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Frontiers of Earth Science

, Volume 11 Issue 2

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Simple statistical models for relating river discharge with precipitation and air temperature—Case study of River Vouga (Portugal)
Front. Earth Sci.. 2017, 11 (2): 203-213.
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Simple statistical models were developed to relate available meteorological data with daily river discharge (RD) for rivers not influenced by melting of ice and snow. In a case study of the Vouga River (Portugal), the RD could be determined by a linear combination of the recent (PR) and non-recent (PNR) atmospheric precipitation history. It was found that a simple linear model including only PR and PNR cannot account for low RD. The model was improved by including non-linear terms of precipitation that accounted for the water loss. Additional improvement of the models was possible by including average monthly air temperature (T). The best model was robust when up to 60% of the original data were randomly removed. The advantage is the simplicity of the models, which take into account only PR, PNR and T. These models can provide a useful tool for RD estimation from current meteorological data.

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GIS model for identifying urban areas vulnerable to noise pollution: case study
Front. Earth Sci.. 2017, 11 (2): 214-228.
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The unprecedented expansion of the national car ownership over the last few years has been determined by economic growth and the need for the population and economic agents to reduce travel time in progressively expanding large urban centres. This has led to an increase in the level of road noise and a stronger impact on the quality of the environment. Noise pollution generated by means of transport represents one of the most important types of pollution with negative effects on a population’s health in large urban areas. As a consequence, tolerable limits of sound intensity for the comfort of inhabitants have been determined worldwide and the generation of sound maps has been made compulsory in order to identify the vulnerable zones and to make recommendations how to decrease the negative impact on humans. In this context, the present study aims at presenting a GIS spatial analysis model-based methodology for identifying and mapping zones vulnerable to noise pollution. The developed GIS model is based on the analysis of all the components influencing sound propagation, represented as vector databases (points of sound intensity measurements, buildings, lands use, transport infrastructure), raster databases (DEM), and numerical databases (wind direction and speed, sound intensity). Secondly, the hourly changes (for representative hours) were analysed to identify the hotspots characterised by major traffic flows specific to rush hours. The validated results of the model are represented by GIS databases and useful maps for the local public administration to use as a source of information and in the process of making decisions.

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Mapping flood and flooding potential indices: a methodological approach to identifying areas susceptible to flood and flooding risk. Case study: the Prahova catchment (Romania)
Front. Earth Sci.. 2017, 11 (2): 229-247.
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Given that floods continue to cause yearly significant worldwide human and material damages, flood risk mitigation is a key issue and a permanent challenge in developing policies and strategies at various spatial scales. Therefore, a basic phase is elaborating hazard and flood risk maps, documents which are an essential support for flood risk management. The aim of this paper is to develop an approach that allows for the identification of flash-flood and flood-prone susceptible areas based on computing and mapping of two indices: FFPI (Flash-Flood Potential Index) and FPI (Flooding Potential Index). These indices are obtained by integrating in a GIS environment several geographical variables which control runoff (in the case of the FFPI) and favour flooding (in the case of the FPI). The methodology was applied in the upper (mountainous) and middle (hilly) catchment of the Prahova River, a densely populated and socioeconomically well-developed area which has been affected repeatedly by water-related hazards over the past decades. The resulting maps showing the spatialization of the FFPI and FPI allow for the identification of areas with high susceptibility to flash-floods and flooding. This approach can provide useful mapped information, especially for areas (generally large) where there are no flood/hazard risk maps. Moreover, the FFPI and FPI maps can constitute a preliminary step for flood risk and vulnerability assessment.

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Passive Super-Low Frequency electromagnetic prospecting technique
Nan WANG, Shanshan ZHAO, Jian HUI, Qiming QIN
Front. Earth Sci.. 2017, 11 (2): 248-267.
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The Super-Low Frequency (SLF) electromagnetic prospecting technique, adopted as a non-imaging remote sensing tool for depth sounding, is systematically proposed for subsurface geological survey. In this paper, we propose and theoretically illustrate natural source magnetic amplitudes as SLF responses for the first step. In order to directly calculate multi-dimensional theoretical SLF responses, modeling algorithms were developed and evaluated using the finite difference method. The theoretical results of three-dimensional (3-D) models show that the average normalized SLF magnetic amplitude responses were numerically stable and appropriate for practical interpretation. To explore the depth resolution, three-layer models were configured. The modeling results prove that the SLF technique is more sensitive to conductive objective layers than high resistive ones, with the SLF responses of conductive objective layers obviously showing uprising amplitudes in the low frequency range. Afterwards, we proposed an improved Frequency-Depth transformation based on Bostick inversion to realize the depth sounding by empirically adjusting two parameters. The SLF technique has already been successfully applied in geothermal exploration and coalbed methane (CBM) reservoir interpretation, which demonstrates that the proposed methodology is effective in revealing low resistive distributions. Furthermore, it siginificantly contributes to reservoir identification with electromagnetic radiation anomaly extraction. Meanwhile, the SLF interpretation results are in accordance with dynamic production status of CBM reservoirs, which means it could provide an economical, convenient and promising method for exploring and monitoring subsurface geo-objects.

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Impact of dams on flood occurrence of selected rivers in the United States
Xuefei MEI, P.H.A.J.M. VAN GELDER, Zhijun DAI, Zhenghong TANG
Front. Earth Sci.. 2017, 11 (2): 268-282.
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A significant large number of dams have been constructed in the past two centuries in the United States. These dams’ ability to regulate downstream flooding has received world-wide attention. In this study, data from 38 rivers distributed over the entire conterminous Untied States with extensive pre- and post-dam annual peak discharge records, were collected to research the impacts of various dams on the flood behaviors at a national scale. The results indicate that dams have led to significant reductions in flood magnitude for nearly all of the sites; the decrease rate in the mean of annual peak discharge varies between 7.4% and 95.14%, except for the Dead River, which increased by 1.46%. Because of dams’ effectiveness, the probability density curve of annual peak flow changes from a flat to peaked shape because both the range and magnitude of high discharges are decreased. Moreover, the potential impact of dams on flood characteristics were closely related to the dam’s geographic location and function, the ratio of the storage capacity of the dam to the mean annual runoff of the river (C/R), and the ratio of reservoir storage capacity to the area of its drainage (C/D). Specifically, the effects of dams on annual peak flows were more related to latitude than longitude. Compared with dams built for other purposes, the dam exclusively used for flood management cut off more flood peaks. Increases in the ratios of C/R and C/D increased the degree of modification of annual maximum discharge.

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Distribution, sources, and risk assessment of polychlorinated biphenyls in surface waters and sediments of rivers in Shanghai, China
Xueping WANG, Jingchao HAN, Chunjuan BI, Xing HUANG, Jinpu JIA, Zhenlou CHEN
Front. Earth Sci.. 2017, 11 (2): 283-296.
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The distribution, sources, and potential risks of polychlorinated biphenyl (PCB) contamination in the rivers of Shanghai, China were investigated. Fourteen PCB congeners in surface waters and sediments, which were collected from 53 sampling sites, were quantified by gas chromatography-mass spectrometer (GC-MS). The total concentrations of PCBs in the dissolved phase, in particulates, and in sediments ranged from not detected (nd) to 34.8 ng·L−1, from 0.76 to 39.71 ng·L−1, and from 1.46 to 46.11 ng·g−1 (dry weight, dw), respectively. The corresponding WHO toxic equivalents (TEQs) of dioxin-like polychlorinated biphenyl s (dl-PCBs) ranged between nd–1135.63 pg TEQ·L−1, 0.02–605.94 pg TEQ·L−1, and 0.05–432.12 pg TEQ·g−1 dw, respectively. The penta-CBs, especially PCB 118 and PCB 105, were the dominant congeners in all samples. Principle Component Analysis (PCA) indicated that the PCBs were mainly influenced by a historical accumulation of commercial PCB products, the burning of house coal, and emissions from municipal solid waste incineration (MSWI) and secondary metallurgy industries. The center of Shanghai was significantly affected by PCB contamination, followed by the industrial parklands and suburban towns, while the farmland of Chongming Island was the least affected area. Adverse biological and health effects would be likely in the central urban areas, industrial parks, and residential towns of Shanghai.

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Patterns of coccolithophore pigment change under global acidification conditions based on in-situobservations at BATS site between July 1990–Dec 2008
Jianhai LV, Yaoqiu KUANG, Hui ZHAO, Andreas ANDERSSON
Front. Earth Sci.. 2017, 11 (2): 297-307.
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Coccolith production is an important part of the biogenic carbon cycle as the largest source of calcium carbonate on earth, accounting for about 75% of the deposition of carbon on the sea floor. Recent studies based on laboratory experiment results indicated that increasing anthropogenic CO2 in the atmosphere triggered global ocean acidification leading to a decrease of calcite or aragonite saturation and calcium carbonate, and to decreasing efficiency of carbon export/pumping to deep layers. In the present study, we analyzed about 20?years of field observations of coccolithophore pigment, dissolved inorganic carbon (DIC), nutrients, and temperatures from the Bermuda Atlantic Time-series Study (BATS) site and satellite remote sensing to investigate the variable tendency of the coccolithophore pigment, and to evaluate the influence of ocean acidification on coccolithophore biomass. The results indicated that there was a generally increasing tendency of coccolithophore pigment, coupled with increasing bicarbonate concentrations or decreasing carbonate ion concentration. The change of coccolithophore pigment was also closely associated with pH, nutrients, mixed layer depth (MLD), and temperature. Correlation analyses between coccolithophores and abiotic parameter imply that coccoliths production or coccolithophore pigment has increased with increasing acidification in the recent 20 y ears.

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Losses of Ecosystem Service Values in the Taihu Lake Basin from 1979 to 2010
Hui ZHANG, Qiao WANG, Guangyu LI, Hanpei ZHANG, Jue ZHANG
Front. Earth Sci.. 2017, 11 (2): 310-320.
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The Taihu Lake Basin, an east-coastal developed area, is one of the fastest-growing metropolitan areas in China. Ecosystem services in the Taihu Lake Basin have been overexploited and jeopardized. Based on land-use and land-cover change (LUCC) data from 1979, 1984, 2000, and 2010, in conjunction with the adjusted ecosystem service values (ESV), changes in ESV were analyzed in detail. Results revealed that LUCC resulted in a substantial decrease in total ESV from $3.92 billion in 1979 to $2.98 billion in 2010. The ESV of cropland decreased from $1.64 billion in 1979 to $1.34 billion in 2010, which represented a 20.28% reduction. The ESV of water areas decreased from $1.08 billion in 1979 to $0.36 billion in 2010, which represented a 65.62% reduction mainly because of a decline in water quality. In terms of annual change rate, cropland and water areas showed a sustained downward trend. Spatially, ESV declines were mainly observed in Suzhou, Wuxi, Changzhou, and Shanghai, probably due to a combination of economic progress, population growth, and rapid urbanization. The research results can be a useful reference for policymakers in mitigating ESV decline.

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Development of defoliating insects and their preferences for host plants under varying temperatures in a subtropical evergreen forest in eastern China
Jun JING, Lingdan XIA, Kai LI
Front. Earth Sci.. 2017, 11 (2): 321-331.
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The aim of this work was to understand the development of defoliating insects and their preferences for host plants under varying temperatures in a subtropical evergreen broad-leaved forest in China. We measured the main developmental parameters of three typical defoliating insects (i.e., Ourapteryx ebuleata szechuana, Biston marginata, and Euproctis angulata) and their preferences for five host plants at temperatures from 16°C to 31°C at 3°C intervals in the Tiantong National Forest Research station in eastern China. The results showed the following. 1) An appropriate rise in temperature increases the survival rate with an increase in the number of offspring. The developmental durations for these three insects were shortened, and pupal weight increased with an increase in temperature. 2) A shift in the preference for host plants for these three insects was observedat elevated temperatures. They all preferred to feed on Schima superba and Castanopsis sclerophylla at elevated temperatures, showing an opposite response to the other three plants. The daily leaf consumption of the three insects was positively correlated with their feeding preference, with more leaves being consumed from the plants they preferred. 3) For O. ebuleata szechuana larvae, daily leaf consumption initially increased and then decreased with increasing temperatures. In contrast, Biston marginata and Euproctis angulata larvae consumed more leaves at elevated temperatures. The feeding preferences of O. ebuleata szechuana and Biston marginata were more sensitive to changing temperatures than that of Euproctis angulata laevae. We concluded that increased numbers of offspring and generations, pupal weights, and a shift in preference to two plants for these three defoliating insects might lead to severe damage to these two plants which would enhance the fragmentation and decrease the stability of the forest communities under changing temperatures. Meanwhile, the variations in the responses of defoliating insects to the changing temperatures should be taken into consideration for the pest management of forests to adapt to the changing climate.

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Tide- and wind-driven variability of water level in Sansha Bay, Fujian, China
Hongyang LIN, Jianyu HU, Jia ZHU, Peng CHENG, Zhaozhang CHEN, Zhenyu SUN, Dewen CHEN
Front. Earth Sci.. 2017, 11 (2): 332-346.
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This study analyzes water-level variability in Sansha Bay and its adjacent waters near Fujian, China, using water-level data observed from seven stations along the coast and wind data observed from a moored buoy near Mazu Island. At super- to near-inertial frequencies, tides dominated the water-level variations, mainly characterized by semi-diurnal (primarily M2, S2, and N2) and diurnal tides (primarily K1, O1). The correlation coefficients between residual (non-tidal) water-level time series and the observed wind-stress time series exceeded 0.78 at all stations, hinting that the wind acting on the study region was another factor modulating the water-level variability. A cross-wavelet and wavelet-coherence analysis further indicated that (i) the residual water level at each station was more coherent and out-of-phase with the alongshore winds mostly at sub-inertial time scales associated with synoptic weather changes; and (ii) the residual water-level difference between the outer and inner bay was more coherent with the cross-shore winds at discrete narrow frequency bands, with the wind leading by a certain phase. The analysis also implied that the monsoon relaxation period was more favorable for the formation of the land-sea breeze, modulating the residual water-level difference.

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Prediction of vertical PM2.5 concentrations alongside an elevated expressway by using the neural network hybrid model and generalized additive model
Ya GAO, Zhanyong WANG, Qing-Chang LU, Chao LIU, Zhong-Ren PENG, Yue YU
Front. Earth Sci.. 2017, 11 (2): 347-360.
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A study on vertical variation of PM2.5 concentrations was carried out in this paper. Field measurements were conducted at eight different floor heights outside a building alongside a typical elevated expressway in downtown Shanghai, China. Results show that PM2.5 concentration decreases significantly with the increase of height from the 3rd to 7th floor or the 8th to 15th floor, and increases suddenly from the 7th to 8th floor which is the same height as the elevated expressway. A non-parametric test indicates that the data of PM2.5 concentration is statistically different under the 7th floor and above the 8th floor at the 5% significance level. To investigate the relationships between PM2.5 concentration and influencing factors, the Pearson correlation analysis was performed and the results indicate that both traffic and meteorological factors have crucial impacts on the variation of PM2.5 concentration, but there is a rather large variation in correlation coefficients under the 7th floor and above the 8th floor. Furthermore, the back propagation neural network based on principal component analysis (PCA-BPNN), as well as generalized additive model (GAM), was applied to predict the vertical PM2.5 concentration and examined with the field measurement dataset. Experimental results indicated that both models can obtain accurate predictions, while PCA-BPNN model provides more reliable and accurate predictions as it can reduce the complexity and eliminate data co-linearity. These findings reveal the vertical distribution of PM2.5 concentration and the potential of the proposed model to be applicable to predict the vertical trends of air pollution in similar situations.

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Measuring the past 20 years of urban-rural land growth in flood-prone areas in the developed Taihu Lake watershed, China
Weizhong SU
Front. Earth Sci.. 2017, 11 (2): 361-371.
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There is growing interest in using the urban landscape for stormwater management studies, where land patterns and processes can be important controls for the sustainability of urban development and planning. This paper proposes an original index of Major Hazard Oriented Level (MHOL) and investigates the structure distribution, driving factors, and controlling suggestions of urban-rural land growth in flood-prone areas in the Taihu Lake watershed, China. The MHOL of incremental urban-rural land increased from M 31.51 during the years 1985–1995 to M 38.37 during the years 1995–2010 (M for medium structure distribution, and the number for high-hazard value). The index shows that urban-rural land was distributed uniformly in flood hazard levels and tended to move rapidly to high-hazard areas, where 72.68% of incremental urban-rural land was aggregated maximally in new urban districts along the Huning traffic line and the Yangtze River. Thus, the current accelerating growth of new urban districts could account for the ampliative exposure to high-hazard areas. New districts are driven by the powerful link between land financial benefits and political achievements for local governments and the past unsustainable process of “single objective” oriented planning. The correlation categorical analysis of the current development intensity and carrying capacity of hydrological ecosystems for sub-basins was used to determine four types of development areas and provide decision makers with indications on the future watershed-scale subdivision of Major Function Oriented Zoning implemented by the Chinese government.

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Economic structure and environmental quality and their impact on changing land use efficiency in China
Chong PENG, Hao XIAO, Yu LIU, Jingjing ZHANG
Front. Earth Sci.. 2017, 11 (2): 372-384.
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Extensive urban land expansion and heavy industrialization have increased energy consumption and caused environmental problems, both of which present serious threats to humans. Consequently, improved land use efficiency and realization of green development are imperative. Based on a detailed analysis of spatial-temporal evolution of urban land use efficiency, this paper analyzes the synergistic effect of industrial structure and city size, as well as the effect of environmental quality, by using panel data from 283 cities at or above prefecture-level in China from 2003 to 2012. It was concluded that 1) environmental quality has an obvious “crowding out effect” on urban land use efficiency and 2) urban land use efficiency shows a significant spatial auto-correlation. The effect of industrial structure is dependent on population size of the city. It has been found that a threshold population size of more than 108.45 (10,000 persons) is needed for an optimized benefit from industrial linkages. The urban population size presents an inverted-U shape against the urban land use efficiency, and the marginal benefit of urban size increases when the industrial structure shifts from secondary industry to tertiary industry. Additionally we found that the actual urban size of 98.2% is less than the cities’ optimal sizes.

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Geomorphic change in Dingzi Bay, East China since the 1950s: impacts of human activity and fluvial input
Qing TIAN, Qing WANG, Yalong LIU
Front. Earth Sci.. 2017, 11 (2): 385-396.
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This study examines the geomorphic evolution of Dingzi Bay, East China in response to human activity and variations in fluvial input since the 1950s. The analysis is based on data from multiple mathematical methods, along with information obtained from Remote Sensing, Geographic Information System and Global Position System technology. The results show that the annual runoff and sediment load discharged into Dingzi Bay display significant decreasing trends overall, and marked downward steps were observed in 1966 and 1980. Around 60%–80% of the decline is attributed to decreasing precipitation in the Wulong River Basin. The landform types in Dingzi Bay have changed significantly since the 1950s, especially over the period between 1981 and 1995. Large areas of tidal flats, swamp, salt fields, and paddy fields have been reclaimed, and aquaculture ponds have been constructed. Consequently, the patterns of erosion and deposition in the bay have changed substantially. Despite a reduction in sediment input of 65.68% after 1966, low rates of sediment deposition continued in the bay. However, deposition rates changed significantly after 1981 owing to large-scale development in the bay, with a net depositional area approximately 10 times larger than that during 1961–1981. This geomorphic evolution stabilized following the termination of large-scale human activity in the bay after 1995. Overall, Dingzi Bay has shown a tendency towards silting-up during 1952–2010, with the bay head migrating seaward, the number of channels in the tidal creek system decreasing, and the tidal inlet becoming narrower and shorter. In conclusion, large-scale development and human activity in Dingzi Bay have controlled the geomorphic evolution of the bay since the 1950s.

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Scale-location specific relations between soil nutrients and topographic factors in the Fen River Basin, Chinese Loess Plateau
Hongfen ZHU, Rutian BI, Yonghong DUAN, Zhanjun XU
Front. Earth Sci.. 2017, 11 (2): 397-406.
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Understanding scale- and location-specific variations of soil nutrients in cultivated land is a crucial consideration for managing agriculture and natural resources effectively. In the present study, wavelet coherency was used to reveal the scale-location specific correlations between soil nutrients, including soil organic matter (SOM), total nitrogen (TN), available phosphorus (AP), and available potassium (AK), as well as topographic factors (elevation, slope, aspect, and wetness index) in the cultivated land of the Fen River Basin in Shanxi Province, China. The results showed that SOM, TN, AP, and AK were significantly inter-correlated, and that the scales at which soil nutrients were correlated differed in different landscapes, and were generally smaller in topographically rougher terrain. All soil nutrients but TN were significantly influenced by the wetness index at relatively large scales (32–72 km) and AK was significantly affected by the aspect at large scales at partial locations, showing localized features. The results of this study imply that the wetness index should be taken into account during farming practices to improve the soil nutrients of cultivated land in the Fen River Basin at large scales.

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Soil organic carbon dynamics in Xilingol grassland of northern China induced by the Beijing-Tianjin Sand Source Control Program
Liangxia ZHANG, Wei CAO, Jiangwen FAN
Front. Earth Sci.. 2017, 11 (2): 407-415.
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To mitigate impacts of sandstorms on northern China, the Chinese government launched the Beijing–Tianjin Sand Source Control Program (BTSSCP) in 2000. The associated practices (i.e., cultivation, enclosure, and aerial seeding) were expected to greatly enhance grassland carbon sequestration. However, the BTSSCP-induced soil organic carbon (SOC) dynamics remain elusive at a regional level. Using the Xilingol League in Inner Mongolia for a case study, we examined the impacts from 2000 to 2006 of the BTSSCP on SOC stocks using the IPCC carbon budget inventory method. Results indicated that over all practices SOC storage increased by 1.7%, but there were large differences between practices. SOC increased most rapidly at the rate of 0.3 Mg C·ha−1·yr−1 under cultivation, but decreased significantly under aerial seeding with moderate or heavy grazing (0.3 vs.0.6 Mg C·ha−1·yr−1). SOC increases varied slightly for grassland types, ranging from 0.10 Mg C·ha−1·yr−1 for temperate desert steppe to 0.16 Mg C·ha−1·yr−1 for temperate meadow steppe and lowland meadow. The overall economic benefits of the SOC sink were estimated to be 4.0 million CNY. Aerial seeding with no grazing was found to be the most cost-effective practice. Finally, we indicated that at least 55.5 years (shortest for cultivation) were needed for the grasslands to reach their potential carbon stocks. Our findings highlight the importance and effectiveness of BTSSCP in promoting terrestrial carbon sequestration which may help mitigate climate change, and further stress the need for more attention to the effectiveness of specific practices.

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A geometric model of faulted detachment folding with pure shear and its application in the Tarim Basin, NW China
Zewei YAO, Guangyu HE, Xiaoli ZHENG, Chuanwan DONG, Zicheng CAO, Suju YANG, Yi GU
Front. Earth Sci.. 2017, 11 (2): 416-426.
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We present an improved geometric model of faulted detachment folding with pure shear that is characterized by core thickening and a ramp-discordant backlimb. The model includes a two-stage evolution: 1) detachment folding involving pure shear with fixed hinges, and 2) faulted detachment folding, in which the core of anticline thrusts above a break-through fault in forelimb by limb rotation. The growth strata patterns of the model are also discussed with respect to factors such as limb rotation, tectonic uplift rate, and sedimentation rate. A thrust-related fold, called a TBE thrust fold, in the Tarim Basin in NW China, is analyzed as an example of the theoretical model. The result indicates that the TBE thrust fold has undergone a two-stage evolution with shortening of a few hundred meters. Both the theoretical model and the actual example indicate that the shortening in the detachment folding stage takes up a large proportion of the total shortening. The structural restoration of the TBE thrust fold also provides new evidence that the formation of a series of thin-skinned structures in the SE Tarim Basin initiated in the Late Ordovician. The model may be applicable to low-amplitude faulted detachment folds.

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Cenozoic tectonic subsidence in the Southern Continental Margin, South China Sea
Penggao FANG, Weiwei DING, Yinxia FANG, Zhongxian ZHAO, Zhibing FENG
Front. Earth Sci.. 2017, 11 (2): 427-441.
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We analyzed two recently acquired multichannel seismic profiles across the Dangerous Grounds and the Reed Bank area in the South China Sea. Reconstruction of the tectonic subsidence shows that the southern continental margin can be divided into three stages with variable subsidence rate. A delay of tectonic subsidence existed in both areas after a break-up, which was likely related to the major mantle convection during seafloor spreading, that was triggered by the secondary mantle convection below the continental margin, in addition to the variation in lithospheric thickness. Meanwhile, the stage with delayed subsidence rate differed along strikes. In the Reed Bank area, this stage is between 32–23.8 Ma, while in the Dangerous Grounds, it was much later (between 19–15.5 Ma). We believe the propagated rifting in the South China Sea dominated the changes of this delayed subsidence rate stage.

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19 articles