用氚讨论中国西部新疆干旱区的水循环率

Tritium concentrations are used to trace water circulation in the Urumqi and Turfan basins in the Xinjiang, western China. Tritium analyses were made for 77 water samples of river waters, groundwaters, spring waters, lake waters and glacier ice collected in summers in 1992 and 1994. The tritium concentrations in the waters are in a wide range from 0 to 125 TU, most of which are considerably high compared with those of most waters in Japan, because tritium levels in precipitation in the area are over ten times as high as those in Japan. River waters originating in glacier regions contain melt glacier, the proportion of which is over 0.5 to river water. The mean resi-dence time of circulating meteoric water in the mountain regions is estimated to be about 15 years. Most groundwaters and spring waters in the flat regions are mainly derived from river waters originating in glacier regions. The groundwater of greatest tritium concentrations in wells in Urumqi City is derived from Urumqi River about 25 years ago. It takes several ten years for river water to pass the underground to many springs. Some groundwaters and spring waters have taken a long time more than 40 years to travel under the ground. Enrichment of tritium in lake water by evaporation is considered to estimate the contribution of groundwater flow to the recharge of lake. Various contributions of groundwater to lakes are inferred for the various type of salinity in closed or semi-closed lakes. The inflow rates of groundwater to salt lakes are small as against fresh water lakes.     

Influence of aquatic plants on the hydrogen isotope composition of sedimentary long-chain n-alkanes in the Lake Qinghai region,Qinghai-Tibet Plateau

The hydrogen isotopic composition(δD) of leaf wax long-chain n-alkanes(C27, C29, and C31) from lacustrine sediments has been widely applied to reconstruct terrestrial paleoclimatic and paleohydrological changes. However, few studies have addressed whether the aquatic-derived n-alkanes can affect the δD values of lake sedimentary long-chain n-alkanes, which are usually regarded as a recorder of the terrestrial hydrological signals. Here we systematically investigated δD values of long-chain n-alkanes from modern aquatic plants, both near-shore and off-shore surface sediments, surrounding terrestrial plant litters, as well as river water and lake water in Lake Qinghai and its satellite lakes on the northeastern Qinghai-Tibet Plateau. Our data showed that(i) δD values of long-chain n-alkanes from aquatic plants varied from-184‰ to-132‰ for n-C27, from-183‰ to-138‰ for n-C29, and from-189‰ to-130‰ for n-C31, respectively, with no significant differences among the three n-alkanes homologues;(ii) δD values of long-chain n-alkanes from aquatic plants were generally more positive than those from surrounding terrestrial plants, possibly because that they recorded the D-enrichment of lake water in this semi-arid region;(iii) δD values of long-chain n-alkanes from surface sediments showed significant differences among the three n-alkanes homologues, due to the larger aquatic input of n-C27 to the sedimentary lipid pool than that of n-C31, and(iv) n-C27 δD values of near-shore aquatic plants and near-shore sediments are more negative than those from off-shore as a result of lower δD values of near-shore lake water. Our findings indicate that in this region(i) the offset between sedimentary n-C27 and n-C31 δD values(ΔδDC27-C31) could potentially be used to evaluate if sedimentary long-chain n-alkanes are derived from a single source;(ii) while δD values of n-C27 may be influenced by lake water hydrological changes, sedimentary n-C31 is derived predominantly from terrestrial plants and thus its δD can serve as a relatively reliable indicator for terrestrial paleoclimatic and paleohydrological reconstructions.     

Estimation of evaporation losses based on stable isotopes of stream water in a mountain watershed

Water stable isotopes(δ~2 H and δ~(18)O) can record surface water evaporation,which is an important hydrological process for understanding watershed structure and function evolution.However,the isotopic estimation of water evaporation losses in the mountain watersheds remains poorly explored,which hinders understanding spatial variations of hydrological processes and their relationships with the temperature and vegetation.Here we investigated δ~2 H,δ~(18)O,and d-excess values of stream water along an altitude gradient of 2130 to 3380 m in Guan'egou mountain watershed at the east edge of the Qinghai-Tibet Plateau in China.The mean δ~2 H(-69.6‰±2.6‰),δ~(18)O(-10.7‰±0.3‰),and dexcess values(16.0‰±1.4‰) of stream water indicate the inland moisture as the major source of precipitation in study area.Water stable isotopes increase linearly with decreasing altitudes,based on which we estimated the fractions of water evaporation losses along with the altitude and their variations in different vegetations.This study provides an isotopic evaluation method of water evaporation status in mountain watersheds,the results are useful for further understanding the relationship between hydrological processes and ecosystem function under the changing climate surrounding the Qinghai-Tibet Plateau.     

Spatial-temporal variation characteristics of global evaporation revealed by eight reanalyses

On the basis of eight atmospheric reanalyses, we analyzed the spatial-temporal characteristics of global evaporation and also briefly evaluated the eight reanalyses. The results indicate that the long-term mean annual evaporation obtained from different reanalyses are consistent over most regions, with significant maritime-continental contrasts, as well as differences in meridional directions, and the land evaporation generally decreases with the increase of altitude. In addition, the temporal evolution of global evaporation varies significantly among the datasets, MERRA, ERA-Interim, NCEP-NCRA, and NCEP-DOE are very similar, whereas CFSR agrees best with ERA-40. Comparison of the inter-annual to inter-decadal variability of land evaporation reveals large differences among the reanalyses, whereas MERRA, CFSR, and NCEP-DOE are exactly similar. The temporal variation of evaporation over the oceans showed a relatively high consistency, which indicates that the quality of the reconstructed evaporation values over the oceans is higher, and even greater uncertainties lie in the estimates of evaporation over the land. In general, MERRA and NCEP-DOE may appropriately reflect the spatial-temporal characteristics of global evaporation, showing strong representativeness. The CFSR and ERA-40 are capable of revealing the characteristics of land evaporation, whereas ERA-Interim, NCEP-NCAR, OAFlux, and HOAPS are relatively applicable for research focused on the evaporation over the oceans. According to ERA-40, NCEP-NCAR, and OAFlux, global evaporation significantly decreased for the period of 1958–1978. In contrast, most of the eight reanalyses show a significant linear increase for the period of 1979–2011, and evaporation over the oceans was even more pronounced. Furthermore, the results are presented for the mean annual cycle of global evaporation, the changes at the low latitudes in the Northern Hemisphere are most distinct, and the monthly variation amplitude of the land evaporation was higher than that of the evaporation over the oceans.     

Eddy covariance measurements of water vapor and CO_2 fluxes above the Erhai Lake

Measurement of turbulence fluxes were performed over the Erhai Lake using eddy covariance(EC) method.Basic physical parameters in the lake-air interaction processes,such as surface albedo of the lake,aerodynamic roughness length,bulk transfer coefficients,etc.,were investigated using the EC data in 2012.The characteristics of turbulence fluxes over the lake including momentum flux,sensible heat flux,latent heat flux,and CO2 flux,and their controlling factors were analyzed.The total annual evaporation of the lake was also estimated based on the artificial neural network(ANN) gap-filling technique.Results showed that the total annual evaporation in 2012 was 1165 ± 15 mm,which was larger than the annual precipitation(818 mm).Local circulation between the lake and the surrounding land was found to be significant throughout the year due to the land-lake breeze or the mountain-valley breeze in this area.The prevailing winds of southeasterly and northwesterly were observed throughout the year.The sensible heat flux over this plateau lake usually had a few tens of W m-2,and generally became negative in the afternoon,indicating that heat was transferred from the lake to the atmosphere.The sensible heat flux was governed by the lake-air temperature difference and had its maximum in the early morning.The diurnal variation of the latent heat flux was controlled by vapor pressure deficit with a peak in the afternoon.The latent heat flux was dominant in the partition of available energy in daytime over this lake.The lake acted as a weak CO2 source to the atmosphere except for the midday of summer.Seasonal variations of surface albedo over the lake were related to the solar elevation angle and opacity of the water.Furthermore,compared with the observation data,the surface albedo estimated by CLM4-LISSS model was underestimated in winter and overestimated in summer.     

Evolution and dynamics of a summertime penetrating front off the Zhejiang-Fujian coast,China

Penetrating fronts are frequently observed off the Zhejiang-Fujian coast,but their life cycles are poorly understood because of the lack of time series data.In this study,Geostationary Ocean Color Imager data are used to describe the complete evolutionary process of a penetrating front,and the impacts of wind and circulation on evolution are explored.Based on the horizontal coverage and the front of the penetrating water,the evolutionary process is divided into three stages of development,maturation and decay.During the development stage,the area of the penetrating water increases rapidly with eastward extension,and the penetrating front is well connected to the Zhejiang-Fujian coastal front in the southwestern area.During the maturation stage,the penetrating water continues to extend eastward at a low speed and finally arrives at the Kuroshio area on the continental slope.Moreover,the southwestern part of the penetrating front is gradually separated from the coastal front.During the decay stage,the coverage of the penetrating water decreases rapidly,and the penetrating front disappears first in the south.In this stage,the penetrating front is rarely moves east but completely separated from the coastal front south of 30°N.Dynamic analysis suggests that the typhoon-induced southward extension of the Changjiang Diluted Water off the Zhejiang-Fujian coast is an important precondition for the generation of the penetrating front.The eastward extension of the penetrating front during the development stage is mainly driven by a southwesterly wind,while in the maturation stage,it is affected by both the wind and the offshore branch of the Taiwan Warm Current.The detachment of penetrating water from coastal water is caused by the inshore branch of the Taiwan Warm Current.Numerical tracer experiments confirm the wind and Taiwan Warm Current impacts on the eastward extension and detachment of penetrating water.In addition,the Kuroshio frontal eddy may play an important role in the dissipation of the penetrating front during the decay stage.     

Theory and Method for Identifying Well Water Level Anomalies in a Groundwater Overdraft Area

The overexploitation of underground water leads to the continuous drawdown of groundwater levels, change of water quality and dry-up in dynamic water level observation wells. Due to land subsidence, the well pipes uplift and the observation piping systems are damaged. These environmental geology problems can present serious difficulties for the identification of earthquake anomalies by groundwater level observation. Basied on hydrogeological theories and methods, the paper analyzes the relations of the water balance state of aquifers with stress-strain conditions and the water level regime, and then discusses preliminarily the theory and method for identifying well water level anomalies in a groundwater overdraft area. The result shows that we can accurately judge the nature of the anomaly according to the diffusion character of the drawdown funnel in the well area in combination with the aforementioned theory and method and multi-year variation patterns obtained from existing data. The results of the research are helpful for distinguishing the influence of single centralized water pumping from the long-term overdraft of water on the water level, correctly recognizing water level anomalies in the groundwater overdraft area and increasing the level of earthquake analysis and prediction.     

Study on the simulation of transparency of Lake Taihu under different hydrodynamic conditions

It was indicated in this study that there were negative relations between the concentrations of suspended solid (SS) and transparency according to the analysis of measured data of Lake Taihu. Their relations in pervious studies were reviewed, which showed that the changes of transparency in Lake Taihu could be reflected by simulating suspended solid concentration (SSC). Measured data showed that the changes of SSC with wind speed were similar at different water depths. SSC increased with the increasing of wind speed. Both wave and lake current of Lake Taihu had positive relations with SSC. However, wave was the main factor affecting sediment suspension, while flow took the second place. In this study, a numerical model coupling lake current, wave and SSC of Lake Taihu was developed. In the SS model, the combined effects of wave and current were included. The amounts of suspended and deposited sediments near the lake bed surface layer were treated separately. The stochastic characteristics of turbulent flow pulsation near lake beds were also considered, and the start-up conditions of sediment suspension were introduced to the model. The model elucidated the mutual exchange processes between sediment particles in SS and active sediments within and on the bed surface layer. Simulated results showed that lake current had relatively significant effects on the SSC at littoral areas of Lake Taihu, while SSC at the central area of the lake was mainly influenced by wave. The changes of transparency with SSC were simulated for Lake Taihu using this model. Calculated results were validated by measured data with good fitness, which indicated that the model is basically suitable for the simulation and prediction of transparency of Lake Taihu.     

Estimation of annual actual evapotranspiration from nonsaturated land surfaces with conventional meteorological data

Land surface evapotranspiration is an important component both in earth surface heat and water bal-ance, on whose budgets weather and climate depend, to a great extent, for their changes are responsible for the formation and variation of vegetation features on the globe. Besides, the evapotranspiration is an im-portant topic of short-term flood forecasting and the estimation of runoff from mountainous sides. As a result, the problem as to the evapotranspiration has been one of the concerns in …     

Land use changes and their relations with carbon cycles over the past 300 a in China

Land use and land cover in China have changed greatly during the past 300 a, indicated by the rapid abrupt decrease of forest land area and the rapid increase of cropland area, which can affect terrestrial carbon cycle greatly. The first-hand materials are used to analyze main characteristics for land use and land cover changes in China during the study period. The following conclusions can be drawn from this study. The cropland area in China kept increasing from 60.78×106 hm2 in 1661 to 96.09×106 hm2 in 1998. Correspondingly, the forest land area decreased from 248.13×106 hm2 in 1700 to 109.01×106 hm2 in 1949. Affected by such changes, the terrestrial ecosystem carbon storage decreased in the mean time. Car-bon lost from land use and land cover changes mainly consist of the loss from vegetation biomass and soil. In the past 300 a, about 3.70 PgC was lost from vegetation biomass, and emissions from soil ranged from 0.80 to 5.84 PgC. The moderate evaluation of soil losses was 2.48 PgC. The total loss from vegetation and soil was between 4.50 and 9.54 PgC. The moderate and optimum evaluation was 6.18 PgC. Such carbon losses distribution varied spatially from region to region. Carbon lost more significantly in Northeast China and Southwest China than in other regions, because losses of forest land in these two regions were far greater than in the other regions during the past 300 a. And losses of carbon in the other regions were also definite, such as Inner Mongolia, the western part of South China, the Xinjiang Uygur Autonomous Region, and the Qinghai-Tibet Plateau. But the carbon lost very little from the traditional agricultural regions in China, such as North China and East China. Studies on the relationship between land use and land cover change and carbon cycle in China show that the land use activities, especially those related to agriculture and forest management, began to affect terrestrial carbon storage positively in recent years.     

Precipitation recycling ratio and water vapor sources on the Tibetan Plateau

Precipitation recycling ratio(i.e.,evaporation-precipitation feedback strength)and water vapor sources are two key aspects of regional water cycle,and their quantification is essential for understanding water cycle processes and their changes.The results of existing studies on the precipitation recycling ratio and water vapor sources for the Tibetan Plateau were highly controversial.This article clarifies different frameworks for understanding the water cycle.It points out that(1)the ratio of evaporation to precipitation depends mainly on climate regimes,while the precipitation recycling ratio is closely related to both the climate regimes and the scale of the region of interest,and(2)the water vapor sources depend on the traced period(precipitating or non-precipitating period)and the degree of tracing.Within the same theoretical framework,there is no fundamental conflict among the results of different studies on the water cycle in the Tibetan Plateau.     

Compound-specific δD and its hydrological and environmental implication in the lakes on the Tibetan Plateau

The hydrogen isotopic composition(δD) of n-alkanes in lacustrine sediments is widely used in palaeoenvironmental studies, but the heterogeneous origins and relative contributions of these lipids provide challenges for the interpretation of the increasing dataset as an environment and climatic proxy. We systematically investigated n-alkane δD values from 51 submerged plants(39 Potamogeton, 1 Myriophyllum, and 11 Ruppia), 13 algae(5 Chara, 3 Cladophora, and 5 Spirogyra) and 20 terrestrial plants(10 grasses and 10 shrubs) in and around 15 lakes on the Tibetan Plateau. Our results demonstrate that δD values of C_(29) nalkane are correlated significantly with the lake water δD values both for algae(R~2=0.85, p0.01, n=9) and submerged plants(R~2=0.90, p0.01, n=25), indicating that δD values of these algae and submerged plants reflect the δD variation of lake water. We find that apparent hydrogen isotope fractionation factors between individual n-alkanes and water(εa/w) are not constant among different algae and submerged plants, as well as in a single genus under different liminological conditions, indicating that the biosynthesis or environmental conditions(e.g. salinity) may affect their δD values. The δD values of submerged plant Ruppia in the Xiligou Lake(a closed lake) are significant enriched in D than those of terrestrial grasses around the lake(one-way ANOVA,p0.01), but the algae Chara in the Keluke Lake(an open lake) display similar δD values with grasses around the lake(one-way ANOVA, p=0.8260.05), suggesting that the n-alkane δD values of the algae and submerged plants record the signal of D enrichment in lake water relative to precipitation only in closed lakes in arid and semi-arid area. For each algae and submerged plant sample, we find uniformed δD values of different chain length n-alkanes, implying that, in combination with other proxies such as Paq and Average Chain Length, the offset between the δD values of different chain length n-alkanes can help determine the source of sedimentary n-alkanes as well as inferring the hydrological characteristics of an ancient lake basin(open vs closed lake).     

一种浅水湖耦合模式系统的发展与应用

Growing developments in lake basins in China, have adversely affected, the water quality of lake, in particular, the water bodies of many famous shallow lake are seriously polluted in recent years. Some projects have been built up to improve the water quality, for example, the sewage interception project (i.e. Xiyuan tunnel project) and four sewage treatment plants etc. have been built up in Dianchi Lake. In order to predict and evaluate the effects of projects on the water quality, it is necessary to develop a coupled model system, which should mainly include wind, circulation and water quality parameters. This paper describes the development and application of a coupled modeling system in a shallow lake, which include a 3D micro-meteorology model (3DMM), a 2D hydrodynamic model (2DHM) and a 2D water quality model(2DWM).The coupled modeling system has been applied to predict the ejfects of environmental protection projects on water quality in Dianchi Lake.     

Holocene vegetational and climatic variation in westerly-dominated areas of Central Asia inferred from the Sayram Lake in northern Xinjiang,China

Changes in the vegetation and climate of the westerly-dominated areas in Central Asia during the Holocene were interpreted using pollen-assemblages and charcoal data from a 300-cm-long sediment core of the Sayram Lake,northern Xinjiang.Accele-rator Mass Spectrometry(AMS) radiocarbon dating methods were applied to bulk organic matter of the samples.Artemisia spp./Chenopodiaceae ratios and results from principal component analysis were used to infer that the lake basin was dominated by desert vegetation before ca.9.6 cal.ka BP,which suggests a warm and dry climate in the early Holocene.Desert steppe/steppe expanded during 9.6-5.5 cal.ka BP,indicating a remarkable increase both in the precipitation and temperature during the mid-Holocene.Desert vegetation dominated between 6.5 and 5.5 cal.ka BP,marking an extreme warmer and drier interval.The steppe/meadow steppe recovered,and temperatures decreased from 5.5 cal.ka BP in the late Holocene,as indicated by the increased abundance of Artemisia and the development of meadows.Holocene temperatures and moisture variations in the Sayram Lake areas were similar to those of adjacent areas.This consistency implies that solar radiation was the main driving factor for regional temperature changes,and that the effect of temperature variations was significant on regional changes in humidity.The evolution of climate and environment in the Sayram Lake areas,which were characterized as dry in the early Holocene and relatively humid in the middle-late Holocene,are clearly different from those in monsoonal areas.Dry conditions in the early Holocene in the Sayram Lake areas were closely related to decreased water vapor advection.These conditions were a result of reduced westerly wind speeds and less evaporation upstream,which in turn were caused by seasonal changes in solar radiation superimposed by strong evaporation following warming and drying local climate.     

A methodological approach for estimating turbidity in a river

During the operations of purging and disposal of sediments of a reservoir it is necessary to know the values of turbidity in the river downstream in natural condition,in the absence of dams or river training works.The paper shows that under these conditions the ratio of the average values of sediment discharge to the annual maximum value of water discharge is a function of the average annual turbidity.Turbidity can be considered as representative synthetic index of the climatic conditions,the lithological features and the land cover of the basin,and the geometric characteristics of the river network.The proposed relationship of sediment discharge as a function of water discharge were validated on the basis of data collected from different Italian regions that have very different morphological,geo-lithological and rainfall features and that are characterised by a basin area changing between a few dozen and thousands of square kilometres.The results can be considered satisfying.     

改善中国太湖水生态环境的新对策—“如何解决太湖流域水质型缺水和环境自然资源退化问题？”

Taihu Lake is one of the famous five great freshwater lakes in China. Taihu Lxike Basin (TLB) is a densely populated and economic developed area in China. The surface water quality in TLB was deteriorated from I-Ⅱ grade in the history to IV-V grade at present. To develop a series of technology of most cost-effective and achievable for improving environment in a local water area of most sensitive for society and improving water quality for more and more areas step by step is the key point of the new strategy. Except the measures for reducing the industrial and domestic pollution load to the lake, some research topics are suggested to be emphasized.     

The Changing Cold Regions Network:Observation,diagnosis and prediction of environmental change in the Saskatchewan and Mackenzie River Basins,Canada

Climate change is causing rapid and severe changes to many Earth systems and processes,with widespread cryospheric,ecological,and hydrological impacts globally,and especially in high northern latitudes.This is of major societal concern and there is an urgent need for improved understanding and predictive tools for environmental management.The Changing Cold Regions Network(CCRN)is a Canadian research consortium with a focus to integrate existing and new experimental data with modelling and remote sensing products to understand,diagnose,and predict changing land,water,and climate,and their interactions and feedbacks over the geographic domain of the Mackenzie and Saskatchewan River Basins in Canada.The network operates a set of 14 unique and focused Water,Ecosystem,Cryosphere and Climate(WECC)observatories within this region,which provide opportunities to observe and understand processes and their interaction,as well as develop and test numerical simulation models,and provide validation data for remote sensing products.This paper describes this network and its observational,experimental,and modelling programme.An overview of many of the recent Earth system changes observed across the study region is provided,and some local insights from WECC observatories that may partly explain regional patterns and trends are described.Several of the model products being developed are discussed,and linkages with the local to international user community are reviewed—In particular,the use of WECC data towards model and remote sensing product calibration and validation is highlighted.Some future activities and prospects for the network are also presented at the end of the paper.     

Dynamics of phosphorus in sediments of a naturally acidic lake

The mechanisms which controls the fixation and/or release of P in sediment of an extremely acidic lake（pH = 2.0 to 3.0） and its response to the influence of eutrophic urban waste water were investigated.The results,in the chemical composition,in the mineralogy of the sediment and in the material as obtained from sediment traps,show that the lake sediments are mainly volcanic material reflecting volcanic features of the basin.The sedimentation rate calculated for the lake(2.5×10^-2 mg m^-2 day^-1) was higher than that observed in other similar glacial lakes in both Andean Patagonia and also elsewhere in the world.The Total Phosphorus concentration in sediments was higher than figures reported by other authors for mining acid lakes,and the main fraction of P was found associated with organic matter.There was no control by Fe or Al on P,because both are in solution at pH < 3.0.It was concluded that changes in the natural input of nutrients（derivatives of Copahue volcano fluid,the discharge of sewage,or basin run-off） are responsible for a high concentration of SRP and N-NH₄⁺ in the lake.Laboratory experiments showed that sediments have no ability to retain phosphorus and a continuous release of P from the sediments into the water column was observed.The assays where the pH was artificially increased showed that the P still remains in solution until at least pH 7.0.It was concluded that changes in the natural input of nutrients due to:1) the volcanic fluids,2) the increase in sewage charges,or 3) surface runoff upstream,maintain a high trophic state with high concentrations of dissolved P and N-NH₄⁺,although the threshold of neutral pH in the lake is exceeded.This study will enable a better understanding about of the mechanism of release/fixation of phosphorus in acidic sediments in order to assist in making decisions regarding the conservation and management of this natural environment.     

Air–water CO_2 flux in an algae bloom year for Lake Hongfeng,Southwest China:implications for the carbon cycle of global inland waters

The carbon cycle of global inland waters is quantitatively comparable to other components in the global carbon budget. Among inland waters, a significant part is man-made lakes formed by damming rivers. Manmade lakes are undergoing a rapid increase in number and size. Human impacts and frequent algae blooms lead to it necessary to make a better constraint on their carbon cycles. Here, we make a primary estimation on the air–water CO_2 transfer flux through an algae bloom year for a subtropical man-made lake—Hongfeng Lake, Southwest China. To do this a new type of glass bottles was designed for content and isotopic analysis of DIC and other environmental parameters. At the early stage of algae bloom,CO_2 was transferred from the atmosphere to the lake with a net flux of 1.770 g·C·m~(-2). Later, the partial pressure(pCO_2) of the aqueous CO_2 increased rapidly and the lake outgassed to the atmosphere with a net flux of 95.727 g·C·m~(-2). In the remaining days, the lake again took up CO_2 from the atmosphere with a net flux of 14.804 g·C·m~(-2). As a whole, Lake Hongfeng released 4527 t C to the atmosphere, accounting for one-third of the atmosphere/soil CO_2 sequestered by chemical weathering in the whole drainage. With an empirical mode decomposition method, we found air temperature plays a major role in controlling water temperature, aqueous pCO_2 and hence CO_2 flux. This work indicates a necessity to make detailed and comprehensive carbon budgets in man-made lakes.     

Study on consumption efficiency of soil water resources in the Yellow River Basin based on regional ET structure

Based on the regional water resources character, the concept of soil water resources is first redefined, and then associated with their transfer relationship in the hydrological cycle, Evapotranspiration (ET)-based consumption structure and consumption efficiency of soil water resources are analyzed. According to ET 's function in productivity, the consumption efficiency of soil water resources is di- vided into three classes: high efficient consumption from vegetation transpiration, low efficient con- sumption from soil evaporation among plants with high vegetation coverage and inefficient consump- tion from soil evaporation among plants with low vegetation coverage and bare soil evaporation. The high efficient and low efficient consumption were further classified as productive consumption. The ineffi- cient consumption is considered non-productive consumption because it is significant in the whole hydrological cycle process. Finally, according to these categories, and employing a WEP-L dis- tributed hydrological model, this paper analyzes the consumption efficiency of soil water resources in the Yel- low River Basin. The results show that there are 2078.89×108 m3 soil water resources in the whole basin. From the viewpoint of consumption structure, the soil water resources are comprised of 381.89×108 m3 transpiration consumption from vegetation and 1697.09×108 m3 evaporation consumption from soil among plants and bare soil. From the viewpoint of consumption efficiency, soil water re- sources are composed of 920.11×108 m3 efficient consumption and 1158.86×108 m3 of inefficient con- sumption. High efficient consumption accounts for 41.5 percent of the total efficient consumption of the whole basin, low efficient for 58.5 percent. Furthermore, consumption efficiency varies by region. Compared with ET from different land use conditions, the whole basin appears to follow the trend of having the greatest proportion of consumption as inefficient consumption, followed by low efficient consumption, and then the least proportion as high efficient consumption. The amount of inefficient consumption in some regions with vegetation is less than in other regions without vegetation. The amount of inefficient consumption in grasslands is much greater than in forestlands. However, the proportion of low efficient consumption is the greatest in crop fields. The amount of high efficient con- sumption in grasslands and forelands is similar to the corresponding low efficient consumption. However, the low efficient consumption in grasslands is larger than in the forelands. Therefore, when adjusting the utilization efficiency of soil water resources, vegetation coverage and plant structure should be modulated in terms of the principle of decreasing inefficient consumption, improving low efficiency ET and increasing high efficiency ET according to area character.