Soil organic carbon (SOC) plays an essential role in the carbon cycle and global warming mitigation, and it varies spatially in relation to other soil and environmental properties. But the national distributions and the impact mechanisms of SOC remain debated in China. Therefore, how soil texture and climate factors affect the SOC content and the regional differences in SOC content were explored by analyzing 7857 surface soil samples with different land-use. The results showed that the SOC content in China, with a mean value of 11.20 g·kg−1, increased gradually from north to south. The SOC content of arable land in each geographical area was lower than in grassland and forest-land. Although temperature also played a specific role in the SOC content, precipitation was the most critical climate factor. The SOC content was positively correlated with the silt and clay content. The lower the temperature, the greater the effect of environmental factors on SOC. In contrast, the higher the temperature, the more significant impact of soil texture on SOC. The regional difference in SOC highlights the importance of soil responses to climate change. Temperature and soil texture should be explicitly considered when predicting potential future carbon cycle and sequestration.
The recent hiatus in global warming has attracted significant attention, yet whether it is a widespread global and/or regional phenomenon remains controversial. Here, we investigate the response of extreme temperature changes since 1961 across China’s cold regions (CCR): Tibetan determine the spatiotemporal characteristics of extreme temperature changes across these cold regions using Mann-Kendall and wavelet transform coherence (WTC) analyses of data from 196 meteorological stations from 1961 to 2018. We further investigate the teleconnection between extreme temperatures and large-scale ocean-atmosphere circulation to determine the potential synoptic scale causes of the observed changes. The results revealed a significant warming slowdown in all extreme temperature indices across CCR from 1998 to 2018. In addition, extreme temperature indices in northwest cold region (NWC) and north cold region (NC) reveal a clear winter warming slowdown and even a significant cooling trend, yet only the cold index in Tibetan platean cold region (TPC) shows a warming hiatus. We conclude that the warming hiatus observed across these regions is primarily driven by extreme temperature index changes in winter. We also find that phase variations in the Atlantic Multi-decadal Oscillation (AMO) and Arctic Oscillation (AO) critically impact on the observed warming hiatus, but the specific atmospheric mechanisms are elusive and warrant further analysis and investigation.
The artificial creation of biocrusts can be a rapid and pervasive solution to reduce wind erosion potential (WEP) in dried-up lakes (e.g., Lake Urmia). So, in this study, we created a biocrust by the inoculation of bacteria and cyanobacteria on trays filled by soils collected from the dried-up bed of Lake Urmia, Iran, to reduce WEP in laboratory conditions. We used the wind erodible fraction of soil (EF) and soil crust factor (SCF) equations to calculate the WEP of the treated soils. EF and SCF were decreased (p < 0.05) through applying the co-inoculation of bacteria and cyanobacteria by 5.6% and 10.57%, respectively, as compared to the control; also, the “cyanobacteria alone” inoculation decreased EF by 3.9%. Our results showed that the artificial biocrusts created by soil inoculation, especially with the co-using of bacteria and cyanobacteria, significantly reduced the WEP of a newly dried-up lakebed. Furthermore, we found that inoculation decreased the WEP of the study soil by increasing the soil organic matter content from 3.7 to 5 fold. According to scanning electron microscopy images, the inoculated microorganisms, especially cyanobacteria, improved soil aggregation by their exopolysaccharides and filaments; thus, they can be used with other factors to estimate the soil erodibility in well-developed biocrusts. The inoculation technique could be considered as a rapid strategy in stabilizing lakebeds against wind force. However, it should be confirmed after additional experiments using wind tunnels under natural conditions.
Artificial island-type reclamation often exerts certain impacts on near-shore sandy shoreline resources and coastal ecological landscapes. The relationship between artificial islands and offshore beach evolution has attracted considerable attention in coastal protection and engineering construction. In this study, we consider Hongtang Bay in Hainan Province, China, as the research object. We adopted the Gao-Collins model to investigate the substrate transport trend in this sea area based on the analysis of the measured hydrologic and sediment data. The shore section from Nanshanjiao to Hongtangling (Taling), including the flat and straight shore sections, is dominated by the lateral transport trend of the vertical shore. The near-shore water has a strong lateral sediment transport capacity, while the outer deep-water area exhibits a sediment transport trend consistent with the tidal current movement. Using multi-year topographic data, the shoreline and seabed alterations in Hongtang Bay were analyzed, and the LITLINE beach evolution model was adopted to simulate the effects of three artificial island layouts with different island filling areas, offshore distances, and plan forms on the near-shore shoreline deformation. The results obtained indicate that the artificial island arrangement with a large offshore distance and a small area has relatively substantial advantages, such as minimizing the adverse effects of artificial island implementation on the near-shore beach.
Comprehensive evaluation of the characteristics and mechanisms of droughts is of great significance to drought risk prediction and prevention. The 3-monthly scale Standardized Runoff Index (SRI-3) and 3-monthly scale Standardized Precipitation Evapotranspiration Index (SPEI-3) were employed herein to characterize hydrological and meteorological droughts, respectively, within the four upper subbasins of the Tarim River Basin (TRB) during 1961–2015. The propagation of droughts was also evaluated. The hydrological drought duration (Dd) and drought severity (Ds) were determined by Run theory, and Copula functions were adopted to investigate the hydrological drought probabilities and return periods. The propagation relationships of hydrological and meteorological droughts were assessed. The results indicated that: 1) hydrological drought index (SRI-3) significantly increased in the TRB from 1961 to 2015; the increase was most significant in winter. Meteorological drought index (SPEI-3) exhibited a weak upward trend through time; 2) the characteristics of hydrological droughts varied between the subbasins; increases in the SRI were most significant in the Yarkand and Hotan Rivers, whereas the Dd and Ds of hydrological droughts were higher in the Kaidu and Yarkand Rivers; 3) Frank Copula was the most closely fitted Copula function in the four subbasins of the TRB and yielded average drought return periods of 4.86, 4.78, 3.72, and 5.57 years for the Kaidu, Aksu, Yarkand, and Hotan River Basins, respectively. The return periods in the four subbasins were generally less than 10 years from 1961 to 2015; 4) a cross wavelet transform (XWT) exhibited a significant positive correlation between hydrological and meteorological droughts, except for the Yarkand River Basin, which exhibited a significant negative correlation. Besides, the propagation relationship of meteorological droughts to hydrological droughts showed remarkable seasonal variations.
The adverse environmental effects of mine tailings disposal on the surrounding ecosystems are worldwide environmental problems. Due to environmental issues related to tailings discharged on land surface, detailed tailings characterization is a prerequisite for a long-term management solution. The tailings from four gold mines in Egypt, namely Fatira, El Sid, Barramiya, and Atud were investigated for their geochemical-mineralogical features and the effect of weathering behavior on the release of their heavy elements. The tailings samples were investigated by mineralogical (XRD and ESEM-EDS), physical (grain-size distribution) and geochemical (XRF) techniques. Most of the tailings have uniform silt-size with fine to very finesand and clay. Atud tailings have coarse to fine sands. High carbonate, predominantly calcite was found for the samples from Fatira and Atud, calcite-ankerite from El Sid and dolomite from Barramiya with little sulfide-content. High-mean of Cr (569287 mg/kg), Ni (89191 mg/kg) and Co (4221 mg/kg) values are coinciding with the ultramafic nature in Atud and Barramiya tailings. El Sid tailings have a high-mean concentration of Zn (1357 mg/kg) and Pb (1349 mg/kg). Barramiya tailings have a high-mean As concentration (2635 mg/kg). The Fatira tailings are characterized by high-mean values of Sr (444 mg/kg) and Cu (280 mg/kg) arising from auriferous mineralization. High Sr concentrations in Fatira tailings are mainly due to its adsorption to iron oxides. Pyrite oxidation is conceded along the cracks and/or the edges of the crystals in the El Sid, Barramiya and Atud tailings. The Threshold Effect Level (TEL) values indicated high contamination from heavy elements to the neighboring ecosystem. The tailings were deposited downstream into the small wadis. Wind and water erosion can dissolve efflorescent materials enriched in toxic elements like As, Zn, and Pb at tailings surface. The release of contaminants could be catastrophic for the environment without mine site rehabilitation strategies.
The pore structures of coal can directly affect the adsorption and seepage capacity of coalbed methane (CBM), which therefore is an important influence on CBM exploration and development. In this study, the pore structures of low-rank coals from the Middle Jurassic Xishanyao Formation in the southern Junggar Basin were analyzed, and the fractal dimensions (D1, D2, D3 and D4 corresponding to pore sizes of 0−5 nm, 5−100 nm, 100−1000 nm and 1000−20000 nm, respectively) were calculated to quantitatively describe these coal pore structures. The results show that Xishanyao coal is characterized by open pore morphology, good pore connectivity and well-developed seepage pores and microfractures, which is beneficial to CBM seepage. The D1 and D2 can be used to characterize the pore surface and structure of adsorption pores respectively. The D3 and D4 can be used to represent the pore structure of seepage pores. Compared with adsorption pores, the structure of seepage pores is more affected by the change of coal rank. The D1 is better than D2 in characterizing the methane adsorption capacity. When D1 > 2.2, D1 is positively correlated with Langmuir volume (VL) and negatively correlated with Langmuir pressure (PL), while D2 shows a weak opposite trend. The coals with the higher D1 and lower D2 are associated with a higher VL, indicating the coal reservoir with more complex pore surfaces and simpler pore structures has stronger methane adsorption capacity. D4 is better than D3 in characterizing the methane seepage capacity. The porosity and permeability of coal reservoirs increases with the increase of D4, while D3 displays an opposite trend, which is mainly related to the well-developed microfractures. The well-developed fracture system enhances the seepage capacity of the Xishanyao coal reservoir. This study reveals the fractal characteristics of pore structure and its significant influence on adsorption and seepage capacity of low-rank coal.
Investigating the impacts of climate and land use changes on the hydrological cycle and water environment at the basin scale is important for providing scientific evidence to manage the trade-offs and synergies among water resources, agricultural production and environmental protection. We used the Soil and Water Assessment Tool (SWAT) with various spatiotemporal data to quantify the contributions of climate and land use changes to runoff, sediment, nitrogen (N) and phosphorus (P) losses in the Haihe River Basin since the 1980s. The results showed that 1) climate and land use changes significantly increased evapotranspiration (ET), transport loss, sediment input and output, and organic N and P production, with ET, sediment input and organic N affected the most; 2) runoff, sediment and ammonia N were most affected by climate and land use changes in the Daqing River Basin (217.3 mm), Nanyun River Basin (3917.3 tons) and Chaobai River Basin (87.6 kg/ha), respectively; 3) the impacts of climate and land use changes showed explicit spatiotemporal patterns. In the Daqing, Yongding and Nanyun River Basins, the contribution of climate change to runoff and sediment kept increasing, reaching 88.6%–98.2% and 63%–77.2%, respectively. In the Ziya and Chaobai River Basins, the contribution of land use was larger, reaching 88.6%–92.8% and 59.8%–92.7%, respectively. In the Yongding, Chaobai, Ziya and Daqing River Basins, the contribution of land use to N and P losses showed an increasing trend over the past 40 years (maximum 89.7%). By contrast, in Nanyun and Luanhe River Basins, the contribution of climate change to N and P losses increased more (maximum 92.1%). Our evaluation of the impacts of climate and land use changes on runoff, sediment, and N and P losses will help to support the optimization of land and water resources in the Haihe River Basin.
The Chezhen Sag, located in the north-western Jiyang Depression, is one of the most important oil-bearing sags in the Bohai Bay Basin. Due to the low degree of exploration in the sag, paleosalinity and sedimentary environment of the sag in the 3rd Member of Paleogene Shahejie Formation (Es3) is not clear. Recovering the paleosalinity and lake level fluctuations is helpful for understanding organic matter rich rocks sedimentation. Therefore, a detailed geochemical, mineralogical and paleontological analysis of the Es3 in the Chezhen Sag was conducted. Index like Sr/Ba ratios, B/Ga ratios, equivalent boron content and methods concluding Adams’ formula and Couch’s method were adopted to reveal the paleosalinity and lake level variations. The results indicate that the lower submember (Lower Es3) was deposited in a salt water with high salinity, accompanied by dry climate and transgression event. The middle submember (Middle Es3) and upper submember (Upper Es3) record a freshwater to brackish environment. The paleosalinity and paleoclimate changes are consistent with the global sea level variations. The type and content of sporopollen indicate a dry climate in Lower Es3, which further confirms the reliability of the reconstruction results of paleosalinity. Combined with the paleoclimate and previous marine paleontological evidence, we proposed that the high salinity period is associated with a high lake level and a large-scale transgression event in Lower Es3. According to salinities and corresponding Lake depths, we established a sedimentary environment variation model of the Es3 Member in Chezhen Sag.
The stress and temperature sensitivities of coal reservoirs are critical geological factors affecting coalbed methane (CBM) well exploitation; in particular it is important to reduce or eliminate their influence on coal reservoir permeability. To investigate coal permeability behavior at various effective stresses and temperatures, CH4 permeability tests were conducted on raw coal samples under a varying effective stress of 2.0–8.0 MPa under five different temperatures (25°C–65°C) in the laboratory. The results show that the permeability of the coal samples exponentially decreases with increasing effective stress or temperature, which indicates obvious stress and temperature sensitivity. Through a dimensionless treatment of coal permeability, effective stress, and temperature, a new stress sensitivity index S and temperature index ST are proposed to evaluate coal stress and temperature sensitivity evaluation parameters. These new parameters exhibit integrality and uniqueness, and, in combination with stress sensitivity coefficient αk, temperature sensitivity coefficient αT, and the permeability damage rate PDR, the sensitivities of coal permeability to stress and temperature are evaluated. The results indicate that coal sample stress sensitivity decreases with increasing effective stress, while it first decreases and then increases with increasing temperature. Additionally, coal sample temperature sensitivity shows a downward trend when temperature increases and fluctuates when effective stress increases. Finally, a coupled coal permeability model considering the impacts of effective stress and temperature is established, and the main factors affecting coal reservoir permeability and their control mechanism are explored. These results can provide some theoretical guidance for the further development of deep CBM.
Bedding-parallel fractures are fractures that are parallel to rock bedding structure planes and have been widely accepted as a key factor for oil and gas production in tight sandstone and shale reservoirs. However, the formation mechanisms of these parallel-bedding fractures are still under debate. In this study, bedding-parallel fractures in Yongjin Oil Field were analyzed using methods including core and microscopic observations, element geochemistry, and carbon and oxygen isotope analysis. Their origin and relations to reservoir quality, faults, and rock mechanical properties were examined. The discovery of bedding-parallel fractures in both the Upper Jurassic and Lower Cretaceous formations indicates that the BPFs are generated later than the early Cretaceous. The filling state of bedding-parallel fractures that with no bitumen and carbonate cement indicate that they formed after oil charging and carbonate cementation. The tensile fracture characteristics in core and thin section observations, and the fact that overburden stress exceeds the pore pressure indicate that the bedding-parallel fractures were neither generated from tectonic compression nor overpressure. The most likely generation mechanism is stress relief during core drilling under high in situ stress conditions. High in situ stress and low tensile strength lead to thinner fracture spacing. The existence of high bedding-parallel fracture density is an indicator of good reservoir quality and result in high oil/gas production.
A series of Cenozoic potassium-rich volcanic rocks developed in the Xiaoguli-Keluo-Wudalianchi-Erkeshan districts, northeast China. The source region and potassium-rich mechanism of the potassic rocks remain highly disputed. In this paper, the major elements, trace elements, and Sr-Nd-Pb isotopes of the volcanic rocks in Keluo (KL) and Wudalianchi (WDLC) volcanic districts were analyzed systematically. The results show that the volcanic rocks are characterized by high K2O (4.36wt.%−6.13wt.%), remarkable enrichment in LREEs and LILEs, as well as the strong fractionation of HREEs. The isotopic characteristics with high 87Sr/86Sr (0.704990–0.705272), low 143Nd/144Nd (0.512306–0.512417), low 206Pb/204Pb (16.546–17.135) and 207Pb/204Pb (15.002–15.783) of the volcanic rocks suggest the involvement of EM-I-type mantle. On the basis of the geochemical characteristics, the potassium-rich volcanic magma originated from the new SCLM forming after delamination of the ancient SCLM, with metasomatism of the potassium-rich fluids released from the ancient lower crust during the Late Mesozoic. The proposed genetic model assumes the source which represented by a phlogopite-bearing garnet peridotite (with modal garnet in the range of 2%–10%) experienced very low degrees (i.e., ~0.5) of partial melting. During Cenozoic, the lithosphere in northeast China was affected by the extension and decompression of continental rift, and the metasomatized SCLM underwent low degree partial melting, resulting in the formation of potassium-rich primitive basaltic magma.
A recent version of the Polar Weather Research and Forecasting model (Polar WRF) has been upgraded to the version 4.X era with an improved NoahMP Land Surface Model (LSM). To assess the model performance over the Antarctic and Southern Ocean, downscaling simulations with different LSM (NoahMP, Noah), WRF versions (Polar WRF 4.1.1 and earlier version 4.0.3, WRF 4.1.1), and driving data (ERA-Interim, ERA5) are examined with two simulation modes: the short-term that consists of a series of 48 h segments initialized daily at 0000 UTC with the first 24 h selected for model spin-up, whereas the long-term component used to evaluate long-term prediction consists of a series of 38−41 day segments initialized using the first 10 days for spin-up of the hydrological cycle and planetary boundary layer structure. Simulations using short-term mode driven by ERA-Interim with NoahMP and Noah are selected for benchmark experiments. The results show that Polar WRF 4.1.1 has good skills over the Antarctic and Southern Ocean and better performance than earlier simulations. The reduced downward shortwave radiation bias released with WRF 4.1.1 performed well with PWRF411. Although NoahMP and Noah led to very similar conclusions, NoahMP is slightly better than Noah, particularly for the 2 m temperature and surface radiation because the minimum albedo is set at 0.8 over the ice sheet. Moreover, a suitable nudging setting plays an important role in long-term forecasts, such as reducing the surface temperature diurnal cycle near the coast. The characteristics investigated in this study provide a benchmark to improve the model and guidance for further application of Polar WRF in the Antarctic.
Based on the 16 historical tropical cyclones (TCs) affecting Shanghai from 2007 to 2019, the suitability of ERA5 for studying TCs affecting Shanghai is systematically evaluated from the perspective of TC track, intensity, 10-m and upper-level wind, using TC best-track data of China Meteorological Administration and surface observations and sounding data. Corresponding to tropical storm (TS), strong tropical storm (STS), typhoon (TY), strong typhoon (STY) and super typhoon (SuperTY), the median TC track bias is 68.1, 52.9, 42.5, 25.4, and 18.2 km, respectively, the median maximum 10-m wind speed (VMAX10m) bias is –3.7, –6.5, –11.4, –21.7, and –32.2 m·s–1, respectively, and the median minimum mean sea level pressure (MSLPmin) bias is 2.2, 5.6, 8.1, 28.2, and 48.7 hPa, respectively. With the increase of TC intensity, the median TC track bias decreases, while the median VMAX10m and MSLPmin bias increase. In general, VMAX10m in ERA5 is lower than observed, and MSLPmin is larger than observed. Under influence of TS, STS, TY and STY, the median 10-m wind speed (V10m) bias in the city is 3.2, 4.2, 4.7, and 5.4 m·s–1, respectively, and is 4.4–5.2 m·s–1 near the east coast, respectively. V10m is mostly biased high, showing an “M” type pattern with the distance between TC and Shanghai. The median 10 m wind direction (WD10m) bias is in a range of –7º to +7º. The median upper-level wind speed (Vupper) bias decreases with height, with a maximum of ~5 m·s–1 at 975 hPa. Below 900 hPa Vupper in ERA5 is typically larger than the radiosonde observation, and its mean bias error (MBE) increases with TC intensity. The upper-level wind direction (WDupper) matches the sounding data well, with a maximum bias of a few degrees only. The results provide a reference for the application of ERA5 to coastal cities affected by TCs.
Developed regions in China have experienced rapid urban expansion and have consequently induced a series of challenging environmental issues since its economic reform and opening-up. Taking Zhejiang as a case study area, the present paper explores the complex types of urban growth over the last four decades as well as land use efficiency. Moreover, it discusses the implications of the aforementioned on China National territorial spatial planning (TSP). The acquired results have shown that: 1) urban expansion has slowed down, exhibiting a three-stage trend of “slight increase (1980−1990)—dramatic growth (1990−2010)—slow growth (after 2010)”; 2) the complex types of urban growth reveal that the urban diffusion has been gradually controlled and the urban form tends to be more condensed; and 3) the mean values for pure technical efficiency (PTE) and scale efficiency (SE) of urban land use are 0.83 and 0.95 respectively, indicating PTE as the main factor restricting the improvement of urban land use. Based on these results, some beneficial policy implications and suggestions for TSP are provided. First, it is suggested that “Inventory Planning” will be the main direction of TSP other than “Incremental Planning”. Secondly, we should pay more attention to the protection of cultivated land and ecological resources. Lastly, TSP should guide the economic growth away from simply relying on resource inputs and steer it toward technology and capital investment.
The three-dimensional Weather Research and Forecasting (WRF) model was used to conduct sensitivity experiments during the landfall of Typhoon Fitow (2013) to examine the impacts of cloud radiative processes on thermal balance. The vertical profiles of heat budgets, vertical velocity, and stability were analyzed to examine the physical processes responsible for cloud radiative effects on surface rainfall for Typhoon Fitow (2013). The inclusion of clouds reduced radiative cooling in ice and liquid cloud layers by reducing outgoing radiation. The suppressed radiative cooling reduced from the ice cloud layers to liquid cloud layers. This was conducive to reducing instability. The decreased instability was associated with the reduced upward motions. The reduced upward motion led to a decreased vertical mass convergence. Consequently, heat divergence was weakened to warm the atmosphere. Together with suppressed radiative cooling, these effects jointly suppressed net condensation and rainfall. Furthermore, the reduced rainfall due to the cloud radiative effects were mainly associated with the reduced convective and stratiform rainfall. The reduced convective rainfall was associated with the reduced net condensation, while the reduced stratiform rainfall was related to the constraint of hydrometeor convergence.
Realizing accurate perception of urban boundary changes is conducive to the formulation of regional development planning and researches of urban sustainable development. In this paper, an improved fully convolution neural network was provided for perceiving large-scale urban change, by modifying network structure and updating network strategy to extract richer feature information, and to meet the requirement of urban construction land extraction under the background of large-scale low-resolution image. This paper takes the Yangtze River Economic Belt of China as an empirical object to verify the practicability of the network, the results show the extraction results of the improved fully convolutional neural network model reached a precision of kappa coefficient of 0.88, which is better than traditional fully convolutional neural networks, it performs well in the construction land extraction at the scale of small and medium-sized cities.