Permeability and water-bearing space are important hydrological characteristics of the loess strata. In this study a systematic experiment was conducted to measure the magnetic susceptibility, grain size, porosity, an...Permeability and water-bearing space are important hydrological characteristics of the loess strata. In this study a systematic experiment was conducted to measure the magnetic susceptibility, grain size, porosity, and infiltration rate of the loess and palaeosol layers on a loess tableland of the central Chinese Loess Plateau, in order to investigate the differences in hydrological conditions between the loess and palaeosol layers. The magnetic susceptibility of the loess layer was lower than that of the palaeosol layer, but the average quasi-steady infiltration rate was about 0.31 mm min^(-1) higher, the coarse silt and very fine sand contents were about7.1% greater, and the porosity was about 5.7% higher. These differences were mainly due to pedogenesis, which was affected by the Quaternary climate. The pedogenesis differences between the loess and palaeosol layers resulted in hydrological property differences in terms of permeability and water-bearing space. The loess layer had a higher permeability and more water-bearing space than the palaeosol layer, which meant that the loess layer is more likely to form aquifers and the palaeosol layer is more prone to form aquitards.The groundwater in the loess strata had a multilayered characteristic, which depended on the relative impermeability of palaeosol layer and the alternate deposition of loess-palaeosol layers. The hydrological characteristics of the loess strata demonstrated that the Quaternary climate had an important control function on the formation and movement of groundwater. This knowledge provides a reliable theoretical basis for water resource development and utilization on the Chinese Loess Plateau, and this study extends the application of Quaternary climate change theory to hydrological systems in loess deposits.展开更多
Through the studies on low temperature susceptibility, frequency dependent susceptibility, isothermal remanent magnetization, low temperature magnetization and demagnetization for loess and palaeosols one can easily r...Through the studies on low temperature susceptibility, frequency dependent susceptibility, isothermal remanent magnetization, low temperature magnetization and demagnetization for loess and palaeosols one can easily reveal some significant characters of rock magnetism for the magnetic minerals of ultrafine grain sizes, those are very difficult to identify by general geological methods. It is shown in the present study that both loess and palaeosols cover magnetic grain size from superparamagnetism, single domain to multidomain. Loess samples with relative high peramagnetic minerals are dominantly of thermally stable characteristics while palaeosols have relatively high percentage of superparamagnetic grain (0.01—0.03μm). The relative grain size of magnetite is always finer in palaeosol with higher susceptibility than in loess, indicating that many tiny ferri-ferromagnetic minerals formed during the process of soll formation, which has caused a higher susceptibility in palaeosols than in loess. The climatic history of Quaternary can therefore be understood in terms of the susceptibility based on Chinese loess/palaeosol sequences.展开更多
Understanding biogeographic patterns and the mechanisms underlying them has been a main issue in macroecology and biogeography, and has implications for biodiversity conservation and ecosystem sustainability. Evergree...Understanding biogeographic patterns and the mechanisms underlying them has been a main issue in macroecology and biogeography, and has implications for biodiversity conservation and ecosystem sustainability. Evergreen broad-leaved woody plants(EBWPs) are important components of numerous biomes and are the main contributors to the flora south of 35°N in China. We calculated the grid cell values of species richness(SR) for a total of 6265 EBWP species in China, including its four growth-forms(i.e., tree, shrub, vine, and bamboo), and estimated their phylogenetic structure using the standardized phylogenetic diversity(SPD) and net relatedness index(NRI). Then we linked the three biogeographical patterns that were observed with each single environmental variable representing the current climate, the last glacial maximum(LGM)–present climate variability, and habitat heterogeneity, using ordinary least squares regression with a modified t-test to account for spatial autocorrelation. The partial regression method based on a general linear model was used to decompose the contributions of current and historical environmental factors to the biogeographical patterns observed. The results showed that most regions with high numbers of EBWP species and phylogenetic diversity were distributed in tropical and subtropical mountains with evergreen shrubs extending to Northeast China. Current mean annual precipitation was the best single predictor. Topographic variation and its effect on temperature variation was the best single predictor for SPD and NRI. Partial regression indicated that the current climate dominated the SR patterns of Chinese EBWPs. The effect of paleo-climate variation on SR patterns mostly overlapped with that of the current climate. In contrast, the phylogenetic structure represented by SPD and NRI was constrained by paleo-climate to much larger extents than diversity, which was reflected by the LGM–present climate variation and topog-raphy-derived habitat heterogeneity in China. Our study highlights the展开更多
We identified climatically stable areas of seasonally dry forests (SDFs) from Central Brazil through time and assessed the effectiveness of the current reserves network in representing these climatically stable areas,...We identified climatically stable areas of seasonally dry forests (SDFs) from Central Brazil through time and assessed the effectiveness of the current reserves network in representing these climatically stable areas, as well as areas of high suitability in the present or in the future only. We used an ensemble approach based on several methods for ecological niche modelling (ENMs) to obtain potential distributions 16 SDF’ species for past (last glacial maximum), present, and future (end of XXI century) climate scenarios. We then computed how many current Brazilian reserves matched both stable areas (suitable areas for all time periods), present and future geographical ranges alone for each species, in a multi-level gap analysis. We found range shifts due to climate changes for SDF’ species. Although the future geographical range and stable areas for all analyzed species matched at least with one reserve, many protected areas will lose importance in protecting suitable areas for species in the future. Moreover, the current Brazilian reserves cover only a small amount of their climatically stable areas. However, some reserves will be suitable for many SDF’ species (90%) at the same time, but climatically stable for only half of them. Our findings show that vegetation community from SDFs may persist in Brazilian territories until the end of XXI century, and challenges about long-term conservation of the SDFs may be partially reached with already existing Brazilian reserve network, however the reserves should be connected to permit habitat tracking.展开更多
During a joint Chinese-German expedition through West Sichuan and the eastern half of Qinghai-Xizang Plateau, in the summer of 1992, geological and geomorphological field observations proved that there did not exist a...During a joint Chinese-German expedition through West Sichuan and the eastern half of Qinghai-Xizang Plateau, in the summer of 1992, geological and geomorphological field observations proved that there did not exist a Pleistocene inland ice. This was corroborated by several TL-data and by the analysis of quartz-grain surfaces by means of the scanning electron microscope. Just like during the 1989 expedition more than 1 250 year-old living juniper trees were found at about 4600 m a.s.l. to the northwest of Qamdo, which helps to understand the climate history of the last 1 500 a there. Dendrochronological investigations on lateral and end-moraines prove that in the area the recent glacier advances happened between 1 820 and 1 860 A.D.展开更多
Micromorphological studies show that a comparision of the loess-paleosol sequence ofthe Karamaydan section, Central Asia, with the upper part of the Luochuan section, China, clearlyindicates that for the Brunhes chron...Micromorphological studies show that a comparision of the loess-paleosol sequence ofthe Karamaydan section, Central Asia, with the upper part of the Luochuan section, China, clearlyindicates that for the Brunhes chron the sequence at Karamaydan is even more detailed than thecorresponding section at Luochuan. Single paleosols at Luochuan correspond to pedocomplexes atKaramaydan; some pedocomplexes at Luochuan are represented by more detailed successions atKaramaydan (fig. 1). The loess-paleosol sequence at Karamaydan should therefore be regarded asa key sequence for reconstructing the climatic history of the Brunhes epoch. Correlation with thedeep-sea oxygen isotope record of Bassinot et al. (1994), which includes an accurate astronomicaltime scale, allows a detailed chronostratigraphical subdivision of the loess-paleosol sequence inKaramaydan for the Brunhes chron. Mineralogical and clay mineralogical investigations show thatthere is little difference in the type and amount of pedogenic clay mineral formation between twoHolocene soils and the paleosols in the Brunhes chron at Karamaydan. These results indicate thatthe climates of the interglacials represented by the B or Bt horizons of the buried paleosols weresimilar to that of the Holocene. In view of these results the Paleopedology Commission shoulddevelop a uniform terminology of mono- and polygenetic paleosols and pedostratigraphic unitswhich can be used globally.展开更多
基金supported by the National Natural Science Foundation of China (Nos. 41772180 and 40672108)the State Key Laboratory of Loess and Quaternary Geology of Institute of Earth Environment, Chinese Academy of Sciences (No. SKLLQG1713)
文摘Permeability and water-bearing space are important hydrological characteristics of the loess strata. In this study a systematic experiment was conducted to measure the magnetic susceptibility, grain size, porosity, and infiltration rate of the loess and palaeosol layers on a loess tableland of the central Chinese Loess Plateau, in order to investigate the differences in hydrological conditions between the loess and palaeosol layers. The magnetic susceptibility of the loess layer was lower than that of the palaeosol layer, but the average quasi-steady infiltration rate was about 0.31 mm min^(-1) higher, the coarse silt and very fine sand contents were about7.1% greater, and the porosity was about 5.7% higher. These differences were mainly due to pedogenesis, which was affected by the Quaternary climate. The pedogenesis differences between the loess and palaeosol layers resulted in hydrological property differences in terms of permeability and water-bearing space. The loess layer had a higher permeability and more water-bearing space than the palaeosol layer, which meant that the loess layer is more likely to form aquifers and the palaeosol layer is more prone to form aquitards.The groundwater in the loess strata had a multilayered characteristic, which depended on the relative impermeability of palaeosol layer and the alternate deposition of loess-palaeosol layers. The hydrological characteristics of the loess strata demonstrated that the Quaternary climate had an important control function on the formation and movement of groundwater. This knowledge provides a reliable theoretical basis for water resource development and utilization on the Chinese Loess Plateau, and this study extends the application of Quaternary climate change theory to hydrological systems in loess deposits.
基金Project supported by the National Natural Science Foundation of China and by ETH Zurich, Switzerland.
文摘Through the studies on low temperature susceptibility, frequency dependent susceptibility, isothermal remanent magnetization, low temperature magnetization and demagnetization for loess and palaeosols one can easily reveal some significant characters of rock magnetism for the magnetic minerals of ultrafine grain sizes, those are very difficult to identify by general geological methods. It is shown in the present study that both loess and palaeosols cover magnetic grain size from superparamagnetism, single domain to multidomain. Loess samples with relative high peramagnetic minerals are dominantly of thermally stable characteristics while palaeosols have relatively high percentage of superparamagnetic grain (0.01—0.03μm). The relative grain size of magnetite is always finer in palaeosol with higher susceptibility than in loess, indicating that many tiny ferri-ferromagnetic minerals formed during the process of soll formation, which has caused a higher susceptibility in palaeosols than in loess. The climatic history of Quaternary can therefore be understood in terms of the susceptibility based on Chinese loess/palaeosol sequences.
基金National Natural Science Foundation of China,No.41790425,No.41701055National Key R&D Program of China,No.2017YFC0505200Major Project of the Yunnan Science and Technology Department,No.2018 FY001(-002)
文摘Understanding biogeographic patterns and the mechanisms underlying them has been a main issue in macroecology and biogeography, and has implications for biodiversity conservation and ecosystem sustainability. Evergreen broad-leaved woody plants(EBWPs) are important components of numerous biomes and are the main contributors to the flora south of 35°N in China. We calculated the grid cell values of species richness(SR) for a total of 6265 EBWP species in China, including its four growth-forms(i.e., tree, shrub, vine, and bamboo), and estimated their phylogenetic structure using the standardized phylogenetic diversity(SPD) and net relatedness index(NRI). Then we linked the three biogeographical patterns that were observed with each single environmental variable representing the current climate, the last glacial maximum(LGM)–present climate variability, and habitat heterogeneity, using ordinary least squares regression with a modified t-test to account for spatial autocorrelation. The partial regression method based on a general linear model was used to decompose the contributions of current and historical environmental factors to the biogeographical patterns observed. The results showed that most regions with high numbers of EBWP species and phylogenetic diversity were distributed in tropical and subtropical mountains with evergreen shrubs extending to Northeast China. Current mean annual precipitation was the best single predictor. Topographic variation and its effect on temperature variation was the best single predictor for SPD and NRI. Partial regression indicated that the current climate dominated the SR patterns of Chinese EBWPs. The effect of paleo-climate variation on SR patterns mostly overlapped with that of the current climate. In contrast, the phylogenetic structure represented by SPD and NRI was constrained by paleo-climate to much larger extents than diversity, which was reflected by the LGM–present climate variation and topog-raphy-derived habitat heterogeneity in China. Our study highlights the
文摘We identified climatically stable areas of seasonally dry forests (SDFs) from Central Brazil through time and assessed the effectiveness of the current reserves network in representing these climatically stable areas, as well as areas of high suitability in the present or in the future only. We used an ensemble approach based on several methods for ecological niche modelling (ENMs) to obtain potential distributions 16 SDF’ species for past (last glacial maximum), present, and future (end of XXI century) climate scenarios. We then computed how many current Brazilian reserves matched both stable areas (suitable areas for all time periods), present and future geographical ranges alone for each species, in a multi-level gap analysis. We found range shifts due to climate changes for SDF’ species. Although the future geographical range and stable areas for all analyzed species matched at least with one reserve, many protected areas will lose importance in protecting suitable areas for species in the future. Moreover, the current Brazilian reserves cover only a small amount of their climatically stable areas. However, some reserves will be suitable for many SDF’ species (90%) at the same time, but climatically stable for only half of them. Our findings show that vegetation community from SDFs may persist in Brazilian territories until the end of XXI century, and challenges about long-term conservation of the SDFs may be partially reached with already existing Brazilian reserve network, however the reserves should be connected to permit habitat tracking.
文摘During a joint Chinese-German expedition through West Sichuan and the eastern half of Qinghai-Xizang Plateau, in the summer of 1992, geological and geomorphological field observations proved that there did not exist a Pleistocene inland ice. This was corroborated by several TL-data and by the analysis of quartz-grain surfaces by means of the scanning electron microscope. Just like during the 1989 expedition more than 1 250 year-old living juniper trees were found at about 4600 m a.s.l. to the northwest of Qamdo, which helps to understand the climate history of the last 1 500 a there. Dendrochronological investigations on lateral and end-moraines prove that in the area the recent glacier advances happened between 1 820 and 1 860 A.D.
文摘Micromorphological studies show that a comparision of the loess-paleosol sequence ofthe Karamaydan section, Central Asia, with the upper part of the Luochuan section, China, clearlyindicates that for the Brunhes chron the sequence at Karamaydan is even more detailed than thecorresponding section at Luochuan. Single paleosols at Luochuan correspond to pedocomplexes atKaramaydan; some pedocomplexes at Luochuan are represented by more detailed successions atKaramaydan (fig. 1). The loess-paleosol sequence at Karamaydan should therefore be regarded asa key sequence for reconstructing the climatic history of the Brunhes epoch. Correlation with thedeep-sea oxygen isotope record of Bassinot et al. (1994), which includes an accurate astronomicaltime scale, allows a detailed chronostratigraphical subdivision of the loess-paleosol sequence inKaramaydan for the Brunhes chron. Mineralogical and clay mineralogical investigations show thatthere is little difference in the type and amount of pedogenic clay mineral formation between twoHolocene soils and the paleosols in the Brunhes chron at Karamaydan. These results indicate thatthe climates of the interglacials represented by the B or Bt horizons of the buried paleosols weresimilar to that of the Holocene. In view of these results the Paleopedology Commission shoulddevelop a uniform terminology of mono- and polygenetic paleosols and pedostratigraphic unitswhich can be used globally.
