Annual Freeze-thaw Cycle Research Articles

Selection of moisture reference year for freeze-thaw damage assessment of historic masonry walls under future climate: A simulation-based approach

Today, there is an increased research effort on improving energy efficiency in heritage buildings through retrofit measures. Hygrothermal simulations tools are often used to assess the long-term performance of building envelopes and determine whether they are suitable for interior insulation. To reduce the high computation time and cost incurred with these simulations, a moisture reference year (MRY) is typically selected based on long-term annual climatic conditions. Simulation results obtained under MRYs are assumed to represent the long-term performance. However, when assessing the risk to freeze-thaw (FT) damage of historic masonry walls, methods selecting climate-based MRYs have failed to represent the actual performance – determined based on results from simulations over the 31 consecutive years. This paper attempts to find an alternative method to select MRYs, based on the hygrothermal simulations of specific constructions. First, a parametric analysis was proposed to identify the parameters that have the greatest influence on FT damage. Then, simulations are performed for a continuous 31-year period and for each single year. A comparison of their results suggests that there is no accumulative effect on the annual freeze-thaw cycles; and therefore, MRYs can be selected as the single year with the 93rd percentile FT damage severity or the worst year commonly found between masonry walls pre and post retrofit. The application of MRYs was then verified for different insulation types and thicknesses. Results showed that simulation-based MRYs are construction and orientation dependent; however, they are reliable to use for retrofitting design decision making.

Combined Effect of Freeze–Thaw Cycles and Biochar Addition on Soil Nitrogen Leaching Characteristics in Seasonally Frozen Farmland in Northeast China

Global climate warming and increased climate variability may increase the number of annual freeze–thaw cycles (FTCs) in temperate zones. The occurrence of more frequent FTCs is predicted to influence soil carbon and nitrogen cycles and increase nitrogen leaching. Biochar has the potential to increase soil organic carbon storage and decrease nitrogen leaching. This study aims to investigate the impact of freeze–thaw cycles (FTCs) on soil nitrogen leaching in temperate zones, considering the potential exacerbation of FTCs due to global climate warming and increased climate variability. This study focuses on how biochar, a carbon-rich material produced from biomass, might mitigate nitrogen leaching by influencing soil characteristics. This study explores the interactions between different laboratory-simulated FTC frequencies (ranging from 0 to 12 cycles) and various biochar addition ratios (0%, 2%, 4%, and 6% w/w) on soil nitrogen leaching based on a total of 60 soil columns. Pearson correlations between the soil quality indicators and nitrogen leaching characteristics were detected, and partial least squares path modeling (PLS-PM) was used to assess the effects of the FTCs, biochar addition ratios, and soil quality indicators on the nitrogen leaching content. The results showed that the amount of leached soil NH4+-N and NO3−-N reached 0.129–1.726 mg and 2.90–7.90 mg, respectively. NH4+-N and NO3−-N first increased and then decreased under the FTCs, with the highest values being observed after the 6th FTC. As the biochar addition ratio increased, the NH4+-N and NO3−-N contents decreased. Correlation analysis showed that the nitrogen leaching content was significantly related to the soil pH, soil organic matter (SOM), NH4+-N content, and microbial biomass carbon content (MBC) (p < 0.01). The results of the conceptual path model revealed that nitrogen leaching characteristics were significantly affected by the pH, SOM, soil nitrogen content, and biochar addition ratio. Our results suggest that biochar addition can help reduce nitrogen leaching in farmland soil in areas with black soil and seasonal freeze–thaw cycles.

Seasonal variation in near-surface seasonally thawed active layer and permafrost soil microbial communities

Understanding how soil microbes respond to permafrost thaw is critical to predicting the implications of climate change for soil processes. However, our knowledge of microbial responses to warming is mainly based on laboratory thaw experiments, and field sampling in warmer months when sites are more accessible. In this study, we sampled a depth profile through seasonally thawed active layer and permafrost in the Imnavait Creek Watershed, Alaska, USA over the growing season from summer to late fall. Amplicon sequencing showed that bacterial and fungal communities differed in composition across both sampling depths and sampling months. Surface communities were most variable while those from the deepest samples, which remained frozen throughout our sampling period, showed little to no variation over time. However, community variation was not explained by trace metal concentrations, soil nutrient content, pH, or soil condition (frozen/thawed), except insofar as those measurements were correlated with depth. Our results highlight the importance of collecting samples at multiple times throughout the year to capture temporal variation, and suggest that data from across the annual freeze-thaw cycle might help predict microbial responses to permafrost thaw.

Spatiotemporal variations of freeze-thaw erosion risk during 1991–2020 in the black soil region, northeastern China

Freeze-thaw (FT) erosion, which occurs in high-altitude and high-latitude regions, has a considerable impact on water and wind erosion. However, studies on long-term variations of FT erosion induced risks are still limited. In the present study, based on 30-year data at 247 meteorological stations, spatiotemporal FT erosion risk in the black soil region, northeastern China was evaluated through the Analytical Hierarchy Process (AHP) and Entropy-weight method (EWM). Six FT erosion-related variables, including annual FT cycle days, soil water content (SWC), fraction vegetation coverage (FVC), slope, soil bulk density (BD), and soil structural stability (SSI) were used to assess FT erosion risk in the study region. Among these variables, the slope was the most important variable (45 %), followed by annual FT cycle days (15 %), FVC (15 %), and SSI (14 %). FT erosion risk differed in different land use types. Woodland, residential land and grassland suffered severe FT erosion risk, and paddy and dryland suffered slight FT erosion risk. Complex topography areas had a higher FT erosion risk. During past 30 years, global warming mitigated the FT erosion risk. This study can help understand soil erosion characteristics and soil loss control for the Chinese black soil region and similar regions in the world.

Comprehensive in-situ freeze-thaw monitoring under a granular-surfaced road system

Annual freeze-thaw cycles significantly impact the performance of granular-surfaced roadways in cold regions. Various methods are employed to limit the damage caused by these events. A seasonal load restriction (SLR) is one of these methods that is imposed by local roads agencies according to the subgrade condition. Subsurface monitoring is a reliable method to help such agencies determine the status and freeze-thaw behavior of the subgrade in real-time. To help improve the capabilities for predicting the depths and timing of soil freeze-thaw events, a comprehensive subgrade sensor network was installed below a granular-surfaced roadway in Hamilton County, Iowa. The network continuously measured temperature, volumetric water content and matric potential at selected depths below the subgrade surface, and also recorded atmospheric conditions using a weather station installed next to the instrumented roadway section. In this study, the collected dataset for the winter 2019–2020 freeze-thaw period was analyzed using contour mapping over the entire road cross-section. The results of the study revealed unsymmetrical behavior under the road surface. The freezing front was found to be deeper towards the west midpoint and shallower at the shoulders. Volumetric water content and matric potential measurements were also found to be coherent with the temperature data during freezing and thawing periods. In addition, soil water retention curves of matric potential versus water content determined in the laboratory were compared to the curves derived from the field measurements. The two datasets were found to be quite different due to both predictable and unpredictable field conditions.

Quantifying Soundscapes in the Ross Sea, Antarctica Using Long-Term Autonomous Hydroacoustic Monitoring Systems

Deployment of long-term, continuously recording passive-acoustic sensors in the ocean can provide insights into sound sources related to ocean dynamics, air–sea interactions, and biologic and human activities, all which contribute to shaping ocean soundscapes. In the polar regions, the changing ocean climate likely contributes to seasonal and long-term variation in cryogenic sounds, adding to the complexity of these soundscapes. The Korea Polar Research Institute and the U.S. National Oceanic and Atmospheric Administration have jointly operated two arrays of autonomous underwater hydrophones in the Southern Ocean, one in the Terra Nova Bay Polynya (TNBP) during December 2015–January 2019 and the other in the Balleny Islands (BI) region during January 2015–March 2016, to monitor changes in ocean soundscapes. In the BI region, we found distinct seasonal variations in the cryogenic signals that were attributed to collisions and thermal/mechanical fracturing of the surface sea ice. This is consistent with sea-ice patterns due to annual freeze–thaw cycles, which are not clearly observed in TNBP, where frequent blowing out of sea ice by katabatic winds and icequakes from nearby ice shelves generate strong noise even in austral winters. Another advantage of passive acoustic recordings is that they provide opportunities to measure biodiversity from classifying spectral characteristics of marine mammals: we identified 1. Leopard seals (Hydrurga leptonyx; 200–400 Hz), most abundant in the BI region and TNBP in December; 2. Antarctic blue whales (Balaenoptera musculus; distinctive vocalization at 18 and 27 Hz), strong signals in austral winter and fall in the BI region and TNBP; 3. Fin whales (B. physalus; fundamental frequency in the 15–28 Hz and overtones at 80 and 90 Hz), maximum presence in the BI region during the austral summer and spring months; 4. Antarctic minke whales (B. bonaerensis; 100–200 Hz), strongest signals from June to August in the BI region; 5. Humpback whales in TNBP; 6. Unidentified whales (long-duration downsweeping from 75 to 62 Hz), detected in TNBP. Long-term soundscape monitoring can help understand the spatiotemporal changes in the Southern Ocean and cryosphere and provide a means of assessing the status and trends of biodiversity in the Ross Sea Region Marine Protected Area.

Automated Coastal Ice Mapping with SAR Can Inform Winter Fish Ecology in the Laurentian Great Lakes

Many freshwater lakes in the temperate zone undergo annual freeze-thaw cycles. Climate change has disrupted these patterns and altered habitat for many species including ecologically, economically, and culturally valuable fish species. To understand the relationship between ice cover and aquatic species, suitable data can be derived from remote sensing. We developed a novel ice classification method with minimal user input using freely available Sentinel-1 data and an adjacent and time-coincident validation dataset. Using image object segmentation and a random forest classifier, ice conditions were classified correctly with >85% overall accuracy. Our ice mapping efforts coincided with a telemetry dataset of tagged Walleye (Sander vitreus) and Northern Pike (Esox lucius) in Hamilton Harbor in western Lake Ontario. Between years with low and high ice covers (2017 and 2019, respectively), we found Walleye appeared to reduce their area of movement when the harbor was covered in ice. Our ice mapping tool can provide a quick and consistent method for agencies to adopt for freshwater resource management as well as provide ice cover information in coastal areas that are important overwintering habitat for many fishes.

A Freezing-Thawing Damage Characterization Method for Highway Subgrade in Seasonally Frozen Regions Based on Thermal-Hydraulic-Mechanical Coupling Model

Seasonally frozen soil where uneven freeze–thaw damage is a major cause of highway deterioration has attracted increased attention in China with the rapid development of infrastructure projects. Based on Darcy’s law of unsaturated soil seepage and heat conduction, the thermal–hydraulic–mechanical (THM) coupling model is established considering a variety of effects (i.e., ice–water phase transition, convective heat transfer, and ice blocking effect), and then the numerical solution of thermal–hydraulic fields of subgrade can be obtained. Then, a new concept, namely degree of freeze–thaw damage, is proposed by using the standard deviation of the ice content of subgrade during the annual freeze–thaw cycle. To analyze the freeze–thaw characteristics of highway subgrade, the model is applied in the monitored section of the Golmud to Nagqu portion of China National Highway G109. The results show that: (1) The hydrothermal field of subgrade has an obvious sunny–shady slopes effect, and its transverse distribution is not symmetrical; (2) the freeze–thaw damage area of subgrade obviously decreased under the insulation board measure; (3) under the combined anti-frost measures, the maximum frost heave amount of subgrade is significantly reduced. This study will provide references for the design of highway subgrades in seasonally frozen soil areas.

STUDY OF THE INFLUENCE OF THE LAYING OF HEATING MAINS ON THE STATE OF THE BASE PAVEMENT AUTOMOBILE ROAD

This article includes the way to prevent deformation of linear constructions which can due to the laying of the heating network because heating promotes ice formation. The considered design of the pavement cover during the laying of the heating network is being built on a section of the road on Pionerskaya street, which belongs to the roads of the third category. There are results of scientific research and engineering calculations of options for rational design of roads when laying the heating network and the example of the Far Eastern section of the road. The development is a generalization of the results of solving engineering, scientific, and settlement applied objectives. There is heating network is being laid, in the area under considerationwhich will subsequently warm up the outer surface of the asphalt concrete due to the heat generation of the pipes. It will cause the formation of ice on the outer surface of the asphalt concrete during period with negative temperatures. This construction imitaties plate in the rubble layers by using an integrated biaxial geogrid, as well as the laying of the heat insulation layer. The analysis of the initial data, as well as during the realization of the work, has established that, in order to be able to evaluate and compare the various indicators, it is necessary to provide calculated and theoretical studies for several construction options. Analysis of possible methods and means for determining rational structure parameters showed that it would be advisable to use geotechnical software systems «FEM models» and «Termoground». These software systems are able to jointly simulate the work of structures by its stress state, as well as by the ongoing thermodynamic processes in the annual freeze-thaw cycle. Numerical simulation of the structure operation using this software geotechnical complex allowed us to estimate the stability of the structure deformations, as well as to limit the heating of the asphalt concrete surface.

Microbial Community Structure and Functional Potential in Cultivated and Native Tallgrass Prairie Soils of the Midwestern United States.

The North American prairie covered about 3.6 million-km2 of the continent prior to European contact. Only 1–2% of the original prairie remains, but the soils that developed under these prairies are some of the most productive and fertile in the world, containing over 35% of the soil carbon in the continental United States. Cultivation may alter microbial diversity and composition, influencing the metabolism of carbon, nitrogen, and other elements. Here, we explored the structure and functional potential of the soil microbiome in paired cultivated-corn (at the time of sampling) and never-cultivated native prairie soils across a three-states transect (Wisconsin, Iowa, and Kansas) using metagenomic and 16S rRNA gene sequencing and lipid analysis. At the Wisconsin site, we also sampled adjacent restored prairie and switchgrass plots. We found that agricultural practices drove differences in community composition and diversity across the transect. Microbial biomass in prairie samples was twice that of cultivated soils, but alpha diversity was higher with cultivation. Metagenome analyses revealed denitrification and starch degradation genes were abundant across all soils, as were core genes involved in response to osmotic stress, resource transport, and environmental sensing. Together, these data indicate that cultivation shifted the microbiome in consistent ways across different regions of the prairie, but also suggest that many functions are resilient to changes caused by land management practices – perhaps reflecting adaptations to conditions common to tallgrass prairie soils in the region (e.g., soil type, parent material, development under grasses, temperature and rainfall patterns, and annual freeze-thaw cycles). These findings are important for understanding the long-term consequences of land management practices to prairie soil microbial communities and their genetic potential to carry out key functions.

Artificial warming-mediated soil freezing and thawing processes can regulate soybean production in Northeast China

Northeast China with seasonally frozen soil is quite sensitive to global warming. The changes in soil freezing and thawing processes initiated by global warming could alter the hydrological cycle of agricultural fields. A paired-plot experiment was conducted in frozen agricultural soils in Northeast China to examine the impacts of simulated warming on soil freezing and thawing processes and on soybean production. Infrared radiators were used to simulate global warming, rising surface soil temperature (5 cm depth) by 2.86 °C. We showed that, artificial warming caused the freeze duration shortened by 22 days, and the thaw duration shortened by 17 days resulting in the mean duration of soil freezing-thawing significantly shortened by 39 days and the maximum frost depth reduced by about 40 cm. Simulated warming had no significant effect on the average annual freeze-thaw cycle frequency. Warming induced a larger water accumulation in the 0–100 cm soil layer during 2014–2015 soil freezing period. In the dry year of 2015, warming did not significantly affect surface soil moisture during period from sowing date to VC (soybean cotyledon) date. Thus, warming-induced an increase in soybean yield in the dry year may be attributable to the positive effect of enhanced soil temperature on soybean growth (aboveground dry matter accumulation) and consequent on soybean production. In the wet year of 2014, warming decreased surface soil moisture from sowing date to the date of VC stage because warming advanced the soil thaw-end date in 20–60 cm layer by 15 days. This decline in surface soil water availability may potentially offset the positive effects of increased soil temperature on soybean yield, thus warming effects on soybean production was neutral in the wet year. Our findings highlight the potential role of seasonally soil freezing and thawing dynamics in regulating soybean to global warming and suggested that warming effects on soil water dynamics during soil freezing and thawing periods, and subsequent on the surface soil water availability at the early vegetative stage and soybean production were associated with the hydrological year. We conclude that under current precipitation patterns, the no response of soil surface water availability to warming during early vegetative growth, coupled with warming-mediated increases in soil temperature, might improve soybean production during dry years in Northeast China.

Freeze–thaw actuator and applications

Significant portions of the earth’s land mass undergo annual freeze–thaw cycles, and although water is abundant and practically a free resource, the possibility of using the water–ice phase transition for smart material applications and actuators for machines has not been studied. This article details some of the characteristics of a freeze–thaw actuator, compares it to other smart material actuators, and presents three experimental demonstrations of its potential for engineering applications. The first application is the conversion of the freeze cycle into electrical energy by coupling the freeze–thaw actuator with a bistable piezoelectric element. The second application demonstrates the ability to store energy mechanically and keep a count of multiple freeze–thaw cycles. This stored energy can then be released after a preset number of freeze–thaw cycles. The third application demonstrates a self-powered mechanism that is capable of moving itself one body length per freeze–thaw cycle.

Drivers of apoplastic freezing in gymnosperm and angiosperm branches.

It is not well understood what determines the degree of supercooling of apoplastic sap in trees, although it determines the number and duration of annual freeze–thaw cycles in a given environment. We studied the linkage between apoplastic ice nucleation temperature, tree water status, and conduit size. We used branches of 10 gymnosperms and 16 angiosperms collected from an arboretum in Helsinki (Finland) in winter and spring. Branches with lower relative water content froze at lower temperatures, and branch water content was lower in winter than in spring. A bench drying experiment with Picea abies confirmed that decreasing branch water potential decreases apoplastic ice nucleation temperature. The studied angiosperms froze on average 2.0 and 1.8°C closer to zero Celsius than the studied gymnosperms during winter and spring, respectively. This was caused by higher relative water content in angiosperms; when branches were saturated with water, apoplastic ice nucleation temperature of gymnosperms increased to slightly higher temperature than that of angiosperms. Apoplastic ice nucleation temperature in sampled branches was positively correlated with xylem conduit diameter as shown before, but saturating the branches removed the correlation. Decrease in ice nucleation temperature decreased the duration of freezing, which could have an effect on winter embolism formation via the time available for gas escape during ice propagation. The apoplastic ice nucleation temperature varied not only between branches but also within a branch between consecutive freeze–thaw cycles demonstrating the stochastic nature of ice nucleation.

Waste Rock Biogeochemistry in a Permafrost Environment: Examination of a Cover Design for a Low-Sulfide, Granitic Waste Rock

ABSTRACTAt the Diavik Waste Rock Project's mine-research site, the microbial colonization and oxidation of waste rock sulfide minerals are attenuated by the extreme freeze-thaw cycle of a permafrost environment. The closure design for the waste rock stockpile consists of a low-sulfide waste rock and low-permeability till, covering a relatively higher sulfide waste rock. This design was examined at the mine site through construction of experimental waste rock piles and active zone lysimeters with and without the till cover. Leachate from these experiments indicates variable pH and SO4 concentrations that correlate with sulfide content and the thermal moderating influence of the till cover. The till initially provided a moderated environment for the production of acid, growth of acidophilic Fe- and S-oxidizing bacteria, and enhanced weathering until wet up and freezing of the till and underlying waste rock as a permafrost. Greater sulfide oxidation was observed above the till cover because of greater exposure to the annual freeze-thaw cycle. An examination of the bacterial communities at the genus level indicates the prevalence of Pseudomonas, Rhodanobacter, Sideroxydans, and Thiobacillus in the waste rock. Pseudomonas spp. were dominant in the drier and more extreme temperature environment above the till cover, while Thiobacillus spp. were dominant in the more sulfide-rich, wetter/frozen environment below the till. A decreasing trend in Thiobacillus spp. from the exterior to the interior and an opposing trend in Acidithiobacillus spp. suggest greater acid generation deeper in the waste rock further from the extreme temperature variation of the tundra climate. The presence of the till cover moderated temperature variations, enhanced the initial rate of sulfide oxidation, and allowed for greater microbial diversity, but the freezing of the till cover and underlying waste rock drastically reduced sulfide oxidation and the generation of acid rock drainage. These results highlight the importance of temperature on microbially catalyzed acid production and our ability to use the extreme temperatures of the tundra climate to minimize potential environmental effects from mining through formation of waste rock permafrost.

In-situ monitoring the thermal regime of foundation backfill of a power transmission line tower in permafrost regions on the Qinghai–Tibet Plateau

The stability of tower foundations in permafrost regions is related to the thermal regime of the adjacent soils. The aim of this study is to investigate the ground temperature evolution in the foundation backfill of a tower, which is constructed by open excavation on the Qinghai–Tibet Plateau. Soil temperature and water content in the backfill were monitored continuously in the first three years after the tower's construction. Results demonstrated that the winter-time construction resulted in lower initial ground temperature around tower footings, and potential natural convection in the loose backfill, which facilitated the cooling in the first winter. In the following summer, the temperature in backfill was higher than that in a nearby natural field, due to the latent heat of infiltration water in the backfill and the heating of warmer undisturbed soils. The events of water infiltration led to a heating rate of 1 to 2 orders higher than that of thermal conduction in the backfill. Whereas, after one annual freeze–thaw cycle, the dominant heat transfer changed to heat conduction in the compacted backfill. The study provides valuable insights for evaluating the constructing technique and proposing mitigative measures for power transmission lines in permafrost regions.

Influence of freeze–thaw dynamics on internal geochemical evolution of low sulfide waste rock

Continuous monitoring of a 15m high heavily instrumented experimental waste rock pile (0.053wt.% S) since 2006 at the Diavik diamond mine in northern Canada provided a unique opportunity to study the evolution of fresh run-of-mine waste rock as it evolved over annual freeze–thaw cycles. Samples were collected from soil water solution samplers to measure pore water properties, from twelve 4 to 16m2 basal collection lysimeters to measure basal leachate properties in the region underlying the crest of the pile (the core), and from basal drains to measure aggregate total pile leachate properties. By 2012, monitoring of pore water geochemistry within the core structure of the test pile revealed an apparent steady state with respect to weathering geochemistry, represented by (i) a flush of pre-existing blasting residuals and applied tracers, (ii) declining pH, (iii) a stepwise progression and subsequent equilibrium with acid-neutralizing phases (depletion of available carbonates; equilibrium with respect to aluminum hydroxide phases and subsequent iron (III) hydroxide phases), and (iv) concordant release of SO4, major cations (Ca, Mg, K, Na, Si), and trace metals (Al, Fe, Ni, Co, Cu, Zn). Distinct, high concentration ‘spring flushes’, characteristic of drainage in northern environments and primarily explained by a combination of fluid residence time and the build-up of oxidation products over the winter, were released from core drainage each season. Following the initial flush, the concentration of all dissolved constituents steadily declined, with distinct minimums prior to freeze-up. The opposite trend was observed in the cumulative pile drainage, in which early season leachate dominated by snowmelt and batter flow had low concentrations and late season leachate dominated by contributions from the core of the pile (indicated by season end merging of core and cumulative drainage geochemistry) had higher concentrations. Northern waste rock pile drainage geochemistry is strongly influenced by freeze–thaw cycling and varying core and batter subsystem contributions to total drainage. A comprehensive understanding of thermal cycling in waste rock piles is an important component of temporal predictions of drainage water composition based on up-scaling or reactive transport modeling.

An estimation method of soil freeze-thaw erosion in the Qinghai–Tibet Plateau

Limited by natural and scientific factors, freeze-thaw (FT) erosion, as a typical erosion process along with wind and water erosion, has not been given enough attention. In this paper, we introduce microwave remote sensing techniques to establish an estimation model of FT erosion. The model includes seven factors: the annual FT cycle days, the average diurnal FT phase-changed water content, average annual precipitation, topographic relief, aspect, annual temperature range and vegetation coverage. The results show that on the whole Qinghai–Tibet Plateau scale, the average intensity of FT erosion belongs to the category of moderate erosion. The spatial extent of the FT erosion region is 163.96 (104) km2, accounting for 63.46 % of the study region. Exhibiting spatial heterogeneity, the distribution of the FT erosion shows an upward trend where the erosion intensity increases from slight erosion in the northwestern region to severe erosion in the southeastern part of the study region. Because of the vast extent of the Qinghai–Tibet Plateau, the dominant impact factors for the FT cycle differ over the area. The mid-west plateau is mainly influenced by the annual FT cycle days, average diurnal phase-changed water content and temperature. The southern and southeastern zones are influenced by precipitation, topographic relief and aspect. During the study period, regions which dominated by alpine shrubs were the most severely affected by FT erosion. The results show significance for the understanding of the mechanism and occurrence of FT erosion and therefore provide a scientific basis for the prevention and treatment of FT erosion.

Early evolution of weathering and sulfide depletion of a low-sulfur, granitic, waste rock in an Arctic climate: A laboratory and field site comparison

Leachate from a humidity cell experiment provided a geochemical framework to evaluate the early evolution of weathering of the same waste rock in an Arctic environment. Comparison of laboratory and field results indicates the hydrogeochemical system within the higher sulfide (0.01–0.27wt.%S) waste rock pile has attained a peak weathering state, indicated by a shift to acid neutralization by weathering products of Al-bearing minerals, stabilization of the pH near 4.5, mobility of metals from sulfide and Al-bearing minerals, and a highly correlated relation between SO4 release and outflow from the waste rock pile. Further weathering of the waste rock should be driven by external environmental factors of temperature and precipitation/infiltration instead of internal factors of wetting and transient acid-neutralization processes. An evaluation of sulfide depletion indicates that 4% of the sulfide in the <6.3-mm fraction of this waste rock pile, corresponding to 2% of the sulfide in the <50-mm fraction, has been removed through oxidation and leaching as SO4. Weathering is strongly seasonal because of the Arctic climate, which produced a daily sulfide-depletion rate corresponding 0–0.02% and a peak annual depletion of 100kg or 1.5% of the remaining sulfide content in the <6.3-mm fraction. Peak sulfide weathering is expected to continue until about 15% of the available sulfide is depleted, similar to an observed decrease in sulfide weathering in the laboratory. Estimates of the reactive surface area of the sulfide minerals and a peak rate constant were used to evaluate the sulfide percent in the fine fraction of rock in the pile undergoing weathering during the annual freeze-thaw cycle, which can be used to estimate a climate rate factor to adjust the weathering mass through the seasonal changes. For modeling of future leachate, laboratory results indicate that an exponential rate limiting factor is necessary to account for slowing of sulfide oxidation after peak weathering because of the formation of secondary minerals that inhibit element release.

Efficiency Measurement of Bridge Management with Data Envelopment Analysis

This study explored the feasibility of data envelopment analysis (DEA) to measure objectively the efficiency of Interstate bridge replacement and rehabilitation programs of the state highway agencies in the United States. Past applications of DEA indicated that this method showed promise for such assessments because of the ability to take into account the effect of uncontrollable factors and scale efficiency. The current study developed a modified input-oriented variable returns to scale model that treated the uncontrollable variables as uncontrollable. The two variables selected as outputs were (a) the change in area of structurally deficient bridges and (b) the change in area of functionally obsolete bridges between two consecutive years. The six variables selected as inputs were (a) expenditures on Interstate bridge replacement and rehabilitation, (b) average daily traffic on Interstate bridges per deck area, (c) proportion of Interstate truck vehicle miles traveled (VMT) to Interstate total VMT, (d) average age of Interstate bridges, (e) annual precipitation, and (f) annual freeze–thaw cycles. For each state, the DEA efficiency score and the corresponding target states were identified. The performances of the states and the possible reasons for inefficiencies were assessed. The Malmquist productivity index model was applied to calculate the technical efficiency change (catch-up effect) and the technological change (frontier shift). Over the analysis period, an overall improvement was observed in the frontier of the studied industry; this improvement suggested within this period a general improvement in the efficiencies of the Interstate highway bridge replacement and rehabilitation programs at highway agencies in the United States.

In situ measured and simulated seasonal freeze–thaw cycle: A 2-year comparative study between layered and homogeneous field soil profiles

Summary Annual freeze–thaw cycles of soil significantly impact agricultural and ecosystem services in cold regions. For advancing our understanding of freeze–thaw process, both improved measurements and simulations of coupled-heat-water-transfer (CHWT) phenomenon are needed under different field conditions. This paper focused on a comparative study between a CHWT-model simulation versus in situ measurements of liquid soil water content (LSWC) and soil temperature (ST) at two agricultural field sites. The first site consisted of a layered soil profile with sandy silt loam (0–60 cm) and clay loam (60–130 cm) layers, and the other site was a uniform sand profile (0–110 cm). Measurements were made over two winters between 2011 and 2013, i.e. the first winter is 2011–2012 (year 1) and the second winter is 2012–2013 (year 2), in the northeast of China employing an access-tube dielectric sensor combined with a temperature measurement array. During the freezing period of the year 1 winter, the soil freezing characteristic curves (SFCCs) were determined in situ in relation to the site-specific data of LSWC and ST and subsequently used for the model calibration. For the thawing process of year 1 and the freeze–thaw process of year 2, the resulting ST simulation time series were well-correlated with field measurements. In terms of the resulting LSWC, the numerical simulations also correlated well (R2 > 0.895, RMSE 0.702, RMSE