Abstract:Since nitrate contamination in surface water is an environmental problem in many regions of the world,methods to trace the source of nitrate and its transformation mechanisms are important for nitrate pollution control.Nowadays,stable nitrogen (¹⁵N) and oxygen (18 O) isotope data can provide meaningful insight for tracing sources of nitrate and have been frequently used to identify nitrate source and its transformation mechanisms in surface water.However,the stable isotope methods have limitations because the complex fractionations caused by multiple N-cycling processes can change the original isotopic values.This review paper systematically summarizes the isotopic composition and its influencing factors of various nitrate sources, the techniques and progresses in research on nitrate sources identification,and load estimation and assessment of denitrification in different types of land-use watersheds using nitrate stable isotope methods.Based upon the previous researches about the application of stable isotope methods, we suggest that in the future it is important to treat a catchment as a unit and to apply several assisted indexes to study the variation of δ¹⁵N-NO₃^- and δ¹⁸O-NO₃^- in different sources under the combined effects of multiple factors.In addition,comparative studies should be conducted to assess the uncertainty between polluting source survey data and the results of model simulation,and to build a better load computational model.Finally,further studies should be made to investigate the scale and extent of denitrification in a catchment/river using the nitrate stable isotope methods,especially in the sediment-water system.

Abstract:Denitrification in anaerobic lake bottom sediments and leachate providing carbon source via flocculated algae were simulated in the laboratory.TN,ammonium,nitrite,nitrate,volatile fatty acids (VFAs),COD,electric potential and pH were analyzed to confirm that the denitrification in sediments was truly promoted by small molecular compounds such as VFAs which were reduced from the plentiful biodegradable carbon in algae.The maximum VFAs content in 2×algae system and 1×algae system were 2232.96 and 1263.36 μl/L,respectively.The maximum TN removal ratio was about 42.1%,nearly 2.43 times of the control.The carbon of flocculated algae is available for heterotrophic microbes but needs some time to be transformed.A sustaining COD reduction rate showed in all the added algae systems after low COD reduction rate,positive electric potential and increasing nitrate had last in them for about 4 days.The maximum COD reduction rate of 2×algae system,1×algae system and the control was 42.08%,32.93% and 14.46%,respectively.The degradation of algae generated VFAs can be directly used by denitrifying bacteria to facilitate denitrification process.The effect that flocculated algae cell as carbon source can promote sediment denitrifying process was verified,and the influence of flocculated algae on C and N of sediments was analyzed.The study could provide technical basis for reducing the internal nitrogen in sediments of eutrophic lakes.

Abstract:Water environment deterioration is critic to the health of lake ecosystem,and trend analysis is considered as the very first step to mitigate water pollution.Based on pollutants monitoring data from 1980 to 2011 in Lake Fuxian,trends of COD_Mn,TN, TP,SD,Chl.a and phytoplankton abundance are quantified using Mann-Kendall and Daniel trend test methods.From the perspectives of human impacts and natural changes,9 indices of driving forces are selected to build the grey relationships between driving factors and water quality.Results show that (1) six indices of water quality changed greatly during the period of 1980-2011, among which TP,TN and phytoplankton abundance fluctuated the most with coefficient of variations greater than 0.6;(2) COD_Mn, TN,SD,Chl.a and phytoplankton abundance showed significant degradation at 0.05 significance level,and results of Mann-Kendall and Daniel are consistent;(3) significant correlation was found between water quality index and selected driving factors in which human population and water temperature are identified as the main factors with correlation coefficient values higher than 0.7.

Abstract:Based on the measured concentration of total nitrogen (TN) and total phosphorus (TP) in Lake Poyang in July 2011,we analyzed the spatial distribution characteristic of TN,TP,and factors affecting them.The nutrient structure and the correlations among nitrogen,phosphorus and chlorophyll-a were discussed.The results show that: The concentration levels of nitrogen and phosphorus have already reached the threshold of eutrophication.TN content has a downward trend from the east part to the west part,and from the south part to the north part,in Lake Poyang.TP contents in several dredging areas were the highest,especially in the border area between south lake and east lake.Phosphorus was limited in Lake Poyang.Comparatively speaking,nitrogen pollution was more serious,and the nitrogen and phosphorus were not the restricting factors of eutrophication.TN content was influenced by suspended sediment concentrations (SSC) as well as the water flow.It was mostly affected by the water flow in the upstream channels which were largely influenced by the land-sourced pollutants.TP content was less affected by the water flow,but it was mainly influenced by the high SSCs and the dredging activities.

Abstract:Danjiangkou Reservoir is the water source area of Mid-route of the South-to-North Water Transfer Project in China,and water quality is one of the critical factors to measure the success.However,the water quality has always been troubled by the water pollution control of input rivers of Danjiangkou Reservoir.This paper analyzed the spatial variations of the water quality in Jianhe River by analyzing regional representative factors such as water quality and man-made interferences based on ecological investigation of the water environment.On the basis of river geographical feature,Jianhe River was divided into four survey sections: upstream, midstream,downstream and Taijihu Reservoir,and the objectives of water environmental management were targeted to level Ⅱ, Ⅲ,Ⅳ and Ⅲ (GB/T 3838-2002),respectively.The results show that under the influence of fertilizing aquaculture,lacking sewage network and a low rate in sewage treatment plant,TN of the whole Jianhe River exceeded threshold fairly and four survey sections all cannot reach the objectives of water environmental management;TP,CODCr,and NH₃-N reached level Ⅱ and Ⅲ,respectively, in upstream and midstream,while only 64%, 64% and 18% in downstream reached level Ⅳ,and only 71%,29% and 0 in Taijihu Reservoir reached level Ⅲ,respectively.The overall pollution patterns are in the form of downstream >Taijihu Reservoir >upstream >midstream,and the major pollutant in Jianhe River was TN (2.27-13.51 mg/L),followed by NH₃-N (0.25-13.31 mg/L),CODCr (7.0-95.5 mg/L) and TP(0.01-0.79 mg/L).Concentrations of CODCr and TP were low and not the main pollutants of Jianhe River.According to the difference analysis of the water quality,the targeted reduction plan was proposed, which provided the scientific basis for better management of water pollution in Danjiangkou Reservoir and water pollution control of the river.

Abstract:In order to solve the problem of lake eutrophication in Lake Erhai,a model based on the analysis of nutrients transport was applied to establish society,economy,technology and environment coupling SD model for Lake Erhai drainage area using VENSIM-DSS.The SD model is consisted of seven subsystems searching for the sources of TN and TP.The research established a set of parameters applicable for the Lake Erhai coupling model.The stimulation results showed 88% of TN was from the subsystems of plantation,animal husbandry,sewage and dry and wet deposition,and 89% of TP was from the subsystems of plantation,animal husbandry,sewage,soil and water loss in Lake Erhai catchment.Based on the results,four kinds of nutrient reduction solutions were set to stimulate the changes of TN and TP for the next ten years.The feasibilities of different reduction solutions were quantitatively estimated by policy evaluation subsystem and DILLON model to put forward the optimal nutrient reduction solutions for Lake Erhai catchment.

Abstract:A three-dimensional hydrodynamic and water quality model has been developed for Lake Erhai and its adjacent embayments based on the Environmental Fluid Dynamic Code (EFDC).The model was calibrated and verified by using the field water quality data monitored from 2001 to 2011.The simulated results are in good agreement with observed data,indicating that the model simulation results are accurate and reliable.The model was applied to determine the contributing rate by each waste load inflow at various water quality control points in the lake.The effects of background water quality condition were included in the model in determining the impact of each waste load inflow.The linear programming Simplex Method was used to calculate the optimal loading for each pollutant source with the consideration of constraints on water quality target at different water quality control points in the lake.The allocated pollutant load for Miqie River,Yong'an River and Luoshi River in the northern region of the watershed is the highest due to higher flow discharge,and the amount of allocated loads for total nitrogen,total phosphorus,and COD_Mn from the three rivers takes up to 47%,53% and 49% of the total load for the entire Lake Erhai watershed,respectively.The pollutant load allocation study can be used to facilitate the development of lake pollution control strategies,and to achieve the targeted water quality objectives for Lake Erhai.

Abstract:The CO₂ and CH₄ fluxes on wetland (water level drawdown) area of reservoirs are crucial parts of the scientific research of reservoir Green House Gas emission.CO₂ and CH₄ fluxes at soil-water interface of Baijiaxi and Yanglu drawdown areas in the Pengxi River were studied from June to September in 2010.Baijiaxi drawdown area has a mean CO₂ flux of 12.38±2.42 mmol/ (m²·h),while its mean CH₄ flux is 0.0112±0.0064 mmol/(m²·h).The mean fluxes of CO₂ and CH₄ at soil-air interface in Yanglu drawdown area are 10.54±5.17 mmol/(m²·h) and 0.14±0.16 mmol/(m²·h),respectively.A significant increase of CO₂ flux and a comparable decrease of CH₄ during the study period have been observed.Recovery of the vegetation and an increase in soil organic matter contents are generally regarded as the primary reason for the increase of CO₂ flux.Loss of water in soils during the period increases the intensities of oxygen transfer from air to soils,which could help to increase the activities of methanotrophic bacteria,and to increase the capability of CH₄ sink in the drawdown zone.However,it is suggested that further study should be taken on elucidating the co-effect of CO₂ and CH₄ fluxes by the reservoir operation and land-use history in this area.

Abstract:This study investigated the spatial and seasonal niche characteristics of the dominant wetland plants in Napahai wetand.Under each disturbance regime,three plots were selected in 2011,and the data were collected in May,July,and October of the year.The results showed that there was a seasonal variation in species niche values under three different disturbance regimes.In spring,the order of the variation in niche breadth (from the highest to the lowest) is Polygonum lapathifolium (0.9731) >Blysmus sinocompressus (0.8040) >Plantago depressa(0.6468) >Cardamine impatiens (0.5021).In summer,the order is changed into Plantago depressa(0.8674) >Cardamine impatiens (0.8581) >Blysmus sinocompressus (0.8440) >Polygonum lapathifolium (0.7814).In fall,the order is Blysmus sinocompressus (0.9698) >Polygonum lapathifolium (0.7730) >Plantago depressa (0.6650) >Potentilla fulgens (0.6647).Similarly,niche overlap and niche differentiation also alter remarkably with seasons.The lowest niche overlap and the highest niche differentiation occur in spring and fall,whereas the highest niche overlap and the lowest niche differentiation occur in summer.Our results provide important information in regard to plant community composition,structure,dynamics,and diversity in Napahai wetland under different disturbance regimes,and help the understanding of the sensitivity of varying wetland plants in responses to different disturbances.

Abstract:In the present study,Phyto-PAM was applied to measure maximal photochemical quantum yield of PSII (Fv/Fm), actual photochemical efficiency of PSII (Φ_PSII),and rapid light response curve (RLC) of phytoplankton samples collected from Lake Gehu and Lake Luoma in spring.Meanwhile,the cell numbers of phytoplankton were counted by microscopy.The results showed that values of Fv/Fm and Φ_PSII of cyanobacteria in Lake Gehu varied from 0.36 to 0.52 and from 0.27 to 0.53,and Bacillariophyta, from 0.25 to 0.37 and from 0.25 to 0.36,respectively,but there was no photochemical vitality of Chlorophyta.RLC has indicated that cyanobacteria has higher photochemical vitality and are prone to form advantage populations in Lake Gehu.On the other hand,the values of Fv/Fm and Φ_PSII of Chlorophyta and Bacillariophyta in Lake Luoma ranged from 0.45 to 0.65, from 0.41 to 0.49,from 0.25 to 0.32,and from 0.19 to 0.25,respectively,and no photochemical vitality were found for cyanobacteria.The density of phytoplankton in Lake Gehu ranged from 530×10⁴ to 4200×10⁴ cells/L,with an average of 2918×10⁴ cells/L.Cyanophyta,Bacillariophyta,Cryptophyta and Euglenophyta were dominant in the phytoplankton community.The density of phytoplankton in Lake Luoma varied from 260×10⁴ to 510×10⁴ cells/L,with an average of 379×10⁴ cells/L,Bacillaryophyta and Chlorophyta were dominant in the phytoplankton community.According to the comparison between nutritional level,the abundance and photochemical vitality of phytoplankton assemblages in the two lakes,the lake eutrophication can increase the abundance of phytoplankton and photosynthetic activity of cyanobacteria,and become in favor of gaining advantages in phytoplankton assemblages.

Abstract:We have investigated seasonally the constitution,abundance and diversity of phytoplankton in Niyang River,the branch of the Yarlung Zangbo River,Tibet from 2008 to 2009,and taken quantitative analyses to study spatio-temporal characteristics of phytoplankton and their responses to environment using multivariate statistics method.The results are as follows.Firstly,phyto-plankton community in Niyang River belongs to 7 phyla,29 families and 48 genus,among them,Bacillariophyta is the dominant phytoplankton.Secondly,Shannon-Wiener diversity index for Niyang River is suitable to the theory about mid-altitude bulge, which is Shannon-Wiener diversity index (or Pielou evenness index) higher at the middle of Niyang River (or lower reaches of Niyang River),descending at either side of Niyang River.Thirdly,using Duncan comparison method to judge the difference among sampling sites and seasons for species richness,total abundance,Shannon-Wiener diversity index and Pielou evenness index,there is no significant difference among four sampling sites for four indices mentioned above.However,there is significant difference between the summer and other three seasons for species richness and total abundance.There is also significant difference between the winter and spring for Shannon-Wiener diversity index,and between the winter and other three seasons for Pielou evenness index.Seasonal succession of phytoplankton in Niyang River is mainly defendant on the supplement of exogenous water source,succession along Niyang River have a close relation with substrate of riverbed.Fourthly,based on the CCA method,there is a close relationship between water physical-chemical property and Naviculaceae algae from Bacillariophyta,and between water physical-chemical property and partial algae from Cyanophyta and Chlorophyta.Finally,we predicted the relationships between the total abundance of phytoplankton and environment factors based on CART method,the relationships between Shannon-Wiener diversity index of phytoplankton and environment factors based on CART method,and the relationships between Pielou evenness index of phytoplankton and environment factors based on CART method.The results reveal that pH value has a strong influence on the total abundance and Pielou evenness index of phytoplankton community in Niyang River.Pielou evenness index of phytoplankton is high at Niyang River sections where pH values are below 8 than those sections where pH values exceed 8.Shannon-Wiener diversity index of phytoplankton community in Niyang River is mainly influenced by substrate of Niyang River,specifically,Shannon-Wiener diversity index for the areas where the substrate is sandstone is higher than those areas where the substrate is clay.The paper also recommends paying close attention to phytoplankton and the environment factors mentioned above owing to their important indication function,in order to warrantee the sustainable development of Niyang River aquatic ecology.

Abstract:Vegetation is an important part of wetland ecosystem in Poyang Lake National Nature Reserve and the analysis of its spatial-temporal variations and the influences of water level changes offer a better understanding of biotic community and habitats of immigrating birds.Hence,the primary concern of this paper is the effects of varying water levels on spatial-temporal variations of biomass in Poyang Lake National Nature Reserve based on MODIS EVI time series data.We also made use of biomass measurements obtained from a field campaign and hydro-meteorological data to assist our study.The main results are as follows: (1) Multi-year annual mean biomass density is between 0 and 1402 g/m².Except Lake Banghu which shows a radial distribution with lower biomass in the center and higher biomass outside,biomass distribution for the rest of the area generally decreases from north to south and is closely related with elevation.(2) Biomass density for flood recession period is about 901 g/m² and firstly increases and then decreases with time.The size of the area of vegetation community increases with the exposure of lake bottom and thereafter remains unchanged.The total biomass exhibits a unimodal distribution with a maximum in November.The annual mean values of biomass from 2001 to 2010 bear comparative fluctuations with the ten-year mean value of 18.3×10⁷ kg,and maximum of 28.2×10⁷ kg in 2006,and minimum of 8.37×10⁷ kg in 2010.(3) Annual mean biomass is significantly related with the exposure days of lake bottom and with the size of the area of vegetation community,with a correlation coefficient of 0.719 and 0.865,respectively.To sum up,the water level is a key factor of biomass variations.

Abstract:Aquatic plants is an important component in lake ecosystem and sediment-water interface is one of the most important interfaces in nutrient cycle.We studied the effects of the contents of N,P etc.in sediments and their overlying water at three different sampling sites in Xiangxi River,Lake Taihu and Lake Donghu,and microelectrodes are applied in this study to investigate the vertical section by the effect of H.verticillata.The results show that H.verticillata grows quickly in different sediments.The growth rates of H.verticillata in different types of sediments are different,and H.verticillata has certain tolerance to pollutants.Secondly,H.verticillata has certain influence on both sediments and the overlying water,such as lowering down the contents of TN and TP and so as to purify water and lake bottom sediments.Thirdly,H.verticillata could increase the content of oxygen in water and the thickness of the aerobic layer,and change oxidation-reduction potential.Fourthly,H.verticillata may change the number and species of microbes in microenvironment in sediments,and then change the contents and/or levels of pH,N₂O,H₂S etc.in overlying water and sediments.

Abstract:To explore the effects of different culture models on growth performance and quality of Chinese mitten crab (Eriocheir sinensis),and the aquaculture water environment,and to estimate the optimum stocking density of crab culture by using natural feed resources in a shallow macrophyte-dominated lake,the Chinese mitten crabs have been raised at different stocking densities as 3000,6000,9000 ind./ha,respectively,in net-pen aquaculture area in the East Lake Taihu by feeding aquatic weeds and snails, and/or by feeding exogenous fish and corn as control for each treatment.The results showed that all crabs from each treatment group achieved 150 g in body weight,but their body size and flesh increment were significantly lower than those of control group fed with exogenous diets.There was no significant difference in yield between the lowest density group (3000 ind./ha) and its control group,while the yields in the other two groups were significantly lower than their control groups.Moreover,the recapture rate of the lowest density group was significantly lower than its control group,while that of the other two higher density groups didn't show difference when compared with their control groups.Results also indicated that the water quality in the treatment area was better than that in the control area with exogenous feed,and the TP contents were significantly lower.It was revealed that exogenous feeding might be responsible for higher levels of nitrogen and phosphorus in aquaculture water and water eutrophication.On the contrary,feeding natural aquatic weeds and snails could effectively handle the overgrowth of hydrophytes.Meanwhile,nutrient of nitrogen and phosphorus could be removed from aquaculture water by harvesting the Chinese mitten crabs,which will play an effective role both on water purification and aquatic ecological restoration.When both ecological effects and economic benefits were considered, it is suggested that the optimum stocking density of Chinese mitten crab aquaculture in shallow macrophyte-dominated lakes should be 6000 ind./ha when natural feed resources are utilized.

Abstract:Two submerged macrohphytes,Myriophyllum spicatum and Ceratophyllum demersum,were selected to investigate their changes in growth,biomass allocation and morphology under ammonium stress of 2 mg/L NH₄⁺-N lasting for 4 days and after removing ammonium stress in water column.Individual biomass,shoot height and biomass allocation of three organs (i.e.,root,stem and leaf) were determined.The results showed that during ammonium stress,shoot height of C.demersum increased compared to the control,while all above parameters of M.spicatum did not change much.When ammonium stress was removed,individual biomass of C.demersum increased significantly in comparison to that of the control,while that of M.spicatum kept unchanged.Both species showed significant higher shoot heights in treatment than in the control.Leaf biomass per unit plant weight of M.spicatum increased,while root biomass per unit plant weight decreased relative to the control after removing ammonium stress.This result suggested that ammonium stress in a short term (4 days) would not inhibit the growth of submerged macrophytes in later period in high irradiance (about 400 μmol/(m²·s)),and M.spicatum was more sensitive to ammonium stress than C.demersum.

Abstract:In July of 2011,the water quality and the structures of plankton community were investigated in Yuqiao Reservoir to evaluate its trophic state.The comprehensive trophic level index (TLI(Σ)) is 45.8,which indicates the reservoir is mesotrophic.59 phytoplankton species in total have been identified.The average phytoplankton abundance is 312.40×10⁴ cells/L,and the average biomass is 5.30 mg/L.The phytoplankton community is mainly composed by Cyanophyta and Chlorophyta.Microcystis aeruginosa, Microcystis flos-aquae and Pediastrum simplex var.duodenarium are dominated species.Total of 16 zooplankton species have been identified.The average zooplankton abundance is 53.2 ind./L,and the average biomass is 11.58 mg/L.The zooplankton community is mainly composed of Bosmina longirostris and Cyclops vicinus.Based upon the analyses of the Shannon-Wiener index, Pielou index and Margalef index,the reservoir is between medium pollution level and heavy pollution level,which is similar to the evaluation results of nutritional status using TLI(Σ).Comparative analysis has been carried out between historical data and the present investigation,and the results show that both abundance and biomass of phytoplankton have been increased,and zooplankton species have reduced while zooplankton biomass has increased.This indicates the evolution of Yuqiao Reservoir from a Bacillariophyta-Cyanophyta dominated reservoir into a Bacillariophyta-Chlorophyta dominated reservoir,and finally into a Cyanophyta-Chlorophyta dominated reservoir.

Abstract:Lake Datong is the largest lake for aquaculture in Hunan Province,and also one of the typical shallow water lakes in the middle and lower reaches of the Yangtze River.Intensive aquaculture in Lake Datong has been enhanced gradually from 1990s onward when fertilization technology in pisciculture was used.At the same time,the fishing of Corbicula fluminea (Müller,1774) in Lake Datong has been increased gradually for these years due to the higher economic benefits.In order to achieve effective conservation and proper usage of C.fluminea,the present study has investigated the morphological characteristics,standing crops and temporal-spatial distribution of C.fluminea in Lake Datong,with special focus on analyzing the effects of intensive aquaculture and fishing of mollusks on the resources of C.fluminea.Results showed that mean (±SE) wet weight (BW),shell length (SL), shell height (SH),shell width (SW),relative height,roundness and convexity of C.fluminea with shell length longer than 6 mm were 1.41±0.03 g,14.82±0.09 mm,13.73±0.09 mm,9.72±0.06 mm,0.930±0.001,0.660±0.001 and 0.710±0.001,respectively.The relationships between shell length-weight,shell height-weight and shell width-weight of C.fluminea were lg BW=-3.45+3.00 lg SL;lg BW=-3.23+2.89 lg SH;lg BW=-2.87+2.97 lg SW,respectively,which showed that the growth of C.fluminea was isometric.Mean (±SE) density and biomass of C.fluminea in Lake Datong increased

Abstract:In order to understand eutrophication levels and characteristics of phytoplankton distribution in Changtan Reservoir in Meizhou City,Guangdong Province,and provide scientific basis for controlling of algae bloom,physico-chemical data,phytoplankton species and densities were determined from October 2011 to July 2012 from 10 sampling sites in Changtan Reservoir.The status of water pollution was evaluated based on trophic level index,Shannon-Wiener index,and analysis characteristics of phytoplankton distribution in Changtan Reservoir.The results showed that the Changtan Reservoir was at middle eutrophication level characterized in April,October and December,and high eutrophication level with downward trend from upstream to the reservoir in July.A total of 16 phytoplankton species have been identified,which belong to 4 phyla and 11 families,among which cyanobacteria and green alga were predominant with obvious seasonal succession.The density of phytoplankton ranged from high to low in order of the following months: July >April >October >December.Shannon-Wiener index value analysis showed that water pollution level was medium for the reservoir water body,and light in the upstream and reservoir catchment area (except July);this is consistent with the trophic level index values.The pollution source survey showed that nitrogen and phosphorus were the main pollutant indices of Changtan Reservoir,and mainly from livestock breeding wastewater.

Abstract:In this paper we studied the core GSA (11 m) which was taken from Lake Tianchi of Liupan Mountain in the areas of magnetic susceptibility,anhysteretic remanent magnetisation,and isothermal remnant magnetization.The results show there are two kinds of magnetic minerals in the GSA: ferromagnetic and anti-ferromagnetism.The changes of sedimentary magnetic characteristics of Lake Tianchi are dominated by two patterns: high (low) dust input showing weak (strong) summer monsoon,and strong (weak) soil development showing strong (weak) summer monsoon.Magnetic susceptibility χ,which has recorded the climate change history of study area,can be divided into two parts: from 6200 to 1300 cal a B.P.,from 1300 cal a B.P.to present.The climate changes in the past 6200 years in the study area were similar to that in the monsoon area in millennial time scales,but much different in century time scales.The reasons could be that the climate of study area was not only controlled by summer monsoon,but also by other factors,such as winter monsoon and human activities which lead to the changes in vegetation of the Loess Plateau.

Abstract:Extreme floods under different climate systems,the pre-industrial time,and the end of the 20th century can provide good comparisons to examine differences among different mechanisms,while numerical models of the climate and hydrology could provide effective ways to simulate processes of the extreme flood changes and analyze the attributions.The paper applied the numerical modeling and statistical analyses to simulate extreme floods of the 1990s and the 1880s in Lake Taihu,driving by different scenarios-climate simulations from four GCMs,and analyzed the flood frequency differences between the end of the 19th and 20th centuries.Results show that extreme flood discharges in 1990s (Q0.1% 2929-3601 m³/s and Q0.5% 1842-1893 m³/s) have exceed statistically those during pre-industrial time (Q0.1% 2069-3119 m³/s and Q0.5% 1436-1561 m³/s).Comparing these floods with those at the end of the 19th century,the highest extreme-flood risks produced by land surface changes due to human activities were 35% increases,and the total highest risks were 60% increases in the end of the 20th century.Thus the highest extreme-flood risk would increase 25% risks attributed from the 20th century climate changes due to the increase of greenhouse gases;this could provide scientific basis for understanding and predicting the flood disasters responding to the global warming.