microbially induced cementation to control sand response to undrained shear current methods to improve the engineering properties of sands are diverse with respect to methodology treatment uniformity cost environmental impact site accessibility requirements etc all of these methods have benefits and drawbacks and there continues to be a need to explore new possibilities of soil improvement particularly as suitable land for development becomes more scarce this paper presents the results of a study in which natural microbial biological processes were used to engineer a cemented soil matrix within initially loose collapsible sand microbially induced calcite precipitation micp was achieved using the microorganism bacillus pasteurii an aerobic bacterium pervasive in natural soil deposits the microbes were introduced to the sand specimens in a liquid growth medium amended with urea and a dissolved calcium source subsequent cementation treatments were passed through the specimen to increase the cementation level of the sand particle matrix the results of both micp and

impact of micro organisms activity on the natural remanent magnetization of the young oceanic crust microbes have been widely reported in the deep subseafloor environment still it is difficult to detect a global chemical signature of bacterial activity in the oceanic crust we carried out experiments up to 355 days exposing very young oceanic basalts to anaerobe sulfate reducing organisms in an in vitro marine environment the natural remanent magnetization of samples was monitored during the whole duration of experiments and within this time frame the most magnetized sub samples lost up to 30 of their original signal scanning electron microscope observations show cycling of iron from the titanomagnetites to iron sulfide phases our results suggest that microbes can have a major and fast impact on the magnetization of young oceanic basalts and could contribute to a global signal as the central anomaly magnetic high seen along ridges axis

filling box flows in porous media we report upon a theoretical and experimental investigation of a porous medium filling box flow by specifically examining the details of the laminar descending plume and its outflow in a control volume having an impermeable bottom boundary and sidewalls the plume outflow initially comprises a pair of oppositely directed gravity currents the gravity currents propagate horizontally until they reach the lateral sidewalls at y pm l the flow then becomes of filling box type with a vertically ascending first front separating discharged plume fluid below from ambient fluid above the flow details are described analytically by first deriving a new similarity solution for darcy plumes with mathit pe o 1 where mathit pe is the peclet number from the similarity solution so obtained we then derive expressions for the plume volume flux and mean reduced gravity as functions of the vertical distance from the source regarding the plume outflow a similarity solution adopted from huppert woods j fluid mech vol 292 1995 pp 55 69 describes the height and front speed of the gravity currents whereas a semi implicit finite difference scheme is used to predict the first front elevation versus time and horizontal distance as with high reynolds number filling box flows that studied here is an example of a coupled problem the gravity current source conditions are prescribed by the plume volume flux and mean reduced gravity conversely discharged plume fluid may be re entrained into the plume be it soon or long after reaching the bottom impermeable boundary to corroborate our model predictions analogue laboratory experiments are performed with fresh water and salt water as the working fluids our experiments consider as independent variables the porous medium bead diameter and the plume source volume flux and reduced gravity predictions for the gravity current front position and height compare favourably against analogue measured data good agreement is likewise noted when considering either the mean elevation or the profile of the first front results from this study may be adopted in modelling geological plumes for example our equations can be used to predict the time required for discharged plume fluid to return to the point of injection in the case of aquifers closed on the sides and below by impermeable boundaries

dispersal of buoyancy driven flow in porous media with inclined baffles here we explore the effect of a series of low permeability tilted baffles on the ascent of a buoyant fluid injected into a porous rock from a linear well motivated by several industrial processes particularly co2 sequestration we first consider both theoretically and experimentally the dynamics associated with flow past an individual inclined baffle if the incident flux is sufficiently large then a pool of injectate grows beneath the baffle and spills over both ends partitioning the flux but otherwise the injectate only flows over the updip end of the baffle leaving a stagnant zone under the downdip part of the baffle in a multi layered system the flow may then be described using nonlinear recurrence relations based on the flow past an individual baffle using this approach in the particular case in which there is a regular distribution of baffles we show that on a scale greater than individual baffles the flow adjusts to a plume of constant width rising at an angle to the vertical which depends on the geometry of the baffles this constant width plume may be described by an effective directional permeability at angles to the vertical where we find where is the effective permeability of the regions between baffles within the boundaries of this plume the majority of pore space is bypassed indeed the plume scale effective porosity is largely associated with the pools of injectate which collect beneath each baffle we show that since the constant width plume has such a large lateral extent the total pore space occupied by the plume per unit height is larger than for a homogeneous formation furthermore these pools lead to a large surface area between injectate and formation water which enhances the reaction of the injectate with the formation water however we also show that in steady state it may be hard to determine this plume scale effective porosity since the ratio of the effective darcy speed and the effective interstitial speed of the plume only relates to the porosity of the updip part of these pools in which the injectate is flowing

geometry bed topography and drainage system structure of the haut glacier d arolla switzerland as part of an integrated study of the hydrology meltwater quality and dynamics of the haut glacier d arolla switzerland the glacier s drainage network structure was determined from patterns of dye recovery in 342 injection experiments conducted from 47 moulins distributed widely across the glacier this structure was compared with theoretical predictions based upon reconstructed patterns of water flow governed by a the subglacial hydraulic potential surface and b the subglacial bedrock surface these reconstructions were based on measurements of ice surface and bedrock topography obtained by a combination of ground survey and radio echo sounding techniques the two reconstructions simulate the drainage system structures expected for a closed channels in which water is pressurized by the overlying ice and b gravity driven open channel flow the closed channel model provides the best fit to the observed structure even though theoretical calculations suggest that under summer discharge conditions open channel flow may be widespread beneath the glacier possible reasons for this apparent discrepancy are discussed

nature of surface electrical conductivity in natural sands sandstones and clays the electrical conductivity of rocks results from conduction through the bulk solution occupying the pores and from surface conduction occurring at the fluid grain interface the nature of the surface electrical conductivity of shaly and clean sands and sandstones is examined surface conduction is characterized by the specific surface conductance which is the sum of three contributions i conduction within the electrical diffuse layer which makes a negligible contribution to the total specific surface conductance ii conduction in the stern layer which is shown to vary significantly with the salinity of the pore fluid at low salinities 10 6 to 10 3 mol 1 1 but becomes independent of salinity at higher salinities iii a mechanism operating directly on the mineral surface independent of salinity and perhaps associated with proton transfer at salinities higher than 10 3 mol 1 1 and at 25 c the specific surface conductance of quartz and clays is equal to 8 9 10 9 s and 2 5 10 9 s respectively equations describing the influence of surface conductivity and microstructure upon the macroscopic electrical conductivity of sands sandstones and shales are also developed

cyanobacterial precipitation of gypsum calcite and magnesite from natural alkaline lake water results from transmission electron microscopy provide direct evidence for cyanobacterial biomineralization of gypsum and calcite in aquatic environments laboratory simulations using filter sterilized natural lake water inoculated with synechococcus sp isolated from fayette ville green lake new york revealed epicellular biomineralization of gypsum calcite and magnesite experimental electron microscopical and sedimentological evidence indicates that synechococcus is responsible for a major proportion of the marl sediment and carbonate bioherms in green lake the elucidated role of synechococcus in biomineralization and its ubiquitous distribution in nature have widespread implications for cyanobacterial mineralization in marine and freshwater environments since late archean time

buoyant currents arrested by convective dissolution 1 when carbon dioxide co2 dissolves into water the density of water increases this seemingly insubstantial phenomenon has profound implications for geologic carbon sequestration here we show by means of laboratory experiments with analog fluids that the up slope migration of a buoyant current of co2 is arrested by the convective dissolution that ensues from a fingering instability at the moving co2 groundwater interface we consider the effectiveness of convective dissolution as a large scale trapping mechanism in sloping aquifers and we show that a small amount of slope is beneficial compared to the horizontal case we study the development and coarsening of the fingering instability along the migrating current and predict the maximum migration distance of the current with a simple sharp interface model we show that convective dissolution exerts a powerful control on co2 plume dynamics and as a result on the potential of geologic carbon sequestration

magnetotactic bacteria and their magnetofossils in sediments abstract living magnetotactic bacteria from freshwater environments show under natural and laboratory conditions a great variety of morphological appearances their magnetosomes vary in number shape and size one species of bacteria yields up to 1000 magnetosomes per cell individual particles reach a size of up to 200 nm as a rule they form elongated chains in bacteria which are held under laboratory conditions loop shaped arrangements and nearly unordered clusters are also found during the laboratory experiments different species of bacteria periodically dominated freshwater samples always exhibited a great variety of different magnetosomes on the other hand samples from marine environment clearly showed the preponderance of one type of particle these observations may reflect specific properties of the physico chemical milieu in which the bacteria grew at the end of our experiments north and south seeking bacteria co existed in roughly equal quantities quaternary unconsolidated sediments from the ammersee bavaria and the antarctic quaternary to tertiary deep sea sediments from the atlantic and pacific and jurassic limestones from the sonnwendgebirge tyrol austria were analyzed for fossil magnetosomes we found that fossil magnetosomes were morphologically similar to those from living bacteria but seemed to be corroded in some cases the observed differences in quantity size and shape of magnetosomes from various sediments may be influenced by variations in bacterial viability and particle stability at different sites but are not determined by geographical latitude

resistivity based monitoring of biogenic gases in peat soils 1 biogenic free phase gas fpg formation was induced in a peat block dimensions 0 28 0 21 0 21 m extracted from a peatland in maine electrical resistivity er surface deformation and methane ch4 flux from the peat surface was monitored over a 48 day period during which the temperature remained constant at 21 1 c er measurements were made on 5 vertical electrode arrays each containing 20 electrodes spaced at 0 01 m intervals surface deformation was monitored using 30 elevation rods equally spaced across the surface of the block and average ch4 flux from the peat surface estimated by integration of measurements obtained with a portable gas detector over a 20 min time period pore water conductivity was recorded at three depths 0 06 0 09 and 0 15 m at a single point in the block er measurements were inverted for the ratio resistivity change relative to a background data set and corrected for changes in pore fluid conductivity permitting an estimate of equivalent change in gas content assuming 1 insignificant surface conduction 2 porosity changes estimated from peat surface expansion and 3 an archie saturation exponent n of 1 3 based on results from a parallel block experiment the resistivity ratios reveal a pattern of fpg evolution consistent with surface deformation and ch4 flux data during the first part of the experiment approximately the first 24 days a gradual buildup in fpg within a layer 4 6 cm below the peat surface water table occurs concurrent with modest surface deformation and low ch4 fluxes in contrast during the latter half of the experiment approximately 25 48 days a complex pattern of more pronounced gas buildup and release at multiple depths occurs concurrent with large rates of surface deformation and higher ch4 fluxes the experiment demonstrates that er monitoring is a viable geophysical technology for imaging and monitoring biogenic gas fluxes in peat soils here the resistivity clearly shows that fpg is preferentially generated in layers about 0 04 0 06 m below the peat surface and that the buildup of gas is spatially nonuniform even in a relatively small peat block furthermore the experimental results suggest that factors other than temperature and atmospheric pressure must control biogenic gas accumulation and release as the method is readily deployable at the field scale possibly in an autonomous monitoring mode resistivity measurements may permit significant improvements in understanding of carbon gas generation and release from northern peatlands

buoyant dispersal of co2 during geological storage carbon capture and storage is currently the only technology that may allow significant reductions in co2 emissions from large point sources seismic images of geological co2 storage show the rise of co2 is influenced by horizontal shales the buoyant co2 spreads beneath impermeable barriers until a gap allows its upward migration the large number and small scale of these barriers makes the prediction of the co2 migration path and hence the magnitude of co2 trapping very challenging we show that steady buoyancy dominated flows in complex geometries can be modeled as a cascade of flux partitioning events this approach allows the analysis of two dimensional plume dispersal from a horizontal injection well we show that the plume spreads laterally with height y above the source according to y h 1 2 l where l is the width of the shales and h is their vertical separation the fluid volume below successive shale layers and therefore the magnitude of trapped co2 increase as y h 5 4 above the source so that every additional layer of barriers traps more co2 than the one below upscaling small scale flow barriers by reducing the vertical permeability common in numerical simulations of co2 storage does not capture the dispersion and trapping of the co2 plume by the flow barriers

investigating the geoelectrical response of hydrocarbon contamination undergoing biodegradation 1 a newly proposed geoelectrical model for hydrocarbon contaminated sites predicts high conductivities coincident with the contaminated zone as opposed to the traditionally accepted low conductivity the model attributes the high conductivities to mineral weathering resulting from byproducts of microbial redox processes to evaluate this conductive model in situ vertical conductivity measurements were acquired from a light non aqueous phase liquid lnapl contaminated site the results showed high conductivities coincident with the zone of contamination and within the smear zone influenced by seasonal water table fluctuations we infer this zone as an active zone of biodegradation and suggest significant microbial degradation under partially water saturated conditions a simple archie s law analysis shows large pore water conductivities necessary to reproduce the bulk conductivity measured at the contaminated location this study supports the conductive layer model and demonstrates the potential of geoelectrical investigations for assessing microbial degradation of lnapl impacted soils

temporal geophysical signatures from contaminant mass remediation we have previously documented changes in bulk electrical conductivity self potential sp and ground penetrating radar gpr reflections in a field setting caused by biogeochemical transformations of hydrocarbon contaminated media these transformations are associated with hydrocarbon biodegradation the results of surface geophysical surveys acquired in 1996 2003 and 2007 document changes in geophysical signatures associated with removing hydrocarbon mass in the contaminated zone initial investigations in 1996 showed that relative to background the contaminated area was characterized by higher bulk electrical conductivity positive sp anomaly and attenuated gpr reflections repeated surveys in 2003 and 2007 over the contaminated area showed that in 2007 the bulk electrical conductivityhad reverted to near background conditions the positive sp anomaly became more negative and the zone of attenuated gpr reflections showed increased signal strength removal of hydrocarbon mass in the vadose zone o

modelling carbon dioxide sequestration in layered strata motivated by the geological sequestration of carbon dioxide co2 we study the propagation of gravity currents in a porous medium bounded by a thin layer of much lower permeability we formulate a model for drainage assuming that the fluid remains simply connected throughout using this model we examine the propagation of both two dimensional and axisymmetric currents numerically we find that for the fixed flux situation solutions approach a steady state which is described analytically the approach to this final solution depends on both the permeability contrast and thickness of the thin layer and in many cases the current first overshoots before relaxing back to its ultimate steady state finally we examine propagation along multiple thin lower permeability layers as a reduced order model of the plume of co2 currently being injected at sleipner in the north sea

geophysical investigation using resistivity and gpr methods a case study of a lubricant oil waste disposal area in the city of ribeirao preto sao paulo brazil geophysics has been shown to be effective in identifying areas contaminated by waste disposal contributing to the greater efficiency of soundings programs and the installation of monitoring wells in the study area four trenches were constructed with a total volume of about 25 000 m3 they were almost totally filled with re refined lubricating oil waste for approximately 25 years no protection liners were used in the bottoms and laterals of the disposal trenches the purpose of this work is to evaluate the potential of the resistivity and ground penetrating radar gpr methods in characterizing the contamination of this lubricant oil waste disposal area in ribeirao preto sp situated on the geological domain of the basalt spills of the serra geral formation and the sandstones of the botucatu formation geophysical results were shown in 2d profiles the geophysical methods used enabled the identification of geophysical anomalies which characterized the contamination produced by the trenches filled with lubricant oil waste conductive anomalies smaller than 185 m immediately below the trenches suggest the action of bacteria in the hydrocarbons as has been observed in several sites contaminated by hydrocarbons in previously reported cases in the literature it was also possible to define the geometry of the trenches as evidenced by the gpr method direct sampling chemical analysis of the soil and the water in the monitoring well confirmed the contamination in the soil analysis low concentrations of several polycyclic aromatic hydrocarbons pahs were found mainly naphthalene and phenanthrene in the water samples an analysis verified contamination of the groundwater by lead pb the geophysical methods used in the investigation provided an excellent tool for environmental characterization in this study of a lubricant oil waste disposal area and could be applied in the study of similar areas

similarity solutions for fluid injection into confined aquifers fluid injection into the deep subsurface such as injection of carbon dioxide co 2 into deep saline aquifers often involves two fluid flow in confined geological formations similarity solutions may be derived for these problems by assuming that a sharp interface separates the two fluids by imposing a suitable no flow condition along both the top and bottom boundaries and by including an explicit solution for the pressure distribution in both fluids when the injected fluid is less dense and less viscous than the resident fluid as is the case for co 2 injection into a resident brine gravity override produces a fluid flow system that is captured well by the similarity solutions the similarity solutions may be extended to include slight miscibility between the two fluids as well as compressibility in both of the fluid phases the solutions provide the location of the interface between the two fluids as well as drying fronts that develop within the injected fluid applications to cases of supercritical co 2 injection into deep saline aquifers demonstrate the utility of the solutions and comparisons to solutions from full numerical simulations show the ability to predict the system behaviour

microbial nucleation of calcium carbonate in the precambrian microbial sulfate reduction is thought to stimulate carbonate precipitation in modern stromatolites yet whether this metabolism was important in shaping precambrian stromatolites is unknown here we use geochemical modeling to suggest that the influence of sulfate reduction on the saturation index of calcite si is negligible when seawater is in equilibrium with high pco 2 as is thought for the precambrian our laboratory experiments with heterotrophic bacteria in a medium mimicking precambrian seawater chemistry show that even if sulfate reduction does not significantly change the si the presence of bacteria stimulates calcite precipitation over sterile controls by effectively increasing the si over a ph range from 7 3 to 7 8 under our experimental conditions dead cells stimulate in situ carbonate precipitation equally if not more than active sulfate reducing bacteria heterogeneous nucleation of calcite by microbial cell material appears to be the driving mechanism that explains this phenomenon

on the slow draining of a gravity current moving through a layered permeable medium we examine the gravitational dispersal of dense fluid through a horizontal permeable layer which is separated from a second underlying layer by a narrow band of much lower permeability we derive a series of analytical solutions which describe the propagation of the fluid through the upper layer and the draining of the fluid into the underlying region the model predicts that the current initially spreads according to a self similar solution however as the drainage becomes established the spreading slows and in fact the fluid only spreads a finite distance before it has fully drained into the underlying layer we examine the sensitivity of the results to the initial conditions through numerical solution of the governing equations we find that for sources of sufficiently large initial aspect ratio defined as the ratio of height to length the solution converges rapidly to the initially self similar regime for longer and shallower initial source conditions this convergence does not occur but we derive estimates for the run out length of the current which compare favourably with our numerical data we also present some preliminary laboratory experiments which support the model

microbial colonization and weathering of silicates in a petroleum contaminated groundwater abstract the influence of native microorganisms on mineral dissolution and precipitation was examined in a petroleum contaminated aquifer near bemidji minnesota in situ microcosms containing clean silicate fragments were established in the contaminated microbially active groundwater over one year periods the recovered minerals were then examined by sem and esem for microbial colonization patterns and weathering features these experiments reveal distinct patterns of colonization and weathering associated with microbial attachment and growth microcline anorthoclase and oligoclase were widely colonized and the colonized surfaces deeply weathered with secondary clays precipitated on some uncolonized surfaces other feldspars in contrast were uncolonized and unweathered specific mineral removal rate was estimated from etch pit depth while bulk weathering rate was estimated from the rate of change of silica concentration in the groundwater in this system the primary control of silicate dissolution is apparently microbial colonization and metabolic activity

evidence for subglacial ponding across taylor glacier dry valleys antarctica hubbard alun lawson w anderson b hubbard b p 2004 evidence for subglacial ponding across taylor glacier dry valleys antarctica annals of glaciology 39 1 79 84 rae2008

evidence for microbial enhanced electrical conductivity in hydrocarbon contaminated sediments 1 bulk electrical conductivity of sediments during microbial mineralization of diesel was investigated in a mesoscale laboratory experiment consisting of biotic contaminated and uncontaminated columns population numbers of oil degrading microorganisms increased with a clear pattern of depth zonation within the contaminated column not observed in the uncontaminated column microbial community structure determined from ribosomal dna intergenic spacer analysis showed a highly specialized microbial community in the contaminated column the contaminated column showed temporal increases in bulk conductivity dissolved inorganic carbon and calcium suggesting that the high bulk conductivity is due to enhanced mineral weathering from microbial activity the greatest change in bulk conductivity occurred in sediments above the water table saturated with diesel variations in electrical conductivity magnitude and microbial populations and their depth distribution in the contaminated column are similar to field observations the results of this study suggest that geophysical methodologies may potentially be used to investigate microbial activity

biogeophysics a new frontier in earth science research 1 biogeophysics is a rapidly evolving earth science discipline concerned with the geophysical signatures of microbial interactions with geologic media it spans the established disciplines of geomicrobiology biogeoscience and geophysics biogeophysics research in the last decade has confirmed the potential for geophysical techniques to measure not simply the physical and chemical properties of the subsurface as already well established but also to detect microbes microbial growth and microbe mineral interactions thus representing a major paradigm shift in geophysical thinking in this review we begin by defining biogeophysics and provide a historical perspective we then consider microbial alterations of petrophysical properties as such alteration is the source of most biogeophysical signals our review then focuses on geophysical interrogation of microbial processes including the direct detection of microbial cells and biofilm formation microbial metabolic by products microbe mediated redox processes and biogeochemical and microbe mineral transformations we conclude by discussing challenges opportunities and potential new applications of biogeophysics to the exploration of life in extreme environments e g the deep biosphere the cryosphere and other planets we find that published biogeophysics studies to date are mostly observation based presenting only empirical relationships between microbial and geophysical variables future research endeavors must focus on developing theoretical and or numerical models for predicting geophysical signals arising from microbial activity

geometric and radiometric correction of tm data of mountainous forested areas methodologies to improve landsat tm thematic mapper forest classifications of alpine regions through the removal of some radiometric and geometric distortions are tested besides correcting for sensor and system induced errors geometric errors are corrected using a digital elevation model then scene related effects such as differences in illumination as well as the height dependent atmospheric influence and adjacency effects are corrected the improvement of the accuracy of a forest classification is demonstrated by comparison with ground truth data

gost a geometric optical model for sloping terrains gost is a geometric optical go model for sloping terrains developed in this study based on the four scale go model which simulates the bidirectional reflectance distribution function brdf of forest canopies on flat surfaces the four scale go model considers four scales of canopy architecture tree groups tree crowns branches and shoots in order to make this model suitable for sloping terrains the mathematical description for the projection of tree crowns on the ground has been modified to consider the fact that trees grow vertically rather than perpendicularly to sloping grounds the simulated canopy gap fraction and the area ratios of the four scene components sunlit foliage sunlit background shaded foliage and shaded background by gost compare well with those simulated by 3 d virtual canopy computer modeling techniques for a hypothetical forest gost simulations show that the differences in area ratios of the four scene components between flat and sloping terrains can reach up to 50 60 in the principal plane and about 30 in the perpendicular plane two case studies are conducted to compare modeled canopy reflectance with observations one comparison is made against landsat 5 thematic mapper tm reflectance demonstrating the ability of gost to model canopy reflectance variations with slope and aspect of the terrain another comparison is made against modis surface reflectance showing that gost with topographic consideration outperforms that without topographic consideration these comparisons confirm the ability of gost to model canopy reflectance on sloping terrains over a large range of view angles

field evidence for geophysical detection of subsurface zones of enhanced microbial activity 1 geochemical data from closely spaced vertical intervals in a hydrocarbon impacted aquifer were used to assess the relationship between bulk conductivity and zones of enhanced microbial activity the bulk conductivity was measured using in situ vertical resistivity probes microbial activity was verified using terminal electron acceptors nitrate sulfate iron and manganese dissolved inorganic carbon dic and major ion chemistry peaks in bulk conductivity in the aquifer overlapped with zones where nitrates and sulfates were depleted total petroleum hydrocarbon iron manganese dissolved ions and dic were elevated suggesting a link between higher electrical conductivity and zones of enhanced microbial activity stimulated by the presence of hydrocarbon thus the subsurface expression of microbial activity is apparently recorded in the bulk conductivity measurements our results argue for combining geophysics with biogeochemistry studies to delineate subsurface zones of enhanced microbial activity

the effect of drainage on the capillary retention of co2 in a layered permeable rock buoyant plumes of co 2 spreading through water saturated permeable rock bounded by layers of lower permeability tend to spread laterally as they advance they may gradually leak through fractures or discontinuities in the lower permeability boundary leading to a gradual waning of the original plume and dispersal of co 2 higher in the formation with a finite release of co 2 the trailing edge of the plume recedes with time and capillary forces tend to trap a fraction of this co 2 within the pore space this also leads to a gradual waning of the plume with time and limits the mass of co 2 which can leak through the boundary and rise higher into the formation we explore the balance between these two effects and calculate some of the controls on the fraction of the co 2 plume which becomes trapped within the original layer of rock

topographic effects on bidirectional and hemispherical reflectances calculated with a geometric optical canopy model the effects of topography on both the bidirectional reflectance distribution function brdf and the hemispherical reflectance surface albedo of a forested scene are investigated with the li strahler geometric optical model the li strahler geometric optical model treats a vegetation canopy as an assemblage of partially illuminated tree crowns of spheroidal shape and through geometric optics and boolean set theory models the proportion of sunlit or shadowed canopy and background as functions of view angle illumination angle and crown geometry the model has been modified to accommodate a sloping surface in its computation of bidirectional and hemispherical reflectance when the brdf of a flat vegetated surface is compared to the brdf of a sloping surface that is similarly vegetated the interaction of the illumination angle and the slope distort the shape of the brdf a hemispherical integration of this distorted brdf provides an albedo for the sloping surface

widespread bacterial populations at glacier beds and their relationship to rock weathering and carbon cycling bacterial populations found in subglacial meltwaters and basal ice are comparable to those in the active layer of permafrost and orders of magnitude larger than those found in ice cores from large ice sheets populations increase with sediment concentration and 5 24 of the bacteria are dividing or have just divided suggesting that the populations are active these findings 1 support inferences from recent studies of basal ice and meltwater chemistry that microbially mediated redox reactions may be important at glacier beds 2 challenge the view that chemical weathering in glacial environments arises from purely inorganic reactions and 3 raise the possibilities that redox reactions are a major source of protons consumed in subglacial weathering and that these reactions may be the dominant proton source beneath ice sheets where meltwaters are isolated from an atmospheric source of co 2 microbial mediation may increase the rate of sulfide oxidation under subglacial conditions a suggestion supported by the results of simple weathering experiments if subglacial bacterial populations can oxidize and ferment organic carbon it is important to reconsider the fate of soil organic carbon accumulated under interglacial conditions in areas subsequently overridden by pleistocene ice sheets

leakage from gravity currents in a porous medium part 2 a line sink we consider the propagation of a buoyancy driven gravity current in a porous medium bounded by a horizontal impermeable boundary the current is fed by a constant flux injected at a point and leaks through a line sink at a distance from the injection point this is an idealized model of how a fault in a cap rock might compromise the geological sequestration of carbon dioxide the temporal evolution of the efficiency of storage defined as the instantaneous ratio of the rate at which fluid is stored without leaking to the rate at which it is injected is of particular interest we show that the efficiency of storage decays like t 2 5 for times t that are long compared with the time taken for the current to reach the fault this algebraic decay is in contrast to the case of leakage through a circular sink neufeld et al j fluid mech vol 2010 where the efficiency of storage decays more slowly like 1 ln t the implications of the predicted decay in the efficiency of storage are discussed in the context of geological sequestration of carbon dioxide using parameter values typical of the demonstration project at sleipner norway we show that the efficiency of storage should remain greater than 90 on a time scale of millennia provided that there are no significant faults in the cap rock within about 12 km of the injection site

geophysical and hydrological evaluation of two bog complexes in a northern peatland implications for the distribution of biogenic gases at the basin scale 1 ground penetrating radar gpr was used to determine peat basin geometry and the spatial distribution of free phase biogenic gasses in two separate units of a northern peatland central and southern unit of caribou bog maine the central unit is characterized by a deep basin structure 15 m maximum depth and a raised eccentric bog topographic profile up to 2 m topographic variation here numerous regions of electromagnetic em wave scattering are considered diagnostic of the presence of extensive free phase biogenic gas in contrast the southern unit is shallower 8 m maximum depth and has a slightly convex upwards bog profile less than 1 m topographic variation and areas of em wave scattering are notably absent the biogenic gas zones interpreted from gpr in the central unit are associated with 1 wooded heath vegetation at the surface 2 open pools at the surface 3 high water table elevations near the center of the basin and 4 a region of overpressure at approximately 5 m depth immediately below the zone of free phase gas accumulation the latter suggests 1 a transient pressure head associated with low hydraulic conductivity resulting from the biogenic gasses themselves or confining layers in the peat that restrict both gas release and groundwater flow and or 2 overpressure in the peat column as a result of the gas buildup itself in contrast the southern unit where zones of em scattering are absent is characterized by 1 predominantly shrub vegetation 2 a lack of open pools 3 only minor variations less than 1 m in water table elevation throughout the entire unit and 4 generally upward groundwater flow throughout the basin the results illustrate the nonuniformity of free phase biogenic gas distribution at the peat basin scale and provide insights into the processes and controls associated with ch4 and co2 accumulation in peatlands

geometric optical bidirectional reflectance modeling of a conifer forest canopy a geometric optical forest canopy model that treats conifers as cones casting shadows on a contrasting background explains the major anisotropies in bidirectional reflectance measurements of a conifer forest canopy taken from the literature the model uses parallelray geometry to describe the illumination and viewing of conifers as three dimensional cones cones are randomly placed and overlap freely cone size height is distributed lognormally and cone form described by the apex angle of the cone is a negative exponential function of height the cones are first presumed to be solid dark gray lambertian objects located on a lighter gray lambertian background to add realism translucence is added and light is allowed to pass through cones with negative exponential attenuation both computer simulation and analytical closed form expressions are implemented the results show a good qualitative agreement with the directional reflectance measurements of the conifer stand indicating that the three dimensional nature of the canopy is a key factor in determining its directional reflectance

geomicrobiology its significance for geology abstract some microorganisms including various kinds of bacteria fungi algae and protozoa serve as geochemical agents in the uppermost lithosphere and in the hydrosphere some promote rock weathering by mobilizing mineral constituents with inorganic or organic acids or ligands that they excrete others promote rock weathering by redox attack of mineral constituents such as fe and mn still others cause active or passive mineral formation by precipitation and subsequent nucleation of crystal formation on or in the cell or in the bulk phase they play a role in some phases of fossil fuel formation and accumulation they modulate the terrestrial and marine cycles of c n s and p and some other elements and they influence the composition of the atmosphere in respect to o 2 co 2 and ch 4 some discriminate between stable isotopes of h c o n and s

a three dimensional model for calculating reflection functions of inhomogeneous and orographically structured natural landscapes abstract a three dimensional reflection model has been developed for calculating the reflection functions of inhomogeneous and orographically structured natural land surfaces the site of an area whose reflection properties are to be modeled can be freely chosen the task is limited however by its allocated cpu time the surface structure of such an area is taken from a digital terrain model the known anisotropic reflection properties of various flat surface types for example coniferous forest hardwood forest grassland and agricultural cover types are taken into account the effects of multiple reflection in the subscale orographic structure of an area are calculated up to the second order of reflection for the test sites a typical difference of 25 in the reflection factors of a vertically structured surface and a corresponding flat surface was found with the higher values for a flat surface the model is validated by comparing simulated radiances with measured radiances in the solar channels of the avhrr onboard noaa 11 and noaa 12 for several test sites in the german alpine region the simulated radiances are calculated with an angular dependent radiative transfer model with the modeled reflection functions as the lower boundary layer of the coupled earth atmosphere system the results show good agreement between measured and simulated satellite data especially in channel 2 if the vertical structure of the surface is considered a statistically significant influence of the orographic structure was found in the simulated radiances as compared with radiances calculated for a corresponding flat surface with the same cover types it is concluded that the developed reflection model is able to simulate correctly the anisotropic reflection properties of vertically structured natural landscape as it can be found in mountainous terrain