shear sonic velocity and other geophysical logs were acquired in gas hydrate bearing sediments on the blake ridge to characterize the very distinct seismic signature of such formations anomalous low amplitudes overlying a strong bottom simulating reflector bsr a comparison of the bulk moduli derived from the logs to standard elastic consolidation models shows that the sediments are overconsolidated above the bsr at 440 meters below seafloor mbsf because of the presence of hydrates below the bottom of the thermodynamic hydrate stability zone at 520 mbsf the high compressibility of the formation and the attenuation of the monopole sonic waveforms are typical of sediments partially saturated with free gas between these two depths gas hydrate and free gas seem to coexist within the gas hydrate stability zone we estimate the amount of gas hydrates using different models based on theories for wave scattering in multiphase media and for grain cementation in close agreement with measurements made on discrete in situ samples the latter describes most accurately the interactions between the matrix the pore fluids and the hydrates this model indicates that 5 to 10 of the pore space is occupied by hydrates deposited uniformly on the surface of the grains the comparison with gassmann s model also show that the amount of free gas below the bsr never exceeds 5 of the pore space but is high enough to generate the bsr the coexistence of free gas and gas hydrates below the bsr may be explained by capillary effects in the smaller pores or by remaining crystalline structures after partial hydrate decomposition

a numerical model to estimate the effects of variable sedimentation rates on methane hydrate formation application to the odp site 997 on blake ridge southeastern north american continental margin

theory and numerical modeling of electrical self potential signatures of unsaturated flow in melting snow 1 we have developed a new theory and numerical model of electrical self potential sp signals associated with unsaturated flow in melting snow the model is applicable to continuous natural melt as well as transient flow phenomena such as meltwater pulses and is tested using laboratory column experiments sp signals fundamentally depend on the temporal evolution of snow porosity and meltwater flux electrical conductivity ec and ph we infer a reversal of the sign of the zeta potential a fundamental electrical property of grain surfaces in porous media consistent with well known elution sequences of ions that cause progressive increases and decreases in meltwater ph and ec respectively injection of fully melted snow samples containing the entire natural range of ions into melting snow columns caused additional temporary reversals of the sign of the zeta potential widely used empirical relationships between effective saturation meltwater fraction ec and ph as well as snow porosity grain size and permeability are found to be robust for modeling purposes thus nonintrusive sp measurements can serve as proxies for snow meltwater fluxes and the temporal evolution of fundamental snow textural hydraulic or water quality parameters adaptation of automated multisensor sp acquisition technology from other environmental applications thus promises to bridge the widely acknowledged gap in spatial scales between satellite remote sensing and point measurements of snow properties sp measurements and modeling may therefore contribute to solving a wide range of problems related to the assessment of water resource availability avalanche or flood risk or the amplification of climatic forcing of ice shelf ice sheet or glacier dynamics

modeling dynamic marine gas hydrate systems dynamically changing marine gas hydrate systems are the subject of this study the changes may result from varying pressure or temperature at the seafloor exploration and exploitation operations rapid sedimentation or wasting at the seafloor etc pressure and temperature may not be used as independent state variables at the same time to specify the overall state of such dynamic systems consequently a pressure enthalpy gas concentration salinity phase balance model is constructed for calculating phase distribution and transition of the system of marine gas hydrate which is assumed to contain a liquid phase consisting of water gas and salt a vapor phase consisting of gas only solid halite and solid gas hydrate consisting of gas and water calculations of phase transition processes demonstrate various dynamic feedback mechanisms involved in dynamically evolving marine gas hydrate systems a comprehensive model of fluid flow and transport of heat water salt and gas in marine sediment is developed simulations show that gas hydrate dissociation resulting from increasing temperature or decreasing pressure at the seafloor may lead to the development of a three phase zone with coexistent gas hydrate free gas and liquid solution and excess pore pressure in marine gas hydrate systems the changes considered in this study are rapid 5 years with respect to the geological time scale but are sufficiently slow 10 2 years to allow thermodynamic equilibrium throughout the applicable pressure temperature and salinity ranges for the calculations used in this study are sufficiently wide to cover those likely occurring in gas hydrate bearing marine sediments

a kinetic model for the pattern and amounts of hydrate precipitated from a gas steam application to the bush hill vent site green canyon block 185 gulf of mexico 1 we construct a linear kinetic model of hydrate crystallization from a gas stream we use this model to predict the fraction of gas that crystallizes as hydrate in the subsurface of bush hill and the depth profile of subsurface hydrate accumulation this is possible because the bush hill vent is fed by reservoir gas from the nearby jolliet field whose composition is known on the average 9 of the vent gas is precipitated as hydrate in the subsurface although other explanations are possible the observed vent gas compositions and the greater range of hydrate gas compositions are consistent with a single source gas whose venting rate varies by a factor of at least 3 over periods of a few years or less the predicted depth profile of hydrate accumulation and the hydrate content of the bush hill mound suggest that between 1 1 109 and 2 8 109 m3 stp of gas may have accumulated as hydrate between the seafloor and 614 m depth for the radiometrically and geologically suggested system age of 10 000 years the time average venting rate is 106 m3 yr 0 7 106 kg yr if distributed evenly across the 600 m diameter mound as suggested by echo sounder images the methane flux is 3 2 kg m2 yr this is 103 times that inferred for hydrates associated with bottom simulating seismic reflectors the subsurface hydrate accumulation and the cumulative methane venting are related we show how both may be estimated from measurements of vent gas composition bottom water temperature and geothermal gradient

assessment of preferential flow processes in a forest reclaimed lignitic mine soil by multicell sampling of drainage water and three tracers abstract predictions of the long term development of newly established forest reclaimed ecosystems are required for land use planning of post mining landscapes the geological and mineralogical composition the small distance heterogeneity and inclined structures of the mine spoil s overburden sediment mixtures as well as the physical and chemical properties of acidic and lignitic mine soil components have raised questions about the water flow and solute transport processes in these soils the objective of this study was to quantify preferential flow processes and spatially resolved solute transport in order to better distinguish between dominating processes for such soils the experimental study was carried out by determining spatially resolved rates of throughfall drainage and tracer leaching from underneath a 110 cm deep mine soil block drainage water was collected using 45 contiguous suction cells of 27 cm edge length a tracer cocktail consisting of bromide terbuthylazine and deuterium was applied at the soil surface and subjected to natural infiltration tracer concentrations in drainage waters were analysed for a period of about 10 months then the mine soil block was sampled completely in the form of 225 cubes of about 27 cm edge length to determine the residual bromide content tracer labelled drainage in 110 cm depth occurred in spring 2001 over about 71 and in autumn 2001 over 35 of the total cross sectional drainage area respectively local drainage maxima shifted from spring to autumn but also within drainage periods by 1 2 cell lengths bromide concentrations of drainage effluents varied by a factor of 4 between individual cells bypass type preferential flow seems not to be a dominating transport mechanism since terbuthylazine in drainage waters occurred only singularly in spring with concentrations just above the detection limit perhaps the dilution in relatively large cells was too effective to detect modest contributions of tracer through preferential flow paths relative concentrations of deuterium and of bromide were akin during both drainage periods indicating similar transport behaviour of both tracers in the mine soil the spatial distribution of residual bromide concentrations in the subsoil seemed to correspond with the inclined spoil ripple structures the spatial patterns of leached bromide suggest a funnelling type flow concentration in this lignitic mine soil preferential flow is presumably caused by the temporarily varying effects of multiple determinants such as inclined dumping structures spatial variability of hydraulic properties water repellence and the properties of lignitic dust and fragments with some immobile porosity

national gas hydrate program expedition 01 offshore india gas hydrate systems as revealed by hydrocarbon gas geochemistry abstract the national gas hydrate program expedition 01 nghp 01 targeted gas hydrate accumulations offshore of the indian peninsula and along the andaman convergent margin the primary objectives of coring were to understand the geologic and geochemical controls on the accumulation of methane hydrate and their linkages to underlying petroleum systems four areas were investigated 1 the kerala konkan basin in the eastern arabian sea 2 the mahanadi and 3 krishna godavari basins in the western bay of bengal and 4 the andaman forearc basin in the andaman sea upward flux of methane at three of the four of the sites cored during nghp 01 is apparent from the presence of seafloor mounds seismic evidence for upward gas migration shallow sub seafloor geochemical evidence of methane oxidation and near seafloor gas composition that resembles gas from depth the kerala konkan basin well contained only co2 with no detectable hydrocarbons suggesting there is no gas hydrate system here gas and gas hydrate from the krishna godavari basin is mainly microbial methane with 13c values ranging from 58 9 to 78 9 with small contributions from microbial ethane 52 1 and co2 gas from the mahanadi basin was mainly methane with lower concentrations of c2 c5 hydrocarbons c1 c2 ratios typically 1000 and co2 carbon isotopic compositions that ranged from 70 7 to 86 6 for methane and 62 9 to 63 7 for ethane are consistent with a microbial gas source however deeper cores contained higher molecular weight hydrocarbon gases suggesting a small contribution from a thermogenic gas source gas composition in the andaman basin was mainly methane with lower concentrations of ethane to isopentane and co2 c1 c2 ratios were mainly 1000 although deeper samples were

preferential flow in a sandy vadose zone 1 field observation abstract field experiments of water movement in the lower portion of an unsaturated zone i e vadose zone are far more difficult to conduct than those in the root zone thus our concept of the transport mechanism in the vadose zone is still primitive and mainly an extrapolation of our understanding of transport in the root zone recent results from field experiments conducted at the hancock agricultural research station indicated that water and solute applied uniformly to soil surfaces did not flow through the entire vadose zone by using dye tracing and profile excavation field experiments were conducted during the 1987 growing season to examine water flow patterns in the unsaturated zone of the central sand area of wisconsin csaw the results confirmed that preferential flow paths constitute the dominant flow pattern at this location water flowing through the root zone was funneled into concentrated flow paths that occupied only a small portion of the soil matrix in the vadose zone yet accounted for most of the transport the observed phenomena of preferential flow in a sandy vadose zone are discussed in this paper the mechanism and implications of preferential flow are presented in a companion paper

air permeability and capillary rise as measures of the pore structure of snow an experimental and theoretical study air permeability and capillary pressure are macroscopic snow properties that are influenced by the pore structure of the snow cover formulas for predicting fluid transport species elution and acoustive wave propagation require parameterization of one or both of these properties we report paired measurements of permeability and capillary rise from snow samples at field sites in hanover new hampshire and sleepers river research watershed danville vermont we augment these data with laboratory tests on sieved snow and glass beads our measurements demonstrate a linear relationship between permeability and the ratio of porosity and the square of capillary rise which we corroborate theoretically using a simple conduit model of the pore space we propose that scatter in the data results in part from the effect of crystal shape on air flow and imbibitior contact angle since the early measurements and classification schemes of bader in 1939 many investigators have expanded the database of permeability observations for a wide range of snow types we summarize these data and report our own recent observations from the new england sites and from an additional site in manitoba canada our measurements are in the high range of reported values however after normalizing our data by the square of grain diameter they follow the empirical function of shimizu fairly closely this agreement supports our measurements and demonstrates the usefulness of shimizu s function for snow types other than the relatively dense fine grained snow used in his analysis our normalized permeability data for low density snow as well as the shimizu function are below theoretical predictions for suspensions of spheres and infinite cylinders by extending the model for spheres to oblate spheroids and discs we estimate permeability that is in closer agreement with our data we suggest that a decrease in surface to volume ratio as snow ages may account for a relative increase in normalized permeability

the methane hydrate formation and the resource estimate resulting from free gas migration in seeping seafloor hydrate stability zone it is a typical multiphase flow process for hydrate formation in seeping seafloor sediments free gas can not only be present but also take part in formation of hydrate the volume fraction of free gas in local pore of hydrate stable zone hsz influences the formation of hydrate in seeping seafloor area and methane flux determines the abundance and resource of hydrate bearing reservoirs in this paper a multiphase flow model including water dissolved methane and salt free gas hydrate has been established to describe this kind of flow transfer reaction process where there exists a large scale of free gas migration and transform in seafloor pore in the order of three different scenarios the conversions among permeability capillary pressure phase saturations and salinity along with the formation of hydrate have been deducted furthermore the influence of four sorts of free gas saturations and three classes of methane fluxes on hydrate formation and the resource has also been analyzed and compared based on the rules drawn from the simulation and combined information gotten from drills in field the methane hydrate mh formation in shenhu area of south china sea has been forecasted it has been speculated that there may breed a moderate methane flux below this seafloor hsz if the flux is about 0 5 kg m 2 a 1 then it will go on to evolve about 2700 ka until the hydrate saturation in pore will arrive its peak about 75 approximately 1 47 x 10 9 m 3 mh has been reckoned in this marine basin finally is about 13 times over preliminary estimate c 2009 elsevier ltd all rights reserved

comparison of methane mass balance and x ray computed tomographic methods for calculation of gas hydrate content of pressure cores abstract gas hydrate saturation was calculated for twelve pressure cores taken during national gas hydrate program nghp expedition 01 in the krishna godavari basin bay of bengal at a location where thin gas hydrate veins were common one of two methods were used to calculate gas hydrate saturation for each core methane mass balance after depressurization and gas collection considered the gold standard for measurement of gas hydrate saturation or voxel intensity analysis rather than binary segmentation of x ray computed tomographic ct reconstructions gas hydrate saturation in cores measured by methane mass balance was calculated to be 17 8 10 9 11 9 13 6 9 5 1 4 and 0 by percent of core volume gas hydrate saturation in similar cores measured by intensity analysis of ct reconstructions was 17 2 9 1 6 7 7 8 and 3 1 by percent of core volume this quantitative ct intensity analysis contained systematic errors and therefore the calculated hydrate saturations are lower bounds the systematic errors can be removed from the quantitative ct analysis by converting the ct intensities to real densities though this was not possible for this study all pressure core gas hydrate saturations were similar in magnitude to each other as well as to independent estimates of gas hydrate saturation from porewater freshening and all variations in saturation could be explained by natural variation between samples ct intensity or preferably density analysis of pressure cores showed promise for calculation of the saturation of vein hydrate in natural samples allowing pressure cores to be used for further analyses under pressure after hydrate quantification theoretical examination of ct density analysis showed that this method would be unable to detect pore filling gas hydrate judicious examination of the results from ct density analysis versus other hydrate quantification methods on the same samples might allow quantification of pore filling hydrate

focussed fluid flow on the hikurangi margin new zealand evidence from possible local upwarping of the base of gas hydrate stability the southern hikurangi subduction margin is characterized by significant accretion with predicted high rates of fluid expulsion bottom simulating reflections bsrs are widespread on this margin predominantly occurring beneath thrust ridges we present seismic data across the porangahau ridge on the outer accretionary wedge the data show high amplitude reflections above the regional bsr level based on polarity and reflection strength we interpret these reflections as being caused by free gas we propose that the presence of gas above the regional level of bsrs indicates local upwarping of the base of gas hydrate stability caused by advective heatflow from upward migrating fluids although we cannot entirely rule out alternative processes simplified modelling of the increase of the thermal gradient associated with fluid flow suggests that funnelling of upward migrating fluids beneath low permeability slope basins into the porangahau ridge would not lead to the pronounced thermal anomaly inferred from upwarping of the base of gas hydrate stability focussing of fluid flow is predicted to take place deep in the accretionary wedge and or the underthrust sediments above the high amplitude reflections sediment reflectivity is low a lack of lateral continuity of reflections suggests that reflectivity is lost because of a destruction of sediment layering from deformation rather than gas hydrate related amplitude blanking structural permeability from fracturing of sediments during deformation may facilitate fluid expulsion on the ridge a gap in the bsr in the southern part of the study area may be caused by a loss of gas during fluid expulsion we speculate that gaps in otherwise continuous bsrs that are observed beneath some thrusts on the hikurangi margin may be characteristic of other locations experiencing focussed fluid expulsion

the role of soil organic matter in the geochemical cycling of chloride and bromide abstract chloride to bromide ratios were determined for rainfall in western australia and groundwaters and surface waters from a number of catchments in western australia victoria and queensland the ratio in rainfall though showing a large short term scatter on average reflected the ratio in ocean water groundwaters and surface waters often showed characteristic differences in cl br presumably associated with the cycling of bromide through soil organic matter to prove this association it is shown that in the leachate of saturated small columns of soil the cl br ratio is governed by chloride and bromide released from decomposing organic matter on leaching the columns of soil the cl br weight ratio decreased rapidly from a high 300 reflecting rainfall to a low 10 reflecting the ratio of chlorine to bromine bound to soil organic matter

testing proposed mechanisms for seafloor weakening at the top of gas hydrate stability on an uplifted submarine ridge rock garden new zealand we evaluate different hypotheses concerning the formation of a peculiar flat topped ridge at rock garden offshore of the north island of new zealand the coincidence of the ridge bathymetry with the depth at which gas hydrate stability intersects the seafloor has been previously used to propose that processes at the top of gas hydrate stability may cause seafloor erosion giving rise to the flat ridge morphology two mechanisms that lead to increased fluid pressure and sediment weakening have previously been proposed 1 periodic formation association and dissociation of gas hydrates during seafloor temperature fluctuations and 2 dissociation of gas hydrates at the base of gas hydrate stability during ridge uplift we use numerical models to test these hypotheses as well as to evaluate whether the ridge morphology can develop by tectonic deformation during subduction of a seamount without any involvement from gas hydrates we apply a commonly used 1d approach to model gas hydrate formation and dissociation and develop a 2d mechanical model to evaluate tectonic deformation our results indicate that 1 tectonics subduction of a seamount may cause a temporary flat ridge morphology to develop but this evolves over time and is unlikely to provide the main explanation for the ridge morphology 2 where high methane flux overwhelms the anaerobic oxidation of methane via sulphate reduction near the seafloor short period temperature fluctuations but on timescales of years not months as proposed originally in the bottom water can lead to periodic association and dissociation of a small percentage of gas hydrate in the top of the sediment column however the effect of this on sediment strength is likely to be small as evidenced by the negligible change in computed effective pressure 3 the most likely mechanism to cause sediment weakening leading to seafloor erosion results from the interaction of gas hydrate stability with tectonic uplift of the ridge provided bulk permeability strongly decreases with increasing hydrate content rather than overpressure developing from dissociation of hydrates at the base of gas hydrate stability as previously thought we found that the weakening is caused by focusing of gas hydrate formation at shallow sediment levels this creates large fluid pressures and can lead to negative effective pressures near the seafloor reducing the sediment strength

methane migration within the submarine gas hydrate stability zone under deep water conditions abstract possible pathways of methane migration and associated gas hydrate accumulation are considered gas hydrates precipitate in water filtration routes when the methane concentration in water exceeds its solubility which significantly decreases within the hydrate stability zone towards the sea floor in the vicinity of the ascending free gas flows gas hydrates are formed within a diffusion aureole resulting from the difference between chemical potentials of gaseous and water dissolved methane the role of diffusion is also essential in the vicinity of gas saturated water flows as well as within and above the sections where biochemical methane is intensively generated a chemical potential gradient of dissolved methane which is a necessary condition for gas hydrate accumulation is created due to inhomogeneity of the geological medium manifested as temperature and water salinity gradients or changes of permeability the thermobaric gas hydrate stability zone is a geochemical barrier for hydrocarbon gas emigrating from sediments into the water column however methane is not completely preserved in a hydrate state it is unknown yet which fraction of migrating methane is detained on this barrier

solute leaching in a sandy soil with a water repellent surface layer a simulation many sandy soils in the netherlands have a water repellent surface layer covering a wettable soil with a shallow groundwater table fingers form in the water repellent surface layer and rapidly transport water and solutes to the wettable soil in which the streamlines diverge although several field observations are available this system has not yet been studied systematically in this paper we present a model with a steady state water flow to which solutes are added as a pulse the model predicts the flow through the distribution zone and through the finger in the water repellent surface layer with a closed form solution and transport in the wettable subsoil numerically model calculations show that the travel time through the water repellent surface layer and the thickness and hydraulic conductivity of the wettable soil have the strongest effect on the arrival time of the solute pulse at groundwater level the calculations also show that assuming transport in the wettable subsoil to take place in fingers the travel time is considerably shorter than when the diverging flow in the wettable soil is included

vapor transport grain growth and depth hoar development in the subarctic snow measurements from the subarctic snowpack are used to explore the relationship between grain growth and vapor flow the fundamental processes of dry snow metamorphism due to extreme temperature gradients the subarctic pack undergoes extensive depth hoar metamorphism by the end of the winter a five layered structure with a pronounced weak layer near the base of the snow evolves grain size increases by a factor of 2 3 while the number of grains per unit mass decreases by a factor of 10 observed growth rates require significant net inter particle vapor fluxes stable isotope ratios show that there are also significant net layer to layer vapor fluxes soil moisture enters the base of the pack and mixes with the bottom 10 cm of snow while isotopically light water vapor fractionates from the basal layer and is deposited up to 50 cm higher in the pack end of winter density profiles for snow on the ground compared with snow on tables indicate the net layer to layer vapor flux averages 6 x 10 7 kg m 2 s 1 though detailed measurements show the net flux is episodic and varies with time and height in the pack with peak net fluxes ten times higher than average a model driven by observed temperature profiles reproduces the layer to layer flux pattern and predicts the observed weak layer at the base of the snow calculated layer to layer vapor fluxes are ten times higher than inter particle fluxes which implies that depth hoar grain growth is limited by factors other than the vapor supply this finding suggests that gain and loss of water molecules due to sublimation from grains takes place at a rate many times higher than the rate at which grains grow and it explains why grains can metamorphose into different forms so readily

excess pore pressure resulting from methane hydrate dissociation in marine sediments a theoretical approach 1 this study quantifies the excess pore pressure resulting from gas hydrate dissociation in marine sediments the excess pore pressure in confined pore spaces can be up to several tens of megapascals due to the tendency for volume expansion associated with gas hydrate dissociation on the other hand the magnitude of excess pore pressure in well connected sediment pores is generally smaller depending primarily on the hydrate dissociation rate and the sediment permeability volume expansion due to gas hydrate dissociation in well connected pore spaces is related via darcy s law to an increase in pore pressure and its gradient in sediment which drives an additional upward fluid flow through the sediment layer overlying the gas hydrate dissociation area the magnitude of this excess pore pressure is found to be proportional to the rate of gas hydrate dissociation and the depth below seafloor and inversely proportional to sediment permeability and the depth below sea level the excess pore pressure is the greatest at low initial pressures and decreases rapidly with increasing initial pressure excess pore pressure may be the result of gas hydrate dissociation due to continuous sedimentation tectonic uplift sea level fall heating or inhibitor injection the excess pore pressure is found to be potentially able 1 to facilitate or trigger submarine landslides in shallow water environments 2 to result in the formation of vertical columns of focused fluid flow and gas migration and 3 to cause the failure of a sediment layer confined by low permeability barriers in relatively deep water environments

chemical modelling of the groundwater composition in aquifers affected by lignite mine dumps discharge surface mine inden germany the oxidation of pyrite results in sulphate concentrations from 1 300 to 2 000 mg l in the dump water of the open cast mine inden which is located in germany under near neutral ph and reduced redox conditions precipitation of siderite feco3 retains up to 85 of the pre liberated ferrous iron so that iron concentrations in the dump water are relatively low as compared to the concentrations of sulphate the highly mineralised dump water will enter the aquifer system northwards of inden during the next centuries this area is used intensely for water extraction model calculations show that there will be no problem of acidification in the adjacent aquifer system and therefore no problem of high heavy metal concentrations during the next centuries the most important problem will be high sulphate concentrations in the groundwater besides dispersion and diffusion there are no chemical mechanisms that lower the sulphate concentrations downstream on the basis of the simulations sulphate plumes of about 1 2 km in width and up to 15 km in length are expected within the core of these plumes sulphate concentrations will be above the drinking water limits

the permeability of a melting snow cover data from snow lysimeters in california and vermont are used to find the saturated permeability of a melting snow cover in the range of 10 40 10 10 m2 depending on snow density the unsaturated permeability increases as about the third power of liquid saturation the gravity flow theory is shown to be an accurate representation of meltwater drainage from snow covers in two diverse areas even though the snow covers are treated as homogeneous units the variation of saturated permeability with snow density occurs about as predicted by shimizu s formula for dry snow although ice layers decrease the permeability somewhat

depressurization experiment of pressure cores from the central ulleung basin east sea insights into gas chemistry abstract we performed depressurization experiments on pressure cores pcs recovered from holes ubgh1 10b and ubgh2 11b which were drilled during two separate expeditions in the ulleung basin ubgh1 and ubgh2 various lines of evidence such as convex curvature in the p v curves obtained by depressurization as well as x ray images and resistivity at bit rab data point to the presence of gas hydrates at these holes we estimated gas hydrate saturation sh at these holes to range from 5 23 based on the amount of gas released from pcs these sh values are in agreement with those reported at other high gas flux settings molecular c1 c2 and isotopic 13cch4 dch4 13cc2h6 indicators delineate a microbial source for the ch4 and c2h6 in core ubgh1 10b 5r the carbon isotopic fractionation factor between co2 and ch4 ec 13cco2 13cch4 was observed to increase from 50 to 68 as pressure was reduced during our experiments these changes illustrate the isotope fractionation that results from the preferential release of 13c depleted co2 during the early stages of depressurization the constant carbon isotope separation 10 20 between co2 in void gases and in the dissolved inorganic carbon dic pool shown in cores from the ulleung basin has also been observed in gas hydrate bearing sediments elsewhere it is important to consider this effect when using carbon isotopic data in carbon cycling models specifically when unraveling metabolic pathways of methane generation in situations where partial co2 degassing of a core is suspected we recommend the use of the carbon isotope ratio of dic instead of the gas measurements to best delineate the methane cycling pathways in marine systems

atmospheric oxidation of the pyritic waste rock in maardu estonia 1 field study and modelling a field survey and modelling of the oxidation and carbonate buffering reactions inside the alum shale containing waste rock dumps located in maardu estonia was accomplished in the slope areas the shale has been altered at high temperatures due to the spontaneous combustion and the pyritic acidity has been eliminated through migration of sox gases out from the dump in the central parts of the waste rock plateaus low temperature pyrite oxidation fronts develop towards the dump depth and towards the centres of individual shale lumps the main secondary phases precipitating in the weathering profile are gypsum ferric oxyhydroxide k jarosite and smectite the respective field data made it possible to calibrate the two stage oxygen diffusion model and the characteristic pyrite oxidation rate 0 06 0 08 mol of pyrite reacted per kg of available water pyrox h2o value was estimated to describe the first tens of years of dump performance the model is capable to compare different shale disposal strategies that are illustrated with two case scenarios the buffering of sulphuric acid by mg calcite appears to be an incongruent reaction with gypsum precipitating that leads to the build up of the high mg ca ratio in the leachate application of the mg ca method estimates the pyrox h2o value in the range of 0 05 0 14 mol kg

modelling the effect of chemical heterogeneity on acidification and solute leaching in overburden mine spoils abstract the generation of acid mine drainage from overburden spoil piles at open pit lignite mines is impacting the quality of groundwater and surface water bodies in large parts of the lusatian mining area in germany values of ph as low as 1 have been observed in the groundwater after decommissioning mine pits are generally converted to lakes which may also be acidic owing to the acidic groundwater discharge the acidic effluent is generated by sulphide oxidation in the unsaturated zone of the spoil pile which generally extends to large depths as a result of dewatering the long term evolution of the acidification is still largely unknown our research focuses on the effects of physical and chemical heterogeneity caused by mixing of soil materials that may have already been oxidized to different degrees during the deposition of the spoil pile processes considered include variably saturated groundwater flow oxygen diffusion in the soil gas kinetic pyrite oxidation and acidic effluent generation advective dispersive transport of the aqueous components equilibrium geochemical reactions between the chemical components and the soil minerals and possible buffering and acid neutralization several existing numerical codes were coupled to represent the complete set of processes simulations were carried out in one and two dimensions using representative characteristics of mine spoil piles with the two dimensional representation being based on spatially heterogeneous random fields of hydraulic conductivity and sulphide mineral fractions results show the long term evolution of the oxidation front the mass flux of oxidation products and the effects of system heterogeneity under conditions of constant flow the system is found to return to neutral conditions over a time period on the order of several decades further work including sensitivity analyses with respect to the controlling parameters and model calibration using site specific field data will be necessary to obtain a full understanding of the complex interacting mechanisms the simulation approach shows promise as a potentially useful tool for predicting the effects of sulphide oxidation on the water quality of pit lakes

geomechanical issues in the exploitation of natural gas hydrate abstract as a clean fossil fuel with great reserves natural gas hydrate ngh is widely regarded as an important future alternative energy source ngh is widely distributed in onshore tundra and shallow sedimentary layers in the deep sea these sedimentary layers typically exit shallow burial depth poor diagenesis and low strength characteristics moreover the decomposition of ngh can also greatly reduce reservoir strength therefore ngh development can easily causes many geomechanical problems including reservoir instability sand production and seabed landslides etc which may further trigger a series of environmental disasters such as tsunamis natural gas leakage and the acceleration of global warming this study mainly reviews the research progress regarding geomechanical issues in ngh development including mechanical properties of ngh bearing sediments borehole stability hydraulic fracturing sand production reservoir settlement and seabed landslides in addition to previous research achievements regarding geomechanical problems in ngh exploitation the limitations and challenges are also discussed and several questions and insightful suggestions are put forward for future research from our point of view