The performance of a 1-D soil model in a semiarid area of North China was investigated using observational data from a cropland station at the Tongyu reference site of the Coordinated Enhanced Observing Period(CEOP)du...The performance of a 1-D soil model in a semiarid area of North China was investigated using observational data from a cropland station at the Tongyu reference site of the Coordinated Enhanced Observing Period(CEOP)during the non-growing period,when the ground surface was covered with bare soil.Comparisons between simulated and observed soil surface energy balance components as well as soil temperatures and water contents were conducted to validate the soil model.Results show that the soil model could produce good simu-lations of soil surface temperature,net radiation flux,and sensible heat flux against observed values with the RMSE of 1.54°C,7.71 W m-2,and 27.79 W m-2,respectively.The simulated volumetric soil water content is close to the observed values at various depths with the maximal difference between them being 0.03.Simulated latent heat and ground heat fluxes have relatively larger errors in relative to net radiation and sensible heat flux.In conclusion,the soil model has good capacity to simulate the bare soil surface energy balance at the Tongyu cropland station and needs to be further tested in longer period and at more sites in semiarid areas.展开更多
Plastic film mulching has been widely used to increase maize yield in the semiarid area of China.However, whether long-term plastic film mulching is conducive to agricultural sustainability in this region remains cont...Plastic film mulching has been widely used to increase maize yield in the semiarid area of China.However, whether long-term plastic film mulching is conducive to agricultural sustainability in this region remains controversial.A field experiment was initiated in 2013 with five different film mulching methods:(i) control method, flat planting without mulching (CK),(ii) flat planting with half film mulching (P),(iii) film mulching on ridges and planting in narrow furrows(S),(iv) full film mulching on double ridges (D), and (v) film mulching on ridges and planting in wide furrows (R).The effects on soil organic carbon (SOC) content, storage, and fractions, and on the carbon management index (CMI)were evaluated after nine consecutive years of plastic film mulching.The results showed that long-term plastic film mulching generally maintained the initial SOC level.Compared with no mulching, plastic film mulching increased the average crop yield, biomass yield, and root biomass by 48.38, 35.06, and 37.32%, respectively, which led to the improvement of SOC sequestration.Specifically, plastic film mulching significantly improved CMI, and increased the SOC content by 13.59%, SOC storage by 7.47%and easily oxidizable organic carbon (EOC) by 13.78%on average,but it reduced the other labile fractions.SOC sequestration and CMI were improved by refining the plastic film mulching methods.The S treatment had the best effect among the four mulching methods, so it can be used as a reasonable film mulching method for sustainable agricultural development in the semiarid area.展开更多
With the rapid development of urban agglomerations in northwest arid and semiarid regions of China, the scope of the urban heat island(UHI) effect has gradually expanded and gradually connected, and has formed a regio...With the rapid development of urban agglomerations in northwest arid and semiarid regions of China, the scope of the urban heat island(UHI) effect has gradually expanded and gradually connected, and has formed a regional heat island(RHI) with a larger range of impact to the regional environment. However, there are few studies on the heat island effect of urban agglomerations in arid and semiarid regions, so this paper selects the urban agglomeration of Hohhot, Baotou and Ordos(HBO) of Inner Mongolia, China as the study area. Based on the 8-day composite Moderate-resolution Imaging Spectroradiometer(MODIS) surface temperature data(156scenes in all) and land use maps for 2005, 2010, and 2015, we analyze the spatiotemporal distributions of regional heat(cool) islands(RH(C)I) and the responses of surface temperatures to land-use changes in the diurnal and interannual surface cities. The results showed that: 1) from 2005 to 2015, urban areas showed the cold island effect during the day, with the area of the cold island showing a shrinking feature;at night, they showed the heat island effect, with the area of the heat island showing a first decrease and then an increase.2) From 2005 to 2015, the land development(unutilized land to building land) brings the greatest temperature increase(ΔT = 1.36°C)during the day, while the greatest temperature change at night corresponds to the conversion of cultivated land to building land(ΔT =0.78°C) exhibited the largest changes at night. From 2010 to 2015, the land development(grassland to building land) bring the greatest temperature increase(ΔT = 0.85°C) during the day, while the great temperature change at night corresponds to the conversion of water areas to building land(ΔT = 1.38°C) exhibited the largest changes at night. Exploring the spatial and temporal evolution of surface urban heat(cool) islands in urban agglomerations in arid and semiarid regions will help to understand the urbanization characteristics of urban agglomerations and provide a reference for the formulation of policies for the coordinated and healthy development of the region and co-governance of regional environmental problems.展开更多
Based on Climatic Research Unit Time Series3.1 temperature and Global Precipitation Climatology Center full data reanalysis version 6 precipitation data,the abilities of climate models from the fifth phase of the Coup...Based on Climatic Research Unit Time Series3.1 temperature and Global Precipitation Climatology Center full data reanalysis version 6 precipitation data,the abilities of climate models from the fifth phase of the Coupled Model Intercomparison Project to simulate climate changes over arid and semiarid areas were assessed.Simulations of future climate changes under different representative concentration pathways(RCPs)were also examined.The key findings were that most of the models are able to capture the dominant features of the spatiotemporal changes in temperature,especially the geographic distribution,during the past 60 years,both globally as well as over arid and semiarid areas.In addition,the models can reproduce the observed warming trends,but with magnitudes generally less than the observations of around0.1–0.3°C/50a.Compared to temperature,the models perform worse in simulating the annual evolution of observed precipitation,underestimating both the variability and tendency,and there is a huge spread among the models in terms of their simulated precipitation results.The multimodel ensemble mean is overall superior to any individual model in reproducing the observed climate changes.In terms of future climate change,an ongoing warming projected by the multi-model ensemble over arid and semiarid areas can clearly be seen under different RCPs,especially under the high emissions scenario(RCP8.5),which is twice that of the moderate scenario(RCP4.5).Unlike the increasing temperature,precipitation changes vary across areas and are more significant under high-emission RCPs,with more precipitation over wet areas but less precipitation over dry areas.In particular,northern China is projected to be one of the typical areas experiencing significantly increased temperature and precipitation in the future.展开更多
Minerals and rocks have distinct 87Sr/86Sr and 143Nd/144Nd ratios, depending on their geological origin and ages, and these isotope ratios are less altered than elemental composition during transport in the atmosphere...Minerals and rocks have distinct 87Sr/86Sr and 143Nd/144Nd ratios, depending on their geological origin and ages, and these isotope ratios are less altered than elemental composition during transport in the atmosphere or after deposition as sediments, thus stable isotopes of Sr and Nd have great potential as tracers for provenance and trans- port of materials. During the hypergene process, Sr isotope ratios of sediments are controlled by their parent rocks, particle sizes and chemical weathering. In general, the higher the Sr isotope ratios of parent rocks, and/or the more the fine-grained fractions, and/or the stronger the chemical weathering, thus the higher the Sr isotope ratios of sediments. On the contrary, there are lower Sr isotope ratios of sedi- ments. Nd isotope ratios of sediments, independent of their particle sizes and chemical weathering, are only associated with parent rocks. For the prove- nance of the Chinese Loess Plateau, different re- seachers drew discordant and even contradictory conclusions by using the method of Sr-Nd isotopic tracing. From the previous Nd isotope data, it is con- sidered that the Tarim Basin, deserts in the central and west parts of Inner Mongolia and the Tibetan Plateau are the main sources of the Chinese Loess Plateau, and are also manufacturers for eolian dust of the Far East regions, together with the Chinese Loess Plateau. Sr isotope ratios of eolian dust are solely affected by wind sorting and weather- ing-pedogenesis due to its homogeneous composi- tion in the Chinese Loess Plateau. Wind sorting isrelated to the East Asian winter monsoon but weath- ering-pedogenesis is mainly associated with the East Asian summer monsoon. Studies on Sr isotopic compositions of the loess-paleosol sequence suggest that 87Sr/86Sr ratios in acid-soluble materials are an index for chemical weathering intensity of the Chi- nese Loess Plateau, indicating the East Asian sum- mer monsoon variations, whereas 87Sr/86Sr ratios in acid-insoluble materials are significantly controlled by particle sizes, and can be used as a proxy indicator reflecting the East Asian winter monsoon variations. Variations of 87Sr/86Sr ratios in acid-insoluble materi- als in the past 2.6Ma further demonstrate that the East Asian winter monsoon gradually strengthened since the beginning of the Quaternary period. This result agrees with the prior conclusion that climate gradually cooled since the onset of the Quaternary Ice Age.展开更多
Diurnal, seasonal and interannual variations of surface albedo of degraded grassland and cropland surfaces at a semiarid area of Tognyu have been investigated based on the continuous three years observational data fro...Diurnal, seasonal and interannual variations of surface albedo of degraded grassland and cropland surfaces at a semiarid area of Tognyu have been investigated based on the continuous three years observational data from 2003 to 2005. The changes of surface albedo with solar elevation angle and soil moisture have been discussed also. It has been found that surface albedo has almost the same diurnal and seasonal variations on degraded grassland and cropland surfaces in the semiarid area, while sur- face albedo is large in winter and small in summer. The diurnal variation of the surface albedo has re- lationship with the weather condition. The diurnal cycle of the surface albedo likes the "U" shape curve in sunny day, while it is low-high after the rain, and high-low after the snow. The surface albedo has large variation in cloudy day, while it has no any variation in overcast day. The large difference of the surface albedo can be 0.04 in winter between two land surfaces, because the snow has large effects on the surface albedo in winter. The rainfall is an important factor in summer on the surface albedo, while the difference of the surface albedo is 0.01 only between two land surfaces. The differences of the surface albedo can also be 0.04 in autumn due to vegetation growing. The seasonal-average surface albeo from 2003―2005 is 0.25, 0.22, 0.24, 0.32 respectively in spring, summer, autumn and winter on the degraded grassland surface,while it is 0.25, 0.21, 0.22, 0.33 respectively in spring, summer, autumn and winter on the cropland surface. The surface albedo becomes smaller with the increase of solar elevation angle. When the solar elevation angle is greater than 40°, the surface albedo changes very little and tends to be a constant. The surface albedo has negative exponent functions with soil moisture in the growing season.展开更多
Here we report a multiyear study on the surface roughness length and bulk transfer coefficients over the degraded grassland and cropland surfaces in a semiarid area of China. Eddy covariance measurement and the meteor...Here we report a multiyear study on the surface roughness length and bulk transfer coefficients over the degraded grassland and cropland surfaces in a semiarid area of China. Eddy covariance measurement and the meteorological profile observation data were used to analyze characteristics of these parameters on the diurnal, seasonal, and annual scales. Significant seasonal and annual variations of the aerodynamic roughness length are observed over the two surfaces. A large variation of kB-1 is measured during the day. Both kB-1 and the bulk transfer coefficients exhibit significant seasonal and annual variations. During the growing season (May to October), average Cd and Ch are 3.1×10-3 and 2.5×10-3 over the degrade grassland surface, and 4.7×10-3 and 3.1×10-3 over the cropland surface respectively. During the non-growing season, average Cd and Ch are 2.3×10-3 and 2.0×10-3 over the degrade grassland surface, and 2.9×10-3 and 2.2×10-3 over the cropland surface respectively.展开更多
There have been significant variations in wind activity over the past five decades in arid and semiarid areas in China.High wind activity occurred from the 1960s to the 1970s,but wind activity has de-creased continuou...There have been significant variations in wind activity over the past five decades in arid and semiarid areas in China.High wind activity occurred from the 1960s to the 1970s,but wind activity has de-creased continuously from the 1980s to the present;as a result,the potential sand transport during the latter period was only 20%-50% of the values during the 1960s and 1970s.Phases of high wind activ-ity were highly consistent with the trends in desertification over the past five decades in arid and semiarid areas in China,but spring precipitation was also a significant factor:rapid desertification during the 1960s and 1970s was due to high wind activity,generally combining with low spring pre-cipitation;subsequent rehabilitation since the 1980s has resulted from the combined effects of low wind activity and higher spring precipitation.Therefore,although modern desertification and rehabili-tation processes are being more or less affected by human activities,both processes appear to be more strongly controlled by climate change.展开更多
Based on eddy covariance measurements over two kinds of land surfaces(a degraded grassland and a maize cropland)in a semiarid area of China in 2005 and 2008,the effects of different gap filling methods,energy balance ...Based on eddy covariance measurements over two kinds of land surfaces(a degraded grassland and a maize cropland)in a semiarid area of China in 2005 and 2008,the effects of different gap filling methods,energy balance closure and friction velocity threshold(u*)on annual net ecosystem exchange(NEE)were analyzed.Six gap filling methods,including mean diurnal variation(MDV),marginal distribution sampling(MDS),and nonlinear regressions method,were investigated by generating secondary datasets with four different artificial gap lengths(ranging in length from single half-hours to 12 consecutive days).The MDS generally showed a good overall performance especially for long gaps,with an annual sum bias error less than 5 g C m-2 yr-1.There was a large positive annual sum bias error for nonlinear regressions,indicating an overestimate on net ecosystem respiration.The offset in the annual sum NEE for four nonlinear regressions was from 8.0 to 30.8 g C m-2 yr-1.As soil water content was a limiting factor in the semiarid area,the nonlinear regressions considering both soil temperature and soil water content as controlling variables had a better performance than others.The performance of MDV was better in daytime than in nighttime,with an annual sum bias error falling between-2.6 and-13.4 g C m-2 yr-1.Overall,the accuracy of the gap filling method was dependent on the type of the land surface,gap length,and the time of day when the data gap occurred.The energy balance ratio for the two ecosystems was nearly 80%.Turbulent intensity had a large impact on energy balance ratio.Low energy balance ratio was observed under low friction velocity during the night.When there was a large fetch distance in a wind direction,a low energy balance ratio was caused by mismatch of the footprints between the available energy and turbulent fluxes.The effect of energy balance correction on CO2 flux was evaluated by assuming the imbalance caused by the underestimation of sensible heat flux and latent heat flux.The results showed an average increase of 10 g C m-2 yr-1 for annual NEE in both ecosystems with an energy balance correction.On the other hand,the u*threshold also have a large impact on annual sum NEE.Net carbon emission increased 37.5 g C m-2 yr-1 as u*threshold increased from 0.1 to 0.2 m s-1,indicating a large impact of imposing u*threshold on net ecosystem carbon exchange.展开更多
Temporally irregular rainfall distribution and inefficient rainwater management create severe constraints on crop production in rainfed semiarid areas. Gravel and plastic film mulching are effective methods for improv...Temporally irregular rainfall distribution and inefficient rainwater management create severe constraints on crop production in rainfed semiarid areas. Gravel and plastic film mulching are effective methods for improving agricultural productivity and water utilization. However, the effects of these mulching practices on soil water supply and plant water use associated with crop yield are not well understood. A 3-yr study was conducted to analyze the occurrence and distribution of dry spells in a semiarid region of Northwest China and to evaluate the effects of non-mulching (CK), gravel mulching (GM) and plastic film mulching (FM) on the soil water supply, plant water use and maize (Zea mays L.) grain yield. Rainfall analysis showed that dry spells of ≥5 days occurred frequently in each of 3 yr, accounting for 59.9-69.2% of the maize growing periods. The 〉15-d dry spells during the jointing stage would expose maize plants to particularly severe water stress. Compared with the CK treatment, both the GM and FM treatments markedly increased soil water storage during the early growing season. In general, the total evapotranspiration (ET) was not significantly different among the three treatments, but the mulched treatments significantly increased the ratio of pre- to post-silking ET, which was closely associated with yield improvement. As a result, the grain yield significantly increased by 17.1, 70.3 and 16.7% for the GM treatment and by 28.3, 87.6 and 38.2% for the FM treatment in 2010, 2011 and 2012, respectively, compared with the CK treatment. It's concluded that both GM and FM are effective strategies for mitigating the impacts of water deficit and improving maize production in semiarid areas. However. FM is more effective than GM.展开更多
Forest and landscape restoration (FLR) practices have been reported to improve soil organic carbon stocks (SOCs) and contributing to climate change mitigation. This study aims to evaluate the impact of combined FLR pr...Forest and landscape restoration (FLR) practices have been reported to improve soil organic carbon stocks (SOCs) and contributing to climate change mitigation. This study aims to evaluate the impact of combined FLR practices, mainly developed in semiarid regions, on SOCs. The SOCs, soil texture, bulk density (ρ), pH, CO<sub>2</sub> emissions, and herbaceous biomass were determined at a 0 - 30 cm depth. The experimental design comprised degraded land without FLR practices and three sets of combined FLR practices. These practices included “zaï” + stone bunds + organic manure + assisted natural regeneration (ANR) used to convert degraded land into forest (GF) and cropland (PARL);“zaï” + stone bunds + crop rotation + crop/fallow successions + ANR used to convert degraded land into cropland (OARL) and “zaï”+ stone bunds + organic manure used to convert degraded land into cropland (KARL). SOCs were highest (20.02 t C ha<sup>−1</sup>) under OARL compared with the other combinations of FLR practices. SOCs increased by 99% (+0.2 t C ha<sup>−1</sup>⋅yr<sup>−1</sup>), 58% (+0.3 t C ha<sup>−1</sup>⋅yr<sup>−1</sup>) and 13% (+0.2 t C ha<sup>−1</sup>⋅yr<sup>−1</sup>) under GF, OARL and KARL, respectively, and decreased by 15% (−0.1 t C ha<sup>−1</sup>⋅yr<sup>−1</sup>) under PARL. This study provides additional information explaining SOC variation in restored degraded land through the implementation of a combination of FLR practices. This is useful for recommending the combination “zaï” + stone bunds + crop rotation + crop/fallow successions + ANR to improve SOCs in the semiarid agroecosystem.展开更多
1. The crux of the environment administration problem is theeconomic development As we Know that the evolution of environment is not only due to Nature itself, but al-so to human being particularly. In the course of h...1. The crux of the environment administration problem is theeconomic development As we Know that the evolution of environment is not only due to Nature itself, but al-so to human being particularly. In the course of history, the Loess Plateau in China, oncewoody and rich in plants has now become a serious soil-erosion area on which lies thou-展开更多
基金supported by the National Basic Research Program of China under Grant 2009CB723904
文摘The performance of a 1-D soil model in a semiarid area of North China was investigated using observational data from a cropland station at the Tongyu reference site of the Coordinated Enhanced Observing Period(CEOP)during the non-growing period,when the ground surface was covered with bare soil.Comparisons between simulated and observed soil surface energy balance components as well as soil temperatures and water contents were conducted to validate the soil model.Results show that the soil model could produce good simu-lations of soil surface temperature,net radiation flux,and sensible heat flux against observed values with the RMSE of 1.54°C,7.71 W m-2,and 27.79 W m-2,respectively.The simulated volumetric soil water content is close to the observed values at various depths with the maximal difference between them being 0.03.Simulated latent heat and ground heat fluxes have relatively larger errors in relative to net radiation and sensible heat flux.In conclusion,the soil model has good capacity to simulate the bare soil surface energy balance at the Tongyu cropland station and needs to be further tested in longer period and at more sites in semiarid areas.
基金This research was supported by the National Key Research and Development Program of China(2021YFE0101302and2021YFD1901102)the National Natural Science Foundation of China(31801314 and 31901475)。
文摘Plastic film mulching has been widely used to increase maize yield in the semiarid area of China.However, whether long-term plastic film mulching is conducive to agricultural sustainability in this region remains controversial.A field experiment was initiated in 2013 with five different film mulching methods:(i) control method, flat planting without mulching (CK),(ii) flat planting with half film mulching (P),(iii) film mulching on ridges and planting in narrow furrows(S),(iv) full film mulching on double ridges (D), and (v) film mulching on ridges and planting in wide furrows (R).The effects on soil organic carbon (SOC) content, storage, and fractions, and on the carbon management index (CMI)were evaluated after nine consecutive years of plastic film mulching.The results showed that long-term plastic film mulching generally maintained the initial SOC level.Compared with no mulching, plastic film mulching increased the average crop yield, biomass yield, and root biomass by 48.38, 35.06, and 37.32%, respectively, which led to the improvement of SOC sequestration.Specifically, plastic film mulching significantly improved CMI, and increased the SOC content by 13.59%, SOC storage by 7.47%and easily oxidizable organic carbon (EOC) by 13.78%on average,but it reduced the other labile fractions.SOC sequestration and CMI were improved by refining the plastic film mulching methods.The S treatment had the best effect among the four mulching methods, so it can be used as a reasonable film mulching method for sustainable agricultural development in the semiarid area.
文摘With the rapid development of urban agglomerations in northwest arid and semiarid regions of China, the scope of the urban heat island(UHI) effect has gradually expanded and gradually connected, and has formed a regional heat island(RHI) with a larger range of impact to the regional environment. However, there are few studies on the heat island effect of urban agglomerations in arid and semiarid regions, so this paper selects the urban agglomeration of Hohhot, Baotou and Ordos(HBO) of Inner Mongolia, China as the study area. Based on the 8-day composite Moderate-resolution Imaging Spectroradiometer(MODIS) surface temperature data(156scenes in all) and land use maps for 2005, 2010, and 2015, we analyze the spatiotemporal distributions of regional heat(cool) islands(RH(C)I) and the responses of surface temperatures to land-use changes in the diurnal and interannual surface cities. The results showed that: 1) from 2005 to 2015, urban areas showed the cold island effect during the day, with the area of the cold island showing a shrinking feature;at night, they showed the heat island effect, with the area of the heat island showing a first decrease and then an increase.2) From 2005 to 2015, the land development(unutilized land to building land) brings the greatest temperature increase(ΔT = 1.36°C)during the day, while the greatest temperature change at night corresponds to the conversion of cultivated land to building land(ΔT =0.78°C) exhibited the largest changes at night. From 2010 to 2015, the land development(grassland to building land) bring the greatest temperature increase(ΔT = 0.85°C) during the day, while the great temperature change at night corresponds to the conversion of water areas to building land(ΔT = 1.38°C) exhibited the largest changes at night. Exploring the spatial and temporal evolution of surface urban heat(cool) islands in urban agglomerations in arid and semiarid regions will help to understand the urbanization characteristics of urban agglomerations and provide a reference for the formulation of policies for the coordinated and healthy development of the region and co-governance of regional environmental problems.
基金supported by the National Basic Research Program of China(2012CB956203)the China Meteorological Administration R&D Special Fund for Public Welfare(Meteorology)(GYHY201006023)the National Key Technologies R&D Program of China(2012BAC22B04)
文摘Based on Climatic Research Unit Time Series3.1 temperature and Global Precipitation Climatology Center full data reanalysis version 6 precipitation data,the abilities of climate models from the fifth phase of the Coupled Model Intercomparison Project to simulate climate changes over arid and semiarid areas were assessed.Simulations of future climate changes under different representative concentration pathways(RCPs)were also examined.The key findings were that most of the models are able to capture the dominant features of the spatiotemporal changes in temperature,especially the geographic distribution,during the past 60 years,both globally as well as over arid and semiarid areas.In addition,the models can reproduce the observed warming trends,but with magnitudes generally less than the observations of around0.1–0.3°C/50a.Compared to temperature,the models perform worse in simulating the annual evolution of observed precipitation,underestimating both the variability and tendency,and there is a huge spread among the models in terms of their simulated precipitation results.The multimodel ensemble mean is overall superior to any individual model in reproducing the observed climate changes.In terms of future climate change,an ongoing warming projected by the multi-model ensemble over arid and semiarid areas can clearly be seen under different RCPs,especially under the high emissions scenario(RCP8.5),which is twice that of the moderate scenario(RCP4.5).Unlike the increasing temperature,precipitation changes vary across areas and are more significant under high-emission RCPs,with more precipitation over wet areas but less precipitation over dry areas.In particular,northern China is projected to be one of the typical areas experiencing significantly increased temperature and precipitation in the future.
文摘Minerals and rocks have distinct 87Sr/86Sr and 143Nd/144Nd ratios, depending on their geological origin and ages, and these isotope ratios are less altered than elemental composition during transport in the atmosphere or after deposition as sediments, thus stable isotopes of Sr and Nd have great potential as tracers for provenance and trans- port of materials. During the hypergene process, Sr isotope ratios of sediments are controlled by their parent rocks, particle sizes and chemical weathering. In general, the higher the Sr isotope ratios of parent rocks, and/or the more the fine-grained fractions, and/or the stronger the chemical weathering, thus the higher the Sr isotope ratios of sediments. On the contrary, there are lower Sr isotope ratios of sedi- ments. Nd isotope ratios of sediments, independent of their particle sizes and chemical weathering, are only associated with parent rocks. For the prove- nance of the Chinese Loess Plateau, different re- seachers drew discordant and even contradictory conclusions by using the method of Sr-Nd isotopic tracing. From the previous Nd isotope data, it is con- sidered that the Tarim Basin, deserts in the central and west parts of Inner Mongolia and the Tibetan Plateau are the main sources of the Chinese Loess Plateau, and are also manufacturers for eolian dust of the Far East regions, together with the Chinese Loess Plateau. Sr isotope ratios of eolian dust are solely affected by wind sorting and weather- ing-pedogenesis due to its homogeneous composi- tion in the Chinese Loess Plateau. Wind sorting isrelated to the East Asian winter monsoon but weath- ering-pedogenesis is mainly associated with the East Asian summer monsoon. Studies on Sr isotopic compositions of the loess-paleosol sequence suggest that 87Sr/86Sr ratios in acid-soluble materials are an index for chemical weathering intensity of the Chi- nese Loess Plateau, indicating the East Asian sum- mer monsoon variations, whereas 87Sr/86Sr ratios in acid-insoluble materials are significantly controlled by particle sizes, and can be used as a proxy indicator reflecting the East Asian winter monsoon variations. Variations of 87Sr/86Sr ratios in acid-insoluble materi- als in the past 2.6Ma further demonstrate that the East Asian winter monsoon gradually strengthened since the beginning of the Quaternary period. This result agrees with the prior conclusion that climate gradually cooled since the onset of the Quaternary Ice Age.
基金the National Basic Research Program of China (973 Program, 2006CB500401)partly by the Chinese Academy of Sciences (Grant No. KZCX2-YW-219)
文摘Diurnal, seasonal and interannual variations of surface albedo of degraded grassland and cropland surfaces at a semiarid area of Tognyu have been investigated based on the continuous three years observational data from 2003 to 2005. The changes of surface albedo with solar elevation angle and soil moisture have been discussed also. It has been found that surface albedo has almost the same diurnal and seasonal variations on degraded grassland and cropland surfaces in the semiarid area, while sur- face albedo is large in winter and small in summer. The diurnal variation of the surface albedo has re- lationship with the weather condition. The diurnal cycle of the surface albedo likes the "U" shape curve in sunny day, while it is low-high after the rain, and high-low after the snow. The surface albedo has large variation in cloudy day, while it has no any variation in overcast day. The large difference of the surface albedo can be 0.04 in winter between two land surfaces, because the snow has large effects on the surface albedo in winter. The rainfall is an important factor in summer on the surface albedo, while the difference of the surface albedo is 0.01 only between two land surfaces. The differences of the surface albedo can also be 0.04 in autumn due to vegetation growing. The seasonal-average surface albeo from 2003―2005 is 0.25, 0.22, 0.24, 0.32 respectively in spring, summer, autumn and winter on the degraded grassland surface,while it is 0.25, 0.21, 0.22, 0.33 respectively in spring, summer, autumn and winter on the cropland surface. The surface albedo becomes smaller with the increase of solar elevation angle. When the solar elevation angle is greater than 40°, the surface albedo changes very little and tends to be a constant. The surface albedo has negative exponent functions with soil moisture in the growing season.
基金supported by the National Basic Research Program of China (Grant Nos. 2010CB951801 and 2006CB400500)
文摘Here we report a multiyear study on the surface roughness length and bulk transfer coefficients over the degraded grassland and cropland surfaces in a semiarid area of China. Eddy covariance measurement and the meteorological profile observation data were used to analyze characteristics of these parameters on the diurnal, seasonal, and annual scales. Significant seasonal and annual variations of the aerodynamic roughness length are observed over the two surfaces. A large variation of kB-1 is measured during the day. Both kB-1 and the bulk transfer coefficients exhibit significant seasonal and annual variations. During the growing season (May to October), average Cd and Ch are 3.1×10-3 and 2.5×10-3 over the degrade grassland surface, and 4.7×10-3 and 3.1×10-3 over the cropland surface respectively. During the non-growing season, average Cd and Ch are 2.3×10-3 and 2.0×10-3 over the degrade grassland surface, and 2.9×10-3 and 2.2×10-3 over the cropland surface respectively.
基金the National Natural Science Foundation of China(Grant No.40301006)
文摘There have been significant variations in wind activity over the past five decades in arid and semiarid areas in China.High wind activity occurred from the 1960s to the 1970s,but wind activity has de-creased continuously from the 1980s to the present;as a result,the potential sand transport during the latter period was only 20%-50% of the values during the 1960s and 1970s.Phases of high wind activ-ity were highly consistent with the trends in desertification over the past five decades in arid and semiarid areas in China,but spring precipitation was also a significant factor:rapid desertification during the 1960s and 1970s was due to high wind activity,generally combining with low spring pre-cipitation;subsequent rehabilitation since the 1980s has resulted from the combined effects of low wind activity and higher spring precipitation.Therefore,although modern desertification and rehabili-tation processes are being more or less affected by human activities,both processes appear to be more strongly controlled by climate change.
基金supported by the National Natural Science Foundation of China(Grant Nos.41275023,41021004))Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA05110102)
文摘Based on eddy covariance measurements over two kinds of land surfaces(a degraded grassland and a maize cropland)in a semiarid area of China in 2005 and 2008,the effects of different gap filling methods,energy balance closure and friction velocity threshold(u*)on annual net ecosystem exchange(NEE)were analyzed.Six gap filling methods,including mean diurnal variation(MDV),marginal distribution sampling(MDS),and nonlinear regressions method,were investigated by generating secondary datasets with four different artificial gap lengths(ranging in length from single half-hours to 12 consecutive days).The MDS generally showed a good overall performance especially for long gaps,with an annual sum bias error less than 5 g C m-2 yr-1.There was a large positive annual sum bias error for nonlinear regressions,indicating an overestimate on net ecosystem respiration.The offset in the annual sum NEE for four nonlinear regressions was from 8.0 to 30.8 g C m-2 yr-1.As soil water content was a limiting factor in the semiarid area,the nonlinear regressions considering both soil temperature and soil water content as controlling variables had a better performance than others.The performance of MDV was better in daytime than in nighttime,with an annual sum bias error falling between-2.6 and-13.4 g C m-2 yr-1.Overall,the accuracy of the gap filling method was dependent on the type of the land surface,gap length,and the time of day when the data gap occurred.The energy balance ratio for the two ecosystems was nearly 80%.Turbulent intensity had a large impact on energy balance ratio.Low energy balance ratio was observed under low friction velocity during the night.When there was a large fetch distance in a wind direction,a low energy balance ratio was caused by mismatch of the footprints between the available energy and turbulent fluxes.The effect of energy balance correction on CO2 flux was evaluated by assuming the imbalance caused by the underestimation of sensible heat flux and latent heat flux.The results showed an average increase of 10 g C m-2 yr-1 for annual NEE in both ecosystems with an energy balance correction.On the other hand,the u*threshold also have a large impact on annual sum NEE.Net carbon emission increased 37.5 g C m-2 yr-1 as u*threshold increased from 0.1 to 0.2 m s-1,indicating a large impact of imposing u*threshold on net ecosystem carbon exchange.
基金financially supported by the National Natural Science Foundation of China (31270553)the National Basic Research Program of China (2009CB118604)the Special Fund for Agro-Scientific Research in the Public Interest of China (201103003)
文摘Temporally irregular rainfall distribution and inefficient rainwater management create severe constraints on crop production in rainfed semiarid areas. Gravel and plastic film mulching are effective methods for improving agricultural productivity and water utilization. However, the effects of these mulching practices on soil water supply and plant water use associated with crop yield are not well understood. A 3-yr study was conducted to analyze the occurrence and distribution of dry spells in a semiarid region of Northwest China and to evaluate the effects of non-mulching (CK), gravel mulching (GM) and plastic film mulching (FM) on the soil water supply, plant water use and maize (Zea mays L.) grain yield. Rainfall analysis showed that dry spells of ≥5 days occurred frequently in each of 3 yr, accounting for 59.9-69.2% of the maize growing periods. The 〉15-d dry spells during the jointing stage would expose maize plants to particularly severe water stress. Compared with the CK treatment, both the GM and FM treatments markedly increased soil water storage during the early growing season. In general, the total evapotranspiration (ET) was not significantly different among the three treatments, but the mulched treatments significantly increased the ratio of pre- to post-silking ET, which was closely associated with yield improvement. As a result, the grain yield significantly increased by 17.1, 70.3 and 16.7% for the GM treatment and by 28.3, 87.6 and 38.2% for the FM treatment in 2010, 2011 and 2012, respectively, compared with the CK treatment. It's concluded that both GM and FM are effective strategies for mitigating the impacts of water deficit and improving maize production in semiarid areas. However. FM is more effective than GM.
文摘Forest and landscape restoration (FLR) practices have been reported to improve soil organic carbon stocks (SOCs) and contributing to climate change mitigation. This study aims to evaluate the impact of combined FLR practices, mainly developed in semiarid regions, on SOCs. The SOCs, soil texture, bulk density (ρ), pH, CO<sub>2</sub> emissions, and herbaceous biomass were determined at a 0 - 30 cm depth. The experimental design comprised degraded land without FLR practices and three sets of combined FLR practices. These practices included “zaï” + stone bunds + organic manure + assisted natural regeneration (ANR) used to convert degraded land into forest (GF) and cropland (PARL);“zaï” + stone bunds + crop rotation + crop/fallow successions + ANR used to convert degraded land into cropland (OARL) and “zaï”+ stone bunds + organic manure used to convert degraded land into cropland (KARL). SOCs were highest (20.02 t C ha<sup>−1</sup>) under OARL compared with the other combinations of FLR practices. SOCs increased by 99% (+0.2 t C ha<sup>−1</sup>⋅yr<sup>−1</sup>), 58% (+0.3 t C ha<sup>−1</sup>⋅yr<sup>−1</sup>) and 13% (+0.2 t C ha<sup>−1</sup>⋅yr<sup>−1</sup>) under GF, OARL and KARL, respectively, and decreased by 15% (−0.1 t C ha<sup>−1</sup>⋅yr<sup>−1</sup>) under PARL. This study provides additional information explaining SOC variation in restored degraded land through the implementation of a combination of FLR practices. This is useful for recommending the combination “zaï” + stone bunds + crop rotation + crop/fallow successions + ANR to improve SOCs in the semiarid agroecosystem.
文摘1. The crux of the environment administration problem is theeconomic development As we Know that the evolution of environment is not only due to Nature itself, but al-so to human being particularly. In the course of history, the Loess Plateau in China, oncewoody and rich in plants has now become a serious soil-erosion area on which lies thou-