• Wave propagation characteristics in frozen saturated soil
• ChengCheng Du, DongQing Li, Feng Ming, YuHang Liu, XiangYang Shi
• DOI: 10.3724/SP.J.1226.2018.00095
• 2018, Vol.10 (2): 95–103 Abstract ( 362) HTML PDF (1442 KB) ( 437 )
• Ultrasonic detection technology is of great significance in the detection and evaluation of physical and mechanical properties of frozen soil, but wave propagation characteristics in frozen soil are unclear. Based on the three-phase composition of frozen saturated soil and the mixture theory, considering Bishop's effective stress formula, the wave propagation equations are establish for frozen saturated soil. In wave propagation, an entropy inequality was introduced to describe the coupling of different phases. The analytic expressions of propagation velocity and attenuation law of waves in frozen soil are obtained, and wave propagation characteristics in frozen saturated soil are discussed. Results show that four types of waves (i.e., P1, P2, P3 and S) are found in frozen saturated soil and all four wave types are dissipative waves, in which the attenuation of P3 is the maximum. The velocity of four waves increases sharply at the excitation frequency range of 10³-10⁹ Hz, but the wave velocity at high-frequency and low-frequency is almost constant. When volume ice content increases, the wave propagation velocity of P1 and S decreases dramatically, and the velocity of P2 increases gradually, but P3 velocity increases first and then decreases to zero with increasing saturation. The attenuation coefficients of P1 and S waves begins to increase gradually when the volume ice content is about 0.4, P2 increases first and then decreases with an increase of volume ice content and P3 increases with the volume ice content and decreases rapidly from extreme to zero.

• Freeze-thaw processes of active-layer soils in the Nanweng'he River National Natural Reserve in the Da Xing'anling Mountains, northern Northeast China
• RuiXia He, HuiJun Jin, XiaoLi Chang, YongPing Wang, LiZhong Wang
• DOI: 10.3724/SP.J.1226.2018.00104
• 2018, Vol.10 (2): 104–113 Abstract ( 375) HTML PDF (2066 KB) ( 387 )
• 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.

• Surface-deformation monitoring in the permafrost regions over the Tibetan Plateau, using Sentinel-1 data
• ZhenMing Wu, Lin Zhao, Lin Liu, Rui Zhu, ZeShen Gao, YongPing Qiao, LiMing Tian, HuaYun Zhou, MeiZhen Xie
• DOI: 10.3724/SP.J.1226.2018.00114
• 2018, Vol.10 (2): 114–125 Abstract ( 498) HTML PDF (2925 KB) ( 676 )
• Differential Interferometric Synthetic Aperture Radar (D-InSAR) has been widely used to measure surface deformation over the Tibetan Plateau. However, the accuracy and applicability of the D-InSAR method are not well estimated due to the lack of in-situ validation. In this paper, we mapped the seasonal and long-term displacement of Tanggula (TGL) and Liangdaohe (LDH) permafrost regions with a stack of Sentinel-1 acquisitions using the Small Baseline Subset InSAR (SBAS-InSAR) method. In the TGL region, with its dry soils and sparse vegetation, the InSAR-derived surface-deformation trend was consistent with ground-based leveling results; long-term changes of the active layer showed a settlement rate of around 1 to 3 mm/a due to the melting of ground ice, indicating a degrading permafrost in this area. Around half of the deformation was picked up on monitoring, in contrast with in-situ measurements in LDH, implying that the D-InSAR method remarkably underestimated the surface-deformation. This phenomenon may be induced by the large soil-water content, high vegetation coverage, or a combination of these two factors in this region. This study demonstrates that surface deformation could be mapped accurately for a specific region with Sentinel-1 C-band data, such as in the TGL region. Moreover, although the D-InSAR technology provides an efficient solution for broad surface-deformation monitoring in permafrost regions, it shows a poor performance in the region with high soil-water content and dense vegetation coverage.

• Source and environmental significance of oxalate in Laohugou Glacier No. 12, Qilian Mountains, Western China
• WeiZhen Sun, XiaoQing Cui, GuangMing Yu
• DOI: 10.3724/SP.J.1226.2018.00126
• 2018, Vol.10 (2): 126–133 Abstract ( 353) HTML PDF (1779 KB) ( 301 )
• Retrieval of oxalate from snow and ice provides information on past environmental changes. In recent years, records of organic acids in middle- and low-latitude glaciers have attracted the attention of researchers globally. In this study, we analyzed oxalates in an ice core from Laohugou Glacier No. 12 on the Qilian Mountains at an elevation of 5,040 m a.s.l. in 2006. Average oxalate concentration was 18.5±2.4 ng/g over the prior 46 years. Oxalate values showed a significantly increasing trend since 1985. From 1985 to 1995, oxalate concentrations had large fluctuations, peaking in about 1987 and exhibiting a slightly decreasing trend since 1995. The result shows that the abrupt increase of oxalate concentration in the ice core since the mid-1980s reflects atmospheric environmental pollution by human and industrial activities.

• Climate change inferred from aeolian sediments in a lake shore environment in the central Tibetan Plateau during recent centuries
• BenLi Liu, JianJun Qu, ShiChang Kang, Bing Liu
• DOI: 10.3724/SP.J.1226.2018.00134
• 2018, Vol.10 (2): 134–144 Abstract ( 294) HTML PDF (2360 KB) ( 436 )
• Studies of the past climate variation on the Tibetan Plateau (TP) are currently limited in number and low in density and temporal resolution. We investigated the climate condition from about 400 years before present (B.P.) in the central TP at the shore of Co (means "lake") Nag using aeolian sediments. A 2.7-m sand profile with 57 sediment samples and six optically stimulated luminescence (OSL) samples were studied through grain-size analysis, geochemical elements and parameters, and depositional rate estimation. A previous assumption was verified that sand deposition at the shore of Lake Co Nag originated from hills to the east. Two significant wet periods between 90–140 and about 380 years B.P. were indicated by the variation of element profiles and sediment depositional rates. Aeolian activity is sensitive to variations from different seasonal changing patterns of climate factors in the study area, and aeolian sediments respond differently to climate conditions during the cold little ice age (LIA) and the warm 20th century. Present day dry seasons of winter and spring might be much warmer and drier compared to seasons of 400 years ago although summer precipitation has increased, resulting in significantly more aeolian activity and higher depositional rate (about 6 times compared to 380–240 years ago) of sandy sediments. Aeolian problems like blown-sand deposition and desertification may be worse in a projected warming future in the central TP as well as other cold and high altitude regions. Our results suggest an agreement with environmental evolution during the little ice age and the 20th century in a broader scale on the TP.

• A method to obtain soil-moisture estimates over bare agricultural fields in arid areas by using multi-angle RADARSAT-2 data
• JunZhan Wang, JianJun Qu, LiHai Tan, KeCun Zhang
• DOI: 10.3724/SP.J.1226.2018.00145
• 2018, Vol.10 (2): 145–150 Abstract ( 336) HTML PDF (2179 KB) ( 285 )
• Soil moisture is an important parameter for agriculture, meteorological, and hydrological studies. This paper focuses on soil-moisture estimation methodology based on the multi-angle high- and low-incidence-angle mode RADARSAT-2 data obtained over bare agricultural fields in an arid area. Backscattering of the high- and low-incidence angles is simulated by using AIEM (advanced integral equation model), with the surface-roughness estimation model built based on the simulated data. Combining the surface-roughness estimation model with the backscattering model of the low-incidence-angle mode, a soil-moisture estimation method is put forward. First, the natural logarithm (ln) of soil moisture was obtained and then the soil moisture calculated. Soil moisture of the study area in Dunhuang, Gansu Province, was obtained based on this method; a good agreement was observed between the estimated and measured soil moisture. The coefficient of determination was 0.85, and the estimation precision reached 4.02% in root mean square error (RMSE). The results illustrate the high potential of the approach developed and RADARSAT-2 data to monitor soil moisture.

• Relationship between the haplotype distribution of Artemisia halodendron (Asteraceae) and hydrothermal regions in Horqin Sandy Land, northern China
• WenDa Huang, XueYong Zhao, YuLin Li, YuQiang Li, YaYong Luo
• DOI: 10.3724/SP.J.1226.2018.00151
• 2018, Vol.10 (2): 151–158 Abstract ( 269) HTML PDF (1731 KB) ( 255 )
• The genetic diversity of Artemisia halodendron (Asteraceae), a constructive and dominant species in Horqin Sandy Land, was investigated to examine the genetic relationships with different hydrothermal regions in Horqin Sandy Land. We sequenced chloroplast DNA (cpDNA) fragments (trnL-F) of 243 plants from 10 populations across the Horqin Sandy Land. The analyses of cpDNA variation identified seven haplotypes. A low level of haplotype diversity (H_d=0.706) and nucleotide diversity (π=0.0013) was detected. Haplotypes clustered into two tentative clades. Low genetic differentiation among regions was consistently indicated by hierarchical analyses of molecular variance (AMOVA). Across the sampled populations, the haplotype distributions were differentiated with hydrothermal gradients.

• Effects of intercropping on rhizosphere soil microorganisms and root exudates of Lanzhou lily (Lilium davidii var. unicolor)
• CuiPing Hua, YaJun Wang, ZhongKui Xie, ZhiHong Guo, YuBao Zhang, Yang Qiu, Le Wang
• DOI: 10.3724/SP.J.1226.2018.00159
• 2018, Vol.10 (2): 159–168 Abstract ( 508) HTML PDF (1727 KB) ( 526 )
• Both yield and quality of Lanzhou lily (Lilium davidii var. unicolor) are seriously affected by continuous cropping. We attempted to understand the effects of intercropping on the obstacles associated with continuous cropping of Lanzhou lily (Lilium davidii var. unicolor). The changes of rhizosphere microbial biomass and diversity in interplanting and monoculturing systems were studied by using the Illumina HiSeq sequencing technique. The contents and composition of lily root exudates were measured by gas chromatography–mass spectrometer (GC–MS). The intercropping results of Lanzhou lily showed: (1) There was no difference in the composition of the rhizosphere soil microbes at the phylum level, but the relative abundance of the microbes decreased; and the relative abundance of harmful fungi such as Fusarium sp. increased. The relative abundance of Pleosporales sp. and other beneficial bacteria were reduced. After OTU (operational taxonomic unit) clustering, there were some beneficial bacteria, such as Chaetomium sp., in the lily rhizosphere soil in the interplanting system that had not existed in the single-cropping system. We did not find harmful bacteria that had existed in the single-cropping systm in the rhizosphere soil of interplanting system. The above results indicated that the changes of relative abundance of soil fungi and bacteria in lily rhizosphere soil was not conducive to improving the ecological structure of rhizosphere soil microbes. At the same time, the microbial composition change is very complex—beneficial and yet inadequate at the same time. (2) Root exudates provide a matrix for the growth of microorganisms. Combined with the detection of root exudates, the decrease in the composition of the root exudates of the lily was probably the reason for the decrease of the relative abundance of microbes after intercropping. At the same time, the decrease of the relative content of phenolic compounds, which inhibit the growth of microorganisms, did not increase the relative content of rhizosphere soil microorganisms. Changes in amino acids and total sugars may be responsible for the growth of Fusarium sp.. The results showed that the intercropping pattern did not noticeably alleviate the obstacle to continuous cropping of Lanzhou lily, and the change of microbial biomass and diversity was even unfavorable. However, the emergence of some beneficial bacteria, the disappearance of harmful fungi, and other changes with intercropping are in favor of alleviation of obstacles to continuous cropping of Lanzhou lily.

• Seasonal characteristics of chlorophyll fluorescence kinetics of heteromorphic leaves in Populus Euphratica
• ZongQiang Chang, Hua Tao, Qiang Zhu
• DOI: 10.3724/SP.J.1226.2018.00169
• 2018, Vol.10 (2): 169–179 Abstract ( 367) HTML PDF (2183 KB) ( 262 )
• Populus euphratica Oliver grown in desert areas have polymorphic leaves, which include lanceolate to serrate oval leaves. This paper measures the chlorophyll fluorescence-induction kinetics curves of two types of heteromorphic leaves (lanceolate and serrate oval) of P. euphratica over the growth season in the Ejina Desert area, China. This is in order to study the electron transport, as well as absoprtion, distribtution, and dissipation of light energy and their adaptation characteristics. The results indicate that (1) serrate oval leaves' photosystem II (PSII) initial light-energy-conversion efficiency (Fv/Fm), potential activity (Fv/F₀), and the light-energy-utilization parameter (PI) are higher than those of lanceolate leaves; the accumulated amount of Q_A-(Vj) and the relative speed of Q_A deoxidation (M₀) are lower than those of lanceolate leaves; (2) the reaction center density (RC/CS₀) and electron-transfer energy (ET₀/CS₀) in the unit cross-sectional area of serrate oval leaves are higher than those of lanceolate leaves; the energy consumed in unit cross-sectional area (DI₀/CS₀), and energy-flow parameters (ABS/RC, ET₀/RC, TR₀/RC, and DI₀/RC) in the unit reaction center of serrate oval leaves are lower than those of lanceolate leaves; (3) the proportion of energy used for photochemical reaction and energy electron transport in serrate oval leaves (Φ_P0, Ψ₀, and Φ_E0) are larger than those in lanceolate leaves, and the maximum quantum yield (Φ_D0) of nonphotochemical reaction is less than that of lanceolate leaves. Thus, serrate oval leaves of P. euphratica have a more efficient energy-distribution strategy and better adaptability to extreme environmental conditions than lanceolate leaves.

• Cash gifts, perception of social sphere and distribution of water resources for rural farmers in a typical oasis area in Northwest China
• QianTao Zhu, WenZhi Zhao, Jian Guo, Hu Liu
• DOI: 10.3724/SP.J.1226.2018.00180
• 2018, Vol.10 (2): 180–186 Abstract ( 342) HTML PDF (1898 KB) ( 255 )
• Face-to-face interviews (n=860) were conducted to determine cash-gift behavior, cognition and complexity of social relations, and family water consumption for agricultural production in a typical oasis area in Northwest China. The survey results revealed cash gifts to be the second-largest expenditure (1,330 Yuan) for rural households, far beyond the average spending on health (854.1 Yuan) or education (890.8 Yuan). The amount of cash-gift expenditures indirectly reflects a family's social relations level, and our developed Social Relations Extent Coefficient—based on cash-gift and food expenditures—can directly reflect the extent or level of these relationships. Different types of farmers or farming families have different coefficients. The coefficient also shows how social station affects a family's water resource utilization, and how water is distributed among different types of farmers. Despite the current inequities, however, promotion of better agricultural techniques and large-scale cultivation in this area could help distribute water resources more equitably and effectively.