We conducted an investigation into the germination of seeds from individual Populus euphratica trees of different ages and growing conditions in order to discover the effect of intraspecific factors on their sexual re...We conducted an investigation into the germination of seeds from individual Populus euphratica trees of different ages and growing conditions in order to discover the effect of intraspecific factors on their sexual reproduction in the Ejina Oasis, Inner Mongolia of China. By carrying out germination experiments of seeds collected at various seed dispersal periods, we found that P. euphratica seeds could be germinated intensively within 8 h from the start of the experiments, that the germination percentage decreased with the time of seed dispersal and that the germination percentage of seeds collected at the early stage of seed dispersal was 1.86 times greater than those collected at the final stage. There was no significant difference in the germination percentage or the germination index between seeds collected at the early and peak stages. The vitality of seeds from the mature forest was clearly higher than that of the half-mature and near-mature forests. The rate of branch dieback only affected seed germination at the final stage. Therefore, we conclude that the mature P. euphratica forest was the main contributor to reproduction. The results show that both the time of seed harvest and stand age were the main factors affecting the germination percentage of P. euphratica seeds.展开更多
The dynamic environments in riparian zones support a variety of life-history strategies, which constitute a fundamental mechanism for development and maintenance of biodiversity in riparian forest ecosystems. To demon...The dynamic environments in riparian zones support a variety of life-history strategies, which constitute a fundamental mechanism for development and maintenance of biodiversity in riparian forest ecosystems. To demonstrate the effect of life-history strategies on biodiversity, we investigated community-level diversity and its relationship to environmental variability in the riparian Populus euphratica forests of the Ejina Oasis. Communities were divided into 14 associations on the basis of their species impor- tance values. The Simpson＇s index, Shannon-Wiener index, Pielou＇s evenness index and the regional Whittaker＇s index were applied to calculate community diversity. An ordination of the sample plots was carried out by correspondence analysis （CA）. Biodiversity was relatively low across the entire study area, but there was high community diversity （flw = 8.09） due to the spatial heterogeneity of habitats in different plots. In addition, we investigated the relationship between biodiversity and several environmental factors, such as water availability, community components and soil conditions. We conclude that the heterogeneity of soil and water availability drives community diversity patterns in riparian zones and that community-level diversity favors the maintenance of species diversity in the P euphratica forests in the Ejina Oasis.展开更多
Groundwater is a key factor controlling the growth of vegetation in desert riparian systems. It is important to recognise how groundwater changes affect the riparian forest ecosystem. This information will not only he...Groundwater is a key factor controlling the growth of vegetation in desert riparian systems. It is important to recognise how groundwater changes affect the riparian forest ecosystem. This information will not only help us to understand the ecological and hydrological process of the riparian forest but also provide support for ecological recovery of riparian forests and water-resources management of arid inland river basins. This study aims to estimate the suitability of the Water Vegetation Energy and Solute Modelling(WAVES) model to simulate the Ejina Desert riparian forest ecosystem changes,China, to assess effects of groundwater-depth change on the canopy leaf area index(LAI) and water budgets, and to ascertain the suitable groundwater depth for preserving the stability and structure of desert riparian forest. Results demonstrated that the WAVES model can simulate changes to ecological and hydrological processes. The annual mean water consumption of a Tamarix chinensis riparian forest was less than that of a Populus euphratica riparian forest, and the canopy LAI of the desert riparian forest should increase as groundwater depth decreases. Groundwater changes could significantly influence water budgets for T. chinensis and P. euphratica riparian forests and show the positive and negative effects on vegetation growth and water budgets of riparian forests. Maintaining the annual mean groundwater depth at around 1.7-2.7 m is critical for healthy riparian forest growth. This study highlights the importance of considering groundwater-change impacts on desert riparian vegetation and water-balance applications in ecological restoration and efficient water-resource management in the Heihe River Basin.展开更多
To characterize the groundwater in the Ejina Basin,surface and groundwater samples were collected in May and October of 2002.On-site analyses included temperature,electrical conductance(EC),total alkalinity(as HCO 3) ...To characterize the groundwater in the Ejina Basin,surface and groundwater samples were collected in May and October of 2002.On-site analyses included temperature,electrical conductance(EC),total alkalinity(as HCO 3) by titration,and pH.Chemical analyses were undertaken at the Geochemistry Laboratory of the Cold and Arid Region Environmental and Engineering Institute,Chinese Academy of Sciences,Lanzhou,China.The pH of the groundwater ranged from 7.18 to 8.90 with an average value of 7.72,indicating an alkaline nature.The total dissolved solids(TDS) of the groundwater ranged from 567.5 to 5,954.4 mg/L with an average of 1,543.1 mg/L and a standard deviation of 1,471.8 mg/L.According to the groundwater salinity classification of Robinove et al.(1958),47.4 percent of the samples were brackish and the remainder were fresh water.The ion concentration of the groundwater along the riverbed and near the southern margin of the basin were lower than those farther away from the riverbed.The groundwater in the study area was of Na +-HCO 3 type near the bank of the Heihe River and in the southern margin of the basin,while Na +-SO 4 2-Cl type samples were observed in the terminal lake region.In the desert area the groundwater reached a TDS of 3,000-6,000 mg/L and was predominantly by a Na +-Cl chemistry.Br/Cl for the water of Ejina Basin indicates an evaporite origin for the groundwater with a strongly depleted Br/Cl ratio(average 0.000484).The surface water was slightly enriched in Br/Cl(average 0.000711) compared with groundwater.The calculated saturation index(SI) for calcite and dolomite of the groundwater samples range from 0.89 to 1.31 and 1.67 to 2.67 with averaged 0.24 and 0.61,respectively.About 97 percent of the groundwater samples were kinetically oversaturated with respect to calcite and dolomite,and all the samples were below the equilibrium state with gypsum.Using isotope and hydrochemical analyses,this study investigated the groundwater evolution and its residence time.The groundwater content was mainly determined by the dissolutions of halite,gypsum,and Glauber’s salt(Na 2 SO 4),as well as Na + exchange for Ca 2+,and calcite and dolomite precipitation.With the exception of a few locations,most of the groundwater samples were suitable for irrigation uses.Most of the stable isotope compositions in the groundwater sampled plotted close to the Global Meteoric Water Line(GMWL),indicating that the groundwater was mainly sourced from meteoric water.There was evidence of enrichment of heavy isotopes in the groundwater due to evaporation.Based on the tritium content in atmospheric precipitation and by adopting the exponential-piston model(EPM),the mean residence time of the unconfined aquifer groundwater was evaluated.The results show that these groundwaters have low residence time(12 to 48 years) and are renewable.In contrast,the confined groundwater had 14 C ages estimated by the Pearson model between 4,087 to 9,364 years BP.Isotopic signatures indicated formation of deep confined groundwaters in a colder and wetter climate during the late Pleistocene and Holocene.展开更多
Water is a primary controlling factor for economic development and ecological environmental protection in the inland river basins of arid western China. And it is groundwater, as the most important component of total ...Water is a primary controlling factor for economic development and ecological environmental protection in the inland river basins of arid western China. And it is groundwater, as the most important component of total water resources, that plays a dominant role in the development of western China. In recent years, the use-ratio of surface water has been raised, the groundwater recharge rate from surface water has been reduced, and groundwater has been exploited on a large scale. This has led to the decline of ground-water levels and the degradation of eco-environments in the Heihe watershed. Therefore, the study on the change in groundwater levels in recent years, as well as simulating and predicting groundwater levels in the future, have become very significant for im-proving the ecological environment of the Heihe River Basin, to coordinate the water contradiction among upper, middle and lower reaches of Heihe River Basin and to allocate the water resources. The purpose of this study is to analyze the groundwa-ter-level variations of the Ejina region based on a large scale, to develop and evaluate a conceptual groundwater model in Ejina Basin, to establish the groundwater flow model using the experimental observation data and combining Modular Three-Dimensional Groundwater Flow Model (MODFLOW) and GIS software, to simulate the regional hydrologic regime in re-cent 10 years and compare various water-delivery scenarios from midstream, and to determine which one would be the best plan for maintaining and recovering the groundwater levels and increasing the area of Ejina oasis. Finally this paper discusses the pos-sible vegetation changes of Ejina Basin in the future.展开更多
Based on gas chromatography and gas chromatography mass spectrometry techniques, the authors examined biomarker characteristics of the Ganquan Formation source rocks in the area of Dahulishan, Ejina, and analyzed the ...Based on gas chromatography and gas chromatography mass spectrometry techniques, the authors examined biomarker characteristics of the Ganquan Formation source rocks in the area of Dahulishan, Ejina, and analyzed the information and petroleum geological significance that were indicated by the source of organic matter, sedimentary environment and maturity and so on. Gas chromatography peak of saturated hydrocarbons from the Ganquan Formation source rocks showed "the former peak" of the single peak distribution, the main peak of carbon being C18 , indicating the main sources of organic matter with marine organic matter. Pr/Ph ranges from 0.3 to 0.6, indicating a strongly reducing sedimentary environment. Biomarker assemblages of the Ganquan Formation source rocks are abundant in tricyclic terpane with long side chains, with a high level of gammacerane, showing dominant distribution of C27 sterane. High contents of gammacerane in organic matter show organic facies of source rocks in the saltwater sedimentary environment. That average hopane/sterane ratio is 0.59, showing that algae have made more contributions to organic matter than bacteria. And the high level of C27 steranes shows that algae are the main source of hydrocarbon precursors. The Ganquan Formation's methylphenanthrene index, which is an effective molecular parameter index to measure thermal evolution of organic matter, ranges from 0.35 to 0.50, and the conversion of vitrinite reflectance Rc from it is within the range of 2.00-2.09, indicating that the Ganquan Formation source rocks are in the over-mature stage of thermal evolution.展开更多
The Ecological Water Requirement (EWR) of desert oasis is the amount of water required to maintain a normal growth of vegetation in the special ecosystems. In this study EWR of the Ejina desert oasis is estimated thro...The Ecological Water Requirement (EWR) of desert oasis is the amount of water required to maintain a normal growth of vegetation in the special ecosystems. In this study EWR of the Ejina desert oasis is estimated through the relational equation between normalized difference vegetation index (NDVI), productivity and transpiration coefficient, which was established by a combination of the RS, GIS, GPS techniques with the field measurements of productivity. The results show that about 1.53×108 m3 water would be needed to maintain the present state of the Ejina Oasis, and the ecological water requirement would amount to 3.49×108 m3 if the existing vegetation was restored to the highest productivity level at present. Considering the domestic water requirement, river delivery loss, oasis vegetation water con-sumption, farmland water demand, precipitation recharge, etc., the draw-off discharge of the Heihe River (at Longxin Mount) should be 1.93×108―2.23 ×108 m3 to maintain the present state of the Ejina Oasis, and 4.28×108―5.17×108 m3 to make the existing vegetation be restored to the highest productiv-ity level at present.展开更多
By using the theories and methods of landscape ecology and the technology of GIS and RS, a study has been carried out on the responses of distribution pattern of desert riparian forest to hydrologic process on the bas...By using the theories and methods of landscape ecology and the technology of GIS and RS, a study has been carried out on the responses of distribution pattern of desert riparian forest to hydrologic process on the basis of the hydrologic data from 1990 to 2000 and the TM image of 2001 year. The results showed that: (1) there appears an even distribution pattern for the relative forest area in oasis, however, the degenerated forest diaplays an increasing tendency from west to east; (2) the desert riparian forest in Ejina is in completely degenerated process at the patch scale; (3) the number of patch is influenced not only by hydrologic process,but also by agricultural activity such as cultivation. The severe deterioration of the degraded vegetation in whole oasis initiates from lower reaches, and gradually impels to upstream; the fragmentation of landscape in the terminal site is more obvious, which is influenced by river shape and decreasing flux of water. It is found that the influence of surface hydrologic process to the ground hydrologic process of desert riparian forest in Ejina oasis is little for the recent ten years. The relative area of the degenerated forest increased with increasing ground water depth in the direction of parallel to river channel. On the contrary, in the direction perpendicular to river channel, there is a decreasing tendency for the average patch area of the forest and the degenerated forest with increasing ground water depth.展开更多
Reconstructing the evolutionary history of the Gobi deserts developed from alluvial sediments in arid regions has great significance in unraveling changes in both tectonic activity and climate.However,such work is lim...Reconstructing the evolutionary history of the Gobi deserts developed from alluvial sediments in arid regions has great significance in unraveling changes in both tectonic activity and climate.However,such work is limited by a lack of suitable dating material preserved in the Gobi Desert,but cosmogenic 10Be has great potential to date the Gobi deserts.In the present study,10Be in quartz gravel from the Gobi deserts of the Ejina Basin in Inner Mongolia of China has been measured to assess exposure ages.Results show that the Gobi Desert in the northern margin of the basin developed 420 ka ago,whereas the Gobi Desert that developed from alluvial plains in the Heihe River drainage basin came about during the last 190 ka.The latter developed gradually northward and eastward to modern terminal lakes of the river.These temporal and spatial variations in the Gobi deserts are a consequence of alluvial processes influenced by Tibetan Plateau uplift and tectonic activities within the Ejina Basin.Possible episodes of Gobi Desert development within the last 420 ka indicate that the advance/retreat of alpine glaciers during glacial/interglacial cycles might have been the dominant factor to influencing the alluvial intensity and water volume in the basin.Intense floods and large water volumes would mainly occur during the short deglacial periods.展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos. 31070553, 30570332)the 11th Five-Year Plan of the National Scientific and Technological Support Projects of China (Grant No. 2008BAD-B0B05)
文摘We conducted an investigation into the germination of seeds from individual Populus euphratica trees of different ages and growing conditions in order to discover the effect of intraspecific factors on their sexual reproduction in the Ejina Oasis, Inner Mongolia of China. By carrying out germination experiments of seeds collected at various seed dispersal periods, we found that P. euphratica seeds could be germinated intensively within 8 h from the start of the experiments, that the germination percentage decreased with the time of seed dispersal and that the germination percentage of seeds collected at the early stage of seed dispersal was 1.86 times greater than those collected at the final stage. There was no significant difference in the germination percentage or the germination index between seeds collected at the early and peak stages. The vitality of seeds from the mature forest was clearly higher than that of the half-mature and near-mature forests. The rate of branch dieback only affected seed germination at the final stage. Therefore, we conclude that the mature P. euphratica forest was the main contributor to reproduction. The results show that both the time of seed harvest and stand age were the main factors affecting the germination percentage of P. euphratica seeds.
基金supported by the National Natural Science Foundation of China (No. 30570332)the 11th Five-Year Plan of the National Scientific and Technological Support Projects (2008BADB0B05)
文摘The dynamic environments in riparian zones support a variety of life-history strategies, which constitute a fundamental mechanism for development and maintenance of biodiversity in riparian forest ecosystems. To demonstrate the effect of life-history strategies on biodiversity, we investigated community-level diversity and its relationship to environmental variability in the riparian Populus euphratica forests of the Ejina Oasis. Communities were divided into 14 associations on the basis of their species impor- tance values. The Simpson＇s index, Shannon-Wiener index, Pielou＇s evenness index and the regional Whittaker＇s index were applied to calculate community diversity. An ordination of the sample plots was carried out by correspondence analysis （CA）. Biodiversity was relatively low across the entire study area, but there was high community diversity （flw = 8.09） due to the spatial heterogeneity of habitats in different plots. In addition, we investigated the relationship between biodiversity and several environmental factors, such as water availability, community components and soil conditions. We conclude that the heterogeneity of soil and water availability drives community diversity patterns in riparian zones and that community-level diversity favors the maintenance of species diversity in the P euphratica forests in the Ejina Oasis.
基金supported by the National Key Research and Development program (2016YFC0400908)the National Natural Science Foundation of China (Nos. 41101026, 31370466)the STS project of Chinese academy of sciences (29Y829731)
文摘Groundwater is a key factor controlling the growth of vegetation in desert riparian systems. It is important to recognise how groundwater changes affect the riparian forest ecosystem. This information will not only help us to understand the ecological and hydrological process of the riparian forest but also provide support for ecological recovery of riparian forests and water-resources management of arid inland river basins. This study aims to estimate the suitability of the Water Vegetation Energy and Solute Modelling(WAVES) model to simulate the Ejina Desert riparian forest ecosystem changes,China, to assess effects of groundwater-depth change on the canopy leaf area index(LAI) and water budgets, and to ascertain the suitable groundwater depth for preserving the stability and structure of desert riparian forest. Results demonstrated that the WAVES model can simulate changes to ecological and hydrological processes. The annual mean water consumption of a Tamarix chinensis riparian forest was less than that of a Populus euphratica riparian forest, and the canopy LAI of the desert riparian forest should increase as groundwater depth decreases. Groundwater changes could significantly influence water budgets for T. chinensis and P. euphratica riparian forests and show the positive and negative effects on vegetation growth and water budgets of riparian forests. Maintaining the annual mean groundwater depth at around 1.7-2.7 m is critical for healthy riparian forest growth. This study highlights the importance of considering groundwater-change impacts on desert riparian vegetation and water-balance applications in ecological restoration and efficient water-resource management in the Heihe River Basin.
基金supported by grants from the National Social Science Foundation (No. 08XJY009)the National Natural Science Foundation of China (Nos. 40701054,Yo11391001 and 40801001)the China Postdoctoral Science Foundation (No. 20090450850)
文摘To characterize the groundwater in the Ejina Basin,surface and groundwater samples were collected in May and October of 2002.On-site analyses included temperature,electrical conductance(EC),total alkalinity(as HCO 3) by titration,and pH.Chemical analyses were undertaken at the Geochemistry Laboratory of the Cold and Arid Region Environmental and Engineering Institute,Chinese Academy of Sciences,Lanzhou,China.The pH of the groundwater ranged from 7.18 to 8.90 with an average value of 7.72,indicating an alkaline nature.The total dissolved solids(TDS) of the groundwater ranged from 567.5 to 5,954.4 mg/L with an average of 1,543.1 mg/L and a standard deviation of 1,471.8 mg/L.According to the groundwater salinity classification of Robinove et al.(1958),47.4 percent of the samples were brackish and the remainder were fresh water.The ion concentration of the groundwater along the riverbed and near the southern margin of the basin were lower than those farther away from the riverbed.The groundwater in the study area was of Na +-HCO 3 type near the bank of the Heihe River and in the southern margin of the basin,while Na +-SO 4 2-Cl type samples were observed in the terminal lake region.In the desert area the groundwater reached a TDS of 3,000-6,000 mg/L and was predominantly by a Na +-Cl chemistry.Br/Cl for the water of Ejina Basin indicates an evaporite origin for the groundwater with a strongly depleted Br/Cl ratio(average 0.000484).The surface water was slightly enriched in Br/Cl(average 0.000711) compared with groundwater.The calculated saturation index(SI) for calcite and dolomite of the groundwater samples range from 0.89 to 1.31 and 1.67 to 2.67 with averaged 0.24 and 0.61,respectively.About 97 percent of the groundwater samples were kinetically oversaturated with respect to calcite and dolomite,and all the samples were below the equilibrium state with gypsum.Using isotope and hydrochemical analyses,this study investigated the groundwater evolution and its residence time.The groundwater content was mainly determined by the dissolutions of halite,gypsum,and Glauber’s salt(Na 2 SO 4),as well as Na + exchange for Ca 2+,and calcite and dolomite precipitation.With the exception of a few locations,most of the groundwater samples were suitable for irrigation uses.Most of the stable isotope compositions in the groundwater sampled plotted close to the Global Meteoric Water Line(GMWL),indicating that the groundwater was mainly sourced from meteoric water.There was evidence of enrichment of heavy isotopes in the groundwater due to evaporation.Based on the tritium content in atmospheric precipitation and by adopting the exponential-piston model(EPM),the mean residence time of the unconfined aquifer groundwater was evaluated.The results show that these groundwaters have low residence time(12 to 48 years) and are renewable.In contrast,the confined groundwater had 14 C ages estimated by the Pearson model between 4,087 to 9,364 years BP.Isotopic signatures indicated formation of deep confined groundwaters in a colder and wetter climate during the late Pleistocene and Holocene.
基金Financial support for this study is from National Natural Science Funds for Distinguished Young Scholar (40725001) National Natural Science Foundation of China (40671010) co-sponsored fellowship are gratefully acknowledged
文摘Water is a primary controlling factor for economic development and ecological environmental protection in the inland river basins of arid western China. And it is groundwater, as the most important component of total water resources, that plays a dominant role in the development of western China. In recent years, the use-ratio of surface water has been raised, the groundwater recharge rate from surface water has been reduced, and groundwater has been exploited on a large scale. This has led to the decline of ground-water levels and the degradation of eco-environments in the Heihe watershed. Therefore, the study on the change in groundwater levels in recent years, as well as simulating and predicting groundwater levels in the future, have become very significant for im-proving the ecological environment of the Heihe River Basin, to coordinate the water contradiction among upper, middle and lower reaches of Heihe River Basin and to allocate the water resources. The purpose of this study is to analyze the groundwa-ter-level variations of the Ejina region based on a large scale, to develop and evaluate a conceptual groundwater model in Ejina Basin, to establish the groundwater flow model using the experimental observation data and combining Modular Three-Dimensional Groundwater Flow Model (MODFLOW) and GIS software, to simulate the regional hydrologic regime in re-cent 10 years and compare various water-delivery scenarios from midstream, and to determine which one would be the best plan for maintaining and recovering the groundwater levels and increasing the area of Ejina oasis. Finally this paper discusses the pos-sible vegetation changes of Ejina Basin in the future.
基金supported jointly by the China Geological Survey Project (Grant Nos. 1212011120972 and 1212010733506)Hubei Provincial Natural Science Foundation (Grant No. 2010CDB04305)CNPC Innovation Foundation (Grant No. 2010D-5006-0105)
文摘Based on gas chromatography and gas chromatography mass spectrometry techniques, the authors examined biomarker characteristics of the Ganquan Formation source rocks in the area of Dahulishan, Ejina, and analyzed the information and petroleum geological significance that were indicated by the source of organic matter, sedimentary environment and maturity and so on. Gas chromatography peak of saturated hydrocarbons from the Ganquan Formation source rocks showed "the former peak" of the single peak distribution, the main peak of carbon being C18 , indicating the main sources of organic matter with marine organic matter. Pr/Ph ranges from 0.3 to 0.6, indicating a strongly reducing sedimentary environment. Biomarker assemblages of the Ganquan Formation source rocks are abundant in tricyclic terpane with long side chains, with a high level of gammacerane, showing dominant distribution of C27 sterane. High contents of gammacerane in organic matter show organic facies of source rocks in the saltwater sedimentary environment. That average hopane/sterane ratio is 0.59, showing that algae have made more contributions to organic matter than bacteria. And the high level of C27 steranes shows that algae are the main source of hydrocarbon precursors. The Ganquan Formation's methylphenanthrene index, which is an effective molecular parameter index to measure thermal evolution of organic matter, ranges from 0.35 to 0.50, and the conversion of vitrinite reflectance Rc from it is within the range of 2.00-2.09, indicating that the Ganquan Formation source rocks are in the over-mature stage of thermal evolution.
基金Spported by the Knowledge Innovation Program of the Chinese Academy of Sciences (Grant No. KZCX3-SW-329)the National Natural Science Foundation of China (Grant No. 40235053)
文摘The Ecological Water Requirement (EWR) of desert oasis is the amount of water required to maintain a normal growth of vegetation in the special ecosystems. In this study EWR of the Ejina desert oasis is estimated through the relational equation between normalized difference vegetation index (NDVI), productivity and transpiration coefficient, which was established by a combination of the RS, GIS, GPS techniques with the field measurements of productivity. The results show that about 1.53×108 m3 water would be needed to maintain the present state of the Ejina Oasis, and the ecological water requirement would amount to 3.49×108 m3 if the existing vegetation was restored to the highest productivity level at present. Considering the domestic water requirement, river delivery loss, oasis vegetation water con-sumption, farmland water demand, precipitation recharge, etc., the draw-off discharge of the Heihe River (at Longxin Mount) should be 1.93×108―2.23 ×108 m3 to maintain the present state of the Ejina Oasis, and 4.28×108―5.17×108 m3 to make the existing vegetation be restored to the highest productiv-ity level at present.
基金supported by Grand Project of Knowledge Innovation Program of Chinese Academy of Sciences(Grand Nos.KZCX3-SW-329 and KZCX1-09)National Natural Science Foundation of China(Grand No.40235053).
文摘By using the theories and methods of landscape ecology and the technology of GIS and RS, a study has been carried out on the responses of distribution pattern of desert riparian forest to hydrologic process on the basis of the hydrologic data from 1990 to 2000 and the TM image of 2001 year. The results showed that: (1) there appears an even distribution pattern for the relative forest area in oasis, however, the degenerated forest diaplays an increasing tendency from west to east; (2) the desert riparian forest in Ejina is in completely degenerated process at the patch scale; (3) the number of patch is influenced not only by hydrologic process,but also by agricultural activity such as cultivation. The severe deterioration of the degraded vegetation in whole oasis initiates from lower reaches, and gradually impels to upstream; the fragmentation of landscape in the terminal site is more obvious, which is influenced by river shape and decreasing flux of water. It is found that the influence of surface hydrologic process to the ground hydrologic process of desert riparian forest in Ejina oasis is little for the recent ten years. The relative area of the degenerated forest increased with increasing ground water depth in the direction of parallel to river channel. On the contrary, in the direction perpendicular to river channel, there is a decreasing tendency for the average patch area of the forest and the degenerated forest with increasing ground water depth.
基金supported by the Knowledge Innovation Program of the Chinese Academy of Sciences(KZCX2-YW-117)the National Natural Science Foundation of China(40841022 and 40373046)
文摘Reconstructing the evolutionary history of the Gobi deserts developed from alluvial sediments in arid regions has great significance in unraveling changes in both tectonic activity and climate.However,such work is limited by a lack of suitable dating material preserved in the Gobi Desert,but cosmogenic 10Be has great potential to date the Gobi deserts.In the present study,10Be in quartz gravel from the Gobi deserts of the Ejina Basin in Inner Mongolia of China has been measured to assess exposure ages.Results show that the Gobi Desert in the northern margin of the basin developed 420 ka ago,whereas the Gobi Desert that developed from alluvial plains in the Heihe River drainage basin came about during the last 190 ka.The latter developed gradually northward and eastward to modern terminal lakes of the river.These temporal and spatial variations in the Gobi deserts are a consequence of alluvial processes influenced by Tibetan Plateau uplift and tectonic activities within the Ejina Basin.Possible episodes of Gobi Desert development within the last 420 ka indicate that the advance/retreat of alpine glaciers during glacial/interglacial cycles might have been the dominant factor to influencing the alluvial intensity and water volume in the basin.Intense floods and large water volumes would mainly occur during the short deglacial periods.
