Table of Content

    25 November 2007, Volume 62 Issue 11 Previous Issue    Next Issue
    The Impact of Land Use/Cover Change on Soil Organic Carbon Stocks and Quality in Mid- subtropical Mountainous Ar ea of Southern China
    YANG Yusheng, XIE Jinsheng, SHENG Hao, CHEN Guangshui, LI Xu
    2007, 62 (11):  1123-1131.  doi: 10.11821/xb200711001
    Abstract ( )   PDF (2611KB) ( )   Save

    Land use/cover change (LUCC) is widely recognized as one of the most important driving forces of global carbon cycles. The influence of LUCC from native forest to plantations, secondary forest, orchard and arable land on soil organic carbon (SOC) stores and quality was investigated by using "space for time" method in mid-subtropical mountainous area of southern China. The results show that LUCC has led to great decreased SOC stocks and quality. Considerable SOC and light-fraction organic carbon (LFOC) have been stored in native forest (142.2 t hm-2 and 14.8 t·hm-2, respectively). When native forest was converted to plantations, secondary forest, orchard and arable land, the SOC stocks decreased by 25.6% -28%.7%, 38.0%, 31.8% and 51.2%, respectively. The LFOC stocks decreased by 52.2-57.2% when native forest was converted to woodland plantations and second forest, and by 82.1% -84.2% when to economic plantation, orchard and arable land. After the conversion, the ratios of LFOC to SOC (0-60 cm) decreased from 13.3% to about 3.0%-10.7%. The SOC and LFOC stored in the upper 20 cm soil were more sensitive to LUCC when compared to the subsurface soil layer. Comparison suggests that the effects of the above mentioned LUCC on carbon release and quality deline were greater than the global average level, which could be explained by the vulnerable natural environment and special human management practices. Thus, it is significant to protect vulnerable environment, restore vegetation coverage and afforest plantation reasonably in mountainous area in mid-subtropics, for enhancing soil carbon sequestration, mitigating elevated atmospheric CO2 and sustainably developing ecological services.

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    The Regional Features of Temper ature Variation Trends over China by Empirical Mode Decomposition Method
    SUN Xian, LIN Zhenshan
    2007, 62 (11):  1132-1141.  doi: 10.11821/xb200711002
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    In this paper, a new and advanced time series analysis method--the empirical mode decomposition (EMD) method is presented into climate analysis field. It is a method developed from analyzing nonlinear and non-stationary data. The oscillations of different scales or trend in the signal are decomposed into a number of characteristic intrinsic mode function components. This decomposition method is adaptive, and, therefore, highly efficient. Thus, we could extract the variation trend from the data. The testing results indicate that EMD method is the best one for extracting data trend at the present time. The climatic trend is very important in temperature change. Therefore, how to eliminate periodic oscillation in temperature change and obtain variation trend is the important process for estimating and comprehending global climate warming. In this study, temperature variation trends of monthly mean temperature data for 740 stations over China from 1951 to 2001 are diagnosed by EMD method, and there are three types of variation trends: ascending trend, descending trend, and fluctuation. Hereby, several temperature change regions have been divided in China and fields have been spatially classified. Simultaneously, the temperature variability of every station is calculated by this method, and classification chart of long term trend and temperature variability distribution chart of China are obtained, supported by GIS, 1km×1km resolution. The results show a large scale warming trend in China, especially Northeast China, Inner Mongolia, Gansu, the west of Qinghai and Tibet, and the north of Xinjiang witnessing marked warming, as opposing to the descending trend patches distributed over Southwest China and the middle and lower Changjiang valley.

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    The Temporal and Spatial Distribution of Seasonal Dry- Wet Changes over the Northwestern China: Based on PDSI
    ZHANG Yong, CHEN Fahu, GOU Xiaohua, JIN Linya, TIAN Qinhua,WANG Yousheng, PENG Jianfeng
    2007, 62 (11):  1142-1152.  doi: 10.11821/xb200711003
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    Using global Palmer drought severity index (PDSI) database, the seasonal and annual PDSI mean values of 56 grid points covering the period 1953-2003 over northwestern China is analyzed by rotated experience orthogonal function (REOF). The results show that the seasonal and annual means display similar anomaly regions, and furthermore there are five main anomaly regions in the northwestern China based on the annual PDSI mean, i.e., the northern and southern parts of Xinjiang, northern part of plateau, western part of Inner Mongolia and eastern part of northwestern China. The opposite changes of dry-wet conditions are discovered after comparing the curves of feature point series and binomial fit between the eastern and western parts of the northwestern China: The western part of the northwestern China influenced by westerly, a trend of wetting gradually occurred since 1980. On the contrary, a trend of drying gradually occurred in the eastern part of the northwestern China which is mainly influenced by Asian monsoon, and especially in summer and autumn, there is notable trend of drying over the southeastern part of the northwestern China. The northwestern China is obviously affected by westerly, Asian monsoon and Tibetan Plateau. There are differences among the responses of the dry-wet conditions to the global warming in different regions.

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    Distribution Pattern of Grain Size in Surface Sediments from Sugan Lake and Its Potential in Recording Aeolian Dust in Arid China
    XIAO Shun, CHEN Fahu, QIANG Mingrui,ZHANG Jiawu, ZHOU Aifeng, SUN Donghuai
    2007, 62 (11):  1153-1164.  doi: 10.11821/xb200711004
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    Sediments from inland enclosed lakes in arid regions of northwestern China provide ideal documents in reconstructing high-resolution history of aeolian dust and aerosols. Sugan Lake in northern Qaidam Basin on the Tibetan Plateau is an enclosed shallow lake mainly fed by groundwater, in which annually laminated varves are well preserved since mid- and late Holocene. Surface sediments from Sugan Lake were collected and analyzed for grain size. Frequency curves of samples indicated multi-components in the surface sediments. Weibull function fitting employed to the grain size distribution suggested that there are four components from clay to sand in the surface sediments characterized by their respective modes. Super-fine component has mode size around 1 μm, fine-grained component has mode of 5-10 μm, coarse-grained component has mode of 50-100 μm, and the mode of sand component is about 500 μm. The main components in the surface sediments appear in fine or coarse grains. Particles trapped in the lake ice in winter and dust storms during the same period present the similar distribution pattern in grain size. The main component of aeolian dust from lake ice is composed of particles sized between 15 and 20 μm, and sand component (with mode size of 452.9 μm) appeared, indicating that sand particles were transported to Sugan Lake during the winter. Dust samples from dust storm period (May) or non-dust storm period (November) prevalently consist of three components without sand grains. During strong dust storm events, however, four components including sand are identified, the main component of which still has a size of 100-200 μm. Our results show that the sand component of the surface sediments in Sugan Lake has been transported by ambient strong dust storm activities; the coarse grains have most likely recorded the regional dust storm events; fine component seems to have indicated the intensity of water supply in the basin; super-fine component as extensively deposited in the Chinese loess, may have represented the background level of atmospheric dust and aerosols in the arid region of northwestern China. Therefore, the sediments from Sugan Lake have documented the regional aeolian dust and dust-storm events and have the potential in reconstructing the history of aeolian dust activities.

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    The Growth Characteristics of Gully Erosion over Rolling Hilly Black Soil Area of Northeast China
    HU Gang,WU Yongqiu, LIU Baoyuan,ZHENG Qiuhong, ZHANG Yongguang, LIU Honghu
    2007, 62 (11):  1165-1173.  doi: 10.11821/xb200711005
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    In this study, short-term gully retreat was monitored from the active gullies selected in representative black soil area, using differential GPS. With the support of GIS, multitemporal digital elevation models (DEM) were constructed in light of the data collected by GPS and used for further analysis. Based on the analysis of multi-temporal DEM, we discussed the erosion-deposition characteristics of a gully and a developing model for black soi l gully area of Northeast China was proposed. The results are: (1) The analysis of the monitored gully data in 2004 indicated that the retreat of gully head reached more than 10 m, gully area extended 170-400 m2, gully net eroded volume 220-320 m3 and gully erosion modulus 2200-4800 t·km-2·a-1. (2) Compared with the mature gully the initial gully grows rapidly, and its erosion parameters are relatively large. The erosion parameters have not only to do with flow energy, but also with growth phase. (3) There are significant seasonal differences in gully erosion parameters. The extension of gully area and width dominates in winter and spring without marked net erosion while changes mainly occur in gully head expansion and net erosion in rainy seasons. (4) It is remarkable for freeze-thaw erosion in the black soil area of NE China. The gully wall of SG2 extended 0.45 m under freeze-thaw effect in 2004, and the distance of gully head retreated maximally 6.4 m. (5) Due to freeze-thaw action and snowmelt, gully is primarily in the interior adjustment process in winter and early spring. There are much more depositions compared with that in autumn, which can almost happen throughout the gully, while erosion mostly occurs near head, esp. for gullies having a relatively long history of development.

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    Chemical Weathering Intensity and Element Migration Features of the Xiashu Loess Profile in Zhenjiang
    LI Xusheng, HAN Zhiyong, YANG Shouye,CHEN Yingyong, WANG Yongbo, YANG Dayuan
    2007, 62 (11):  1174-1184.  doi: 10.11821/xb200711006
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    The chemical weathering intensity and element migration features of the Xiashu loess profile in Zhenjiang are studied in this paper. Based on the comparison with other aeolian-dust deposits, i.e. Quaternary loess-palesol and late-tertiary red-clay profiles in the Loess Plateau, and aeolian dust red earth in Xuancheng of Anhui province, we draw the following conclusions: (1) The Xiashu loess profile underwent moderate chemical weathering, which was stronger than that of the loess and palesol in Luochuan, much weaker than that of the aeolian dust red earth in Xuancheng, and similar to that of late-tertiary red-clay in Xifeng. The chemical weathering differences among the studied aeolian-dust deposits were mainly induced by the distinction of the climate condition, which imposed important influence on the geochemical environment through the mean annual temperature and annual precipitation. It seems that the annual precipitation has more important influence on the chemical weathering process. (2) The major elements such as Si, K, Na, Ca, Mg, Mn and P were migrated and leached, while the elements Fe and Ti were slightly enriched during the chemical weathering process. According to the migration ability, the major elements are ranked in the following order: P > Na > Ca > Mg > K > Fe2+ > Si > Mn > Al > Ti > Fe3+. The migration features of the major elements reveal that the Xiashu loess finished the primary process of chemical weathering characterized by leaching of Ca and Na, and almost reached the secondary process characterized by leaching of K. Except the elements Sr and Ga, other trace elements such as Th, Ba, Cu, Zn, Co, Ni, Cr and V were enriched during the chemical weathering process. And this enrichment might be caused by both the biogeochemical process and the adsorption of trace elements by clay mineral and organic materials during the chemical weathering. (3) The difference of element migration down the Xiashu loess profile reveals that the climate was warm and wet at the early-middle stage of the Middle Pleistocene (before 0.24 Ma), however, bearing the feature of an alternate dry and wet fluctuation. At the end of the Middle Pleistocene, it became dry and cool, which resulted in the weakest weathering and element migration. At the early stage of the Late Pleistocene, the paleoclimate became warm and wet again, which led to rather strong pedogenesis and the formation of the paleosol S1 in the Xiashu loess profile. As a whole, the paleoclimate generally became drier and cooler in this region from the beginning of the Middle Pleistocene.

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    Temporal-spatial Variation of the Channel in Jiangsu Reach of the Yangtze River during the Last 44 Years
    WANG Jian, LIU Ping, GAO Zhengrong, BAI Shibiao, CAO Guangjie, QU Guixian
    2007, 62 (11):  1185-1193.  doi: 10.11821/xb200711007
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    River channel sedimentation in the lower reaches of the Yangtze River can be affected by both rising sea level due to global warming and the construction of reservoirs in the upper river that reduces the amount of sand discharge. To evaluate the dynamic changes of sedimentation and erosion of the Jiangsu reach of the Yangtze River (about 330 km in length) from 1958 to 2003, databases of five periods Digital Elevation Mode (DEM) of underwater topography were designed and constructed on the basis of the Jiangsu River Relief Map in 1959, 1970, 1985, 1992 and 2003 (1:25000-1:60000). The result indicated that the main course of Yangtze River in Jiangsu Province had experienced an obvious switch from sedimentation to erosion around 1985 because of the decreasing amount of sediment yield from the upper Yangtze River after that year. The sedimentation process in the main course of Jiangsu reach of the Yangtze River demonstrated propulsive phenomena of "down-reach-ward accumulation". Between 1985 and 2003, the erosion rate of the lower segment was greater than those of the middle and upper segments. The reason is probably the bigger shortage of sediment yield due to the decrease of sediment source from the upper reach and the strengthening protection of the bank erosion in the lower reach.

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    Vertical Mass Flux Profiles of Different Grain Size Groups in Aeolian Sand Transport
    FENG Dajun, NI Jinren, LI Zhenshan
    2007, 62 (11):  1194-1203.  doi: 10.11821/xb200711008
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    This paper presented the vertical mass flux profiles of different grain size groups in aeolian sand transport, which is the hot issue of non-uniform sand transport research but is rarely studied recently. The sand samples of vertical mass flux were further investigated using a particle size analyzer that were measured in a wind tunnel experiment conducting with non-uniform sands and five different stream velocities. Results show that the vertical mass flux profiles of coarse sand groups are similar to that of all sands measured in the wind tunnel, exhibiting an exponential decay distribution with a positive deviation occurring in the near-bed region; however, the vertical mass flux profiles of fine sand groups decayed exponentially in the whole height. Based on the results above, this study simulated the vertical mass flux profiles of different grain size groups in terms of equilibrium saltation theory. It is revealed that in the non-uniform sand transport, the launch speed and angle distributions of coarse sand are exponential function; the launch speed of fine sand is exponential function but the launch angle of it is Gaussian function. The mean sand launch speed occur between 0.4u* and 2.2u*, decaying with the increase of wind speed (u*) and grain size.

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    Land Use Changes in Xuzhou Coal Mining Area
    HU Zhaoling, DU Peijun, ZHAO Xin
    2007, 62 (11):  1204-1214.  doi: 10.11821/xb200711009
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    Based on the three temporal satellite remote sensing TM images of Tongshan county located in Xuzhou city, basic data about land use of Xuzhou coal mining area are obtained with the neural network classification module from 1987 to 2003. According to the basic data of land use, the land use change is quantified by way of computing the index models of regional land use change. The following results were obtained: (1) The areas of construction land and water body have continually increased from 1987 to 2003. In this period the area of construction land has increased by 4761.09 hm2. On the contrary, the area of cropland has constantly decreased with a decrease of 27528.21 hm2. (2) From 1987 to 2003, both the construction land and unused land were chiefly transformed into cropland. From 1987 to 1994, the water body was chiefly transformed into woodland. The cropland was chiefly transformed into unused land and construction land. The woodland was chiefly transformed into cropland. From 1994 to 2003, the water body was infrequently transformed. The cropland was chiefly transformed into unused land and woodland. (3) From 1987 to 2003, the variation index of land use degree and the dynamic degree index of land use demonstrate that land use in Tongshan county was in a decline period and the changes were drastic.

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    Effects of Land Use/Cover Change on Wetland Landscape of Honghe Nature Reserve
    LIU Hongyu, LI Zhaofu
    2007, 62 (11):  1215-1222.  doi: 10.11821/xb200711010
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    Analysis of land use/cover change in six periods from 1954 to 2005 was conducted with the aid of remote sensing and GIS techniques on the watershed scale. The landscape diversity of wetlands within Honghe Nature Reserve and the surrounding area in the watershed was calculated by using landscape diversity index to reflect landscape diversities and their changes in historical periods. At the same time, the landscape connectivity of the Honghe Nature Reserve with the surrounding area of the watershed was calculated to study the effects of landscape isolation on landscape diversity of the wetlands. Results show that the large-scale land reclamation started in the 1980s resulted in an annual increase of 101 km2 of agricultural land. The direct land use/cover change brought about the decline of wetland landscape diversity in watershed, and also impacted the diversity of wetlands in Honghe Nature Reserve. Decline of landscape connectivity between wetlands within the nature reserve and the surrounding area of the watershed due to land use changes has seriously segmented the original relationship between the nature reserve and its surrounding area, which directly resulted in the decline of wetland landscape diversity within the Honghe Nature Reserve. At present, the decline of landscape diversity of the wetlands in the Honghe Nature Reserve has serious negative effects on wetland structure and its ecological function. So it is necessary not only to conserve the wetlands in the nature reserve, but also to protect the wetlands in the surrounding area. We should restore certain area of the marsh wetlands to keep a high diversity of the landscape and landscape structure of the wetlands within the nature reserve, as well as to restore certain area of the wetlands in the surrounding area of the nature reserve for maintaining a high landscape connectivity in the watershed so that good conservation benefits of the nature reserve in the Sanjiang Plain can be achieved.

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    Landscape Pattern Optimization Based on RS and GIS in Northwest of Beijing
    YUE Depeng, WANG Jiping, LIU Yongbing,LI Hailong, XIE Huaici, WANG Dongmei
    2007, 62 (11):  1223-1231.  doi: 10.11821/xb200711011
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    Heterogeneity of landscapes is supposed to be of significant importance for biodiversity and ecological function in urban ecosystems.However, land use activities caused primarily by urbanization process has a profound and far-reaching impact on stability of landscape and differences of landscape structure at the regional scale. Therefore, in this paper, the northwest region of Beijing is chosen as a study area and the technologies of remote sensing (RS) and geographical information system (GIS) is applied, and meanwhile the priority is been given to understanding of the spatial-temporal characteristics of landscape pattern change through visually interpreting Landsat TM images of 1989, 1996 and 2005 respectively. It is believed that there are a series of landscape ecological problems because of city expansion, such as low landscape ecological connectivity, simplified landscape structure and more obvious fragmentation of green land patch in the plain areas. Moreover, spatial distribution of green land is unbalanced. In order to solve those problems, according to the principle that the movements of flow, energy and material in a landscape are related to some factors such as distance, time, impedance, etc., this study adopts an accumulative cost distance model, combines with ecosystem services and spatial interactions of landscape types, analyzes the spatial difference of the ecological function and the compactness of landscape structure in the study area, and further discusses the landscape pattern optimization proposal.

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