Changjiang Basin Research Articles

Ecological rehabilitation effect assessment of soil and water conservation model—A case study of the upper reaches of Liangdang River,Changjiang Basin

Ecological rehabilitation models of soil and water conservation combining artificial measures and natural power in the upper reaches of Liangdang River of Changjiang Basin were advanced in accordance with environmental characteristics of the study area.The models include recovery model of deteriorated forests,rehabilitation model of barren mountains and farmlands and ecological support measures.The effect of ecological rehabilitation was assessed using on-the-spot investigation and Remote Sensing methods.Results show significant improvements in degenerated land area of the ecosystem over a relatively short period through natural and artificial restoration measures.Farmland ecosystem rehabilitation is significant,and there is an equally significant improvement in vegetation expansion rate,forest plant species number.The ecosystem on the whole tends to be vibrantly recovering.

Runoff characteristics of the Changjiang River during 2006: Effect of extreme drought and the impounding of the Three Gorges Dam

In 2006, the Changjiang basin runoff reached its lowest level in the last 50 years, and the water level in the Three Gorges Dam (TGD) was raised from 135 m to 156 m. Based on routine water level and runoff measurements at 10 field stations, the water level in flood season during the last 50 years was lowest in 2006, a situation here we describe as “no flood in the flood season” (NFFS). In contrast, there was no obvious change in runoff of the mid‐lower reaches of the Changjiang river (MLRCR) in the drought season in 2006, which we correspondingly describe as “no drought in the drought season (NDDS)”. The extreme drought of Changjiang and impounding of TGD contributed to NFFS. However, the adjustment of TGD and the replenishment from tributaries and lakes resulted in NDDS. Meanwhile, 54% of the water flux was lost at Datong during September 20 to October 27, 2006, in comparison with the same period in 2005. It can be estimated that the impounding of TGD and the extreme drought in 2006 contributed 9% and 45% of this loss, respectively.

Poyang Hu (Jiangxi Province, P. R. of China) Area Variations between January 2004 and June 2006 Using ENVISAT Low and Medium Resolution Time Series

Poyang Hu, one of the most regularly flooded areas in China, can be considered as a key hydrological element in flood control and reduction within the middle Changjiang basin. This area was selected as a major test site of the Flood DRAGON Project, part of the MOST-ESA DRAGON Programme. Over two and half years, water extent was monitored based on sixty-four ENVISAT low and medium resolution ASAR and MERIS FR images. It's the first time that such an amount of ENVISAT data was used in monitoring inland lake water extent variations. This original integration approach involves: lake surface variation analysis, yearly submersion time estimation, and a spatial recognition of three major hydrological sub-systems. The results highlight the great potential of ENVISAT, and more largely Earth Observation Medium Resolution data, for large inland water body monitoring and management. This approach can be applied worldwide in the context of global climate change.

Dialect Contact and the Production of Contaminated Forms — A Reconstruction of the History of Chinese Words for “Knee”

This paper attempts to reconstruct the history of Chinese words for “knee” by using the methodology of linguistic geography. Word forms are classified into five major types according to morphological features, and then their geographical distributions are observed. Observation suggests that dialect contact produces various types of “contaminated” forms (linguistic blends) in Chinese dialects. Three types of blend formations are discernible: prefixed, infixed and suffixed types. As a rule, the dialects accept part of the new form, which is transmitted from the adjacent areas, as conforming to the morphology of the original form. The suffixed-type blending is currently distributed along the Changjiang basin. The infixed-type is typical of the Wu dialects, which is assumed to have accepted the northern form [kʰɑ] as the second component of a trisyllabic structure. The prefixed-type is currently observable in some northern dialects, and it is assumed that the same process might have once occurred in the northern area, where the unaspirated prefix [kɑk] changed to the aspirated one, i.e., [kʰɑk], due to contamination by the form [kʰɑ]. The etymology and historical formation of the newest type, “p-l-k” > “k-l-p”, is also discussed. Finally, historical changes of the “knee” forms are reconstructed.

Sensitivity of the Penman–Monteith reference evapotranspiration to key climatic variables in the Changjiang (Yangtze River) basin

Sensitivity analysis is important in understanding the relative importance of climatic variables to the variation of reference evapotranspiration (ETref). In this study, a non-dimensional relative sensitivity coefficient was employed to predict responses of ETref to perturbations of four climatic variables in the Changjiang (Yangtze River) basin. ETref was estimated with the FAO-56 Penman–Monteith equation. A 41-year historical dataset of daily air temperature, wind speed, relative humidity and daily sunshine duration at 150 national meteorological observatory stations was used in the analysis. Results show that the response of ETref can be precisely predicted under perturbation of relative humidity or shortwave radiation by their sensitivity coefficients; the predictive power under perturbations of air temperature and wind speed depended on the magnitude of the perturbation, season and region. The prediction errors were much smaller than the seasonal and regional variation of their sensitivity coefficients. The sensitivity coefficient could also be used to predict the response of ETref to co-perturbation of several variables. The accuracy of the prediction increases from the lower to the upper region. Spatial variations of long-term average monthly and yearly sensitivity coefficients were obtained by interpolation of station estimates. In general, relative humidity was the most sensitive variable, followed by shortwave radiation, air temperature and wind speed. The actual rank of the four climatic variables in terms of their sensitivity varied with season and region. The large spatial variability of the sensitivity coefficients of all the climatic variables in the middle and lower regions of the basin was to a large extent determined by the distinct wind-speed patterns in those two regions.

HSPF Simulation of Runoff and Sediment Loads in the Upper Changjiang River Basin, China

To evaluate the performance of a computer model simulating runoff and sediment load in the upper region of the Changjiang (Yangtze River) basin over a relatively short time interval, including examining the applicability of the input precipitation data generated from global circulation models and satellite data, we used a spatially distributed model, HSPF with the International Satellite Land Surface Climatology Project (ISLSCP) precipitation data for 1987 and 1988 as input data. The Nash–Sutcliffe coefficient (R2) for 5-day average streamflow was 0.94 in the calibration period and 0.95 in the verification period for the whole upper region. Moreover, the model simulated the 5-day average streamflow well in each main tributary, as shown by R2 values of 0.46–0.96, except that it underestimated the peak flow rates during the flood season over 2 years by up to 71% in Tuojiang and 61% in Jialingjiang. The model simulated the 5-day concentrations of suspended solids (SS) fairly well in the headwaters and upper regions of the Jinshajiang, Yalongjiang, and Minjiang watersheds, as shown by R2 values of 0.31–0.65. In the other regions, however, the model underestimated the SS load by up to 72%, and rarely simulated the fluctuation of SS concentration in each river channel during the flood season. These errors led to the underestimation of sediment runoff volume from the whole upper region during the flood season, as shown by the ratio of the simulated sediment load to the observed data at Yichang: 0.69 in the calibration period and 0.68 in the verification period. The ISLSCP precipitation tended to be more frequent and less intense than the measured precipitation. This was probably the main reason why the HSPF did not perform well in all regions at all times.

EFFECT OF THREE GORGES DAM ON FLOOD PROTECTION IN THE MIDDLE REGION OF THE CHANGJIANG RIVER BASIN IN CASE OF THE OCCURRENCE OF 1998 TYPE FLOOD

To evaluate the protection effect of the Three Gorges Dam Project (TGP) on the flood in the middle region of the Changjiang River basin, we applied the integrated watershed hydrological model using gauged daily precipitation data of 1998 when the second largest flood occurred in the basin in the last century. From the results simulated by applying the discharge volume controlled by each upper limitation value from 40, 000 m3/s to 60, 000 m3/s, we could not find the clear effect on the reduction of the water level during flood period not only in the Dongting Lake but also in the Changjiang mainstream in the cases that the upper limitation discharge value were over 50, 000 m3/s. In the case that the upper limitation value was 40, 000m3/s, although the flood protection effect was clearly exerted in both the mainstream and the lake, the simulated storage volume of TGP remarkably exceeded the total flood control volume (221.5×108 m3) at the peak of inflow to TGP. These results suggested that TGP flood control ability does not efficiently work for the decrease of flood damage in the middle region of the Changjiang basin in case of the occurrence of 1998 type flood phenomena.

Two unique weathering regimes in the Changjiang and Huanghe drainage basins: geochemical evidence from river sediments

The present research reconstructs the histories of chemical weathering in the drainage basins of the Changjiang and Huanghe based on the chemical compositions of the river sediments. The silicate weathering of the Changjiang Basin is strong and Na- and Ca-silicate minerals are considerably dissolved, while other silicate minerals are less attacked. In comparison, the Huanghe Basin is characterized by very weak silicate weathering, and the weathering degree corresponds well with that of the loess which is the predominant source of the Huanghe sediment. Overall, the Changjiang and Huanghe basins constitute a consistent weathering spectrum from the early to intermediate stage. The similarity of chemical compositions between upper continental crust and the Huanghe sediments as well as the low degree of chemical weathering in the Huanghe Basin imply that the river sediments can be considered to be the representative of UCC and are suitable for studying the evolution of continental crust. Our observations indicate that climate is the predominant factor controlling silicate weathering in both river basins, while controls by source rocks and relief are subordinate. Highly erosive river basins such as the Huanghe produce poorly weathered materials, which casts doubt on the idea that strong physical weathering naturally contributes much to chemical weathering. Differences in silicate weathering processes between the Changjiang and Huanghe basins may provide more constraints in estimating atmospheric CO 2 budget in China.

How do nitrogen inputs to the Changjiang basin impact the Changjiang River nitrate: A temporal analysis for 1968–1997

We present estimates of nitrogen (N) inputs to the Changjiang River basin for the period 1968–1997. The total N input is approximately 7.8 × 109 kg in 1997, which is a threefold increase over 1968 levels. N fixation was often a dominant input before 1978, providing about 2.2 × 109 kg year−1, while N fertilizer dominated N input after 1983, supplying an additional input of some 4.4 × 109 kg year−1. More than 40% of total N inputs is converted into manure N, and half of total manure N is returned to agricultural soil. We estimate that the river nitrate concentration and flux have increased about tenfold from 1968 to 1997. Our study suggests that the percent of N inputs to the basin that are exported by the river as NO3‐N has increased steadily over the 30‐year period and that about 30% of total N input is transported through the river. The integrated N input, budget, and storage have been linked to the increasing temporal trends of Changjiang River nitrate. N fertilizer application and human population density, as well as manure N production in the basin, are good predictors of the river's nitrate concentration and flux. Therefore, how N balance is kept (especially for effective application of N fertilizer) is a crucial problem to the sustainable development of the basin.

Human impacts on the Changjiang (Yangtze) River basin, China, with special reference to the impacts on the dry season water discharges into the sea

The annual mean discharge from the upper Changjiang (Yangtze) basin has shown a significant decreasing trend since the end of the 19th century. Since the 1970s, the monthly mean discharge to the sea has also shown a dramatic decrease during dry seasons. This paper examines the human impacts on the major hydrological processes in the Changjiang River basin, with a special focus on their influence on the discharge from the drainage basin to the sea during the dry season. Climatic warming has been obvious since the 1960s in the headwater area, resulting a continuous retreat of glaciers, while the increased evaporation is responsible for the dropping of lake water levels and decrease in water area. Such a trend continuing into the coming decades will significantly change the seasonal hydrological processes, especially the dry-season discharges from the upper basin. The decreasing vegetation cover and the increasing reservoir volume capacity also impacted on the water discharge over the past decades, although in different ways. The possible impacts of the Three Gorges Dam on the monthly variation of water discharge to the sea are discussed with special emphasis. In the middle basin discussions are focused on the effect of decreasing lake area, of increasing reservoir capacity, and of irrigated agriculture on the temporal changes of water discharge since the 1950s. The human impacts on water discharge from the lower basin to the sea are mostly attributed to water transfer to both tributary and neighboring drainage basins by a large number of electric pumping stations and sluices. The total water transferring capacity is more than 5000 m 3/s along the lower river. Studies indicate that in a dry season the water discharge to the sea is greatly reduced and results in strong saltwater intrusion in the estuary.

Strategies for biodiversity conservation and coordinated economic development of the Changjiang Basin

Strategies for biodiversity conservation and coordinated economic development of the Changjiang Basin

The preliminary syudy of medium-scale cloud clusters over the Changjiang basin in summer

It is shown that the medium-scale could cluster is a major one of precipitation systems from analysing the rainstorms along the Changjiang River during the plum rain period of 1980–1983. The medium-scale cloud clusters do not always correspond to the moving vortex, but they are in good agreement with the convergence center for the divergent component of wind at 850 hPa. The favourable environmental conditions for the genesis and development of medium-scale cloud cluster, such as the large-scale circulation situation, patterns of temperature and moisture, potential instability, and the structure of cloud cluster are given. A model on large-scale cloud pattern for the genesis of medium-scale cloud cluster is presented.

Chemical dynamics of the Changjiang estuary

A reconnaissance of the chemical dynamics of the estuary and plume of the Changjiang was carried out on cruises in the summer of 1980 and the winter of 1981. In summer vigorous turbulence in the main channel of the inner estuary maintains high concentrations of suspended material in the surface layers which suppresses biological activity. Plankton blooms occur only on the inner shelf at salinities greater than about 20 ppt. In winter there is no significant photosynthetic activity over the entire mixing zone. Therefore a wide variety of inorganic processes can be studied in detail. Of the nutrients, nitrate is present in the river in very high concentrations and suffers only minor depletion in the biologically active areas. The distribution of silica is similar. Phosphate shows major release from the suspended particles and complete depletion in the plankton blooms. Among the trace elements, iron decreases rapidly to 5 ppt, beyond which mixing is conservative; comparison with the nutrient trends indicates that the element is chemically adsorbed onto the particulates. In contrast manganese undergoes desorption out to about 12 ppt beyond which it mixes conservatively. Copper and beryllium behave conservatively over the entire mixing zone while nickel and barium are desorbed rapidly at low salinity. Cadmium is undetectable in the river waters (< 10pmol kg −1) but displays a broad desorptive maximum at intermediate salinities in the mixing zone. These data allow fluxes to be calculated for the net transport of dissolved material from the Changjiang Basin to the surface waters of the East China Sea and their comparison with those of other large rivers of the world.