Table of Content

    25 May 2007, Volume 62 Issue 5 Previous Issue    Next Issue
    Ecological Water Demand of Vegetation Based on Eco-hydrological Processes in the Lower Reaches of Tarim River
    YE Zhaoxia, CHEN Yaning, LI Weihong
    2007, 62 (5):  451-461.  doi: 10.11821/xb200705001
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    This paper appraised the relationships between soil moisture, groundwater depth and plant species diversity in the lower reaches of the Tarim River, western China, by analyzing the field data from 25 monitoring wells across eight study sites and 25 vegetation survey plots in 2005. The results showed that groundwater depth, soil moisture and plant species diversity had close relativity. It was proved that the critical phreatic water depth was 5 m in the lower reaches of the Tarim River. Averaging the two results of the phreatic evaporations calculated by Аверъянов formula and Qunke formula, the mean phreatic evaporations of different groundwater levels in each month were acquired. Based on the calculation of two methods of vegetation acreage classification, the total ecological water demand (EWD) of natural vegetation was 3.2×108 m3 in the lower reaches of the Tarim River. Analyzing the monthly EWD, it was found that the EWD in the growth season (from April to September) was 81% of the year's total, with May, June and July accounting for 47% of the year's total, which would supply a gist for choosing the best time to deliver water. This research aimed to realize water resources sustainable development and provide scientific basis for water resource management and sound collocation of the Tarim River Basin.

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    Bio-geomorphologic Growth Process of Tamarix nabkha in the Hotan River Basin of Xinjiang
    LI Zhizhong, WU Shengli, WANG Xiaofeng, HE Mudan,GE Lin, MU Hetaer, XU Guoqiang
    2007, 62 (5):  462-470.  doi: 10.11821/xb200705002
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    The characteristics of Tamarix shrub's plant ecology, community and environment and its regularities of distribution in space have been investigated in the Hotan River basin of Xinjiang. The shape data of 223 Tamarix nabkhas have been measured, and the structural characteristics of 4 Tamarix nabkha's sand driving wind have been observed at two field observational points. Based on the shape data surveyed and the sand flow materials observed, models of nabkhas have been made according to the proportion. In the wind tunnel, the flow patterns of different shapes of nabkhas have been imitated separately. The results indicated that Tamarix ecological type in the study area belongs to tugaic soil habitat which is based on soil of Populus and shrub forest. This habitat type can be further divided into three sub-habitats of juvenile, mature and post-mature Populus forests, in which Tamarix eco-geographical community is sequential succession. The change of ecological characteristics of Tamarix community in different sub-habitats induces variation of disturbance to sand flow and sand aggregation capability by Tamarix shrub in different stages. Therefore, the development of Tamarix nabkha presents phased succession. Compared with ecological characteristics and nabkha shapes of Phragmites and Alaghi, Tamarix shrubs can more intensely perturb wind-borne sand movement on the ground because of its longer life expectancy, the rigid shoot lignified, stool germination easily with endurance to be buried by sand and resistance to deflation. The wind speed section at the top of Tamarix nabkha is different from nabkhas of Phragmites and Alaghi.

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    Assessment of Grassland Ecological Restoration Project in Xilin Gol Grassland
    ZHUO Li, CAO Xin, CHEN Jin, CHEN Zhongxin, SHI Peijun
    2007, 62 (5):  471-480.  doi: 10.11821/xb200705003
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    Xilin Gol grassland has been experiencing severe degradation since the livestock kept on increasing in the past decades. Recent 'Grassland Ecological Restoration Project' is being developed for improvement of the degraded grassland and sustainable development. However, due to the short-time of the project implementation, it is difficult to monitor the restored area and assess the effect of the project. In this study, SPOT-VGT maximum value composite (MVC) NDVI temporal series data from 1999 to 2004 of Xilin Gol was used to model climate-vegetation response relationships in pixel scale. The model was based on the maximum NDVI in the neighborhood and their climate factors including accumulated temperature and accumulated precipitation. Then the restored areas were identified by positive trend of normalized residuals between model predicted NDVI and actual values. The result was validated by grazing pressure index (GPI), which was defined as the sheep unit divided by NPP. Negative relationship was found between the trend of residual and GPI at county level, which proved the effectiveness of the method for short-term temporal data.

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    Typical Alpine Wetland System Changes on the Qinghai-Tibet Plateau in Recent 40 Years
    WANG Genxu, LI Yuanshou, WANG Yibo, CHEN Lin
    2007, 62 (5):  481-491.  doi: 10.11821/xb200705004
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    The wetlands in the source regions of the Yangtze and Yellow rivers and the Zoige wetland were selected as the typical wetland systems on the Qinghai-Tibet Plateau. This study evaluated changes in wetland components, spatial pattern and hydro-ecological function of the typical wetlands on the Qinghai-Tibet Plateau on the basis of three sets of remote sensing data (1969, 1986 and 2000) and field investigations. In recent 40 years, the degradation of wetlands on the Qinghai-Tibet Plateau was prevailing with the declining area exceeding 10%. Among the three typical wetland systems, the most serious wetland degradation took place in the source region of the Yangtze River, and wetland area decreased by 29% and dried-up area of the lakes by 17.5%. The fragmentation and island of wetlands in the source region of the Yellow River and the Zoige region were accelerated. The degradation of the alpine wetlands resulted in the changes of their hydrological functions. In the source region of the Yangtze River and the Zoige region, where the wetlands declined more severely, the low water runoff decreased, the frequency of rare larger runoff increased and the frequency of regular runoff decreased. The water regulation capacity of all the wetlands was declined. The wetlands degradation was related with the air temperature rise. Under the air temperature rise by 2.3 folds of the average increasing magnitude during recent 40 years, the degradation of wetland systems was accelerated after the mid-1980s. Since the precipitation increased and glacier thawed, the wetland degradation was the main cause for river runoff decrease.

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    Climatic Change of Sunshine Duration and Its Influencing Factors over Tibet during the Last 35 Years
    DU Jun, BIAN Duo, HU Jun, LIAO Jian, ZHOU Mingjun
    2007, 62 (5):  492-500.  doi: 10.11821/xb200705005
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    Using the data of monthly sunshine duration, mean cloudiness, surface vapor pressure and precipitation at 25 meteorological stations over Tibet from 1971 to 2005, the trend variation of the sunshine duration are analyzed by using linear trend analysis. Main results are as follows: (1) In terms of linear trend, the annual sunshine duration increases with an average rate of (8.8-52.1) h/10a in Ngari district, Tingri, Amdo, Mshung and Chali counties, especially in Mshung. But the tendency of annual sunshine duration decreases mostly in other stations with a decreasing rate of (10.9-138.4) h/10a, and the maximum is in Nagqu. In summer, the sunshine duration has a decreasing trend in most parts of Tibet. In winter, the increasing trend of sunshine duration occurred in Ngari district, northern Chamdo district and most parts of Nagqu district. In most parts of Tibet, the annual and seasonal total cloudiness has shown a decreasing tendency during recent 35 years, and the low cloudiness trend reduced. The trend of annual and seasonal mean surface vapor pressure increased over Tibet, especially in summer. (2) On an average in Tibet, the annual sunshine duration has shown a significant decreasing tendency during recent 35 years with a decreasing rate of 34.1 h/10a. Except for no obvious trend in winter, the decreasing trend occurred in other seasons. Specifically, in recent 25 years, the reducing range of sunshine duration increased in summer and autumn, as a result, the annual sunshine duration reduced. (3) In the 1970s, the sunshine durations are more sufficient in spring and summer, while lower in autumn and winter. The sunshine duration of positive anomaly occurred in all seasons in the 1980s, especially in autumn. But to the contrary in the 1990s, the sunshine durations are lower in all seasons, especially in summer. (4) Also, the annual and summer sunshine durations are more anomalous years in the 1980s, whereas less anomalous years in the 1990s. In winter, more anomalous years occurred in 1987 and less anomalous years in 1995 and 2005. (5) Results indicate that the principal causes for the increase of sunshine duration are the obvious decrease of cloudiness and decrease of precipitation in Ngari district, and that the decrease of sunshine duration is mainly caused by the significant increase of surface vapor pressure in other parts of Tibet.

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    Seasonal Air Temper ature Variations Retr ieved from a Geladaindong Ice Core, Tibetan Plateau
    ZHANG Yongjun, KANG Shichang, QIN Dahe, REN Jiawen,ZHANG Yulan, Bjorn GRIGHOLM, Paul MAYEWSKI
    2007, 62 (5):  501-509.  doi: 10.11821/xb200705006
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    A 70-year history of precipitation δ18O record has been retrieved using an ice core drilled from a plat portion of the firn area in the Guoqu Glacier (33o34'37.8"N, 91o10'35.3"E, 5720 m a.s.l.) on Mt. Geladaindong (the source region of the Yangtze River) during October and November, 2005. Based on the seasonality of δ18O records and the significant positive relationships between monsoon/non-monsoon δ18O values and summer/spring air temperature from the nearby meteorological stations, the history of summer and spring air temperature have been reconstructed for the last 70 years. The results show that both summer and spring air temperature variations present similar trends during the last 70 years. Regression analysis indicates that the slope of the temperature - δ18O relationship is 1.3 oC/‰ for non-monsoon δ18O values and spring air temperature, and 0.4 oC/‰ for monsoon δ18O values and summer air temperature. Variation of air temperature recorded in the ice core is consistent with that in the Northern Hemisphere (NH), however, the warming trend in the Geladaindong region is more intense than that in the NH, reflecting a higher sensitivity to global warming in the high elevation regions. In addition, warming trend is greater in spring than in summer.

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    Variations of δ18O in Pr ecipitation of the Yar lung Zangbo River Basin
    LIU Zhongfang, TIAN Lide, YAO Tandong, GONG Tongliang,YIN Changliang, YU Wusheng
    2007, 62 (5):  510-517.  doi: 10.11821/xb200705007
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    The paper reveals the temporal and spatial variations of stable isotope in precipitation of the Yarlung Zangbo River Basin based on the variations of precipitation δ18O at four stations (Lazi, Nugesha, Yangcun and Nuxia) in 2005. The results show that the δ18O of precipitation has distinct seasonal variations in the Yarlung Zangbo River Basin. The maximum value of δ18O occurs in spring prior to monsoon precipitation, and the minimum value occurs during monsoon precipitation. From the spatial variations, with the "altitude effect" and rainout process during moisture transport along the Yarlung Zangbo River valley, δ18O of precipitation is gradually depleted. Thus δ18O of precipitation reduced gradually from the downstream to the upstream, and the lapse rate of δ18O in precipitation is approximately 0.34‰/100m and 0.7‰/100km due to the two reasons. During monsoon precipitation, spatial variations of δ18O in precipitation is dominated by "amount effect" in the large scale synoptic condition.

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    Chemical Weather ing of the Milanggouwan Paleosols in the Salawusu River Valley and Their Paleoclimatic Implication during the Last Interglacial Period
    OUYANG Chuntao, LI Baosheng, OU Xianjiao, WEN Xiaohao,ZENG Lanhua, YANG Yi, LIU Yufei
    2007, 62 (5):  518-528.  doi: 10.11821/xb200705008
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    There are five layers of paleosols in Milanggouwan section in Salawusu River valley of Inner Mongolia during the last interglacial period. We have observed the morphological features of these paleosols and analyzed their grain-size, surface textural features and chemical weathering. The results showed that: (1) These paleosols have some morphological features just like the recent cinnamon soils in North China. (2) They are similar to the recent cinnamon soils that have higher clay contents in the middle part than in the other parts of the soil and SiO2 solution and precipitation can be observed on the surface of the quartz grain, indicating that chemical weathering and pedogenic process have taken place. (3) On the basis of CaO/MgO, K2O/Na2O, Al2O3/Na2O, MnO/Al2O3, CIA and A-CN-K diagram, the comparison results show that the intensity of chemical weathering in paleosols is very similar to the recent cinnamon soils in North China. (4) Using the regression equation of CIA, the values of annual temperature and precipitation of those paleosols can be calculated respectively, and with those values, it is easy to ascertain that the climate conditions are similar to that of North China.

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    Spatial and Tempor al Changes of Deser tification in the Headwater Ar ea of the Yellow River Using Remote Sensing
    ZENG Yongnian, FENG Zhaodong
    2007, 62 (5):  529-536.  doi: 10.11821/xb200705009
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    The objective of this paper is to detect desertification in the headwater area of the Yellow River with remote sensing. Firstly, the desertification classification scheme was established through field works and analysis on ancillary data of the headwater area of the Yellow River. Then, based on desertification detecting model, the spatial and temporal changes of desertification were detected in the headwater area of the Yellow River from 1986 to 2000 using Landsat TM/ETM+ images. The results revealed that the desertified land of the study area was about 3519.97 km2 in 2000, of which light desertified land was major portion. The result further showed that desertified land has increased and intensified seriously with an annual increasing rate of 21.8% from 1987 to 1996. During the 1990s, desertification has expanded and intensified, although the annual increasing rate is slower than that in the 1980s. Since the late 1980s, the desertification has kept intensifying in the headwater area of the Yellow River, although desertification has reversed in some regions. The headwater area of the Yellow River is one of the seriously desertified regions in the upper reach of the Yellow River and the Qinghai-Tibet Plateau. Therefore, it is urgent to combat desertification and protect eco-environment in the headwater area of the Yellow River.

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    Pr ecipitation Cycles in the Middle and Lower Yellow River
    HAO Zhixin, ZHENG Jingyun, GE Quansheng
    2007, 62 (5):  537-544.  doi: 10.11821/xb200705010
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    Based on the long-term precipitation series with annual time resolution in the middle and lower Yellow River and its four sub-regions during 1736-2000 reconstructed from the rainfall and snowfall archives of the Qing Dynasty, the precipitation cycles are analyzed by wavelet analysis and the possible climate forcings, which drive the precipitation changes, are explored. The results show that the precipitation in the middle and lower Yellow River has inter-annual and inter-decadal oscillations like 2-4a, quasi-22a and 70-80a. The 2-4a cycle is linked with El Nino events, and the precipitation is lower than normal year in the occurrence of the El Nino year or the next year; for the quasi-22a and 70-80a cycles, Wolf Sun Spot Numbers and Pacific Decadal Oscillation (PDO) coincide with the two cycle signals. However, on 70-80a time scale, the coincidence between solar activity and precipitation is identified before 1830, and strong (weak) solar activity is generally correlated to the dry (wet) periods; after 1830, the solar activity changes to 80-100a quasi-century long oscillation, and the adjusting action to the precipitation is becoming weaker and weaker; the coincidence between PDO and precipitation is shown in the whole time series. Moreover, in recent 100 years, PDO is becoming a pace-maker of the precipitation on 70-80a time scale.

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    Variation of Sediment Discharge of the Pear l River Basin from 1955 to 2005
    DAI Shibao, YANG Shilun, CAI Aimin
    2007, 62 (5):  545-554.  doi: 10.11821/xb200705011
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    Draining at the southern part, the Pearl River is the third largest river in China. The Pearl River is the collective name of West River, North River and East River. Based on long series data (1955-2005) of the water and sediment discharge at the main hydrological stations and the precipitation in the drainage basin, this paper aimed to reveal the variation pattern of the sediment discharge and the causes of the Pearl River. The results are: (1) sediment discharge at Shijiao (North River), Boluo (East River), Qianjiang and Gaoyao (West River) stations show a decreasing trend, while Liuzhou (at Liujiang River, a tributary of West River) and Nanning (at Yujiang River, a tributary of West River) an increasing trend in 1955-2005; (2) the average sediment discharge into the sea from the Pearl River (the sum of the North River, East River and West River) in 1955-2005 is 7529×104 t/yr with a decreasing trend (not significant statistically). The main conclusions are: (1) the variation of precipitation contributed greatly to the yearly fluctuation of the sediment flux, but little to the decreasing trend of the sediment discharge into the sea; (2) the phased variation trend of sediment discharge into the sea is relevant to soil loss and water and soil conservation; (3) dam construction is the main cause of the decrease of the sediment discharge into the sea; and (4) a further decrease of the sediment discharge into the sea may occur in the future decades, which may cause serious environmental problems at the estuary such as slowdown of coastline progradation or even retreat. Further and in-depth study is urgently needed in view of the economic significance of the Pearl River Delta in China and the environmental issues in the estuary, including the coastal region of Hong Kong.

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