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This study investigated the influence of movable oil on the pore structure of various shale types, analyzing 19 shale samples from Well X in the Mahu Sag of the Junggar Basin. Initially, X-ray diffraction (XRD) analysis classified the shale samples. Subsequently, the geochemical properties and pore structures of the samples, both pre and post oil Soxhlet extraction, were comparatively analyzed through Total Organic Carbon (TOC) content measurement, Rock-Eval pyrolysis, and nitrogen adsorption experiments. Additionally, fractal theory quantitatively described the impact of movable oil on the pore structure of different shale types. Results indicated higher movable oil content in siliceous shale compared to calcareous shale. Oil extraction led to a significant increase in specific surface area and pore volume in all samples, particularly in siliceous shale. Calcareous shale predominantly displays H2–H3 type hysteresis loops, indicating a uniform pore structure with ink-bottle-shaped pores. Conversely, siliceous shale exhibited diverse hysteresis loops, reflecting its complex pore structure. The fractal dimension in calcareous shale correlated primarily with pore structure, exhibiting no significant correlation with TOC content before or after oil extraction. Conversely, the fractal dimension changes in siliceous shale samples do not have a clear correlation with either TOC content or pore structure, suggesting variations may result from both TOC and pore structure. [ABSTRACT FROM AUTHOR]

Runoff and sediment characteristics can be the important indicators on the soil erosion. However, it is still unclear on the runoff and sediment variations of the watershed in the red soil region of southern China, especially after a continuous soil erosion control. This study aims to investigate the characteristics of runoff and sediment in the small watershed after the long-term soil and water conservation in the red soil region of southern China. The Zhuxi watershed in Changting County Fujian Provence was taken as the study area to collect the rainfall and hydrological data from 2017 to 2020. A systematic analysis was implemented to determine the runoff and sediment relationships of the flood events using redundancy analysis (RDA), multiple stepwise regression equations, and sediment concentration (C)-discharge (Q) hysteresis loop methods. The results showed that: 1) The monthly average runoff and sediment concentration were consistent with the trend of monthly rainfall changes during the study period. The annual flood runoff depth and sediment yield were 282.30-892.50 mm and 35.80-179.50 t/km², respectively. The sediment modulus of the flood events was distributed mainly in 0-20.0 t/km². But the total flood sediment yield were determined by a few flood events with the sediment modulus greater than 5.0 t/km². 2) Rainfall (P), the maximum rainfall intensity of 30 min (I30), and rainfall erosivity (R) were the main rainfall characteristics that affected the runoff and sediment. However, the contribution rates of rainfall characteristics to the variations of runoff and sediment were 68.99% and 49.28%, respectively. It infers that the rainfall characteristics were more closely related to the runoff indicators than to the sediment indicators. The runoff was the most important influencing factor of sediment. Thus, the great fitting was achieved in the R² range of 0.624-0.870 with estimating the sediment yield (S), average sediment concentration (Cm), and the maximum sediment concentration (Cmax) of flood events using main runoff indicators, including the runoff depth (H), average discharge (Qm), and peak flow (Qmax). 3) There were six types of C-Q hysteresis loops in the flood events with the sediment modulus greater than 0.1 t/km². Among them, the occurrence frequencies of the single-valued and complex loop were 55% and 22%, respectively. The counterclockwise loop was more appeared in the flood events with the small sediment modulus. The highest occurrence frequency was found in the single-valued loop. The variation of C with Q in the single-valued flood events was characterized by the phased method. The critical C value was about 0.1 g/L, as the C-Q relationship changed. The sediment carrying capacity of runoff was significantly changed at a sediment concentration of about 0.1 g/L. Moreover, the single-valued loops were also dominated in the C-Q hysteresis loop for the large-scale flood event in the watershed. There were the low sediment yields of the flood events and the great influence of the runoff on the flood sediment in the watershed of the red soil region after a long-term soil erosion control. The sediment supply of the flood events, including the large-scale flood events, in the watershed was generally in a continuous and limited state. The findings can provide the much more comprehensive understanding of the runoff and sediment processes in the watershed with continuous soil and water conservation, in order to reveal the development of soil erosion in the red soil region of southern China. [ABSTRACT FROM AUTHOR]

Hydraulic consistency between a prototype pump and its hydraulic model is generally considered to be satisfied, that is, the energy performance and the flow structures conform to the similarity law. However, such hydraulic consistency may not always exist in actual engineering projects. Head change and vibration enhancement in large-scale bulb tubular pumps are exhibited, but the reason for this inconsistency is still unclear. In this article, a case study was performed for the South-to-North Water Diversion Project in China, and the pressure characteristics in the impeller were explored under the optimal condition. An interesting new phenomenon, pressure polarization oscillation, is found. Its most important feature is the constant difference in average pressure values among axisymmetric blades, that is, the blades with axisymmetric structures exhibit large-amplitude pressure oscillations around different average pressure values, and one revolution is equivalent to one rotating cycle due to the failure of hydraulic consistency. Further in-depth analysis reveals that pressure oscillations are realized by the adjustment of the resultant force between the Coriolis force and the potential rothalpy gradient to fluid motions under the sinusoidal disturbance of gravity, and its action path presents a hysteresis loop with the impeller rotating. This adjustment mode leads to a special conversion between the gravity potential energy, pressure energy, and the kinetic energy, and, thus, the hydrostatic pressure difference at the initial phase cannot be fully eliminated; the pressure transition between the sides along and against the gravity is inconsistent. This finding suggests that the difference induced by the hydraulic inconsistency should be considered if the conventional similarity conversion is applied to large-scale tubular pumps. [ABSTRACT FROM AUTHOR]

• The 209 rainfall events were classified by hysteresis index and hysteresis loop. • The figure-of-eight and complex are the main hysteresis types in small watershed. • The peak rainfall intensity have significant impact on hysteresis types. • The main contributions types to soil erosion are figure-of-eight and complex. Suspended sediment concentration and discharge (SSC-Q) hysteresis characteristics during storm events can be used to indicate water–sediment response relationships. Evaluating SSC-Q hysteresis characteristics and their controlling factors is critical for watershed sediment management and the development of effective soil erosion control strategies. In this study, rainfall-runoff-sediment characteristics were analyzed under 209 flood events based on observed data from 2016 to 2022 to assess the sediment sources and hysteresis characteristics of a watershed in southern China. Principal component analysis was employed to further explain the control of antecedent rainfall conditions, conventional rainfall characteristics, rainfall fluctuation in the peak zone, and runoff characteristics on sediment transport under different hysteresis types. The results indicated that the figure-of-eight and complex was the predominant hysteresis patterns, accounting for 60.76 % of all events. Hydrological variables such as rainfall and runoff exerted different controls and explanations on the four hysteresis patterns: clockwise, anticlockwise, figure-of-eight, and complex. Water-sediment characteristics under different hysteresis types were more strongly correlated with the peak rainfall intensity, compared to the conventional rainfall intensity (I 30 , I ave). Peak rainfall intensity and runoff coefficient were the main factors controlling the clockwise and anticlockwise hysteresis patterns, respectively; the figure-of-eight was mainly affected by rainfall intensity and discharge, and the peak rainfall intensity and the antecedent precipitation mainly controlled the complex hysteresis patterns. Figure-of-eight and complex events were usually characterized by long duration, heavy rainfall, and high rainfall intensity, and produced runoff and sediment loads that accounted for 70.40 % and 80.88 % of all events in 7 years, respectively. Therefore, in the management and regulation of water and sediment in small watersheds, soil erosion brought about under figure-of-eight and complex flood events needs to be emphasized. [ABSTRACT FROM AUTHOR]

To be a typical flexible structure with small damping, a high-rise television (TV) transmission tower is sensitive to wind excitations. The response control of TV transmission towers by semi-active friction dampers under strong external excitations is still very limited and the parametric study on control performance has not been systematically investigated. To this end, the semi-active control of a wind-excited TV transmission tower by piezoelectric friction dampers is conducted in this study. A fine finite element (FE) model of a real TV transmission tower is constructed and then a two-dimensional (2D) dynamic model is also established. The analytical model of a semi-active friction damper based on piezoelectric actuators is then established with damper stiffness considered. The equations of motion of the tower with friction dampers are then established. The local feedback control algorithm based on nonlinear Reid damping mechanisms is used to command piezoelectric friction dampers for wind-excited towers. A high-rise TV transmission tower in China is used to investigate the validity of the proposed semi-active control approach and compared with that of passive control. Furthermore, a detailed parametric investigation is conducted to examine the influence of gain coefficient, damper stiffness, hysteresis loops, damper force, and wind loading intensity on control efficacy. The analytical results indicate that piezoelectric friction dampers with optimal parameters are beneficial to the vibration mitigation of TV transmission towers under different wind loading intensities. [ABSTRACT FROM AUTHOR]

The mechanical behavior of the joints inside a loess layer is greatly important in weak intercalation studies owing to its involvement in a wide range of landslides in the loess region in China. The shear behavior of the joints in the loess stratum during direct shear and cyclic loadings was investigated using the PFC2D discrete element software. Loess mudstone and mudstone with weak intercalated layer materials were subjected to direct testing, and cyclic shear tests were conducted with consideration to the influence of normal stress and shear velocity. The macroscopic properties and damage patterns were obtained for six numerical configurations; namely, loess-weathered mudstone with 0°, 10°, and −10° joints and weathered mudstone with 0°, 10°, and −10° weak intercalated layers. The numerical test results revealed that, in the direct shear tests, the shear stress and shear displacement of the samples increased with the normal stress. In the cyclic shear tests with a total cycle number N=20, the shear stress-shear strain curve of the six different configurations exhibited a hysteresis loop. The numerical tests also revealed that, under cyclic shear, the normal stress and shear velocity affected the shear strength. The degree of damage increased as the shear velocity decreased from 0.1 mm/s to 0.005 mm/s for all six numerical configurations. Compared with the damage pattern of the direct shear tests, the damage of the cyclic shear tests mainly comprised shear cracks and fractures, some shaking consolidation settlement and fewer shear strain occurred around the joints. In the direct shear tests, more compression cracks and fractures occurred in the samples. The damage mainly developed along the joints, and shearing-off damage occurred. The results obtained by this study further elucidate the failure mechanism and microscopic damage response of the joints in the loess stratum in Northwest China. [ABSTRACT FROM AUTHOR]

Purpose: Analysis of sediment transport is an effective approach for identifying sediment sources and for catchment management. However, a long-term analysis of sediment variability at multiple time scales is less available, especially in mountainous catchments. This study aims to determine sediment sources and to identify sediment transport dynamics, as well as the influencing factors, through analyzing long-term sediment fluxes at different time scales. Materials and methods: In this paper, 32 years of sediment flux in an instrumented mountainous catchment in eastern Zhenjiang Province, China, was investigated at multiple time scales (i.e., monthly, seasonal, annual, and event). Sediment yields (SYs) during three time periods (i.e., 1964–1977, 1978–1989, and 2010–2015) were first classified by the Mann-Kendall and cumulative anomaly tests, and then sediment fluxes for each period were investigated and compared at multiple time scales. Results and discussion: Annual SYs ranged from 29 to 308 t year−1 during the recording period and were significantly influenced by several high magnitude flood events. The mean annual SYs decreased from 153.82 t year−1 in 1964–1977, to 97.79 t year−1 in 1978–1989, and to 91.08 t year−1 in 2010–2015 due to improved soil conservation measures and increased reservoirs. At the seasonal scale, over 92% of the sediment was transported in spring and summer over the recording period. Heterogeneous sediment sources, partial areal distribution of rainfalls, and other factors led to complex suspended sediment concentration versus water discharge hysteresis loop patterns at the event and monthly scales. Conclusions: The improved soil conservation measures and increased reservoirs over the recent decades decreased sediment availability, and the number and the magnitude of flood events from 1964 onward. However, the flood sediment fluxes in a few months were still high due to extreme precipitation events in recent years. The work can provide guidance for addressing sediment problems in this and/or other similar catchments. [ABSTRACT FROM AUTHOR]

Nanjing is located in the subtropical monsoon climate zone of China. In this study, a series of monthly collections of atmospheric dustfall was performed in different directions from a high-rise building in Nanjing from February 2015 to March 2016. A series of magnetic parameters including χ, χ fd %, χ ARM , SIRM, magnetic hysteresis loops, high-temperature κ-T curves and SEM images was measured from atmospheric dustfall samples. The research shows that the type and size of magnetic minerals within atmospheric dustfall samples in Nanjing are similar to those found in northern cities in China, but the atmospheric dustfall samples in Nanjing have higher magnetic mineral concentrations. Coarse-grained magnetite dominated magnetic minerals. The peak concentrations of magnetic minerals contained from atmospheric dustfall of Nanjing occurred in summer. The relationship between magnetic parameters and meteorological data shows that the high values are mainly influenced by precipitation rather than by wind direction. Combined with results of the SEM images and the weak relationship between magnetic parameters and the data of PM 2.5 and PM10, all these indicate that the atmospheric dustfall of Nanjing is mainly from near-source polluted dustfall rather than from long-distance dustfall. This research suggests that environmental magnetism as a simple, economic and nondestructive technology, will be a useful tool in atmospheric dustfall research. • A series of magnetic parameters from atmospheric dustfall in Nanjing was established. • Coarse-grained magnetite dominated magnetic minerals of atmospheric dustfall. • The peak concentrations of magnetic minerals occurred in summer. • Atmospheric dustfall in Nanjing was influenced by near-source polluted dustfall. [ABSTRACT FROM AUTHOR]

• The nanoscale storage spaces of the Da'anzhai carbonates are well developed. • The nanopore structure of the Da'anzhai carbonates is more complex than other rocks. • The Da'anzhai nanoscale storage spaces are mainly from terrestrial minerals. • The authigenic CaCO 3 minerals are negatively correlated with the nanoscale pores. • Weathering, salinity, climate and hydrodynamic conditions can control nanoscale pores. Compared with the studies of nanoscale pores in shale, coal, and tight sandstone, studies associated with lacustrine tight carbonate nanoscale pores and their control mechanisms, particularly quantitative studies combining reservoir evaluation and geochemistry, remain scarce. To address this disparity, lacustrine tight carbonate samples collected from the Jurassic Da'anzhai Member in the central Sichuan Basin of China were quantitatively investigated. Similar to other unconventional reservoirs, lacustrine tight carbonate reservoirs contain well-developed intraparticle pores, interparticle pores, and micro-cracks with nanoscale storage spaces that dominate the full-scale reservoirs. The relatively small pores (3–5 nm) make a dominant contribution to the nanoscale storage space. Isotherms and hysteresis loops are Type II and Type H 3 , respectively, indicating wedge-shaped pores. However, the hysteresis loops indicate more dead-end pores, larger pores, and more complex microstructures than those found in other unconventional reservoirs. The mineral in lacustrine carbonate provides a link between the reservoir and the formation environment. Strong paleo-weathering, low salinity, a humid (rainy) paleo-climate and poor hydrodynamic conditions are favorable to improve the storage spaces and terrestrial mineral contents but harmful to the formation of authigenic minerals. Terrestrial minerals, including primarily quartz, clay, and dolomite, have well-developed nanoscale pores and are positively correlated with the nanoscale storage space, whereas authigenic minerals, primarily calcite, have strong cementation and filling effects and are negatively correlated with the nanoscale storage space. [ABSTRACT FROM AUTHOR]

Red clay is widely distributed in Zhejiang Province, China. Rain-induced shallow landslides easily occur on red clay slopes due to the reduction in shear strength caused by rainwater infiltration. The aim of this paper was to study the soil–water characteristic of red clay and its application on analyzing the stability of red clay slope. A series of field tests at different depths of red clay slope were carried out to monitor the variations of water content and matric suction under typical climate conditions. The results showed that the distribution of water content in red clay slope is complex because of long-term wetting–drying cycles. The water content within shallow layer is sensitive to external environment, and the response time of the water content is related to rainfall intensity. It is also observed that the soil water characteristic curve (SWCC) varies at different depths. The SWCCs of red clay can be fitted by linear function. The SWCCs from laboratory tests illustrated that saturated water content is more than 40%. Most of the SWCCs obtained at the depth of 90 cm are within the hysteresis loops of the SWCCs from laboratory test. The short-term rainfall has less effect on the stability of the slope, but the stability continuously decreases after the rain stops. The SWCCs obtained from laboratory were applied to analyze slope stability. Considering the influence of cracks, the computed results are close to field data. The study has a certain directive significance to the design of red clay slopes. [ABSTRACT FROM AUTHOR]

To evaluate pore networks of the lower Cambrian Niutitang Shale in the Cen-gong Block, multiple techniques, including geochemical analysis, low-pressure gas (CO2 and N2) adsorption, mercury intrusion capillary porosimetry (MICP) and field-emission scanning electron microscope (FE-SEM), were performed to investigate pore structure, including pore-size distribution (PSD), pore volume and surface area of black organic-rich shales from two wells to better understand the mechanism of shale-gas accumulation. Geochemical analysis shows that equivalent vitrinite reflectance ranges from 2.1 to 3.5% and are overmature. Surface areas and pore volumes of micropores calculated from CO2 adsorption, which vary from 8.23 to 37.39 m2/g and from 3.06  10−3 to 10.89  10−3 cm3/g, respectively, can provide large amounts of adsorptive sites for shale-gas accumulation. N2 adsorption shows reversed S-shaped isotherms, which are classified into type H2 and H3 hysteresis loops, indicative of ink-bottle pores and slit-or plate-like pores. N2 adsorption and MICP analysis indicates that the inorganic-associated pores in shales may play a significant role in the storage and production of hydrocarbons. High-resolution FE-SEM analysis suggests that OM pores (OMPs) are common in Niutitang samples with a dominant diameter less 50 nm, but a sample with the highest total organic carbon (TOC) of 10.01 wt% has few OMPs, whereas a sample with the TOC of 7.51 wt% has more OMPs. The percentage of OMP area vs total organic matter area (Øs) ranges from 1.70 to 7.92%. The pore structure characteristics of TX1 well, calculated by multiple techniques, are better than samples from TM1 well. In addition, pore types are dominated by interparticle, intraparticle and organic matter pores, and the minor amounts of OMPs in TM1 well indicates that most of the organic matter may have lost the potential to generate hydrocarbons owing to the release of formation pressure with some graphitisation and high-angle fractures larger in the TX1 well. TOC content, mineral composition and tectonically related thermal maturity may be the main controlling factors of the pore structure and the lower Cambrian Niutitang Shale demonstrates the greatest potential for shale-gas production in South China. [ABSTRACT FROM AUTHOR]

Abstract Investigating the suspended sediment dynamic is useful for gaining a more comprehensive understanding of runoff and sediment yield process. The study analyzes the sediment flow behavior in relation to the flood patterns in the Xichuan River catchment on the Loess Plateau. Based on 23-year hydrological data collected from Zaoyuan hydrological station and K-medoids clustering method, one hundred and twelve flood events data were classified into four flood patterns. The hydrologic features of different flood patterns exhibit significant differences. The values of the mean runoff depth, the mean flood duration, and the mean flood peak discharge decreased as the following order: Pattern A > Pattern C > Pattern D > Pattern B. Each flood pattern results in differing levels of the event sediment yield (SY), the SY of Pattern A (10,275.33 t·km−2) and Pattern C (1196.39 t·km−2) were larger than those from Pattern B (218.84 t·km−2) and Pattern D (693.84 t·km−2). These results indicated that greater attention should be paid to Pattern A and Pattern C because of the largest sediment delivery effect. Multiple stepwise regressions analysis suggested that the contribution of main runoff-related factors to event sediment yield varied with different flood patterns. In addition, hysteretic analysis between suspended sediment concentration and runoff suggested that counter-clockwise and figure-eight loops were the dominant loops. The results provided a useful information to flood pattern classifications and suspended sediment dynamics research, and enriched the sediment control theory at the watershed scale. Highlights • Screen the key/dominant hydrological variables that have a major influence on sediment yield and delivery • Explore sediment flow behavior under different flood regimes • Identify the sediment sources based on different SSC-Q hysteresis loops [ABSTRACT FROM AUTHOR]

[Display omitted] • The connectivity of shales can be estimated effectively based on percolation theory through analyzing sorption hysteresis. • The connectivity of shales is mainly influenced by the TOC content. • The maturity and illite content are controlling factors for the percolation cluster length of shales. Pore connectivity is a key parameter affecting the hydrocarbon yield of shale reservoirs, and a quantitative study on it is helpful to evaluate the exploration and development potential of shale gas. In this paper, the shales from the Jurassic Yangxia and Kezilenur Formations in the Kuqa Depression, Tarim Basin, China, were taken as an example, and organic petrography analysis, X-ray diffraction analysis, field emission scanning electron microscope (FE-SEM), gas adsorption and helium pycnometry were carried out to determine their petrological, organic geochemical characteristics and pore distribution features. A method for estimating the connectivity of shale with isotherm adsorption curves of a H3 hysteresis loop was established and used to characterize the connectivity of shale pores. The results show that the total pore volume of shale ranges from 2.479 × 10-3 to 20.379 × 10-3 cm3/g, and the specific surface area (SSA) ranges from 1.222 cm2/g to 12.668 cm2/g. The samples' coordination number (Z) is between 1.215 and 3.064, and the percolation cluster length (L) is between 2.429 and 3.859. Shale with more micropores or higher TOC has a larger Z value, indicating that organic matter pores and micropores have better connectivity. There is no correlation between Z and T max , meaning that the effect of maturity on Z is insignificant. The impact of TOC on the L value is also not substantial. Besides, T max and illite content show a negative correlation with L, indicating that the high maturity and illite content impede the development of the percolation cluster. [ABSTRACT FROM AUTHOR]

• We identified hysteresis patterns in karst watersheds. • The monthly sediment–discharge relationship was mainly clockwise hysteresis loops. • An improved differential hysteresis index (HI K) quantified degree of hysteresis. • The effects of climate factors and extent of vegetation on HI K were decoupled. Hysteresis loop models are one of the most common and effective tools for quantifying time-scale dynamics of sediment-discharge relationships. These models can successfully characterize sediment dynamics in watersheds and facilitate developing effective measures to manage sediment-discharge resources. Considering the characteristics of a proportional hysteresis index, an improved differential hysteresis index was developed. The improved model was used to quantify typical patterns of monthly sediment-discharge relationships in six karst watersheds in southwest China during 2003–2019. Partial least squares structural equation modeling was conducted to decouple the effects of climatic factors and vegetation extent on the hysteresis index. The results indicate that clockwise hysteresis accounted for 74 % of the total hysteresis occurring in the watersheds, whereas counterclockwise and 8-shaped hysteresis accounted for only 22 % and 3.9 %, respectively. The improved hysteresis index varied from −10 to 10, effectively reflecting the degree of hysteresis occurring in the watersheds. Partial least squares structural equation modeling shows that climatic factors (e.g., temperature and precipitation) and vegetation extent in the Hongshui, Yujiang, Liujiang and Wujiang watersheds explained 50 %∼75 % of the hysteresis between sediment concentration and water discharge. The combined effect of temperature and precipitation on the hysteresis index was larger than that of vegetation extent. The improved differential hysteresis index proposed in this study effectively extended the applicability of differential hysteresis indices and facilitated comparing the degree of hysteresis among watersheds with different sediment concentrations. This study can improve the understanding of sediment sources and transport pathways and provide valuable information for decision making on soil erosion control in karst watersheds. [ABSTRACT FROM AUTHOR]

This study aimed to investigate the differential characteristics of high-pressure adsorption-desorption of supercritical CO 2 and CH 4 at main temperatures of 36 ℃, 42 ℃, and 48 ℃ and the pressure of 0–20 MPa in low permeability coal, a case from the tectonic coal area of Huainan-Huaibei coalfield, eastern China. Combining the variation characteristics of adsorption capacity with pressure, gas free phase density, the prediction of CO 2 adsorbed phase density, the correction method of gas adsorption capacity, the sequestration capacity of CO 2 in low permeability coal, and the adsorption hysteresis index of adsorbed gas were assessed. The controlling factors of gas adsorption capacity were revealed based on the general discussion of the relation between the gas adsorption capacity and the conditions such as temperature, pressure, coal maceral, coal quality, and pore structure. The results show that the lowest equilibrium pressure associated with the CH 4 excess adsorption peak is 9 MPa, which is larger than most of the experimental pressures for the CH 4 isothermal adsorption test. CO 2 excess adsorption capacity of the different coal samples has characteristic of an obvious peak at the experimental pressure near 6 MPa under different experimental temperatures, all CO 2 excess adsorption capacity changes with CO 2 free phase density in a two-step pattern, CH 4 or CO 2 adsorbed phase density can be predicted by the truncation method. Desorption of CH 4 or CO 2 in coal has an obvious "hysteresis loop", the cumulative adsorption hysteresis index (CAHI) and the incremental adsorption hysteresis index (IAHI) of CH 4 based on the calculation of CH 4 excess adsorption capacity are controlled by the temperature and pressure, it has the obvious rise during the stage of low pressure (less than 4 MPa), whether IAHI or CAHI of CO 2 , it shows characteristics of complex changes. Variations in CAHI and IAHI for CH 4 or CO 2 are governed by the development of pore structure in coal, and the temperature. Coal maceral, coal quality, and coal grade have an effect on gas adsorption in coal by affecting the growth, filling, and deformation of pores in coal; the adsorption capacity of the gas depends both on the surface area of the pores and the pore volume of the pores in the coal. The differential mechanism for the gas adsorption capacity from the low permeability coal requires further understanding. • High-pressure adsorption-desorption of CH 4 and CO 2 of low permeability coal samples was conducted. • Synthetically investigate differential characteristics of adsorption-desorption on CH 4 and CO 2 in low permeability coal. • Reveal the importance of the correction in adsorption phase density of gas for understanding CO 2 sequestration potential. • Preliminarily point out that the differential mechanism of CH 4 and CO 2 in coal should be further understood. [ABSTRACT FROM AUTHOR]

Suspended sediment dynamics were investigated in the Loushui River basin, a secondary tributary of the Yangtze River in southern China. The variations of suspended sediment transport were analyzed at different time scales (among different years, monthly and seasonal, and within-flood event) based on 25-year hydrological data from the outlet hydrometric station, and explained by the contribution of flood events, precipitation and human activities. Four stages were classified by the non-parametric statistical method of Pettitt change-point test and Cumulative anomaly test. At the annual scale, the relationship between suspended sediment concentration ( SSC ) and water discharge ( Q ) varied at four stages. The suspended sediment load ( SSL ) showed parabolic relationship with annual precipitation and significantly influenced by floods (contribution averaged at 78% before 1985; at 55% after 2007). SSL drastically decreased after 2007, mainly induced by the construction of the Jiangya reservoir. Sediment ‘store-release’ phenomenon was used to explain the seasonal variations of suspended sediment load. Monthly SSC – Q hysteresis loops indicated that the sediment storage seasons swung between winter/spring and late autumn at different stages. At the within-flood scale, three types of SSC – Q hysteresis loops were observed for the maximum flood events, including clockwise pattern (44%), counter-clockwise pattern (24%) and figure-eight pattern (32%). The variations of SSC – Q hysteresis patterns at four stages implicated the changing suspended sediment source materials with time. During the years 1966–1978, the suspended sediment mainly came from channels for the maximum flood events, while, materials from the upper reaches or slopes dominated the later period 1979–1985 and 2007–2011. [ABSTRACT FROM AUTHOR]

• Sediment connectivity is influenced by vegetation, slope and watersheds area. • Anticlockwise loop is the most frequent hysteresis type and transport the most sediment. • Indices of connectivity showed a high correlation with sediment parameters and hysteresis index. Sediment connectivity is an important property influencing landscape evolution. Understanding the link between sediment connectivity and hydrologic processes plays an important role in developing strategies for soil and water conservation measures. Based on 10 years of observations for 30 hydrologically monitored watersheds on the Loess Plateau, measurements for 926 hydrologic events were analyzed and the index of connectivity (IC) was calculated. The high-frequency runoff and sediment data were analyzed, and a normalized hysteresis index (HI) was calculated to assess the dominant hysteresis patterns for each watershed. Correlation analysis was conducted to determine the relationship between IC and HI. The results showed that the watersheds with low IC values were located in regions with dense vegetation and flat terrain and were dominated mainly by a clockwise hysteresis pattern, while the watersheds with high IC values were located in regions with sparse vegetation and steep terrain and were dominated by an anticlockwise hysteresis pattern. The anticlockwise hysteresis pattern was the most frequent and the most efficient type in terms of sediment transport among the 30 watersheds. The anticlockwise hysteresis type was more likely to occur as the IC values increased. A significant negative correlation was observed between the IC values and HI values during small and medium hydrologic events. The link is correlated with the notion that the separation into two components in connectivity indexes are similar to the two sediment sources controlling the hysteresis type. The outcomes from this study are helpful for determining the relationship between sediment connectivity and hydrologic behavior and thus for providing insight into the hydrologic processes that are essential to facilitate sustainable watershed management. [ABSTRACT FROM AUTHOR]

Deformation and failure of coal is a complex process with damage evolution, so it's important to study the energy mechanism during coal damage process under all kinds of loading conditions. A serial of cyclical loading and unloading tests of coal were conducted under different confining pressures by means of an advanced conventional triaxial compression testing system. The damage process of coal under confining pressure was discussed carefully. Experimental results show that hysteresis loops of coal occurs under cyclical loading and unloading conditions and correspondingly damage dissipation energy increase with increasing stress. Elastic modulus of coal would decrease with increasing cyclical stress under low confining pressure or uniaxial compression, but it would not decrease with increasing cyclical stress under high confining pressure. It indicates that damage mechanism changes due to the effect of confining pressure. So a new definition of coal damage variable was suggested based on energy analysis and the corresponding damage evolution regular was given. Such definition avoids the default of traditional definition of damage variable based on elastic modulus and can well describe the damage content of coal under different confining pressures. [ABSTRACT FROM AUTHOR]

Event-based suspended sediment dynamics (ESSD) provides insights into soil erosion and sediment transport and signals of changing environments within catchments, but it is still poorly understood in the middle Yellow River basin (MYRB). This study focuses on the hysteresis relationship between suspended sediment concentration (SSC) and flow discharge (Q), interpreting the ESSD and its spatial variation. The datasets in the 1960s from 73 hydrologic gauging stations were analyzed as the baseline of the MYRB without experiencing significant climate change and human disturbances. The Q -SSC hysteresis loops were first analyzed in terms of their direction and shape, and the Lloyd et al.'s (2016a) hysteresis index (HI) was adopted to quantify the hysteresis characteristics. Two types of catchments have been identified across the MYRB in terms of the dominant hysteresis pattern and the sign of the HI value. The dominant loops of the Type A catchments are clockwise with positive HI values and located in the southernmost rock mountain regions; Type B appears elsewhere, i.e., in the softstone, aeolian, and loess regions, where most of the events present anticlockwise or complex loops with generally negative HI values. The HI follows an upward-concave parabolic curve with either mean annual precipitation (P m) or vegetation cover (NDVI). Two sets of thresholds are determined as P m or NDVI increases. At P m = 670 mm or NDVI = 0.74, a transition from Type B to Type A occurs as the HI value changes from negative to positive because the vegetation cover is too high to change the catchment from non-limited to limited supply. At P m = 490 mm or NDVI = 0.40, the negative HI value reaches its minimum, suggesting the maximum availability of sediment in Type B due to the change in the dominant factor of soil erosion from precipitation erosivity to erosion resistance of vegetation. This study highlights the overall dynamics of soil erosion and sediment transport in the MYRB, which helps prioritize watershed management measures on the Loess Plateau under a changing environment. • Sediment supply environment is identified across the middle Yellow River basin. • Hysteresis index follows an upward-concave parabola with precipitation or NDVI. • Two sets of thresholds of spatial variations in suspended dynamics are determined. [ABSTRACT FROM AUTHOR]

SUMMARY Hysteresis loop measurements and thermomagnetic experiments were carried out to characterize magnetic mineralogy and magnetic grain size in a suite of particle-size fractioned samples from the Chinese Loess Plateau, representing the main changes in magnetic properties over the last 22 Myr. We find that (1) the ferrimagnets in the detrital fractions (>8 μm) younger than 14 Ma show a magnetite-type Curie temperature, whereas those older than 15 Ma have a Curie temperature slightly over 600 °C owing to low-temperature oxidation. (2) The dominant ferrimagnets in the clay fractions (<2 μm) are most likely to be maghemite. (3) Both the hysteresis plots and thermomagnetic experiments reinforce previous indications from low-temperature experiments that paramagnetic minerals make a major contribution to the clay fractions in all the samples considered. (4) The degree of oxidation indicated by the thermomagnetic curves is highest in the clays and next highest in the oldest coarse fractions. (5) Day plots provide limited and potentially misleading information on the differences between fine-grained pedogenic and coarse-grained detrital ferrimagnetic assemblages, even when allowance is made for the effects of hematite on the quotients used. This study reinforces the view that measurements on bulk samples alone obscure critical distinctions between pedogenic and detrital components. [ABSTRACT FROM AUTHOR]

Abstract: Environmental contamination due to uncontrolled e-waste recycling is an emerging global problem. The aim of this study is to test the applicability of magnetic methods for detecting the metal pollutants emitted from e-waste recycling activities. Dust samples collected from a typical e-waste recycling region in Guiyu, Guangdong Province, China, were investigated using magnetic, geochemical, micro-morphological and mineralogical analysis. The values of mass-specific susceptibility (χ) and saturation isothermal remanent magnetization (SIRM) in dusts from e-waste recycling impacted areas ranged from 101 to 636×10−8 m3 kg−1 and from 10.5 to 85.2×10−3 Am2 kg−1, respectively. There was a significant correlation between SIRM and χ (r2 =0.747, p <0.001), indicating that ferrimagnetic minerals were dominating χ in the dust samples. The values of χfd% varied from 2.6 to 4.6% with a mean of 3.4%, which suggested that magnetic carriers in the dusts are predominately coarse-grained particles. Two shapes of magnetic particles, spherule (10–150μm) and angular-shaped particles (30–300μm), were identified by scanning electron microscope (SEM) and energy dispersive X-ray spectrometer (EDX) analyses. κ-T curves, magnetic hysteresis loops and X-ray diffraction (XRD) analysis indicated that these magnetic particles were magnetite and goethite. There were significant correlations between SIRM and heavy metals (especially Cd, Co, Fe, Ni and Zn) as well as the Tomlinson pollution load index (PLI) of the dust, indicating that SIRM can be used as an efficient proxy for metal pollution in the e-waste recycling impacted area. [Copyright &y& Elsevier]

Sediment dynamics is still imperfectly understood, especially at spatial scale in the highly erodible region of the Loess Plateau, and few studies have been heretofore conducted. Using 5-year continuous water and sediment records, three plots and three basins in the gullied rolling loess region were selected and sediment dynamics at spatial scale was studied. Results showed that the floods, where the peak discharge ( Q) did not come earlier than the sediment peak, were predominant in slope zones, occupying >90 and >70% of the total for the Mao slope and for the Entire slope, respectively. However, in basins, most of the sediment peaks ( C) lagged behind Q, implying that slope zone was the main origin of sediment. More than 50% of the events presented clockwise hysteresis loops in the Mao slope area, while almost all the events had anticlockwise hysteresis loops in basins. This can be attributed to less occurring frequency of hyperconcentrated flow, as well as its instability in slope zones, compared to those in the basins. Within these contexts, gravitational erosion made the highest sediment concentration ( C) in Tuanshangou basin and median developing status of C-discharge ( C- Q) relationships in the Entire slope area. This study provides insights into the protection of slope surface and disruption of the development of hyperconcentrated flow to reduce soil loss. [ABSTRACT FROM AUTHOR]

The article reports on a study which analyzes the variability in suspended sediment load at different temporal scales using a dataset up to eight years long in the Lower Chabagou Creek, on the Loess Plateau in China. Results of the study show that most of the sediment peaks lag behind peak discharges within flood scale. This implies that slope zones are the main sediment source area. At the annual scale, the high variability in concentration and sediment yield are highly correlated with water yield, which results from the number and magnitude of floods.

Subtropical mixed forest ecosystems are experiencing dramatic changes in precipitation and different plant functional types growing here are expected to respond differently. This study aims to unravel the water use patterns of different plant functional types and their responses to environmental changes in a typical subtropical mixed forest in southern China. Diurnal and seasonal sap flux densities of evergreen broad-leaved trees (EBL), deciduous broad-leaved trees (DBL), and conifers (CON), as well as environmental variables, were recorded simultaneously from May 2016 to March 2019. The results showed that the sap flux density of EBL was significantly higher than those of CON and DBL in all seasons, irrespective of dry or wet seasons. Path analysis revealed that seasonal differences in sap flux density were mainly due to variations in photosynthetic photon flux density (PPFD). At saturating PPFD, changes in sap flux density during the day were in response to vapor pressure deficit (VPD). Regression analyses showed that sap flux density increased logarithmically with PPFD, irrespective of functional type. The hysteresis loops of sap flux density and VPD were different among different plant functional types in wet and dry seasons. Our results demonstrated converging response patterns to environmental variables among the three plant functional types considered in this study. Our findings contribute to a better understanding of the water use strategies of different plant functional types in subtropical mixed forests. [ABSTRACT FROM AUTHOR]

Nine as-received core samples were selected from four wells drilled in the lacustrine Kongdian Formation, which is a source rock located in Cangdong Sag, Bohai Bay Basin, China, and their geochemistry and pore structure characteristics were investigated by Rock-Eval pyrolysis, low-pressure nitrogen physisorption (LNP), mercury intrusion porosimetry (MIP), and spontaneous imbibition (SI) tests. Various models were employed to investigate the fractal characteristics of pore systems, and discuss the relationships between pore structure parameters and fractal dimension (D f). The results show that the samples can be divided into two groups (A and B) according to the different types of hysteresis loops from LNP isotherms, as well as geochemistry and pore structure parameters of samples. Negative relationship among BJH (Barrett-Joyner-Halenda) pore volume and S 1 value, and obviously higher average pore diameter of Group B samples with significantly higher S 1 values, indicate a blockage of residual hydrocarbons on small pores. According to the different D f − MIP values from MIP tests, the pore-throats of samples can be divided into four categories of A to D in the following sequence: microscopic (diameters less than 50 nm), small (50 nm-8 μm), medium (8 μm–20 μm) and large (greater than 20 μm) pore-throats/pores. The difference of D f from LNP and MIP tests is probably due to different sample sizes used and pore types assessed, while the difference of D f between MIP and SI tests is attributed to the mixed wettability of pores in shale samples. In addition, from the results of LNP tests with a measurable pore size of 2–200 nm, obvious positive relationships exist between D f − LNP − C (LNP test-derived D f value for Region C) and BJH pore volume, BET (Brunauer-Emmett-Teller) surface area and average pore size, as well as microscopic pore volume and percentage. The D f − LNP − C can be considered as an effective parameter to reflect the degree of development of microscopic pores in samples. • Paleogene-aged Lacustrine Kongdian shale was studied for pore structure characteristics. • Fractal analyses on various laboratory tests were used to link with shale properties. • Two groups of shale were derived from different hysteresis loops of N 2 physisorption. • Four categories of pore-throats were obtained from mercury intrusion porosimetry. [ABSTRACT FROM AUTHOR]

Pore types strongly influence fluid mobility of reservoirs. For a given porosity in different rocks, the movable fluid saturation can differ >30%. Previous studies commonly attribute this phenomenon to the differences in throat but ignore the importance of pore types. An effective method, which integrates nuclear magnetic resonance, LAVFS-SEM and nitrogen gas adsorption experiments, was established to quantitatively investigate the abundance and size distributions of different pore types, and their control on fluid mobility in conglomerates from the Mahu Sag, China. Furthermore, the geological control of intergranular (dissolution) pores (InterG-Ds) is analyzed. The pores characterized by N 2 GA are mainly clay-related pores (CRPs), and the shape of hysteresis loop is related to the type of clay minerals. InterG-Ds are mainly distributed > 1 μm, corresponding to the P3 and P2 in T 2 spectrum. Intragranular dissolution pores range from tens of nanometers to ten micrometers, associated with P2 and P1. CRPs are below 900 nm and associated with P1. The content of InterG-Ds controls fluid mobility of conglomerates. 190 × 10−4mL/g is the lower limit of InterG-D volume, which can judge that the continuous percolation network (CPN) is composed by only InterG-Ds. 45 × 10−4mL/g is the upper limit of the InterG-D volume to determine that the CPN consists of only CRPs. With the decrease of InterG-D volume, both movable fluid porosity and permeability reduce. Good sorting and abundant rigid particles are prerequisites for the development of InterG-Ds. Cementation can significantly reduce InterG-Ds volume, while feldspar dissolution can increase InterG-D volume. [ABSTRACT FROM AUTHOR]

To understand the intricate runoff-sediment relationship in the middle Yellow River basin (MYRB), the Toudaoguai, Longmen, Tongguan and Huayuankou sites in the MYRB were selected to analyze the deterministic equilibrium and uncertainty relations of runoff-sediment based on 55-year hydrological data at multi-time scales. The Johansen test and wavelet neural network were used to verify the cointegration relationship among hydrological series. Runoff-sediment uncertain statistical relations and dynamics in the MYRB were also analyzed based on rating curves and hysteresis loops. The results showed that the logarithmic sequences of sediment load (SL), runoff and suspended sediment concentration (SSC) conformed to a linear cointegration relationship at the Toudaoguai station or in spring, winter or under small flow at other stations, but a nonlinear cointegration relationship was observed in other cases at other stations. Regarding runoff-sediment uncertain relationships, the rating curves, and hysteresis loops differed in stations (Toudaoguai and the other stations), as well as discharge (threshold: 1000 m3/s), season (ice-flood and rainy season) and saturation of flow at flood and monthly scales. At the annual scale, phased and unsynchronized characteristics of runoff and sediment load were evident with a decreasing trend. This study on the runoff-sediment relationship can rationally provide a theoretical basis for the management and development of the Yellow River and other similar rivers with sufficient sediment, especially for areas with serious soil erosion. [ABSTRACT FROM AUTHOR]

• There was a diurnal hysteresis between GPP and CH 4 flux in an alpine meadow. • Similar hysteresis was observed between CH 4 and PAR, and between PAR and Ta. • The hysteresis between CH 4 and GPP attributes to the hysteresis of PAR and Ta. The relationship between methane (CH 4) and gross primary productivity (GPP) remains elusive and the underlying mechanism is even far from clear. To explore this relationship, we continually monitored CH 4 flux and CO 2 flux by eddy covariance technique in an alpine meadow on the Qinghai–Tibetan Plateau, China, during June 2015–December 2017. We found a parabolic-like relationship of net CH 4 flux with GPP change in both the morning and afternoon at diurnal scale. However, with similar GPP, CH 4 uptake was stronger in the morning than that in the afternoon, forming an anti-clockwise hysteretic relationship between CH 4 and GPP in all the three years. Meanwhile, similar hysteresis loop was also observed between CH 4 flux and photosynthetically active radiation (PAR), and between PAR and air temperature (Ta) during all the three years, with stronger CH 4 uptake (or lower Ta) in the morning than that in the afternoon at the same PAR. Results from our study suggested that the hysteretic relationship between CH 4 flux and GPP might be mainly induced by the hysteresis between PAR and Ta. The similar hysteresis pattern between CH 4 flux (or Ta) and PAR in the non-growing season further confirmed our hypothesis. The findings provide new insights into the coupling of plant photosynthetic activity and net CH 4 flux and help to improve model parameterization for simulating CO 2 –CH 4 interaction processes. [ABSTRACT FROM AUTHOR]