Search Results (270)

Bridge decks are exposed to chloride ingress from deicing salts, freeze–thaw cycling, and repeated wetting and drying, which gradually degrades the concrete over time. Many existing models treat concrete conditions as static and do not capture time-varying chloride exposure. This study develops deterioration envelopes for concrete bridge decks to predict long-term loss of compressive strength and internal integrity by integrating accelerated laboratory wet–dry and freeze–thaw testing with in-service bridge-deck core measurements from Delaware bridges. The model is supported by three data sources: accelerated laboratory tests, cores from in-service bridges provided by the Delaware Department of Transportation (DelDOT), and climate and asset datasets from the National Oceanic and Atmospheric Administration (NOAA) and the Federal Highway Administration’s (FHWA) InfoBridge™ database. Laboratory specimens (n = 300) were reproduced based on Delaware mix designs from the 1970s and 1980s and were tested in accordance with ASTM and ACI protocols. Environmental conditioning applied wet–dry and freeze–thaw cycles at chloride contents of 0, 3, and 15 percent to replicate field exposure within a shortened test period. Measured properties included compressive strength, modulus of elasticity, resonance frequency, and chloride penetration. The results show a gradual, near-linear reduction in compressive strength and resonance frequency with increasing chloride content over 160 cycles, which corresponds to about 2 to 5 years of service exposure. Resonance frequency was the most sensitive indicator of internal damage across the tested chloride contents. By combining test results, core data, and bridge inspection history into a single durability index, the deterioration envelopes forecast long-term degradation under different chloride exposures, providing a basis for prediction that extends beyond visual inspection. Full article

This study focuses on the core issue of sustainably utilizing shells to enhance the performance of cement mortar. The influence of shell powder on the slump flow, setting time, mechanical strengths, drying shrinkage rate and carbonation depth of cement mortar is investigated. The flexural and compressive strengths of cement mortar incorporating calcium formate after 12 h, 3-day and 28-day curing periods are examined. The effect of basalt fibers on the attenuation of cement mortar’s mechanical properties (flexural and compressive strengths) after NaCl freeze–thaw cycles is also studied. Scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) is employed to elucidate the underlying mechanisms. Results show that the slump flow, setting time and mechanical strengths have cubic function relationships with the shell powder’s mass ratio, while the drying shrinkage rate and carbonation depth follow quadratic function changes. Cement mortar with 15% shell powder by mass of the total binder materials demonstrates the highest slump flow and mechanical strengths. At this shell powder mass ratio, cement mortar shows the lowest drying shrinkage rate and carbonation depth. Calcium formate positively influences the 12-h mechanical strengths. After 3 days of curing, the mechanical strengths of cement mortar with 0.3% calcium formate are the highest. The calcium carbonate powder reduces the drying shrinkage rate of mortar and increases the content of Ca and C elements. The mass ratio of calcium formate exhibits a negative correlation with the cement mortar’s mechanical strengths after being cured for 28 days. The addition of basalt fibers enhances resistance to chloride salt freeze–thaw and dry-wet alternations erosion performance. These findings will provide a sustainable and effective strategy for utilizing agricultural by-products in concrete structures. Full article

The seasonal freeze–thaw cycle induces a fundamental regime shift in lake ecosystems, primarily through the restructuring of microbial communities. This study investigated the dynamics and mechanisms of species diversity maintenance in protistan communities in Gonghai Lake, a shallow subalpine lake in China, across both ice-covered and ice-free periods. During ice cover, the protistan community exhibited a vertically stratified structure dominated by cryotolerant diatoms such as Stephanodiscus. Following thaw, the community transitioned to a more homogeneous, resource-driven assembly. Concurrently, the key environmental controls shifted from physical stratification (proxied by depth) to resource availability (notably NO₃⁻ and TOC), a change reflected in the taxonomic succession from Ochrophyta to Chlorophyta. Nevertheless, depth retained ecological relevance mediated by benthic–pelagic coupling, which supported a distinct near-sediment community. Our findings demonstrate that freeze–thaw-mediated terrestrial nutrient inputs directly modified protistan diversity and community structure. These alterations have fundamental implications for ecosystem functions in subalpine lakes, including nutrient cycling rates and energy flow through the microbial loop. Full article

This study investigated the physicochemical properties and nutrient dynamics on the Romanian shelf of the northwestern Black Sea in July 2024, collecting data across 36 stations (13–1116 m depth) heavily influenced by Danube discharges. Vertical CTD profiling revealed a pronounced seasonal thermocline and a deep-lying permanent halocline. The Cold Intermediate Layer (CIL) boundary, defined by the 8 °C isotherm, was absent, indicating warmer subsurface waters. Surface nutrient concentrations, particularly for nitrate (NO₃) and phosphate (PO₄), were considerably lower than peak eutrophication periods, approaching pre-1970s values, suggesting a positive trend due to reduced anthropogenic loading. They are also comparable to or lower than other coastal regions in the Black Sea. Vertical nutrient profiles confirmed the typical anoxic Black Sea structure, but with regional specifics: the PO₄ maximum was slightly deeper, and the NO₃ maximum position and concentration mirrored the pre-eutrophication period, further supporting reduced anthropogenic nitrogen input. Silicate (SiO₄) concentrations were consistently low throughout the water column, suggesting the northwest shelf functions as a SiO₄ sink compared to the southeastern Black Sea. Overall results indicate a shift towards a less eutrophic state on the Romanian shelf while highlighting the continued dominance of Danube-driven hydrodynamics. In addition to those investigations, this study assessed nutrient preservation techniques, finding that pasteurization was significantly superior to freezing for maintaining the stability of PO₄ and NOx (losses up to 20% and 47% for frozen samples, respectively) over six months. Though SiO₄ was stable under both methods, the freezing produced lower concentrations, possibly from incomplete depolymerization during thawing. These findings stress that pasteurization could be taken into consideration as a reliable preservation technique for long-term storage of nutrient samples. Full article

Animal manure application is widely recognized for its agronomic benefits in enhancing soil fertility and crop productivity through organic matter enrichment and nutrient supply, but the critical application time governing its greenhouse gas emission trade-offs remains unresolved. The objective of this study was to investigate the effects of pig manure compost application timing on nitrous oxide (N₂O) emissions and maize yields in Northeast China through a four-year field experiment. The treatments included: (1) inorganic fertilizers (NPK); (2) NPK plus pig manure compost applied in spring (NPK-MS); and (3) NPK plus pig manure compost applied in autumn (NPK-MA). The N₂O fluxes, NH₄⁺-N contents, NO₃⁻-N contents, and maize yields were analyzed. The results showed that compared with NPK, NPK-MA increased N₂O emissions by 44.4%. Applying pig manure compost in autumn promotes N₂O emissions during the freeze–thaw period. However, there was no significant effect of NPK-MS on N₂O emissions compared with NPK (p > 0.05). Spring-applied manure compost (NPK-MS) resulted in an 11.9% increase in maize yield compared to NPK. In contrast, autumn-applied manure compost (NPK-MA) did not significantly affect maize yield (p > 0.05). Furthermore, yield-scaled N₂O emissions were significantly increased in NPK-MA (p < 0.05). Overall, spring application of pig manure compost is recommended for increasing maize yield without significantly increasing N₂O emissions while in Northeast China. Full article

To address the frost heave damage issue of the trapezoidal lined canals in seasonally frozen regions and further ensure the stable operation of canals while reducing operation and maintenance costs, this study conducted a gradient sand-gravel cushion replacement experiment on the main canal of the Jingdian Irrigation District, China. For the experiment, east–west and north–south-oriented canal sections were selected, with frost heave meters and soil temperature-humidity meters installed. Dynamic changes in canal ground temperature, moisture content, and frost heave were monitored over two full freeze–thaw cycles. The results indicate the following: (1) The variation of ground temperature lags behind air temperature by 2–3 days; the ground temperature change on the canal slope is more pronounced than that at the canal bottom; and for the east–west-oriented canal, the ground temperature on the sunny slope is higher than that on the shady slope, while the ground temperatures on the two slopes of the north–south-oriented canal are similar. (2) The moisture content of the east–west-oriented canal changes drastically during the freezing period, showing a decreasing trend in the early freezing stage and a significant increasing trend in the thawing stage, whereas the moisture content of the north–south-oriented canal fluctuates slightly. (3) Canals with different orientations exhibit spatial differences in frost heave due to variations in solar radiation distribution. (4) The frost heave is negatively correlated with ground temperature, and its variation lags behind ground temperature by 1–2 days. (5) Increasing the replacement thickness of sand-gravel can significantly reduce the frost heave, with a reduction rate exceeding 50%. Under the action of freeze–thaw cycles, canals with gradient sand-gravel exhibit remarkable anti-frost effects. Thus, for trapezoidal lined canals in seasonally frozen regions, a gradient replacement scheme is recommended: For east–west canals, the replacement thickness is 40–100 cm for shady slopes and 30–70 cm for sunny slopes; for north–south canals, the replacement thickness is 30–70 cm for both slopes. In conclusion, gradient sand-gravel replacement is an effective anti-frost heave measure, providing a theoretical basis for the design of sand-gravel replacement for lined canals in seasonally frozen regions. Full article

Straw return is crucial for sustainable agriculture, but its efficiency is limited by low temperatures in cold regions, especially in saline-alkali soils. This study investigates the degradation process of maize straw and the response of soil properties and microbial communities during the winter low-temperature period in the alkaline farmland of Anda, China. A two-year field experiment with straw return (SR) and no return (NR) treatments was conducted. Straw degradation rates and structural changes (as observed via scanning electron microscope, SEM) were monitored. Soil physicochemical properties and enzyme activities were analyzed. Microbial community composition was characterized using 16S rRNA and ITS sequencing. The cumulative straw degradation rate over two years reached 94.81%, with 18.33% occurring in the first winter freeze–thaw period. Freeze–thaw cycles significantly damaged the straw structure, facilitating microbial colonization. Straw return significantly improved soil properties after winter, increasing field water capacity (3.45%), content of large aggregates (6.57%), available nutrients (P 38.17 mg/kg, K 191.93 mg/kg), and organic carbon fractions compared to NR. Microbial analysis revealed that low temperatures filtered the community, enriching cold-tolerant taxa like Pseudogymnoascus, Penicillium, and Pedobacter, which are crucial for lignocellulose decomposition under cold conditions. The winter period plays a significant role in initiating straw degradation in cold regions. Straw return mitigates the adverse effects of winter freezing on soil quality and promotes the development of a cold-adapted microbial consortium, thereby enhancing the sustainability of alkaline farmland ecosystems in Northeast China. Full article

With the Longzhong Water Conservation and Ecological Water Supply and Storage Reservoir Project (Upper Yellow River) as the engineering background, this study selected sulfate sandy soil from Jingtai County (Baiyin City, Gansu Province, the project area) as the test soil to explore the effects of moisture content and salt content on the frost heave characteristics of sulfate sandy soil in seasonal frozen soil areas, and to avoid engineering problems caused by its frost heave deformation. Indoor freeze–thaw experiments and data analysis were conducted; water and salt content gradients were set in line with the actual engineering conditions, and indoor unidirectional freezing frost heave tests were carried out to simulate the natural freeze–thaw environment. The test results show that temperature is a key factor regulating soil frost heave: the frost heave rate varies in an “S-shaped” pattern with decreasing temperature (slightly decreasing at 10~0 °C, increasing rapidly at 0~−10 °C with the most significant growth at 0~−5 °C, and stabilizing below −10 °C). Under constant compaction, the frost heave rate increases parabolically with moisture content (the growth rate slows down after 15% and stabilizes at 17%) and linearly with salt content (with a small increment). Based on the test data, a frost heave rate prediction model considering moisture content and salt content was established; the correlation between the calculated values of the model and the measured values is strong (R² > 0.92), which can provide a reference for predicting the frost heave rate of such sulfate sandy soil. The key conclusions are as follows: The frost heave of the soil is dominated by temperature and moisture content (the effect of salt content is secondary); the temperature range of 0~−5 °C is the critical period for engineering frost heave prevention. This study provides technical support for the frost heave prevention design of the Longzhong Reservoir and similar engineering projects in seasonal frozen soil areas of Northwest China. Full article

To investigate differences in water and salt transport during irrigation, freezing, and thawing periods in typical saline-affected paddy fields and saline-affected upland fields, field-based automated in situ monitoring was conducted in both types of saline-affected farmland (May 2023 to May 2024). Correlation analysis identified seasonal drivers of water–salt migration, while the HYDRUS-3D model simulated transport and equilibrium processes. The HYDRUS-3D model, equipped with a freeze–thaw module, accurately simulated complex water–salt transport in cold arid regions. Key findings include: (1) During freeze–thaw periods, soil moisture content and electrical conductivity (Ec) increased with the retreating frost front in both upland and paddy soils. During the irrigation period, maximum soil moisture content and Ec values occurred at 80 cm depth in dryland soils and 60 cm depth in paddy soils, primarily influenced by irrigation and capillary rise. (2) Groundwater salt ions significantly affected soil salinization in both farmland types. During the freeze–thaw period, Ec positively correlated with soil temperature. During the irrigation period, Ec positively correlated with evapotranspiration and negatively correlated with precipitation. (3) Salt changes during the irrigation, freezing, and thawing periods were −565.4, 326.85, and 376.55 kg/ha for upland fields, respectively; corresponding changes for paddy fields were −1217.0, 280.07, and 299.35 kg/ha. (4) Both land types exhibited reduced salinity during the irrigation period, with paddy fields showing a reduction 3.36 times greater than dryland fields. During the freezing and thawing periods, both land types experienced salinity accumulation, with dryland fields accumulating higher salinity levels than paddy fields. These results indicate that paddy field irrigation and drainage systems help mitigate salinization, while dryland fields are more prone to springtime salt accumulation. These findings provide a basis for developing targeted management strategies for saline–alkali soils. Full article

Against the backdrop of global climate change intensifying seasonal freeze–thaw cycles, deteriorating soil conditions in farmland within seasonal frost zones constrain agricultural sustainability. This study employed an in situ field experiment during seasonal freeze–thaw periods in the black soil zone of Northeast China to investigate the joint regulatory effects of seasonal freeze–thaw processes and tillage practices on multidimensional features of soil bacterial communities. Key results demonstrate that soil bacterial communities possess self-reorganization capacity. α-diversity exhibited cyclical fluctuations: an initial decline followed by a rebound, ultimately approaching pre-freeze–thaw levels. Significant compositional shifts occurred throughout this process, with the frozen period (FP) representing the phase of maximal differentiation. Actinomycetota and Acidobacteriota consistently dominated as the predominant phyla, collectively accounting for 33.4–49% of relative abundance. Bacterial co-occurrence networks underwent dynamic topological restructuring in response to freeze–thaw stress. Period-specific response patterns supported sustained soil ecological functionality. Furthermore, NCM and NST analyses revealed that stochastic processes dominated community assembly during freeze–thaw (NCM R² > 0.75). Tillage practices modulated this stochastic–deterministic balance: no-tillage with straw mulching (NTS) shifted toward determinism (NST = 0.608 ± 0.224) during the thawed period (TP). Across the seasonal freeze–thaw process, soil temperature emerged as the primary driver of temporal community variations, while soil water content governed treatment-specific differences. This work provides a theoretical framework for exploring agricultural soil ecological evolution in seasonal frost zones. Full article

Understanding the spatiotemporal dynamics of runoff and its drivers is essential for water resources management in mid–high latitude basins. This study investigates runoff changes in the Songhua River Basin, Northeast China, during 1980–2022 using the Budyko framework, combined with Mann–Kendall trend analysis, Pettitt tests, Hurst index, and wavelet analysis. Results indicate significant climatic shifts, with basin-wide warming, heterogeneous precipitation changes, and declining relative humidity, leading to intensified cold-season drying. Temperature and evapotranspiration showed strong persistence, while precipitation exhibited high variability and periodicities linked to ENSO and East Asian monsoon anomalies. Runoff increased significantly in the mainstream Songhua and Nenjiang basins, especially in autumn, with abrupt changes clustered between 2009 and 2015. The Second Songhua Basin displayed weaker variability, largely influenced by reservoir regulation and land-use change. Attribution analysis confirmed precipitation as a primary driver, with elasticity coefficients exceeding 3 in the Nenjiang Basin during some summers, indicating extreme sensitivity. Evapotranspiration suppressed runoff under high temperatures, while freeze–thaw processes and human interventions became critical in spring and autumn. The aridity index revealed persistent winter deficits and rising spring–autumn drying trends after 2000, posing risks for snowmelt runoff and baseflow sustainability. Overall, runoff evolution reflects a shift from gradual to threshold-triggered regime changes driven by both climate variability and human regulation. These findings provide a basis for adaptive, basin-specific water management and climate resilience strategies in Northeast China. Full article

Condition assessment of reinforced concrete structures presents a significant challenge worldwide as structures built in the post-war construction period (1950s–1970s) reach end of service life. The alkali-silica reaction (ASR) is one of several damage mechanisms which commonly affect infrastructure in Canada. Frequent freeze-thaw cycles and heavy use of de-icing salts in winter as well as high heat and humidity in summer are expected to have intensified ASR-induced damage. This work investigates five segments of a pier cap—PC, which had undergone encapsulation repair, and four segments of a pier shaft—PS, which represented dry and semi-submerged conditions, removed from a highway bridge constructed starting in 1957. Preliminary evaluation through visual inspection (conventional, qualitative and quantitative using the cracking index—CI) and non-destructive techniques (rebound hammer—RBH, ultrasonic pulse velocity—UPV and surface resistivity) was conducted on both internal (i.e., cut during decommissioning) and external (i.e., exposed while in service) surfaces of five PC segments and four PS segments. Differences in geometry, exposure conditions and repair history from the two members were found to have limited impact on the results of quantitative tests (i.e., CI, RBH and UPV results with average values of 1.6 mm/m, 37 MPa and 2.4 Km/s, respectively) while still exhibiting qualitative differences in visual determination (i.e., crack patterns, surface appearance and crack widths). Full article

With the global climate warming, the temperature conditions in permafrost regions have changed significantly, and the stability of permafrost slopes is facing serious threats. This paper focuses on the construction of the instability mechanism and prediction model of permafrost slopes considering the influence of temperature. By analyzing the thermokarst collapse process of permafrost slopes, the characteristics and causes of stages such as the soil loosening period and the surface sloughing period were studied. Based on the Mohr–Coulomb strength criterion, combined with the simplified Bishop method and the Morgenstern–Price method, a mechanical analysis of the critical state was carried out, and a safety factor formula applicable to the critical state of permafrost slopes was derived. From the curves of the total cohesion and effective internal friction angle of the experimental soil changing with temperature, an influence model of temperature on the strength parameters was fitted. Considering the factor of freeze–thaw cycles, a safety factor model for permafrost slopes was constructed. Through a large amount of data calculation and analysis of the model, the reliability of the model was verified. This model can be used to predict slope states in practical assessments and optimize slope support structure design parameters in cold regions, providing important references for ensuring engineering safety, reducing geological disasters, and promoting sustainability in cold regions. Finally, potential mitigation measures for frozen soil slope instability based on the findings are briefly discussed. Full article

Cyanobacterial blooms in urban rivers present critical ecological threats worldwide, yet their mechanisms in fluvial systems remain inadequately explored compared to lacustrine environments. This study addresses this gap by investigating bloom dynamics in the eutrophic Majiagou River (Harbin, China) through phytoplankton resource use efficiency (RUE), calculated as chlorophyll-a per unit TN/TP. Seasonal sampling (2022–2024) across 25 rural-to-urban sites revealed distinct spatiotemporal patterns: urban sections exhibited 1.9× higher cyanobacterial relative abundance (RAC, peaking at 40.65% in autumn) but 28–30% lower RUE than rural areas. Generalized additive models identified nonlinear RAC–RUE relationships with critical thresholds: in rural sections, RAC peaked at TN-RUE 40–45 and TP-RUE 25–30, whereas urban sections showed lower TN-RUE triggers (20–25) and suppressed dominance above TP-RUE 10. Seasonal extremes drove RUE maxima in summer and minima during freezing/thawing periods. These findings demonstrate that hydrological stagnation (e.g., river mouths) and pulsed nutrient inputs reduce nutrient conversion efficiency while lowering bloom-triggering thresholds under urban eutrophication. The study establishes RUE as a predictive indicator for bloom risk, advocating optimized N/P ratios coupled with flow restoration rather than mere nutrient reduction. This approach provides a science-based framework for sustainable management of urban river ecosystems facing climate and anthropogenic pressures. Full article

Under tropical conditions, seasonal variations may also influence the sperm characteristics of Bos indicus. The objective was to evaluate the motility of thawed sperm of bulls from the Peruvian tropics throughout the year. Over 24 months, 129 ejaculates were evaluated based on semen quality and subjected to slow horizontal freezing in 0.5 mL straws. After thawing, the individual, seasonal period, and season effect on motility and kinetic parameters were analyzed using a Sperm Class Analyzer^® (Microptic S.L.U., Barcelona, Spain). There was an individual effect on volume, motility, fresh concentration, and kinetic parameters when thawed. In the dry period, higher straight-line velocity (VSL) (p < 0.05) and beat cross frequency (BCF) were found than in the rainy period (p < 0.01). In summer and autumn, there was greater total motility, fast, circular routes, curvilinear velocity, average path velocity, VSL, amplitude of lateral displacement of the head, and BCF (p < 0.01). Greater volume and motility were found in winter and spring, but in summer and autumn, greater speed and vigor of movement were obtained in thawed sperm. The variation in annual climate patterns influences the seminal quality of bulls, and its effect needs to be assessed to propose adaptation strategies to climate change in tropical areas. Full article