Based on the data collected from 74 vegetation plots and groundwater depth monitoring wells (2006 to 2007) in the middle and lower reaches of the Tarim River, the groundwater table was divided into six gradients (0-2, 2-4, 4-6, 6-8, 8-10 and >10 m) to compare the influence of groundwater level on coverage, plant diversity and plants appearance frequency. The results showed that plant diversity was the highest at the 2-4 m level, followed by 4-6 m and then 0-2 m. When the groundwater depth dropped to below 6 m species diversity decreased tremendously, and the slope of the Hill's index (diversity ordering) tended to level off. Thus, the optimum groundwater level for major plants growth is 2-4 m and the threshold groundwater depth is about 6 m. To restore vegetation and ecosystem of the lower reaches of the Tarim River, the groundwater depth must be kept at a minimum of 6 m.
Pan evaporation, an indictor of potential evaporation, has decreased during the last several decades in many parts of the world; the trend is contrary to the expectation that global warming will be accompanied by an increase in evapotranspiration, known as the pan evaporation paradox. What is the essential relation between pan evaporation and evapotranspiration? This is still an uncertain problem. In this paper, the trends of pan evaporation and evapotranspiration in Xinjiang from 1960 to 2005 are investigated using observational data and the observation-constrained simulations using of the NCAR Community Land Model (CLM). Our analysis suggests that decreasing trend of annual pan evaporation accompanies increasing trend of annual evapotranspiration, the tendency has statistical significance. We also find that there is the same turning point of 1986 for precipitation, pan evaporation and evapotranspiration, and either before the point or after the point, pan evaporation has the inverse trend with evapotranspiration and precipitation has the same trend with evapotranspiration. The above analyses indicate pan evaporation and evapotranspiration have complimentary relationship. These results support the solution of the evaporation paradox described by Brutsaert and Parlange (1998) and suggest that decreases in pan evaporation indicate an increase in terrestrial evaporation in Xinjiang. The correlation analyses show that diurnal temperature range (DTR), wind speed, low cloud cover and precipitation are most likely the driving force for the reduction of pan evaporation and the ascending evapotranspiration.q
Water resources constraint force on urbanization has become one of the important exogenic forces which exert great influence on the speed of urbanization process and socio-economic development in arid and water deficient regions. It is of great significance to the measurement and probing into its temporal and spatial variations, thus promoting water resoureces sustainable utilization and accelerating the urbanization process. By qualitative and quantitative methods, an integrated indicator system was constructed, and an AHP model reformed by entropy technology was established to measure the water resources constraint intensity on urbanization. Using this model, the temporal and spatial variations of water resources constraint intensity on urbanization in the Hexi Corridor from 1985 to 2005 were calculated. Results show that: (1) Water resources constraint intensity on urbanization decreased from east to west in the Hexi Corridor. Of the five prefecture-level cities, Wuwei belongs to the very strong constraint type, Jinchang belongs to the strong constraint type, Zhangye belongs to the less strong constraint type to the strong constraint type, Jiuquan belongs to the less strong constraint type, and Jiayuguan belongs to the weak constraint type to the less strong constraint type. (2) Water resources constraint intensity on urbanization has changed into the strong constraint type from the less strong constraint type in recent 20 years. It increased continuously on the whole. However, in recent years, it decreased appreciably. (3) The integrated indexes of water resoureces system and urbanization system in the Hexi Corridor are both comparatively small. Inconsistencies between water shortage and regional development are serious. It is a great challenge to lessen water resources constraint intensity and accelerate the urbanization process. However, most parts in the Hexi Corridor belong to the less strong or strong constraint type. Through rational regulation of water resources constraint intensity on urbanization, the Hexi Corridor can still realize sustainable development.
The soil temperature data of 60 meteorological stations on the Qinghai-Xizang Plateau from 1960 to 2005 were used to analyze the time evolution tendency and spatial distribution using Mann-Kendall test, power spectral analysis and principal component analysis methods. The results show that the surface soil temperature of most of the stations on the Qinghai-Xizang Plateau has a significantly increasing trend in the last 45 years, and the abrupt changes are detected from 1969 to 1970. The soil temperature at depths from 40 to 320 cm shows a 3.25a cycle variation, also the spatial features of surface soil temperature was mainly reflected as a coincident type in the whole region and a reverse changing type in north-south direction. At the same time discussion on the variation of surface soil temperature gradient (10 to 20 cm) indicated that there is a rise-fall mechanism between the surface soil temperature gradient and the difference between ground soil and air temperature, indicating that there may be a relationship of dissipative structures between the atmosphere and ground surface on the Tibetan Plateau. In addition, the spatial pattern of surface soil temperature gradient reflects clearly the distribution of permafrost on the Qinghai-Xizang Plateau.
The interannual, interdecadal variations and anomalous years of the annual and seasonal mean temperature and precipitation are investigated in the context of the monthly data at 9 meteorological and hydrological stations in the Yamzho Yumco Lake basin of Tibet from 1961 to 2005 by using modern statistical diagnostic methods such as the linear trend, and the relationship between lake level and precipitation is discussed. The results show that the annual temperature presented a significant increasing trend and the rate of increase is about 0.25 oC/10a during recent 46 years, indicating that the warming trend is obvious in autumn and winter. In recent 25 years (1981-2005), the precipitation presents a decreasing trend in winter, while the increasing trend is apparent in other seasons with a rate of (11.4-30.0) mm/10a, especially in summer. Finally, the annual precipitation shows an obviously increasing trend and the rate is 54.2 mm/10a. In terms of interdecadal variations, the mean temperature increases apparently in most seasons, except in summer. The summer precipitation is less in the 1980s, more in the other three decades. On the contrary, in winter the precipitation is more in the 1980s, less in the other three decades. Also, the warm anomalous years of annual mean temperature occurred three times in the end of the 1990s and the early 2100s. The more precipitation anomalous years occurred in the end of the 1960s and the early 1970s. Since generation of electricity with the water of the Yamzho Yumco Lake in 1997, the trend of annual precipitation has increased. The mean precipitation is about 409.7 mm in the basin, which is higher than the balanced rainfall, and presents an obvious increasing trend of the lake level. The water level rise is directly correlated with precipitation increase and sunshine decrease, while the apparent rise of temperature and the increase of snowmelt are also important factors.
Eco-geographical region system is an important result of China's regionalizational development quantitatively, systematically and dynamically. In order to probe into the topic thoroughly, based on the data from the second China's national soil survey and the provincial soil resource information, by principal analysis and discriminant analysis, this paper discusses the appropriate soil indicators as the complement of eco-geographical region indicator systems and the relationship between these soil indicators and soil types in regionalization. The results show that five soil indicators are used in eco-geographical regionalization in mid-temperate zone of eastern China, which are the content of organic matter, cation exchange content, pH, clay capacity and soil bulk density in topsoil. With a regression-kriging approach, the maps of soil indicators in mid-temperate zone of eastern China are compiled with a resolution of 1 km in every grid and the indicative meaning of these soil indicators is discussed. By a cluster analysis, it is proved that these soil indicators are better than the soil types and soil regionalization in delineating eco-regionalization zones.
The reducible sulfur associated ore was brought into soil in many ways, which will further acidify its surrounding area. In the Huanjiang River of Guangxi, more than 600 hm2 of farmland have been acidified, so the formation of soil acidification and the distribution characteristics of acidity were studied. The chemical analysis results showed that soil acidification came from oxygenation of reducible sulfur. Based on the results from mineral (X-ray), sulfur speciation (EXAFS) and Pb isotope analysis, the cause for the formation of soil acidification can be found out: In 2001, the flood destroyed the tailing dam located in the upstream of the Huanjiang River, and carried the tailing into farmland, so the reducible sulfur in tailings was oxygenated into H+ after a certain period of time. The area on both banks of the Huanjiang River was all affected by flooding, which should be given more attention. The spatial variabilities of pH, St, SO42- (Ss), TAA, TPA and Fe in the investigated area were very large, but the contents of acidity, iron and sulfur in flooded soil were much higher than those in the unflooded soil. The soil near mining sites was not acidified because of secondary pollution by alkaline tailings, but has potential acidification risk; while the soil in mid- and down-stream of the river had been acidified more or less, and most soil still has potential acidification probability. It is supposed that acid pollution was more serious in dry soil than in paddy soil, so converting dry land into paddy land could decrease the oxidative rate of reducible sulfur.
Based on archaeological excavations, 217 samples were collected, of which 63 were used for identification analysis of foraminifera, plant debris and seed fossils. The authors used four samples for 14C dating and correlation analysis. Through experiments, some conclusions can be drawn as follows. First, Bentic foraminifera was found in the 10th layer, such as Ammonia compressiuscula and Ammonia cff. sobrina, which shows that between 7500-5400 BC, before the appearance of the Majiabang culture, Luotuodun Site and its neighbouring regions had experienced transgression events. Second, we found 450 plant fossils at this site, such as Polygonum sp., Scirpus sp., Najas sp., Physalis sp., which lived in lakes, swamps and other aquatic environments.
After the investigation on the middle reaches of the Beiluohe River, we chose the slackwater deposits for the palaeohydrology study, which were obvious along the bedrock gorge of the study reaches. On the basis of field survey, we collected samples of the slackwater deposits and analyzed the grain size distribution, the magnetic susceptibility variation, the loss on ignition and the content of calcium carbonate. All of these evidences showed that the slackwater deposits were typical in the study area, and we concluded that the corresponding palaeoflood occurred in the middle and late Holocene through the stratigraphic correlation. When we applied the hydrological technique to the slackwater deposits series, the reconstructed peak discharges of the palaeoflood recorded by them were 12350-14730 m3s-1. We also measured the muddy mark on the pier at the Dongwanghe cross at a distance of 20 km from the previous cross. The reconstructed peak discharge was 6670 m3s-1, which showed that the calculation of the palaeohydrolodgy was credible and reasonable. The results provide significant information for engineering construction, flood control and disaster alleviation in the middle reaches of the Beiluohe River.
A total of 71 surficial sediment samples are collected in the eastern Beibu Gulf, and then the moment parameters (i.e. mean size, sorting coefficient and skewness) are obtained by grain size analysis. By using kriging interpolating methods, the regular meshes of grain size parameters are calculated. A geostatistic analysis is applied to study the spatial autocorrelation for these parameters; while the range, a parameter in the semivariogram metering the bound of the spatial autocorrelation, is estimated. It shows that the range for sorting coefficient is physically meaningful, and also the obtained grain size trends are consistent with the annual ocean circulation pattern and sediment transport rates from previous studies. Thus, the range from the sorting coefficient variogram can be used as the characteristic distance in the grain size trend analysis model, which may remove the bias caused by traditional determination of characteristic distance (e.g. based on experience or testing methods). The sediment transport patterns are retrieved on the basis of grain size parameters interpolated with varied distances, which indicates that the small interpolation distance can produce better transport pattern with high resolution and give more detailed information. Hence, the results from geostatistic analysis can be guidable in determination of sampling stations density in the future field work.
De-farming slope farmland has been an effective measure in recent years for the improvement of the eco-environment and the mitigation of soil and water loss on the Loess Plateau. This paper, taking the Yangou Basin as a case study and using day-by-day meteorological data of Yan'an station in 2005, simulated and analyzed the quantitative relation between crop yield, soil and water loss and topographic condition with the aid of WIN-YIELD software. Results show that: 1) Topographic gradient has important influence on crop yield. The bigger the gradient is, the lower the crop yield. Yields of sorghum and corn decrease by 15.44% and 14.32% respectively at 25o in comparison to the case of 0o. In addition, yields of soya, bean and potato decrease slightly by 5.26% , 4.67% and 3.84% , respectively. The influences of topographic height and slope aspect on crop yield are slight. 2) Under the same topographic condition, different crops' runoff and soil loss show obvious disparity. The benefit of soil and water conservation from high to low ranks soya, bean, potato, corn and sorghum. Topographic gradient has important influence on soil and water loss. In general, the changing trend is that the soil and water loss aggregates with the increase of gradient, and the maximal amount occurs around 20o. The influence of topographic height is slight. Topographic aspect has a certain effect, and the fundamental characteristic is that values are higher at the aspect of south than north. 3) Topographic gradients of 5o and 15o are two important thresholds. The characteristics about soil and water loss with the variation of topographic gradients show that: the slope farmland with gradients less than 5o could remain unchanged, and the slope farmland more than 15o should be de-farmed as early as possible.
