Percolation Depth Research Articles

Grain size dependant high-temperature hot corrosion (HTHC) degradation behavior in Alloy 617 during exposure in Na2SO4 + NaCl + V2O5 salt mixture

In the present investigation, the implication of grain size on the high-temperature hot corrosion (HTHC) response in Alloy 617 is studied. Towards this, specific thermal and thermo-mechanical processing schedules were employed to attain a wide range of grain sizes (7–70 µm), while maintaining other microstructural features like Σ3 n (n ≤ 3) boundary fraction, retained strain, and precipitate fraction nearly at constant. Subsequently, these specimens were exposed to Na 2 SO 4 + NaCl + V 2 O 5 (75 wt% + 20 wt% + 5 wt%) salt mixture at 1273 K for 24 h. Post-corrosion analyses reveal the formation of a highly porous and thick oxide scale on the as-received (AR) specimen (~32 µm), a relatively less porous and non-uniform oxide scale on the very coarse-grained specimen (~70 µm), and a homogeneous and dense Cr-rich scale on the very fine-grained microstructure (~7 µm). Such a protective scale on the very fine-grained specimen, developed due to the enhanced diffusivity of Cr, obstructs the entry of corrodents and thereby minimizes the percolation depth (~60 µm). The percolation depth is relatively higher (~130 µm) in the very coarse-grained specimen due to the development of a porous and non-uniform oxide scale. However, its percolation depth is still lower than the AR specimen (~ 305 µm), because of the reduced grain boundary area available for the diffusion of the corrosive species into the substrate. The AR specimen has exhibited the maximum percolation depth due to the simultaneous presence of fine and coarse grains, leading to the failure of both the aforementioned resistive mechanisms i.e., the accelerated formation of a protective Cr-rich scale and lesser availability of diffusion paths for the ingression of the corrosive species. • Very fine and very coarse-grained microstructures are resistant to HTHC damage. • AR specimen with inhomogeneous grain size distribution underwent maximum damage. • Grain refinement accelerates Cr-oxide formation that blocks entry of corrodants. • Grain coarsening decreases the channels for ingression of corrodants into the alloy. • Inhomogeneous grain size distribution in AR fails to activate resistive mechanisms.

Preferential flow patterns in forested hillslopes of east Tibetan Plateau revealed by dye tracing and soil moisture network

AbstractPreferential flow (PF) through soil and regolith results in a rapid vertical and lateral water movement within the profile. This study focused on quantifying PF in contrasting forested hillslopes of the Hailuo Valley, located on China's east Tibetan Plateau. Quantifying PF in this region is challenging since the underlying matrix is complex, with shallow soils, thick underlying saprolite, and the combined effect of moraines and weathered residual material. We developed new methods that integrated dye tracing with a high‐frequency soil moisture monitoring network to characterise PF pathways and quantity PF frequency on contrasting forested hillslopes (coniferous and broadleaved). Dye tracing experiments showed that soil‐root interfaces in the upper soil layer (10–50 cm) and soil‐rock interfaces in the deeper soil layer (50–100 cm) were the primary PF pathways and that large rocks strongly influence the percolation depth of water. The high‐frequency soil moisture network revealed that the mean PF frequency was 67.8% and 71.7% in the coniferous and broadleaved forests, respectively. The frequency of PF in the deeper soil layer increased from upslope to the downslope locations on both forested hillslopes, highlighting the tendency for PF to occur downslope. In addition to matrix conditions (e.g., stony saprolite soil), the total amount and maximum intensity of precipitation (as throughfall in this study) were identified as factors that control PF occurrence. In contrast, the initial soil water conditions (at 10, 50 and 100 cm depth) were insignificant in predicting PF occurrence. Results of this field‐based study highlight that PF is a ubiquitous and critical subsurface flow mechanism that regulates rainfall‐runoff relationships in forests of the Tibetan Plateau, underscoring the need to consider PF in hillslope hydrological modelling.Highlights Combined dye tracing and soil moisture monitoring network were applied to explore PF on forested hillslopes. Root networks and rock fragments constituted the main PF paths. PF frequency increased from upslope to downslope in two forest types. Initial soil moisture conditions showed no controlling effect on PF occurrence.

A novel approach combining grain boundary engineering and grain boundary serration to enhance high-temperature hot corrosion resistance in Alloy 617

In this work, a novel idea of combining two established microstructural engineering approaches viz., grain boundary engineering (GBE) and grain boundary serration (GBS) through optimization of thermomechanical and thermal processing in Alloy 617 is investigated and the superior resistance of GBE+GBS microstructure to the high-temperature hot corrosion is demonstrated. To achieve the GBE+GBS microstructure, the GBS treatment was introduced as a part of the GBE processing schedule (i.e., incomplete GBE+GBS) and following the GBE treatment (i.e., complete GBE+GBS). The extent of GBS is found to be similar in all the processed specimens. However, the extent of GBE is observed to be lower in the specimens undergoing incomplete GBE+GBS. This is due to the occurrence of recrystallization and consequent infrequent multiple twinning. On the other hand, a higher extent of GBE is achieved in the specimens subjected to complete GBE+GBS owing to the retention of the optimized GBE microstructure following the GBS treatment. The synergistic influence of GBE and GBS on the hot corrosion behavior is assessed by exposing the as-received (AR) as well as optimized grain boundary engineered and serrated (GBES) specimens to a salt mixture at 1273 K. The percolation depth after 24h and 48h exposure is significantly lower in the GBES specimen (∼55 µm and ∼115 µm, respectively) than the AR condition (∼305 µm and ∼630 µm, respectively). This is ascribed to the incorporation of Σ3n (n ≤3) and serrated boundaries in the GBES microstructure which obstructed the infiltration of harmful species into the alloy.

Strain-induced microstructural evolution and its implication on high-temperature hot corrosion (HTHC) phenomena in Alloy 617

The influence of various extents of strain on the microstructure and the high-temperature hot corrosion (HTHC) behavior in Alloy 617 is examined in this study. Electron backscatter diffraction characterization revealed an increase in the spread in the local misorientation zones from the vicinity of boundaries to the grain interiors with the extent of strain. Moreover, the increase in the degree of deformation also increased the connectivity of the random high angle grain boundaries (HAGBs), as corroborated by the fractal analysis, since most of the twin boundaries changed their character from ‘special’ to ‘random’ on the application of strain. The HTHC behavior of the as-received and the strained specimens is evaluated by exposing them to a salt mixture (Na 2 SO 4 + NaCl+V 2 O 5 ) at 1273 K for 24 h. The hot corrosion damage is assessed based on oxide scale characteristics (morphology, thickness, and composition), internal percolation depth, Micro-CT (porosity), and Mott-Schottky (passive film defects) analyses. In-depth characterization of the corroded specimens unveils an improved resistance to HTHC in the highly strained specimens due to the enhanced Cr diffusion through the defects and connected random HAGBs which facilitated the formation of a continuous, and compact Cr-rich oxide film. Importantly, the occurrence of recrystallization and the evolution of the Cr-rich carbides in the strained specimens in the course of the HTHC test increased its likelihood of resisting the aggressive environment for a prolonged duration. • Local misorientations, TTBs, and random HAGBs connectivity increased on straining. • Oxide layer formed on strained specimens is continuous, dense and protective. • Higher HTHC resistance in strained specimens is attributed to greater Cr diffusion. • The enhanced Cr diffusion is due to increased defects and random HAGBs connectivity. • Straining even led to superior resistance against damage during prolonged HTHC test.

Firn Evolution at Camp Century, Greenland: 1966–2100

Camp Century is an American military base built in 1959 under the surface of the Greenland ice sheet and decommissioned in 1967. Here, we use outputs from RACMO2.3p2 and CanESM2 climate models, adjusted to meteorological observations, and a firn model to simulate the firn density and temperature at Camp Century between 1966 and 2100. The model output is evaluated against an extensive set of firn 3observations and three Representative Concentration Pathways (RCP2.6, 4.5 and 8.5) are considered as future scenarios. Our model suggests that the upper horizon of the Camp Century debris field – observed at a depth of 32 m in 2017 – will continue to be buried by persistent net accumulation over the next eighty years under all RCP scenarios. This horizon depth will be between 58 and 64 m in 2100, depending on the RCP scenario. We estimate a maximum meltwater percolation depth of 1.1 m under all RCP scenarios. We therefore find it extremely unlikely that surface meltwater interacts with the subsurface debris field at Camp Century before 2100 under all RCP scenarios. Camp Century’s future is representative of the firn area in northwestern Greenland, bound to shift from dry snow to a percolation regime. Our model suggests that 10 m firn temperatures at Camp Century will increase from −24.0°C in 1966 to −21.3, −20.0 and −18.6°C in 2100 under the RCP2.6, 4.5 and 8.5 scenarios, respectively. We reveal a previously unknown warm bias in air temperatures simulated at Camp Century by both RACMO2.3p2 and CanESM2 climate models which needs to be accounted for when using these models to predict melt, firn evolution and sea-level contribution of the Greenland ice sheet. We also present novelin situmeasurements of firn compaction rates, which indicate that about 25% of firn compaction of the top 62 m of firn occurs below 20 m depth. This highlights the importance of deep-firn compaction measurements for model evaluation and correction of altimetry products.

Precipitate evolution during aging and its individual role on high-temperature hot corrosion response in Alloy 617

In this work, we report the results of a systematic study on the evolution of the precipitates during aging in a Ni-based superalloy (Alloy 617) and their effect on the high-temperature hot corrosion (HTHC). It was observed that the extent of Cr-rich precipitation increased with the aging time while the other microstructural parameters such as grain size, retained strain, and Σ3n (n ≤ 3) boundaries fraction did not change in comparison to the as-received (AR) condition. To evaluate the role of precipitation on hot corrosion, the AR and the aged specimens were subjected to the HTHC test involving complete immersion of the specimens in a 75 wt% Na2SO4 + 20 wt% NaCl + 5 wt% V2O5 salt mixture at 1273 K for 24 h. The characterization of surface and cross-section morphologies of the corroded layers through scanning electron microscopy revealed that the oxide film formed on the AR specimen is highly porous and loose. In contrast, the layer formed on the specimen aged for 100 h (AR-100 h) is significantly thinner and dense. Post-HTHC analysis aided with the thermodynamic and diffusion calculations revealed that the improved HTHC performance of the AR-100 h specimen is due to the rapid formation of an oxide layer owing to the enhanced supply of Cr as a consequence of carbide dissolution. Also, the undissolved carbides at the grain boundaries acted as a potential obstruction to the inward transport of corrosive species, resulting in a significantly lower percolation depth in the AR-100 h specimen (~66 ± 6 µm) than the AR condition (~305 ± 15 µm).

The firn meltwater Retention Model Intercomparison Project (RetMIP): evaluation of nine firn models at four weather station sites on the Greenland ice sheet

Abstract. Perennial snow, or firn, covers 80 % of the Greenland ice sheet and has the capacity to retain surface meltwater, influencing the ice sheet mass balance and contribution to sea-level rise. Multilayer firn models are traditionally used to simulate firn processes and estimate meltwater retention. We present, intercompare and evaluate outputs from nine firn models at four sites that represent the ice sheet's dry snow, percolation, ice slab and firn aquifer areas. The models are forced by mass and energy fluxes derived from automatic weather stations and compared to firn density, temperature and meltwater percolation depth observations. Models agree relatively well at the dry-snow site while elsewhere their meltwater infiltration schemes lead to marked differences in simulated firn characteristics. Models accounting for deep meltwater percolation overestimate percolation depth and firn temperature at the percolation and ice slab sites but accurately simulate recharge of the firn aquifer. Models using Darcy's law and bucket schemes compare favorably to observed firn temperature and meltwater percolation depth at the percolation site, but only the Darcy models accurately simulate firn temperature and percolation at the ice slab site. Despite good performance at certain locations, no single model currently simulates meltwater infiltration adequately at all sites. The model spread in estimated meltwater retention and runoff increases with increasing meltwater input. The highest runoff was calculated at the KAN_U site in 2012, when average total runoff across models (±2σ) was 353±610 mm w.e. (water equivalent), about 27±48 % of the surface meltwater input. We identify potential causes for the model spread and the mismatch with observations and provide recommendations for future model development and firn investigation.

Woody plant encroachment enhances soil infiltrability of a semiarid karst savanna

Semiarid karst landscapes are often the source areas for regionally important groundwater supplies. Like savannas across the globe, these landscapes are experiencing an increase in woody plant cover—often referred to as woody plant encroachment. Although this phenomenon is commonly viewed as leading to increased transpiration and reduced groundwater recharge, this may not be true of all ecosystems. For example, in the Edwards Plateau region of central Texas—where the underlying geology is karst—dramatic increases in baseflows have occurred concurrently with the expansion of woody plants. It has been suggested that in this context woody plants, especially juniper (Juniperus spp.), are partially responsible for boosting recharge by improving soil infiltrability, but this hypothesis has not been systematically evaluated. Our study examined the effects of an important encroaching shrub (Redberry juniper) on soil infiltrability in the Edwards Plateau. We carried out a large number of infiltration tests to determine soil infiltrability and used a dye tracer followed by soil profile excavation to estimate the potential for deep percolation. Tests were performed at increasing distances under juniper shrubs of five size classes, ranging from young seedlings to mature shrubs. We found that in soils underlying shrubs, infiltrability was quintupled and percolation depth almost tripled compared with soils in intercanopy zones. Surprisingly, shrub size was not a significant factor. Even the soils beneath the smallest shrubs had much higher infiltrability than intercanopy soils, showing that these woody plants modify soil properties at very early stages. We also found that both infiltrability and percolation depth gradually increased with proximity to the trunk and showed a strong correlation with litter thickness. Our results provide support for the hypothesis that in semiarid karst landscapes, woody plant encroachment—especially the invasion of juniper—can play an important role in enhancing groundwater recharge by improving the soil infiltrability.

Serpentinite and the search for life beyond Earth.

Hydrogen from serpentinization is a source of chemical energy for some life forms on Earth. It is a potential fuel for life in the subsurface of Mars and in the icy ocean worlds in the outer solar system. Serpentinization is also implicated in life's origin. Planetary exploration offers a way to investigate such theories by characterizing and ultimately searching for life in geochemical settings that no longer exist on Earth. At present, much of the current context of serpentinization on other worlds relies on inference from modelling and studies on Earth. While there is evidence from orbital spectral imaging and martian meteorites that serpentinization has occurred on Mars, the extent and duration of that activity has not been constrained. Similarly, ongoing serpentinization might explain hydrogen found in the ocean of Saturn's tiny moon Enceladus, but this raises questions about how long such activity has persisted. Titan's hydrocarbon-rich atmosphere may derive from ancient or present-day serpentinization at the bottom of its ocean. In Europa, volcanism or serpentinization may provide hydrogen as a redox couple to oxygen generated at the moon's surface. We assess the potential extent of serpentinization in the solar system's wet and rocky worlds, assuming that microfracturing from thermal expansion anisotropy sets an upper limit on the percolation depth of surface water into the rocky interiors. In this bulk geophysical model, planetary cooling from radiogenic decay implies the infiltration of water to greater depths through time, continuing to the present. The serpentinization of this newly exposed rock is assessed as a significant source of global hydrogen. Comparing the computed hydrogen and surface-generated oxygen delivered to Europa's ocean reveals redox fluxes similar to Earth's. Planned robotic exploration missions to other worlds can aid in understanding the planetary context of serpentinization, testing the predictions herein. This article is part of a discussion meeting issue 'Serpentinite in the Earth System'.

The Effect of Foehn‐Induced Surface Melt on Firn Evolution Over the Northeast Antarctic Peninsula

AbstractSurface meltwater ponding has been implicated as a major driver for recent ice shelf collapse as well as the speedup of tributary glaciers in the northeast Antarctic Peninsula. Surface melt on the NAP is impacted by the strength and frequency of westerly winds, which result in sporadic foehn flow. We estimate changes in the frequency of foehn flow and the associated impact on snow melt, density, and the percolation depth of meltwater over the period 1982–2017 using a regional climate model and passive microwave data. The first of two methods extracts spatial patterns of melt occurrence using empirical orthogonal function analysis. The second method applies the Foehn Index, introduced here to capture foehn occurrence over the full study domain. Both methods show substantial foehn‐induced melt late in the melt season since 2015, resulting in compounded densification of the near‐surface snow, with potential implications for future ice shelf stability.

Physical model study on the clay–sand interface without and with geotextile separator

In most marine reclamation projects, sand fill is placed directly on soft marine seabed soils. The sand particles can easily penetrate into the soft marine soils, and the soft soil can also move into the pore spaces inside the sand at the initial contact interface between the sand and the soft marine soil. In this case, the permeability and the volume of the sand above the initial surface are reduced. To avoid this problem, a geotextile separator is often placed on the surface of the soft marine soils before placing the sand. In this study, a two-dimensional physical model is utilized to study the geotextile separator effects. The initial conditions of a clayey soil, sand fill, and surcharge loading were kept the same in the physical model test with the only difference being that a geotextile separator was either placed on the clay surface or omitted. The settlements of the initial interface were recorded and compared for the two cases without or with the geotextile separator. The particle size distribution of the soils taken across the interface zone for different time durations was then measured, analyzed, and compared. Based on an analysis of the results, the sand percolation depth was 40 mm and fine particle suffusion was apparent when the sand was placed directly on the marine slurry surface without a geotextile separator. However, when a geotextile separator was used sand percolation was avoided, and the fine particle suffusion was effectively diminished. A relative fine particle fraction is defined to illustrate the migration of fine particles from the clay to the sand soils. The fine particle percentages of the Hong Kong Marine Deposits–sand mixtures were calculated for the cases with and without a geotextile separator using an empirical formula and micromechanical modeling to obtain a better understanding of the effects of geotextile separators in practice.

Coupled Snow Cover and Avalanche Dynamics Simulations to Evaluate Wet Snow Avalanche Activity

We present physics‐based snowpack simulations for four snow seasons with detailed wet snow avalanche activity records. The distributed, spatially explicit simulations using the Alpine3D and SNOWPACK model show that the simulated snowpack in the release areas of documented wet snow avalanches often exhibits its first wetting of the season on the release day. This first wetting is accompanied in the simulations by liquid water accumulating on capillary barriers, often formed by depth hoar layers. The strongest water accumulations and largest increases in percolation depth are found on the day of avalanche release. For individual avalanche paths, however, this only holds in 25%–30% of the cases. Assuming that the depth of the strongest water accumulation corresponds to the avalanche fracture depth, the avalanche dynamics model RAMMS‐Extended was run using simulated snowpack properties as initial conditions in the release area and boundary conditions along the avalanche path. On average, the simulated affected area by the avalanche and runout distance for the release day are statistically significant in closer agreement with the observations than two days before the release. This does not hold for the simulations of 1 day before and 1 and 2 days after the release. This suggests that fracture depths and the temporal evolution of percolation depths are adequately simulated within a ±1‐day period. The results show a large potential for distributed snow cover and avalanche dynamics simulations to assess wet snow avalanche hazards, although predictions for individual avalanche paths remain challenging.

Seasonal monitoring of melt and accumulation within the deep percolation zone of the Greenland Ice Sheet and comparison with simulations of regional climate modeling

Abstract. Increasing melt over the Greenland Ice Sheet (GrIS) recorded over the past several years has resulted in significant changes of the percolation regime of the ice sheet. It remains unclear whether Greenland's percolation zone will act as a meltwater buffer in the near future through gradually filling all pore space or if near-surface refreezing causes the formation of impermeable layers, which provoke lateral runoff. Homogeneous ice layers within perennial firn, as well as near-surface ice layers of several meter thickness have been observed in firn cores. Because firn coring is a destructive method, deriving stratigraphic changes in firn and allocation of summer melt events is challenging. To overcome this deficit and provide continuous data for model evaluations on snow and firn density, temporal changes in liquid water content and depths of water infiltration, we installed an upward-looking radar system (upGPR) 3.4 m below the snow surface in May 2016 close to Camp Raven (66.4779∘ N, 46.2856∘ W) at 2120 m a.s.l. The radar is capable of quasi-continuously monitoring changes in snow and firn stratigraphy, which occur above the antennas. For summer 2016, we observed four major melt events, which routed liquid water into various depths beneath the surface. The last event in mid-August resulted in the deepest percolation down to about 2.3 m beneath the surface. Comparisons with simulations from the regional climate model MAR are in very good agreement in terms of seasonal changes in accumulation and timing of onset of melt. However, neither bulk density of near-surface layers nor the amounts of liquid water and percolation depths predicted by MAR correspond with upGPR data. Radar data and records of a nearby thermistor string, in contrast, matched very well for both timing and depth of temperature changes and observed water percolations. All four melt events transferred a cumulative mass of 56 kg m−2 into firn beneath the summer surface of 2015. We find that continuous observations of liquid water content, percolation depths and rates for the seasonal mass fluxes are sufficiently accurate to provide valuable information for validation of model approaches and help to develop a better understanding of liquid water retention and percolation in perennial firn.

Strain-Annealing Based Grain Boundary Engineering to Evaluate its Sole Implication on Intergranular Corrosion in Extra-Low Carbon Type 304L Austenitic Stainless Steel

Strain-annealing based thermo-mechanical processing has been performed to promote grain boundary engineering (GBE) in an extra-low carbon type austenitic stainless steel without altering the grain size and residual strain to evaluate its sole influence on intergranular corrosion. Single-step processing comprising low pre-strain (~ 5 and 10 pct) followed by annealing at 1273 K for 1 hour have resulted in a large fraction of Σ3 n boundaries and significant disruption in random high-angle grain boundaries (RHAGBs) connectivity. This is due to the occurrence of prolific multiple twinning in these specimens as confirmed by their large twin-related domain and twin-related grain size ratio. Among the iterative processing, the schedule comprising two cycles of 10 and 5 pct deformation followed by annealing at 1173 K for 1 hour has yielded the optimum GBE microstructure with the grain size and residual strain akin to the as-received condition. The specimens subjected to the higher number of iterations failed to realize GBE microstructures due to the occurrence of partial recrystallization. Owing to the optimum grain boundary character distribution, the GBE specimen has exhibited remarkable resistance against sensitization and intergranular corrosion as compared to the as-received condition. Furthermore, the lower depth of percolation in the GBE specimen is due to the significant disruption of RHAGBs connectivity as confirmed from its large twin-related domain and lower fractal dimension.

Effect of Soil Sample Size on Saturated Soil Hydraulic Conductivity

ABSTRACTSaturated hydraulic conductivity (Ksat) is regarded as a key soil physical variable to determine soil infiltration rate, percolation depth and other hydrological processes. The purpose of this study was to determine the best soil sampling’s ring size for measuring Ksat. For this purpose, 25 rings with five different diameters (2, 3, 4, 5 and 6 inch) and with the same depth of 20 cm (five replicates) were hammered in close vicinity to each other into the ground of undisturbed loess deposits of a small farm to measure Ksat and bulk density. Hydraulic conductivity was measured at three constant loads of 22, 27 and 32 cm. The results showed that the ring with the internal diameter of 6 inches had the minimum variation coefficient and maximum Ksat for all the three hydraulic heads. In addition, the bulk density of this ring size was less than the other rings.

Importance of lateral flux and its percolation depth on organic carbon export in Arctic tundra soil: Implications from a soil leaching experiment

AbstractTemperature rise in the Arctic is causing deepening of active layers and resulting in the mobilization of deep permafrost dissolved organic matter (DOM). However, the mechanisms of DOM mobilization from Arctic soils, especially upper soil horizons which are drained most frequently through a year, are poorly understood. Here we conducted a short‐term leaching experiment on surface and deep organic active layer soils, from the Yukon River basin, to examine the effects of DOM transport on bulk and molecular characteristics. Our data showed a net release of DOM from surface soils equal to an average of 5% of soil carbon. Conversely, deep soils percolated with surface leachates retained up to 27% of bulk DOM while releasing fluorescent components (up to 107%), indicating selective release of aromatic components (e.g., lignin and tannin), while retaining nonchromophoric components, as supported by spectrofluorometric and ultrahigh‐resolution mass spectroscopic techniques. Our findings highlight the importance of the lateral flux of DOM on ecosystem carbon balance as well as processing of DOM transport through organic active layer soils en route to rivers and streams. This work also suggests the potential role of leachate export as an important mechanism of C losses from Arctic soils, in comparison with the more traditional pathway from soil to atmosphere in a warming Arctic.

Parameterizing Deep Water Percolation Improves Subsurface Temperature Simulations by a Multilayer Firn Model

Deep preferential percolation of melt water in snow and firn brings water lower along the vertical profile than a laterally homogeneous wetting front. This widely recognized process is an important source of uncertainty in simulations of subsurface temperature, density and water content in seasonal snow and in firn packs on glaciers and ice sheets. However, observation and quantification of preferential flow is challenging and therefore it is not accounted for by most of the contemporary snow/firn models. Here we use temperature measurements in the accumulation zone of Lomonosovfonna, Svalbard, done in April 2012 – 2015 using multiple thermistor strings to describe the process of water percolation in snow and firn. Effects of water flow through the snow and firn profile are further explored using a coupled surface energy balance - firn model forced by the output of the regional climate model WRF. In situ air temperature, radiation and surface height change measurements are used to constrain the surface energy and mass fluxes. To account for the effects of preferential water flow in snow and firn we test a set of depth-dependent functions allocating a certain fraction of the melt water available at the surface to each snow/firn layer. Experiments are performed for a range of characteristic percolation depths and results indicate a reduction in root mean square difference between the modeled and measured temperature by up to a factor of two compared to the results from the default water infiltration scheme. This illustrates the significance of accounting for preferential water percolation to simulate subsurface conditions. The suggested approach to parameterization of the preferential water flow requires low additional computational cost and can be implemented in layered snow/firn models applied both at local and regional scales, for distributed domains with multiple mesh points.

Simplified continuous simulation model for investigating effects of controlled drainage on long-term soil moisture dynamics with a shallow groundwater table.

Accurate modeling of soil water content is required for a reasonable prediction of crop yield and of agrochemical leaching in the field. However, complex mathematical models faced the difficult-to-calibrate parameters and the distinct knowledge between the developers and users. In this study, a deterministic model is presented and is used to investigate the effects of controlled drainage on soil moisture dynamics in a shallow groundwater area. This simplified one-dimensional model is formulated to simulate soil moisture in the field on a daily basis and takes into account only the vertical hydrological processes. A linear assumption is proposed and is used to calculate the capillary rise from the groundwater. The pipe drainage volume is calculated by using a steady-state approximation method and the leakage rate is calculated as a function of soil moisture. The model is successfully calibrated by using field experiment data from four different pipe drainage treatments with several field observations. The model was validated by comparing the simulations with observed soil water content during the experimental seasons. The comparison results demonstrated the robustness and effectiveness of the model in the prediction of average soil moisture values. The input data required to run the model are widely available and can be measured easily in the field. It is observed that controlled drainage results in lower groundwater contribution to the root zone and lower depth of percolation to the groundwater, thus helping in the maintenance of a low level of soil salinity in the root zone.

Modeling of the residue transport of lambda cyhalothrin, cypermethrin, malathion and endosulfan in three different environmental compartments in the Philippines

Abstract This study aims to determine the environmental transport and fate of the residue of four Philippines priority chemicals; i.e., lambda cyhalothrin (L-cyhalothrin), cypermethrin, endosulfan and malathion, in three different environmental compartments (air, water and soil). In the Philippines, pesticide application is the most common method of controlling pests and weeds in rice and vegetable farming. This practice aided the agricultural industry to minimize losses and increase yield. However, indiscriminate use of pesticides resulted to adverse effects to public health and environment. Studies showed that 95% of the applied pesticides went to non-target species. Data from previous studies in Pagsanjan Laguna, Philippines were used as input data. Dispersion, Gaussian plume, and regression equations were employed to simulate the behavior of L-cyhalothrin, cypermethrin, endosulfan and malathion in air, water and soil. Substance decay was calculated using first order reaction. This study showed how L-cyhalothrin, cypermethrin, endosulfan, and malathion behaved in the environment after release from nozzle spray, and its possible duration of stay in the environment. It will also show a tool in determining the percolation depth through soil by endosulfan. This tool can be utilized in determining the depth of contaminated soil during remediation strategic planning and project implementation of similar environmental condition.

The Syabru‐Bensi hydrothermal system in central Nepal: 2. Modeling and significance of the radon signature

AbstractThe Syabru‐Bensi hydrothermal system (SBHS), located in the Nepal Himalayas, is characterized by numerous hot (>30°C) springs and the release of dry, cold (<35°C) CO2 associated with radon‐222, detailed in the companion paper. In the SBHS, CO2 and radon fluxes on the ground vary over 5–6 orders of magnitude, reaching exceptional mean values of 100 kg m−2 d−1 and 12 Bq m−2 s−1, respectively. This paper extends the companion paper by developing three quantitative models for the radon signature of CO2 based on measurements of radon and radium concentrations in the spring waters and effective radium concentration of rocks and soils. The first model considers near‐surface radon and CO2 degassing from water, considered unlikely unless there exist currently unidentified large discharges of hydrothermal water. The second model considers CO2, arising from deeper hydrothermal sources, incorporating radon from shallow radium sources as it percolates upward toward the surface, considered more likely as a percolation depth of 100 m is sufficient to account for the observed radon discharge. The third model considers the observed peak radon concentrations in the gas zones and assumes that gaseous CO2 can be transported from kilometer‐scale depths through a fault network connected to the zones. This latter model affords the possibility that variations of physical parameters at depths associated with earthquake nucleation might be detectable at the surface. Gas‐dominated transport might operate in other locations in Himalayas and elsewhere and may be an important aspect of the coupled mechanisms associated with seismically active orogens.