The Impact of Soil Freezing/Thawing Processes on Water and Energy Balances

A frozen soil parameterization coupling of thermal and hydrological processes is used to investigate how frozen soil processes affect water and energy balances in seasonal frozen soil. Simulation results of soil liquid water content and temperature using soil model with and without the inclusion of freezing and thawing processes are evaluated against observations at the Rosemount field station. By comparing the simulated water and heat fluxes of the two cases, the role of phase change processes in the water and energy balances is analyzed. Soil freezing induces upward water flow towards the freezing front and increases soil water content in the upper soil layer. In particular, soil ice obviously prevents and delays the infiltration during rain at Rosemount. In addition, soil freezingthawing processes alter the partitioning of surface energy fluxes and lead the soil to release more sensible heat into the atmosphere during freezing periods.

How freezing and thawing processes affect black-soil aggregate stability in northeastern China

Laboratory experiments were carried out to investigate the effect of freezing and thawing processes on wet aggregate stability （WAS） of black soil. Wet aggregate stability was determined by different aggregate size groups, different water contents, various freeze-thaw cycles, and various freezing temperatures. The results showed that, when at suitable water content, aggregate stability was enhanced, aggregate sta-bility will be disrupted when moisture content is too high or too low, especially higher water content. Temperature also had a significant ef-fect, but moisture content determined the suitable freezing temperatures for a given soil. Water-stable aggregate （WSA〉0.5）, the total aggre-gate content, and mean weight diameter decreasing with the freeze-thaw cycles increase, reached to 5 percent significance level. The reason for crumbing aggregates is the water and air conflict, thus raising the hypothesis that water content affects the aggregate stability in the process of freezing and thawing.

The Surface Energy Budget and Its Impact on the Freeze-thaw Processes of Active Layer in Permafrost Regions of the Qinghai-Tibetan Plateau

The surface energy budget is closely related to freeze-thaw processes and is also a key issue for land surface process research in permafrost regions.In this study,in situ data collected from 2005 to 2015 at the Tanggula site were used to analyze surface energy regimes,the interaction between surface energy budget and freeze-thaw processes.The results confirmed that surface energy flux in the permafrost region of the Qinghai-Tibetan Plateau exhibited obvious seasonal variations.Annual average net radiation(R_(n))for 2010 was 86.5 W m^(-2),with the largest being in July and smallest in November.Surface soil heat flux(G_(0))was positive during warm seasons but negative in cold seasons with annual average value of 2.7 W m^(-2).Variations in R_(n) and G_(0) were closely related to freeze-thaw processes.Sensible heat flux(H)was the main energy budget component during cold seasons,whereas latent heat flux(LE)dominated surface energy distribution in warm seasons.Freeze-thaw processes,snow cover,precipitation,and surface conditions were important influence factors for surface energy flux.Albedo was strongly dependent on soil moisture content and ground surface state,increasing significantly when land surface was covered with deep snow,and exhibited negative correlation with surface soil moisture content.Energy variation was significantly related to active layer thaw depth.Soil heat balance coefficient K was>1 during the investigation time period,indicating the permafrost in the Tanggula area tended to degrade.

Effects of Nitrogen Application on N_2O Flux from Fluvo-Aquic Soil Subject to Freezing-Thawing Process

A lab-incubation experiment was conducted to investigate the effects of different forms of nitrogen application （ammonium, NH4＋-N; nitrate, NO3--N; and amide-N, NH2-N） and different concentrations （40, 200 and 800 mg L-1） on N2O emission from the fluvo-aquic soil subjected to a freezing-thawing cycling. N2O emission sharply decreased at the start of soil freezing, and then showed a smooth line with soil freezing. In subject to soil thawing, N2O emission increased and reached a peak at the initial thawing stage. The average N2O emissions with addition of NH4＋-N, NO3 -N and NH2-N are 119.01, 611.61 and 148. 22 ug m-2 h-1, respectively, at the concentration of 40 mg L-1; 205.28, 1 084.40 and 106.13 ug m2 h-1 at the concentration of 200 mg L-1; and 693.95, 1 820.02 and 49.74 ug m-2 h4 at the concentration of 800 mg L-1. The control is only 100.35 ug m-2 h-1. N2O emissions with addition of NH4＋-N and NO3--N increased with increasing concentration, by ranging from 17.49 to 425.67% for NH4＋-N, and from 563.38 to 1458.6% for NO3--N compared with control. There was a timelag for N2O emission to reach a steady state with an increase of concentration. In contrast, by adding NH2-N to soil, N2O emission decreased with increasing concentration. In sum, NH4＋-N or NO3--N fertilizer incorporated in soil enhanced the cumulative N2O emission from the fluvo-aquic soil relative to amide-N. This study suggested that ammonium and nitrate concentration in overwintering water should be less than 200 and 40 mg L-1 in order to reduce N2O emissions from soil, regardless of amide-N.

Freeze-thaw processes of active-layer soils in the Nanweng'he River National Natural Reserve in the Da Xing'anling Mountains,northern Northeast China

The active-layer soils overlying the permafrost are the most thermodynamically active zone of rock or soil and play important roles in the earth-atmosphere energy system. The processes of thawing and freezing and their associated complex hydrothermal coupling can significantly affect variation in mean annual temperatures and the formation of ground ice in permafrost regions. Using soil-temperature and-moisture data obtained from the active layer between September 2011 and October 2014 in the permafrost region of the Nanweng'he River in the Da Xing'anling Mountains, the freeze-thaw characteristics of the permafrost were studied. Based on analysis of ground-temperature variation and hydrothermal transport characteristics, the thawing and freezing processes of the active layer were divided into three stages:(1) autumn-winter freezing,(2) winter freeze-up, and(3) spring-summer thawing. Variations in the soil temperature and moisture were analyzed during each stage of the freeze-thaw process, and the effects of the soil moisture and ground vegetation on the freeze-thaw are discussed in this paper. The study's results show that thawing in the active layer was unidirectional, while the ground freezing was bidirectional(upward from the bottom of the active layer and downward from the ground surface).During the annual freeze-thaw cycle, the migration of soil moisture had different characteristics at different stages. In general, during a freezing-thawing cycle, the soil-water molecules migrate downward, i.e., soil moisture transports from the entire active layer to the upper limit of the permafrost. In the meantime, freeze-thaw in the active layer can be significantly affected by the soil-moisture content and vegetation.

Effects of thawing-induced softening on fracture behaviors of frozen rock

Due to the presence of ice and unfrozen water in pores of frozen rock,the rock fracture behaviors are susceptible to temperature.In this study,the potential thawing-induced softening effects on the fracture behaviors of frozen rock is evaluated by testing the tension fracture toughness(KIC)of frozen rock at different temperatures(i.e.-20℃,-15℃,-12℃,-10℃,-8℃,-6℃,-4℃,-2℃,and 0℃).Acoustic emission(AE)and digital image correlation(DIC)methods are utilized to analyze the microcrack propagation during fracturing.The melting of pore ice is measured using nuclear magnetic resonance(NMR)method.The results indicate that:(1)The KIC of frozen rock decreases moderately between-20℃ and-4℃,and rapidly between-4℃ and 0℃.(2)At-20℃ to-4℃,the fracturing process,deduced from the DIC results at the notch tip,exhibits three stages:elastic deformation,microcrack propagation and microcrack coalescence.However,at-4℃e0℃,only the latter two stages are observed.(3)At-4℃e0℃,the AE activities during fracturing are less than that at-20℃ to-4℃,while more small events are reported.(4)The NMR results demonstrate a reverse variation trend in pore ice content with increasing temperature,that is,a moderate decrease is followed by a sharp decrease and-4℃ is exactly the critical temperature.Next,we interpret the thawing-induced softening effect by linking the evolution in microscopic structure of frozen rock with its macroscopic fracture behaviors as follow:from-20℃ to-4℃,the thickening of the unfrozen water film diminishes the cementation strength between ice and rock skeleton,leading to the decrease in fracture parameters.From-4℃ to 0℃,the cementation effect of ice almost vanishes,and the filling effect of pore ice is reduced significantly,which facilitates microcrack propagation and thus the easier fracture of frozen rocks.

Effect of Freezing-Thawing Process on Wetland Soil Iron

The iron concentrations of snows,semi-melting snows,snowmelts,and ditch waters were observed in four typical microhabitats,Carex lasiocarpa marsh(Ⅰ), Calamagrostis angustifolia wet meadow(Ⅱ),dry land (Ⅲ)and paddy field(Ⅳ),of Sanjiang Plain Wetland, Northeast China.Each sample was collected from three sites of one microhabitat,mixed together, filtrated with 0.45μm membrane,and tested using atomic absorption spectrometry(AAS)for iron measurement.The iron concentrations of soil solutions were investigated as well.Each soil solution was in-situ extracted by negative pressure,filtrated with 0.45μm membrane,and tested using AAS,too. The results showed that the wet precipitation of iron from snow were little to detect.The loss of iron was attributed to the interaction of water and soil surface. The iron concentrations of snowmelts were 7.4,15,

Study of polluted soil remediation based on freezing and thawing cycles

It is generally known that soil pollution poses a terrible hazard to the environment, but the present techniques of contaminated soil remediation cannot control this growing threat. This paper compares the pollutant extraction efficiency of traditional pumping and treating, which is a typical washing technology for the remediation of contaminated soils, with methods that utilize freeze-thaw cycles. In the soil freezing process, water shifts from unfrozen soils to the freezing front, and the permeability of soil will be enhanced under certain temperature gradients and water conditions. Therefore, this paper discusses the purification of contaminated soil through freeze-thaw action. We conducted a cleansing experiment on clay and silica sand infused with NaCl（simulation of heavy metals） and found that the efficiency of purification was enhanced remarkably in the latter by the freeze-thaw action. To assess the effective extraction of DNAPLs in soil, we conducted an experiment on suction by freezing, predicated on the different freezing points of moisture and pollutants. We found that the permeability coefficient was significantly increased by the freezing-thawing action, enabling the DNAPL contaminants to be extracted selectively and effectively.

Comparison of the water change characteristics between the formation and dissociation of methane hydrate and the freezing and thawing of ice in sand

Hydrate formation and dissociation processes are always accompanied by water migration in porous media, which is similar to the ice. In our study, a novel pF-meter sensor which could detect the changes of water content inside sand was first applied to hydrate formation and dissociation processes. It also can study the water change characteristics in the core scale of a partially saturated silica sand sample and compare the differences of water changes between the processes of formation and dissociation of methane hydrate and freezing and thawing of ice. The experimental results showed that the water changes in the processes of formation and dissociation of methane hydrate were basically similar to that of the freezing and thawing of ice in sand. When methane hydrate or ice was formed, water changes showed the decrease in water content on the whole and the pF values rose following the formation processes. However, there were very obvious differences between the ice thawing and hydrate dissociation.

Response of Freezing/Thawing Indexes to the Wetting Trend under Warming Climate Conditions over the Qinghai–Tibetan Plateau during 1961–2010:A Numerical Simulation

Since the 1990s,the Qinghai–Tibetan Plateau(QTP)has experienced a strikingly warming and wetter climate that alters the thermal and hydrological properties of frozen ground.A positive correlation between the warming and thermal degradation in permafrost or seasonally frozen ground(SFG)has long been recognized.Still,a predictive relationship between historical wetting under warming climate conditions and frozen ground has not yet been well demonstrated,despite the expectation that it will become even more important because precipitation over the QTP has been projected to increase continuously in the near future.This study investigates the response of the thermal regime to historical wetting in both permafrost and SFG areas and examines their relationships separately using the Community Land Surface Model version 4.5.Results show that wetting before the 1990s across the QTP mainly cooled the permafrost body in the arid and semiarid zones,with significant correlation coefficients of 0.60 and 0.48,respectively.Precipitation increased continually at the rate of 6.16 mm decade–1 in the arid zone after the 1990s but had a contrasting warming effect on permafrost through a significant shortening of the thawing duration within the active layer.However,diminished rainfall in the humid zone after the 1990s also significantly extended the thawing duration of SFG.The relationship between the ground thawing index and precipitation was significantly negatively correlated(−0.75).The dual effects of wetting on the thermal dynamics of the QTP are becoming critical because of the projected increases in future precipitation.

黄河包头段冻融期水体荧蒽残留及光降解行为

作者分别于流凌期、封河期及开河期,采集黄河包头段干流水体样品,分析该河段荧蒽(Fla)的残留水平及时空变异特性,通过光降解实验探究Fla的降解过程及光敏化剂对降解行为的影响。结果表明,冻融过程中8个采样断面均有Fla检出,且未超过标准值。大部分采样点Fla含量在稳定封河期及开河期较高,各个采样点Fla含量在0.05水平上具有显著性差异,S2、S5断面浓度相对较高,S4、S6和S7点浓度较低。水中Fla可以发生直接光降解,且符合一级反应动力学方程,72 h后降解率几乎达到90%。在避光进行暗反应时,Fla浓度基本不发生变化。添加丙酮、泥沙及低浓度H2O2均可抑制Fla的降解,反应仍符合一级反应动力学方程,而较高浓度的H2O2会促进Fla的光降解,且降解反应不再符合一级反应动力学方程。

冻融循环下沥青混合料损伤特性研究

目的 探究季节冻土地区温差和冻融循环等气候特点对沥青混合料使用性能的影响,为我国不同地区的沥青路面设计、养护、寿命评估和冻融损伤评估提供依据。方法 采用室内冻融循环模拟试验,根据不同温度配置和不同循环次数下沥青混合料的弯拉强度、疲劳寿命和单轴压缩动态模量的衰减,研究冻融循环作用前后沥青混合料的损伤特征,明确冻融循环下沥青混合料的性能衰变特征,最终提出沥青混合料冻融损伤温度等效效应。结果 冻融循环对沥青混合料低温抗裂性能造成严重破坏,冻融循环30次后性能的衰减幅度总体上超过50%。融化温度和冻结温度对沥青混合料损伤的影响存在差异,且归因于结冰过程、经典热力学和膨胀力三个方面。在仅冻融循环作用下,沥青混合料的性能衰减表现出先快速下降,后缓慢下降的特征。结论 冻融循环对沥青混合料性能的影响程度受循环次数和温度条件影响,其中融化温度较冻结温度对性能的影响更为显著。不同温度配置下冻融30次后的沥青混合料性能表现出相似的分布规律,明确了温度等效效应。建立了混合料冻融循环后的残余抗裂性能的等效模型,将损伤程度简化为三个等级。

砂岩冻结/解冻过程蠕变特性研究

寒区岩体长期经受荷载与冻融的共同作用,若不考虑冻融过程对其长期力学行为的影响,将会给寒区工程建设和安全运营带来重大的安全隐患。为此,以寒区某边坡工程砂岩为研究对象,通过开展不同冻结温度下的冻结/解冻过程单轴分级加载蠕变试验,使岩石在同一应力状态下处于冻结和解冻过程,真实再现寒区工程岩体长期力学响应特征。以此研究冻结/解冻过程对岩体长期力学特性的影响,并对其蠕应变、稳态蠕变速率及长期强度等宏观力学指标进行量化分析。结果表明:(1)砂岩冻结过程先后经历冷缩阶段、冻胀阶段和稳态蠕变阶段,解冻过程只经历融缩阶段和稳态蠕变阶段;冷缩阶段和融缩阶段砂岩发生收缩变形,冻胀阶段则发生膨胀变形;(2)冻结/解冻温度为-5℃/25℃、-10℃/25℃、-15℃/25℃时,砂岩蠕应变较常温状态下蠕应变增幅范围分别为102%~193%、81%~126%、105%~194%,解冻后稳态蠕变速率较冻结前最大增长3.65倍、4.31倍、5.56倍,冻结/解冻过程蠕变砂岩的长期强度是常温状态下长期强度的96.33%、88.52%、75.44%;(3)应力对冷缩、冻胀变形的产生起抑制作用而对融缩变形的产生起促进作用;冻结温度越低,冻胀变形和解冻后融缩变形越明显。文章提出的将蠕变与冻融过程相结合的试验方法能较为真实地反映工程实际,该方法为寒区岩体工程长期稳定性评价提供新途径。

原料肉解冻方式对狮子头品质特性的影响

为了探究不同解冻方式对狮子头品质特性的影响,该文以经过冷藏解冻、室温解冻、超声解冻以及微波解冻4种解冻方式的猪肉作为原料制作狮子头,以新鲜猪肉为对照,探究不同解冻方式下的狮子头在色差、蒸煮得率、保水性、质构、微观结构等方面的变化。结果表明,微波解冻组的狮子头品质具有更显著的降低,狮子头的保水性、保油性、L^(*)值、弹性和咀嚼性都显著低于其他解冻处理组。室温解冻组和超声解冻组保水性较好,解冻损失和蒸煮损失最低。室温组和超声波解冻组狮子头在L^(*)、a^(*)、b^(*)上都与鲜肉组无明显差异,因此这2种解冻方法能较好地保持肉的色泽。从质构来看,室温组和超声解冻组能保持肌肉的弹性,但与鲜肉组相比硬度显著降低。经过冷冻及解冻过程的狮子头肌纤维结构均受到了不同程度的损伤,冷藏和室温解冻组的损伤程度较小,微波解冻处理的肌原纤维结构破坏最严重。综合来看,可以考虑室温解冻或超声解冻作为狮子头原料肉的最佳解冻方式,以应用于狮子头的规模化生产。

不同解冻及加工方式对植物基培根的品质影响研究

该研究对大豆植物基培根在不同的解冻(流水、静水、微波、常温解冻)和加工方式(蒸制、烤制、煎制)处理后的营养和品质变化及其影响进行了分析和研究。结果表明,在解冻方式中,微波解冻对植物基培根品质影响最大,其解冻后的样品脂肪含量(1.43%)显著高于其他组,亮度L^(*)值(31.78)和黄蓝b^(*)值(15.69)显著低于其他组,且微观结构与其他组差异较大,呈无序多孔状。在加工方式中,蒸制对植物基培根的影响程度最小,煎制与烤制对植物基培根的营养成分和质构影响较大,蒸制处理后的样品水分活度(68.09%)显著高于其他组,蛋白质含量(2.75%)显著低于其他组,其硬度、弹性和咀嚼性均与其他组形成显著性差异。该研究内容可以为后续植物基培根的生产加工提供建议。

反复冻融法制备灵芝多糖工艺优化、结构表征及抗氧化活性分析

为提高灵芝多糖的提取得率,获得抗氧化活性更高的多糖组分,利用响应面试验优化反复冻融提取灵芝多糖的工艺条件,采用乙醇分级法对冻融多糖进行分离得到3种多糖(GLPf30、GLPf60、GLPf80),评价热水浸提(G. lucidumpolysaccharidewater, GLPw)、反复冻融多糖(GLPf)及乙醇分级的多糖GLPf30、 GLPf60、GLPf80的抗氧化活性,以高效阴离子交换色谱(HPAEC)和红外光谱(FT-IR)进行结构表征。结果显示,最佳冻融条件为:溶胀比14:1(mL/g),冻融时间140 min,冻融次数3次。在此条件下,灵芝多糖提取得率为2.71%,明显高于传统水提(2.36%)。HPAEC和FT-IR结果表明,5种多糖均是由六种单糖(岩藻糖、葡糖胺、半乳糖、葡萄糖、木糖和甘露糖)组成的以吡喃糖为骨架的酸性多糖,但它们的单糖组成和理化性质有较大差异,尤其是GLPf30的氨基葡萄糖(GlcN)占比最高(达到37.66%)。GLPf30的抗氧化能力明显高于其他两种多糖(GLPf60和GLPf80)及其前体物GLPf。研究结果为灵芝多糖的合理开发和高值化利用提供科学依据。

液氮冻融对不同含水率煤岩力学与渗流特性影响研究

为探究液氮冻融对不同含水率煤岩力学渗流特性的影响规律,采用非接触式数字图像技术测量流固耦合试验系统,进行不同含水率下冻融煤岩三轴加载及渗流实验研究.研究结果表明:(1)经液氮冻融2次处理的煤岩,在围压相同轴压加载试验中,随含水率增加,煤体细观损伤增强,轴向峰值应变、峰值强度和弹性模量逐渐降低,泊松比逐渐增加.(2)液氮冻融下不同含水率的煤样在压密、弹性、屈服和破坏4阶段的轴向应变场中应变集中现象强烈,在压密、弹性和屈服阶段应变场存在负值,媒体产生膨胀变形.(3)液氮冻融引起的裂隙扩展增加了煤体的渗透性,含水率3%~6%煤样较含水率0%~3%渗透率增长1.31倍,含水率6%~9%煤样渗透率较3%~6%煤样增长1.43倍,含水率9%煤样渗透率可达9.37×10^(-12)cm^(2).本文研究结果可为深部低渗煤层瓦斯抽采效率提供理论指导.

黑龙江省冻融侵蚀强度分级评价及空间分布特征

黑龙江省肩负维护国家生态安全、保障国家粮食安全的重任,近年来因冻融侵蚀影响,自然环境和黑土资源受到严重威胁。为了定量揭示黑龙江省冻融侵蚀强度的空间异质性及其影响因素,该研究选取10个冻融侵蚀强度评价指标,并确定其权重。通过构建多元回归模型得到冻融侵蚀下限,将权重和赋值结果代入综合评价指数模型,利用自然断点法对冻融侵蚀强度进行分级。研究结果表明:1)黑龙江省冻融侵蚀总面积为1.917×10~5 km^(2),占全省面积的40.53%,其中强烈和极强烈侵蚀分别占冻融侵蚀总面积的20.66%和10.54%。2)黑龙江省中度冻融侵蚀以上的区域呈现三区一带的特征。三区分别为大兴安岭地区、小兴安岭地区和张广才岭地区;一带为西北—东南走向的“三岭一平原”廊道。3)黑龙江省冻融侵蚀强度在空间上表现出明显的正相关和集聚性特征,强度相近的冻融侵蚀区在空间上积聚,高强度和低强度的冻融侵蚀区在空间上分异,产生了多个高强度和低强度的冻融侵蚀区。4)植被覆盖度的增加可以降低冻融侵蚀强度,在植被覆盖度小于20%的地方,冻融侵蚀尤为剧烈;冻融侵蚀主要发生在土壤含水量为0.2~0.3 m^(3)/m^(3)的区域,而极少发生在土壤水分含量小于0.2 m^(3)/m^(3)的区域。研究结果通过对比验证显示出较高的可靠性,可为该地区冻融侵蚀的防护和管理提供依据,并为类似区域提供借鉴方法和技术参考。

射频处理对冷冻鸡胸肉解冻效果的影响

本研究旨在探究射频处理工艺参数对射频解冻时间和均匀性的影响。实验采用27.12 MHz、6 kW的射频装置处理冷冻鸡胸肉,研究极板间距(8、9、10、11cm)、阳极高压(70%、75%、80%)和冻肉厚度(4、5、6cm)对射频升温及均匀性的影响规律。结果表明,随着极板间距的减小、阳极高压和样品厚度的增加,样品的升温速率加快,均匀性指数降低。基于冷冻鸡胸肉的解冻时间和温度分布,选取最佳工艺参数极板间距为9cm,阳极高压为75%,探究射频解冻和20℃常温解冻对冷冻鸡胸肉的解冻效果。与20℃常温解冻(6h)相比,射频解冻时间缩短至54.67min,鸡胸肉的菌落总数、汁液损失和总挥发性盐基氮含量均显著降低(P<0.05)。该研究结果可为射频技术在肉品解冻领域的实际应用提供理论依据和技术支撑。

正融过程中盐渍土路基抗剪强度影响因素分析

对冀北地区非饱和盐渍土进行了正融过程中三种压实度和10个温度节点的直剪试验,用土壤参数速测平台记录了正融过程中土体的温度发展及孔隙水相变过程,并分析了未冻水、压实度对其力学特性的影响关系。结论如下:在正融过程中,该盐渍土未冻水含量的变化呈现出“四阶段”,其中未冻水速增阶段相较于盐结晶失水阶段,增速较快。随着压实度的增大,土体温度变化速率、未冻水含量的增长以及试件强度下降速率都越快,黏聚力增加程度明显大于内摩擦角。当压实度较小、温度较低时,应力应变曲线则呈现脆性破坏特征。此外,土体黏聚力随温度的升高而显著降低,内摩擦角则出现很小幅度的增大,在-2℃到1℃之间,两者均出现短暂回滞现象。