Carbon storage capacity of different plantation types under sandstorm source control program in Hebei Province,China

Afforestation and reforestation are effective and ecological ways of mitigating elevated atmospheric carbon dioxide(CO2) concentration and increasing carbon(C) storage in terrestrial ecosystems. In this study, we measured the above-ground(tree, herbaceous plants and litter) and below-ground(root and soil) C storage in an aspen plantation(Populus davidiana) monoculture(PD), a larch plantation(Larix pincipis-rupprechtii) monoculture(LP), a pine plantation(Pinus tabulaeformis) monoculture(PT), a larch and birch mixed plantation(L. pincipis-rupprechtii and Betula platyphlla mixed)(MLB), and an apricot plantation(Armeniaca sibirica) monoculture(AS) under the Desertification Combating Program in Hebei Province, the northern China. The objective was to assess the effect of afforestation species on ecosystem C pools of different plantation types. Results showed that C storage of LP stand(258.0 Mg/ha) and MLB(163.4 Mg/ha) were significantly higher than the C storage in PD(45.5 Mg/ha), PT(58.9 Mg/ha) and AS(49.4 Mg/ha), respectively. Soil C was the main carbon pool of the ecosystem C storage in the five plantation stands, ranging from 31.4 Mg/ha to 232.5 Mg/ha, which accounted for 69.0%–90.1% of the total ecosystem C storage. The C storage in tree layer was about 5.2%–23.2% of ecosystem C storage. The herbaceous plants and litter layers contained 1.0%–6.0% and 1.5%–3.3% of ecosystem C storage, respectively. Our results suggest that tree species should be incorporated to accurately develop regional C budget of afforestation program, and also imply that substantial differences in ecosystem C stocks among plantation types can facilitate decision making on C management.     

Carbon sequestration in forest vegetation of Beijing at sublot level

Based on forest inventory data (FID) at sublot level,we estimated the carbon sequestration in forest vegetation of Beijing,China in 2009.In this study,the carbon sequestration in forest vegetation at sublot level was calculated based on net biomass production (ΔB) which was estimated with biomass of each sublot and function relationships between ΔB and biomass.The biomass of forested land was calculated with biomass expansion factors (BEFs) method,while those of shrub land and other forest land types were estimated with biomass,coverage and height of referred shrubs and shrub coverage and height of each sublot.As one of special forested land types,the biomass of economic tree land was calculated with biomass per tree and tree number.The variation of carbon sequestration in forest vegetation with altitude,species and stand age was also investigated in this study.The results indicate that the carbon sequestration in forest vegetation in Beijing is 4.12 × 106 tC/yr,with the average rate of 3.94 tC/(ha·yr).About 56.91% of the total carbon sequestration in forest vegetation is supported by the forest in the plain with an altitude of < 60 m and the low mountainous areas with an altitude from 400 m to 800 m.The carbon sequestration rate in forest vegetation is the highest in the plain area with an altitude of < 60 m and decreased significantly in the transitional area from the low plain to the low mountainous area with an altitude ranging from 200 m to 400 m due to intensive human disturbance.The carbon sequestration of Populus spp.forest and Quercus spp.forest are relatively higher than those of other plant species,accounting for 25.33% of the total.The carbon sequestration in vegetation by the forest of < 40 years amounts to 45.38% of the total.The carbon sequestration rate in forest vegetation peaks at the stand age of 30–40 years.Therefore,it would be crucial for enhancing the capability of carbon sequestration in forest vegetation to protect the forest in Beijing,to limit human disturbance in the transitional area from the plain to the low mountain area,and to foster the newly established open forest.     

Carbon sequestration effects of shrublands in Three-North Shelterbelt Forest region,China

Three-North Shelterbelt Forest(TSF) program, is one of six key forestry programs and has a 73-year construction period, from 1978 to 2050. Quantitative analysis of the carbon sequestration of shrubs in this region is important for understanding the overall function of carbon sequestration of the forest and other terrestrial ecosystems in China. This study investigated the distribution area of shrubland in the TSF region based on remote sensing images in 1978 and 2008, and calculated the carbon density of shrubland in combination with the field investigation and previous data from published papers. The carbon sequestration quantity and rate from 1978 to 2008 was analyzed for four sub-regions and different types of shrubs in the TSF region. The results revealed that: 1) The area of shrubland in the study area and its four sub-regions increased during the past thirty years. The area of shrubland for the whole region in 2008 was 1.2 × 10~7 ha, 72.8% larger than that in 1978. The Inner Mongolia-Xinjiang Sub-region was the largest shrubland distribution area, while the highest coverage rate was found in the North China Sub-region. 2) In decreasing order of their carbon sequestration, the four types of shrubs considered in this study were Hippophae rhamnoides, Caragana spp., Haloxylon ammodendron and Vitex negundo var. heterophylla. The carbon sequestration of H. rhamnoides, with a maximum mean carbon density of 16.5 Mg C/ha, was significantly higher than that of the other three species. 3) The total carbon sequestration of shrubland in the study region was 4.5×10~7 Mg C with a mean annual carbon sequestration of 1.5 ×10~6 Mg C. The carbon density in the four sub-regions decreased in the following order: the Loess Plateau Sub-region, the North China Sub-region, the Northeast China Sub-region and the Inner Mongolia-Xinjiang Sub-region. The paucity of studies and data availability on the large-scale carbon sequestration of shrub species suggests this study provides a baseline reference for future research in this area.     

Carbon storage and sequestration of national key ecological restoration programs in China: An introduction to special issue

<正>Although a crucial objective of ecosystem management should be the avoidance of degradation at the beginning,an unfortunate truth is that ecosystems have been substantially exploited,degraded and destroyed in the last century as a result of the global increase in economic and societal prosperity(Suding,2011).More than 60%of ecosystems have been converted for human use or degraded through unsustainable harvest,pollution,     

基于时序InSAR的京津高铁北京段地面沉降监测

京津高铁是中国第一条高速运行的城际铁路,其安全运行对轨道的平顺性有着严格的要求。地面沉降,尤其是不均匀地面沉降会引起部分路基和桥梁变形,威胁着高速铁路的运营安全。合成孔径雷达干涉测量技术可以大范围监测地表形变,对高速铁路沿线地面沉降具有较好的监测能力。本文以45景高分辨率TerraSAR-X 数据为基础,采用 PS-InSAR技术监测京津高铁北京段沿线地面沉降,获取京津高铁北京段沿线地面沉降的分布信息,从动静载荷视角结合北京地区地下水、断裂带、地质条件和含水层系统介质等数据,综合分析高铁沿线不均匀地面沉降的原因,为京津高铁的安全运营提供技术支撑。研究结果表明：京津高铁北京段沿线地面沉降发展在空间上存在一定差异性,北京南站至十里河区间,年沉降速率小于10 mm/a; 至十八里店区间,年沉降速率在10~40 mm/a范围内浮动;过亦庄站至东石村以东区间,最大年沉降速率达到90 mm/a;至永隆村以西,年沉降有所缓解,往东至坨堤村,沉降较为稳定,年沉降速率小于10 mm/a。地下水超采是沿线区域地面沉降的主要因素,动静载荷共同作用下对地面沉降产生一定的影响,沿线地面沉降一定程度上受到南苑—通县断裂带和旧宫断裂带构造控制,沉降量较大的路段位于粘土层较厚的大兴迭隆起。     

Biomass carbon sequestration by planted forests in China

The planted forest area and carbon sequestration have increased significantly in China, because of large-scale reforestation and afforestation in the past decades. In this study, we developed an age-based volume-to-biomass method to estimate the carbon storage by planted forests in China in the period of 1973–2003 based on the data from 1209 field plots and national forest inventories. The results show that the total carbon storage of planted forests was 0.7743 Pg C in 1999–2003, increased by 3.08 times since the early 1970s. The carbon density of planted forests varied from 10.6594 Mg/ha to 23.9760 Mg/ha and increased by 13.3166 Mg/ha from 1973–1976 to 1999–2003. Since the early 1970s, the planted forests in China have been always a carbon sink, and the annual rate of carbon sequestration was 0.0217 Pg C/yr. The carbon storage and densities of planted forests varied greatly in space and time. The carbon storage of Middle South China was in the lead in all regions, which accounted for 23%–36% of national carbon storage. While higher C densities (from 17.79 Mg/ha to 26.05 Mg/ha) were usually found in Northeast China. The planted forests in China potentially have a high carbon sequestration since a large part of them are becoming mature and afforestation continues to grow.     

Regional variation in carbon sequestration potential of forest ecosystems in China

Enhancing forest carbon(C) storage is recognized as one of the most economic and green approaches to offsetting anthropogenic CO_2 emissions. However, experimental evidence for C sequestration potential(C_(sp)) in China's forest ecosystems and its spatial patterns remain unclear, although a deep understanding is essential for policy-makers making decisions on reforestation. Here, we surveyed the literature from 2004 to 2014 to obtain C density data on forest ecosystems in China and used mature forests as a reference to explore C_(sp). The results showed that the C densities of vegetation and soil(0–100 cm) in China's forest ecosystems were about 69.23 Mg C/ha and 116.52 Mg C/ha, respectively. In mature forests, the C_(sp) of vegetation and soil are expected to increase to 129.26 Mg C/ha(87.1%) and 154.39 Mg C/ha(32.4%) in the coming decades, respectively. Moreover, the potential increase of C storage in vegetation(10.81 Pg C) is estimated at approximately twice that of soil(5.01 Pg C). Higher C_(sp) may occur in the subtropical humid regions and policy-makers should pay particular attention to the development of new reforestation strategies for these areas. In addition to soil nutrients and environment, climate was an important factor influencing the spatial patterns of C density in forest ecosystems in China. Interestingly, climate influenced the spatial patterns of vegetation and soil C density via different routes, having a positive effect on vegetation C density and a negative effect on soil C density. This estimation of the potential for increasing forest C storage provided new insights into the vital roles of China's forest ecosystems in future C sequestration. More importantly, our findings emphasize that climate constraints on forest C sequestration should be considered in reforestation strategies in China because the effects of climate were the opposite for spatial patterns of C density in vegetation and soil.Enhancing forest carbon(C) storage is recognized as one of the most economic and green approaches to offsetting anthropogenic CO2 emissions. However, experimental evidence for C sequestration potential(Csp) in China's forest ecosystems and its spatial patterns remain unclear, although a deep understanding is essential for policy-makers making decisions on reforestation. Here, we surveyed the literature from 2004 to 2014 to obtain C density data on forest ecosystems in China and used mature forests as a reference to explore Csp. The results showed that the C densities of vegetation and soil(0–100 cm) in China's forest ecosystems were about 69.23 Mg C/ha and 116.52 Mg C/ha, respectively. In mature forests, the Csp of vegetation and soil are expected to increase to 129.26 Mg C/ha(87.1%) and 154.39 Mg C/ha(32.4%) in the coming decades, respectively. Moreover, the potential increase of C storage in vegetation(10.81 Pg C) is estimated at approximately twice that of soil(5.01 Pg C). Higher Csp may occur in the subtropical humid regions and policy-makers should pay particular attention to the development of new reforestation strategies for these areas. In addition to soil nutrients and environment, climate was an important factor influencing the spatial patterns of C density in forest ecosystems in China. Interestingly, climate influenced the spatial patterns of vegetation and soil C density via different routes, having a positive effect on vegetation C density and a negative effect on soil C density. This estimation of the potential for increasing forest C storage provided new insights into the vital roles of China's forest ecosystems in future C sequestration. More importantly, our findings emphasize that climate constraints on forest C sequestration should be considered in reforestation strategies in China because the effects of climate were the opposite for spatial patterns of C density in vegetation and soil.     

基于浅水三角洲沉积的供源差异与砂体分布空间配置关系——以松辽盆地长垣西部葡萄花油层为例

为明确松辽盆地长垣西部葡萄花油层前缘河道砂体受不同因素影响的发育特征及其差异,根据测井 、岩心等资料,结合多种矿物含量分析交汇,定量识别长垣西部地区受水动力条件、供源成分及方向影响的不同物源交汇范围,根据相对湖平面变化和物源供给等方面的耦合关系,以水下分流河道砂体为骨架,分析不同供源方向沉积成因的砂体岩相组合及发育特征...     

Response of Vegetation Cover Change to Drought at Different Time-scales in the Beijing-Tianjin Sandstorm Source Region,China

Dominated by an arid and semiarid continental climate, the Beijing-Tianjin Sandstorm Source Region(BTSSR) is a typical ecologically fragile region with frequently occurring droughts. To provide information for regional vegetation protection and drought prevention, we assessed the relations between vegetation cover change(measured by the Normalized Difference Vegetation Index,NDVI) and the Standardized Precipitation Evapotranspiration Index(SPEI) at different time-scales, in different growth stag...     

Length of stay in urban areas of circular migrants from the mountainous areas in China

Currently, there is limited literature dealing with the length of stay of circular migrants in urban areas (LSCMU), although many studies have discussed the phenomenon of migration and the determinants of migration. This study attempts to fill that gap using survey data from the mountainous areas of Chongqing, Southwest China. From a comparative perspective, this study divided workers into two groups (a young group aged between 16 and 35 years and an old group aged between 36 and 65 years). The average LSCMU values for the young and old groups were 225 days and 174 days, respectively. Two multi-regression models were used to estimate the determinants of LSCMU in the two groups. The results showed that LSCMU was closely related to individual factors in both groups, including gender, age and job training. Family and community factors, including household size, arable land per capita and the distance from market, had much weaker effects on the dependent variable, especially in the older group. It was noticeable that job training had significant positive effects on LSCMU in both groups; these findings have special implications for the urbanization process in China.     

京津风沙源区生态环境时空变化的遥感监测分析

本文利用由遥感影像解译获得的土地利用数据和MODIS NDVI产品,采用空间转移矩阵、最大值合成法、均值法和一元线性回归模拟等方法,分析了2000年以来京津风沙源区生态环境变化的时空特征.结果表明:(1)2000-2005年京津风沙源区耕地开垦、林草地减少的趋势有所减缓,但区域气候变化趋于干旱,水域面积明显减少,草地退...     

Liquefaction of sand under low confining pressure

Undrained behaviour of sand under low cell pressure was studied in static and cyclic triaxial tests. It was found that very loose sand liquefies under static loading with the relative density being a key parameter for the undrained behaviour of sand. In cyclic triaxial tests, pore water pressures built up during the cyclic loading and exceeded the confining cell pressure. This process was accompanied by a large sudden increase in axial deformation. The necessary number of cycles to obtain liquefaction was related to the confining cell pressure, the amplitude of cyclic loading and the relative density of sand. In addition, the patterns of pore water pressure response are different from those of sand samples with different relative densities. The test results are very useful for expounding scour mechanism around coastal structures since they relate to the low stress behaviour of the sand.     

SOIL EROSION AND ITS IMPACTS ON ENVIRONMENT IN YIXING TEA PLANTATION OF JIANGSU PROVINCE

Soil erosion on sloping field has led to a lot of environmental problems. In order to reveal the seriousnessof the damage of soil erosion on sloping fields 137^Cs tracer method was used to estimate soil erosion rate. 137^Cs referenceinventory of 2200Bq/m^2 in Yixing, southern Jiangsu Province, was estimated and a model for estimating erosion of cultivat-od soil was established in order to avoid overestimating soil erosion rates. Then based on the soil erosion rates and mea-sured soil physical and chemical properties, direct and indirect impacts of soil erosion on environment were further dis-cussed. Direct impacts of erosion on environment included on-site and off-site impacts. The on-site impacts were thatsoil layer became thin, soil structure was deteriorated and soil nutrients decreased. The off-site impacts were that waterbodies were polluted. The indirect impacts of soil erosion on environment were the increase of fertilizer application andenergy consumption, and change of adaptability of land uses. Although erosion intensity was not serious in the studyarea, its environmental impacts should not be ignored because of great soil nutrient loss and coazseness of soil particles.     

Effects of sand sedimentation and wind erosion around sand barrier: Numerical simulation and wind tunnel test studies

Based on numerical simulations, this study highlights the sedimentation and erosion problems around a sand barrier through the relationship between the shear stress of the surface around the sand barrier and the critical shear stress of sand grains. The numerical simulation results were verified using data measured by the wind tunnel test.The results showed that when the porosity was the same, the size and position of the vortex on the leeward side of the sand barrier were related to the inlet w...     

ELECTROCHEMICAL STUDY ON CORROSION BEHAVIOUR OF STEELS IN SAND WITH WATER

ImooUcr0NCormsinnofsodinconatisnowrognindasaseriousproblemwithlargeere-nondconSequenas.Thecormsionproducofondatthesurfaeeofrenfontin-dutaltenSioninthernaterial,resultinginfraCtureandspillingoftheconcretefromtherenfoot(Madrinaldetal.,l99l).Asaasult,theconCretestructure'sIneCanhalstwthisgreatiytalued.0wingtothephyShaldfultyofconduCtingforchdricalexperiInentsinconare,muCoftheworkintheaasofndanisticdCtendnationsforcormsionofstalincon-~wereconduedinalkalinesolution,generallyofporewatCr(Romirz…     

Identifying the priority areas for enhancing the ecosystem services in hilly and mountainous areas of southern China

Ecosystem services can be enhanced through ecological restoration,industrial structure adjustment,land-use optimization,and agricultural and forestry ecosystem ...     

Influence of grain segregation on the behavior of sand in triaxial tests

As a common phenomenon in granular flow, grain segregation plays a great role in affecting the behavior of granular soil by causing a great change of grain-void distribution in granular soil. This paper presents an experimental study on the influence of grain segregation on the behavior of sand, by a number of triaxial tests to interpret the characteristic behavior, friction and dilatancy behavior, excess pore water pressure behavior and critical state behavior of sand incorporating grain segregation. An index-grain segregation index was proposed to quantify grain segregation. Grain segregation affected greatly the characteristic behavior of sand, causing the movement of void ratio-dilatancy relation of sand towards the increase of void ratio and dilatancy of sand. In the drained tests, the mobilized friction angle of sand showed a decrease followed by an increase but the mobilized dilatancy angle of sand increased, with increasing grain segregation index. An increase in grain segregation index impaired the basic friction of sand. In the undrained tests, the mobilized friction angle of sand showed an increase followed by a decrease with increasing grain segregation index. However, grain segregation caused an increase of the mobilized dilatancy of sand followed by a different development. An increase in grain segregation resulted in a higher summit of the dilatancy of sand but with a faster decrease along axial strain. In the q-p′ plane, grain segregation caused a reciprocating rotation of the dilatancy line and failure line of sand. Grain segregation resulted in enhancement of the peak-state dilatancy of sand, affecting greatly peakstate friction angle and peak-state basic friction angle of sand as well as the normalized excess pore water pressure. The excess friction angle of sand showed an increase followed by a decrease in the drained tests but increased linearly in the undrained tests, with increasing grain segregation index. The excess friction angle-over-maximum dilatancy angle of sand decreased in up convexity while increasing grain segregation index. Grain segregation resulted in rotation and translation of the critical state line of sand in the e-p′α=0.7 plane. However, in the q-p′ plane, the critical state line of sand showed an anticlockwise rotation followed by a clockwise rotation with increasing grain segregation index.     

The record of younger dryas event in eolian sand deposit in qaidam basin

DansgaardandothersholdtheviewthatsevereclimaticfluctuationinthelateglacialiscausedbyadjustmentoftheNorthAtlanticcurrent,whichmainlyaffectstheclimateintheNorthAtlanticOCean.ButtherePOrtsabouttheYoungerDryaseventfoundin..varioussedimentsofdifferentplacesprovethatYoungerDryaseventisaclimaticeventoverthegloberatherthanaregion.InrecentyearstherearemanyrePOrtsaboutYoungerDryaleventfoundinmarineandcontinentalsedimentsofmiddlelatitudeinChina.NowitisindubitablethattheYoungerDryaseventexistsinCh…     

Mechanical property of calcareous sand under action of compaction

Calcareous sand is a kind of special medium which is composed of calcium carbonate and other difficult soluble carbonate substances. Because of its rich in inner pore space and easy crashed,the mechanical property is very different from conventional quartz sand. Based on the compaction test and direct shear test of calcareous sand,by means of data fitting,the coupling relationship between compaction density and mechanical property under different water contents was obtained; meanwhile,the shear strength expression was built on the basis of the relationship between water content and dry density.