High Water Abundances Research Articles

High-contrast JWST-MIRI Spectroscopy of Planet-forming Disks for the JDISC Survey

The JWST Disk Infrared Spectral Chemistry Survey (JDISCS) aims to understand the evolution of the chemistry of inner protoplanetary disks using the Mid-InfraRed Instrument (MIRI) on the James Webb Space Telescope (JWST). With a growing sample of >30 disks, the survey implements a custom method to calibrate the MIRI Medium Resolution Spectrometer (MRS) to contrasts of better than 1:300 across its 4.9–28 μm spectral range. This is achieved using observations of Themis family asteroids as precise empirical reference sources. The high spectral contrast enables precise retrievals of physical parameters, searches for rare molecular species and isotopologues, and constraints on the inventories of carbon- and nitrogen-bearing species. JDISCS also offers significant improvements to the MRS wavelength and resolving power calibration. We describe the JDISCS calibrated data and demonstrate their quality using observations of the disk around the solar-mass young star FZ Tau. The FZ Tau MIRI spectrum is dominated by strong emission from warm water vapor. We show that the water and CO line emission originates from the disk surface and traces a range of gas temperatures of ∼500–1500 K. We retrieve parameters for the observed CO and H2O lines and show that they are consistent with a radial distribution represented by two temperature components. A high water abundance of n(H2O) ∼ 10−4 fills the disk surface at least out to the 350 K isotherm at 1.5 au. We search the FZ Tau environs for extended emission, detecting a large (radius of ∼300 au) ring of emission from H2 gas surrounding FZ Tau, and discuss its origin.

Typification of hydrogeological conditions in mineral deposits by system analysis method

The paper presents a non-standard approach to the typification of mineral deposits in Eastern Siberia (Russia) according to hydrogeological conditions under insufficiency and unevenness of the initial information. The most rational way to solve this problem at initial research stages is to identify a number of easily determined indirect indicators that determine the selection of sites promising for drilling hydrogeological wells. The author uses the method of system analysis including two main stages of analysis and synthesis, which result in the typification of the objects under study in accordance with the assigned tasks. The developed methodology is used for various purposes: structural hydrogeological zoning of the Ilim-Lena plateau with associated main iron ore deposits of Eastern Siberia, typification of alluvial deposits of the Lena gold ore region according to the complexity degree of engineering hydrogeological conditions, identification of the sites with high water abundance in the oil and gas fields of Eastern Siberia.

Safety level assessment of shield tunneling in water rich sandy pebble strata with large particle size

Shield tunneling method is widely used in urban metro construction. The construction stability is closely related to the engineering geological conditions. Sandy pebble strata have a loose structure and low cohesion, resulting in great engineering-induced stratigraphic disturbance. Meanwhile, the high water-abundance and strong permeability are extremely detrimental to construction safety. It is of great significance to evaluate the dangerousness of shield tunneling in water-rich pebble strata with large particle size. In this paper, risk assessment of engineering practice is carried through with Chengdu metro project in China as a case study. Referring to the special engineering situations and assessment workload, seven evaluation indices, including compressive strength of pebble layer, boulder volume content, permeability coefficient, groundwater depth, grouting pressure, tunneling speed and tunnel buried depth are selected to establish an evaluation system. A complete risk assessment framework is established based on the cloud model, AHP and entropy weight method. Further, the measured surface settlement is taken as the risk degree characterization to verify the results. This study can provide reference for method selection and evaluation system establishment in the risk assessment of shield tunnel construction in water-rich sandy pebble strata, and contribute to proposing safety management in similar engineering projects.

Revealing a High Water Abundance in the Upper Mesosphere of Mars With ACS Onboard TGO

AbstractWe present the first water vapor profiles encompassing the upper mesosphere of Mars, 100–120 km, far exceeding the maximum altitudes where remote sensing has been able to observe water to date. Our results are based on solar occultation measurements by Atmospheric Chemistry Suite (ACS) onboard the ExoMars Trace Gas Orbiter (TGO). The observed wavelength range around 2.7 μm possesses strong CO2 and H2O absorption lines allowing sensitive temperature and density retrievals. We report a maximum H2O mixing ratio varying from 10 to 50 ppmv at 100–120 km during the global dust storm (GDS) of Martian Year (MY) 34 and around southern summer solstice of MY 34 and 35. During other seasons water remains persistently below ∼2 ppmv. We claim that contributions of the MY34 GDS and perihelion periods into the projected hydrogen escape from Mars are nearly equivalent.

Water abundance prediction of sandstone aquifers based on the distance function

To establish a more accurate roof water abundance evaluation model and mitigate the difficulties in roof water abundance prediction and evaluation in the coal mine production process, the 2101 working face of the Yingpanhao coal mine was studied. Combined with the hydrogeological characteristics and drilling data of the study area and based on the lithology and structure, four controlling factors, including the equivalent thickness of sandstone, the lithological coefficient of sandstone, the degree of fracture development, and the sand-mud interlayer coefficient, were selected as evaluation indexes for the prediction of roof water abundance zones of sandstone aquifers. In the case of limited borehole data, the distance function was used to couple the improved analytic hierarchy process with the entropy weight method. The errors caused by subjective and objective factors were effectively reduced, and on this basis, a water abundance prediction model of roof sandstone was built. With the use of geophysical exploration results, the model predictions were combined with geophysical survey data to generate a comprehensive water abundance zone map, which divided the study area into three zones according to the water abundance. The results show that the high water abundance areas were mainly concentrated in the west of the working face, and the water abundance throughout the study area was generally low. The prediction results were verified by the data from drainage holes exposed by drilling, which provided a scientific and practical method for the prediction of the water abundance of coal seam roofs.

Optimization of group borehole drainage of a mine above a high pressure, low permeability aquifer

Abstract Drainage to lower water pressure is an effective measure for preventing and controlling water ingress when mining above a confined aquifer. The deep limestone aquifer in the Huaibei mining area, China, generally has high pressure, low permeability and variable water abundance, so it is difficult to meet single-borehole drainage requirements. In order to achieve good drainage, and take into account engineering and environmental protection requirements, a multi-objective optimization model of group borehole drainage was established. The model takes the minimization of single-hole flow and borehole numbers as the objective functions, and the drawdown in drainage boreholes and the water level control point as the constraint conditions. The particle swarm optimization algorithm was used to solve the model. The results indicate that, for a low permeability aquifer, measures such as using partially penetrating wells, increasing the number of drainage boreholes appropriately and reducing individual borehole yield have good drainage effects. The extent of drilling and amount of drainage are also relatively small. This is all to the good for the drainage. When the optimization results were applied to coal-face drainage in Huaibei the outcome was good.

Dust Continuum Emission and the Upper Limit Fluxes of Submillimeter Water Lines of the Protoplanetary Disk around HD 163296 Observed by ALMA

Abstract In this paper, we analyze the upper limit fluxes of submillimeter ortho-H2 16O 321 GHz, para-H2 18O 322 GHz, and HDO 335 GHz lines from the protoplanetary disk around the Herbig Ae star HD 163296, using the Atacama Large Millimeter/Submillimeter Array. These water lines are considered to be the best candidate submillimeter lines to locate the position of the H2O snowline, on the basis of our previous model calculations. We compare the upper limit fluxes with the values calculated by our models with dust emission included, and we constrain the line-emitting region and the dust opacity from the observations. We conclude that, if the outer edge of the region with a high water abundance and the position of the water snowline are both beyond 8 au, then themillimeter dust opacity κ mm will have a value larger than 2.0 cm2 g−1. In addition, the position of the water snowline must lie inside 20 au if the millimeter dust opacity κ mm is 2.0 cm2 g−1. Future observations of the dust continuum emission at higher angular resolution and submillimeter water lines with a longer observation time are required to clarify the detailed structures and the position of the H2O snowline in the disk midplane.

What is Neptune's D/H ratio really telling us about its water abundance?

We investigate the deep water abundance of Neptune using a simple 2-component (core + envelope) toy model. The free parameters of the model are the total mass of heavy elements in the planet (Z), the mass fraction of Z in the envelope (f_env), and the D/H ratio of the accreted building blocks (D/H_build ). We systematically search the allowed parameter space on a grid and constrain it using Neptune's bulk carbon abundance, D/H ratio, and interior structure models. Assuming solar C/O ratio and cometary D/H for the accreted building blocks forming the planet, we can fit all of median ~ 7%), and the rest the constraints if less than ~ 15% of Z is in the envelope (f_env is locked in a solid core. This model predicts a maximum bulk oxygen abundance in Neptune of 65 \times solar value. If we assume a C/O of 0.17, corresponding to clathrate-hydrates building blocks, we predict a maximum oxygen abundance of 200 times solar value with a median value of ~ 140. Thus, both cases lead to an oxygen abundance significantly lower than the preferred value of Cavali\'e et al. (2017) (~ 540 times solar), inferred from model dependent deep CO observations. Such high water abundances are excluded by our simple but robust model. We attribute this discrepancy to our imperfect understanding of either the interior structure of Neptune or the chemistry of the primordial protosolar nebula.

Soil properties impacting denitrifier community size, structure, and activity in New Zealand dairy-grazed pasture

Abstract. Denitrification is an anaerobic respiration process that is the primary contributor of the nitrous oxide (N2O) produced from grassland soils. Our objective was to gain insight into the relationships between denitrifier community size, structure, and activity for a range of pasture soils. We collected 10 dairy pasture soils with contrasting soil textures, drainage classes, management strategies (effluent irrigation or non-irrigation), and geographic locations in New Zealand, and measured their physicochemical characteristics. We measured denitrifier abundance by quantitative polymerase chain reaction (qPCR) and assessed denitrifier diversity and community structure by terminal restriction fragment length polymorphism (T-RFLP) of the nitrite reductase (nirS, nirK) and N2O reductase (nosZ) genes. We quantified denitrifier enzyme activity (DEA) using an acetylene inhibition technique. We investigated whether varied soil conditions lead to different denitrifier communities in soils, and if so, whether they are associated with different denitrification activities and are likely to generate different N2O emissions. Differences in the physicochemical characteristics of the soils were driven mainly by soil mineralogy and the management practices of the farms. We found that nirS and nirK communities were strongly structured along gradients of soil water and phosphorus (P) contents. By contrast, the size and structure of the nosZ community was unrelated to any of the measured soil characteristics. In soils with high water content, the richnesses and abundances of nirS, nirK, and nosZ genes were all significantly positively correlated with DEA. Our data suggest that management strategies to limit N2O emissions through denitrification are likely to be most important for dairy farms on fertile or allophanic soils during wetter periods. Finally, our data suggest that new techniques that would selectively target nirS denitrifiers may be the most effective for limiting N2O emissions through denitrification across a wide range of soil types.

An Improved Vulnerability Assessment Model for Floor Water Bursting from a Confined Aquifer Based on the Water Inrush Coefficient Method

Pressurized confined water below coal seams are serious threats to mining. The conventional water inrush coefficient method fails to accurately assess the risk of floor water inrush under some specific conditions, such as high water pressure and low water yield in the source aquifers. Large amounts of water inrush data including water inrush flow rate, water inrush coefficient (T s ), floor aquiclude thickness (M), and water abundance, were collected and statistically analyzed. The results indicated that inrushes mostly occurred when M was less than 30 m and that the critical T s increased linearly with M. The occurrence of a water inrush and water inrush yield amount (Q in L/s) were related to both the values of T s and the unit water inflow (q in L/(s m)). In addition, 97.7% of the large- and medium-sized inrush events occurred when q > 2 L/(s m) and only a small proportion (3.2%) of the small-sized inrushes happened when q < 0.1 L (s m). T s , M and q were comprehensively analyzed and used to evaluate vulnerability to floor water inrush. By analyzing the distribution of water inrush points and the scale of water inrush events, the vulnerability was divided into four levels (safe, moderately safe, potentially dangerous, and highly risky) based on T s –M and T s –q models. Successful application of these models in the Huaibei mining area proved that they are feasible in practice. The T s –M and T s –q charts can be used independently or jointly. These new methods should improve the accuracy of predictions and evaluations during deep exploitation where the aquifers are often characterized with high pressure but low water abundance. The results could also help reduce the amount spent on mine water prevention and control.

Efficient photochemistry of coronene:water complexes

The photochemistry of ices with polycyclic aromatic hydrocarbons (PAHs) has been extensively studied, but to date no investigation has been made of PAHs in interaction with low numbers (n&lt; 4) of molecules of water. We performed photochemical matrix isolation studies of coronene:water complexes, probing the argon matrix with FTIR spectroscopy. We find that coronene readily reacts with water upon irradiation with a mercury vapour lamp to produce oxygenated PAH photoproducts, and we postulate a reaction mechanism via a charge transfer Rydberg state. This result suggests that oxygenated PAHs should be widely observed in regions of the ISM with sufficiently high water abundances, for example near the edges of molecular clouds where water molecules begin to form, but before icy layers are observed, that is at AV&lt; 3. In order to explain the low derived observational abundances of oxygenated PAHs, additional destruction routes must be invoked.

Food and Chemistry Toxicology: Safety of Locally-Sold Food (Nutritional Distribution of Select Fruits and Vegetables in an Urban Food Desert)

There has been an increase of heavy metals in agricultural soil. The potentially harmful metals in the soil may come from the bedrock, waste deposits, agricultural inputs and urban emissions. Moreover, contaminated food is considered the main source by which humans are exposed to toxic elements. Fruits and vegetables are regarded as containing a low percentage of toxic compounds due to their high water abundance. However, dried fruits, which are often sold in areas where the abundance of fresh fruits and vegetables is low, may contain more toxic elements. Within considering all of the factors the trace metals induce on humans via the consumption of plants, one is able to analyze then disproportionate availability of toxin less foods in certain areas. Reasons that people do not consume fruits and vegetables that are not toxic are complex. This disproportionate representation is evident mainly in urban areas. Studies have shown that urban African Americans who shopped at their local neighborhood small- food stores consumed fewer fresh fruits and vegetables than their higher income peers who were able to shop in suburban supermarkets. Environmental barriers have been found the main cause for the limited availability of fresh fruits and vegetables. This research project will engage whether or not there is a disproportionate availability of toxin less foods in West End Atlanta community area by utilizing the Inductively Coupled Plasma Optic Emission Spectroscopy (ICP-OES), which will analyze the trace metal contents of arsenic, cadmium and lead in apples, bananas, and potatoes.

Food and Chemistry Toxicology: Safety of Locally-Sold Food (Nutritional Distribution of Select Fruits and Vegetables in an Urban Food Desert)

There has been an increase of heavy metals in agricultural soil. The potentially harmful metals in the soil may come from the bedrock, waste deposits, agricultural inputs and urban emissions. Moreover, contaminated food is considered the main source by which humans are exposed to toxic elements. Fruits and vegetables are regarded as containing a low percentage of toxic compounds due to their high water abundance. However, dried fruits, which are often sold in areas where the abundance of fresh fruits and vegetables is low, may contain more toxic elements. Within considering all of the factors the trace metals induce on humans via the consumption of plants, one is able to analyze then disproportionate availability of toxin less foods in certain areas. Reasons that people do not consume fruits and vegetables that are not toxic are complex. This disproportionate representation is evident mainly in urban areas. Studies have shown that urban African Americans who shopped at their local neighborhood small- food stores consumed fewer fresh fruits and vegetables than their higher income peers who were able to shop in suburban supermarkets. Environmental barriers have been found the main cause for the limited availability of fresh fruits and vegetables. This research project will engage whether or not there is a disproportionate availability of toxin less foods in West End Atlanta community area by utilizing the Inductively Coupled Plasma Optic Emission Spectroscopy (ICP-OES), which will analyze the trace metal contents of arsenic, cadmium and lead in apples, bananas, and potatoes.

Relatedness between contemporary and subfossil cladoceran assemblages in Turkish lakes

Cladocerans are valuable indicators of environmental change in lakes. Their fossils provide information on past changes in lake environments. However, few studies have quantitatively examined the relationships between contemporary and sub-fossil cladoceran assemblages and no investigations are available from Mediterranean lakes where salinity, eutrophication and top-down control of large-bodied cladocerans are known to be important. Here we compared contemporary Cladocera assemblages, sampled in summer, from both littoral and pelagic zones, with their sub-fossil remains from surface sediment samples from 40 Turkish, mainly shallow, lakes. A total of 20 and 27 taxa were recorded in the contemporary and surface sediment samples, respectively. Procrustes rotation was applied to both the principal components analysis (PCA) and redundancy analysis (RDA) ordinations in order to explore the relationship between the cladoceran community and the environmental variables. Procrustes rotation analysis based on PCA showed a significant accord between both littoral and combined pelagic–littoral contemporary and sedimentary assemblages. RDA ordinations indicated that a similar proportion of variance was explained by environmental variation for the contemporary and fossil Cladocera data. Total phosphorus and salinity were significant explanatory variables for the contemporary assemblage, whereas salinity emerged as the only significant variable for the sedimentary assemblage. The residuals from the Procrustes rotation identified a number of lakes with a high degree of dissimilarity between modern and sub-fossil assemblages. Analysis showed that high salinity, deep water and high macrophyte abundance were linked to a lower accord between contemporary and sedimentary assemblages. This low accord was, generally the result of poor representation of some salinity tolerant, pelagic and macrophyte-associated taxa in the contemporary samples. This study provides further confirmation that there is a robust relationship between samples of modern cladoceran assemblages and their sedimentary remains. Thus, sub-fossil cladoceran assemblages from sediment cores can be used with confidence to track long-term changes in this environmentally sensitive group and in Mediterranean lakes, subjected to large inter-annual variation in water level, salinity and nutrients.

Terrestrial planets in high-mass disks without gas giants

Fil: de Elia, Gonzalo Carlos. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - La Plata. Instituto de Astrofisica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronomicas y Geofisicas. Instituto de Astrofisica la Plata; Argentina

FORMATION OF WATER IN THE WARM ATMOSPHERES OF PROTOPLANETARY DISKS

The gas-phase chemistry of water in protoplanetary disks is analyzed with a model based on X-ray heating and ionization of the disk atmosphere. Several uncertain processes appear to play critical roles in generating the column densities of warm water that are detected from disks at infrared wavelengths. The dominant factors are the reactions that form molecular hydrogen, including formation on warm grains, and the ionization and heating of the atmosphere. All of these can work together to produce a region of high water abundances in the molecular transition layer of the inner disk atmosphere, where atoms are transformed into molecules, the temperature drops from thousands to hundreds of Kelvins, and the ionization begins to be dominated by the heavy elements. Grain formation of molecular hydrogen and mechanical heating of the atmosphere can play important roles in this region and directly affect the amount of warm water in protoplanetary disk atmospheres. Thus, it may be possible to account for the existing measurements of water emission from T Tauri disks without invoking transport of water from cooler to warmer regions. The hydroxyl radical OH is underabundant in this model of disk atmospheres and requires consideration of additional production and excitation processes.

Circumstellar water vapour in M-type AGB stars: radiative transfer models, abundances, and predictions for HIFI

Aims: By performing a detailed radiative transfer analysis, we determine fractional abundances of circumstellar H2O in the envelopes around six M-type asymptotic giant branch stars. The models are also used to predict H2O spectral line emission for the upcoming Herschel/HIFI mission. Methods: We use Infrared space observatory long wavelength spectrometer spectra to constrain the circumstellar fractional abundance distribution of ortho-H2O, using a non-local thermal equilibrium, and non-local, radiative transfer code based on the accelerated lambda iteration formalism. The mass-loss rates and kinetic temperature structures for the sample stars are determined through radiative transfer modelling of CO line emission based on the Monte-Carlo method. The density and temperature profiles of the circumstellar dust grains are determined through spectral energy distribution modelling using the publicly available code Dusty. Results: The determined ortho-H2O abundances lie between 1e-4 and 1.5e-3 relative to H2, with the exception of WX Psc, which has a much lower estimated ortho-H2O abundance of only 2e-6, possibly indicating H_2O adsorption onto dust grains or recent mass-loss-rate modulations. The estimated abundances are uncertain by, at best, a factor of a few. Conclusions: The high water abundance found for the majority of the sources suggests that either the `normal' chemical processes are very effective in producing H2O, or else non-local thermal equilibrium atmospheric chemistry, grain surface reactions, or a release of H_2O (e.g. from icy bodies like Kuiper belt objects) play a role. We provide predictions for ortho-H2O lines in the spectral window of Herschel/HIFI.

Mars low-latitude neutron distribution: Possible remnant near-surface water ice and a mechanism for its recent emplacement

The Mars Odyssey Gamma-Ray Spectrometer/Neutron Spectrometer/High Energy Neutron Detector has provided measurements of near-surface hydrogen, generally interpreted as resulting from water, in the equatorial and mid-latitudes. Water abundances as great as 10% by mass are inferred. Although such high abundances could be present as adsorbed water in clays or water of hydration of magnesium salts, other measurements suggest that this is not likely. The spatial pattern of where the water is located is not consistent with a dependence on composition, topography, present-day atmospheric water abundance, latitude, or thermophysical properties. The zonal distribution of water shows two maxima and two minima, which is very reminiscent of a distribution that is related to an atmospheric phenomenon. We suggest that the high water abundances could be due to transient ground ice that is present in the top meter of the surface. Ice would be stable at tens-of-centimeters depth at these latitudes if the atmospheric water abundance were more than about several times the present value, much as ice is stable poleward of about ±60° latitude for current water abundances. Higher atmospheric water abundances could have resulted relatively recently, even with the present orbital elements, if the south-polar cap had lost its annual covering of CO 2 ice; this would have exposed an underlying water-ice cap that could supply water to the atmosphere during southern summer. If this hypothesis is correct, then (i) the low-latitude water ice is unstable today and is in the process of sublimating and diffusing back into the atmosphere, and (ii) the current configuration of perennial CO 2 ice being present on the south cap but not on the north cap might not be representative of the present epoch over the last, say, ten thousand years.

Far-Infrared Detection of H[TINF]3[/TINF]O[TSUP]+[/TSUP] in Sagittarius B2

We report the first far-infrared detection of the hydronium ion (H3O+) toward the Sagittarius B2 molecular cloud, near the Galactic center. Using the Infrared Space Observatory Long-Wavelength Spectrometer, we have detected three lines arising from the ν2 ground-state inversion mode (0+ → 0-) at 55.3 cm-1. All transitions are observed in absorption against the optically thick infrared continuum emission of the dust. Two different absorption regions can be distinguished, the H3O+ associated with the Sgr B2 extended envelope and that of foreground gas along the line of sight. The derived abundances for both components are rather similar, 1 × 10-9, and may explain the high water abundance found in the low-density gas toward Sgr B2 as its dissociative recombination leads to the formation of important molecules OH and H2O. Contribution of the Q(1, 1) line of para-H3O+ to the 212-101 line of H218O is also analyzed. This allows a better determination of water abundance from far-infrared observations. The corrected H2O abundances are ≤10-6 for the diffuse clouds along the line of sight and a few times 10-6 for the gas associated with the Sgr B2 envelope, in good agreement with water vapor observations from the Submillimeter Wave Astronomy Satellite.

The Postshock Chemical Lifetimes of Outflow Tracers and a Possible New Mechanism to Produce Water Ice Mantles

We have used a coupled time-dependent chemical and dynamical model to investigate the lifetime of the chemical legacy in the wake of C-type shocks. We concentrate this study on the chemistry of and O2, two molecules which are predicted to have abundances that are significantly affected in shock-heated gas. Two models are presented: (1) a three-stage model of preshock, shocked, and postshock gas; and (2) a Monte Carlo cloud simulation where we explore the effects of stochastic shock activity on molecular gas over a cloud lifetime. For both models we separately examine the pure gas-phase chemistry as well as the chemistry including the interactions of molecules with grain surfaces. In agreement with previous studies, we find that shock velocities in excess of 10 km/s are required to convert all of the oxygen not locked in CO into before the gas has an opportunity to cool. For pure gas phase models the lifetime of the high water abundances, or H2O legacy, in the postshock gas is approximately (4-7) x 10(exp 5) yr, independent of the gas density. A density dependence for the lifetime of is found in gas-grain models as the water molecules deplete onto grains at the depletion timescale. Through the Monte Carlo cloud simulation we demonstrate that the time-average abundance of H2O, the weighted average of the amount of time gas spends in preshock, shock, and postshock stages, is a sensitive function of the frequency of shocks. Thus we predict that the abundance of H2O, and to a lesser extent O2, can be used to trace the history of shock activity in molecular gas. We use previous large-scale surveys of molecular outflows to constrain the frequency of 10 km/s shocks in regions with varying star formation properties and discuss the observations required to test these results. We discuss the postshock lifetimes for other possible outflow tracers (e.g., SiO and CH3OH) and show that the differences between the lifetimes for various tracers can produce potentially observable chemical variations between younger and older outflows. For gas-grain models we find that the abundance of water-ice on grain surfaces can be quite large and is comparable to that observed in molecular clouds. This offers a possible alternative method to create water mantles without resorting to grain surface chemistry: gas heating and chemical modification due to a C-type shock and subsequent depletion of the gas-phase species onto grain mantles.