Quantifying the 2022 drought and spatiotemporal evolution of TWSA in the Dongting Lake Basin over the past two decades

Extreme hydrological events such as droughts and floods have been increasingly influenced by abnormal atmospheric disturbances caused by human activity and global warming.The Dongting Lake Basin(DLB)has experienced challenging circumstances over the past 20 years due to complex climatic variations,leading to extreme flooding and drought.This study aims to investigate the spatiotemporal variation in terrestrial water storage anomalies(TWSA)over the DLB using data from the GRACE/GRACE-FO and GLDAS spanning the latest two decades.A significant decline trend in TWSA is unveiled from July 2019 to May 2023,with the rate of change determined as-1.94 cm/year and-1.99 cm/year based on the GRACE/GRACE-FO and GLDAS,respectively.The GRACE-Drought Severity Index(DSI)is employed to identify and evaluate the severity and spatiotemporal evolution of the 2022 drought event in the DLB.The results accurately capture the drought event,which began in July 2022 and continued until March 2023,with the most severe conditions occurring in October 2022,when the GRACE-DSI value stood at-2.06 and the TWSA decreased by 15.24 cm and 33.51 cm relative to the same month in 2021 and 2020,respectively.Additionally,the daily water level variation at the Chenglingji hydrological gauging station in 2022 broke previous records,reaching a minimum of only 19 m.Comparing the 2022 drought event with the drought events in 2006 and 2011,the impact of drought on vegetation growth conditions was relatively small,but there was still significant vegetation degradation across the DLB.

Inconsistent increasing of climate potential productivity resulting from global warming and land use transitions in the Dongting Lake Basin,from 2000 to 2020

In the face of global warming and increasing impervious surfaces,quantifying the change of climate potential productivity(CPP)is of great significance for the food production planning.Targeting the Dongting Lake Basin,which is a key area for food production in China,this paper uses meteorological data,as well as Climate Change Initiative Land Cover,and Shuttle Radar Topography Mission digital elevation model to investigate the CPP and its changes from 2000 to 2020.The suitability of land for cultivation(SLC),and the land use/land cover change(LUCC)are also considered.The results showed that the CPP varied from 9,825 to 20,895 kg ha^(-1).Even though the newly added impervious surfaces indirectly resulted in the decrease of CPP by of 9.81×10~8 kg,overall,the CPP increased at an average rate of 83.7 kg ha^(-1)a^(-1).Global warming is the strongest driver behind CPP increase,and CPP has played an important role in the conversions between cultivated land and other land types.The structure of land types tends to be optimized against this challenge.

Morphological Difference and Karyotype of Pelteobagrus fulvidraco in Dongting Lake Water System

[Objective] The research aimed to study the morphological characteristics and karyotype of Pelteobagrus fulvidraco in Dongting Lake water system.[Method] By using the conventional biological morphometry,PHA and colchicine injection method in vivo,the morphological characteristics and karyotype of P.fulvidraco in Yuanshui River and Lishui River of Dongting Lake were analyzed.[Result] In three ratio traits including standard length/head length,standard length/caudal peduncle depth,head length/snout length,P.fulvidraco of Yuanshui River and Lishui River had significant differences（P0.05）.However,the number and karyotype of their chromosomes were same.The chromosome number was 2n = 52,and the karyotype formula was 20M＋12SM＋10ST＋10T.The number of chromosome arm was 84.[Conclusion] The research result had certain theoretical guidance significance for the protection and utilization of wild P.resource in Dongting Lake water system.

The Singular Value Decomposition Analysis between Summer Precipitation in the Dongting Lake Region and the Global Sea Surface Temperature

By dint of the summer precipitation data from 21 stations in the Dongting Lake region during 1960-2008 and the sea surface temperature(SST) data from NOAA,the spatial and temporal distributions of summer precipitation and their correlations with SST are analyzed.The coupling relationship between the anomalous distribution in summer precipitation and the variation of SST has between studied with the Singular Value Decomposition(SVD) analysis.The increase or decrease of summer precipitation in the Dongting Lake region is closely associated with the SST anomalies in three key regions.The variation of SST in the three key regions has been proved to be a significant previous signal to anomaly of summer rainfall in Dongting region.

Embryonic Development of Silnrus asotus in Dongting Lake

[Objective] The research aimed to provide technical basis for fry rearing of Silnrus asotus in Dongting Lake.[Method] The induced spawning medicine was used in the experiment to conduct artificial induced spawning and fertilization for obtaining round green fertilized eggs.According to embryonic development,the morphological characteristics of embryo at different developmental stages were recorded detailedly through microscope.[Result] The embryonic development of Silnrus asotus in Dongting Lake was divided into 7 stages,namely, blastoderm stage,cleavage stage, blastula stage, gastrula stage,neurula stage,organogenesis stage and pre-hatching stage.After hatched for 37 h 20 min in water at 22-24 ℃, fries were come out.[Conclusion] The time sequence of Silnrus asotus in Dongting Lake was basically similar to that of other catfish,while its hatching time was shorter than that of other fish in Siluriformes.

Role and Protection of Dongting Lake

Water and sediment in four-inlet river system and the water level at Chenglingji reflect the current relationship between Yangtze River and Dongting Lake. Since the flow in four-inlet river system is reduced gradually, the lake water level is also reduced, resulting in shrunk lake area, channelized lake, narrowed channel and reduced rfve beach. Facing the changed relationship the River and the Lake after the utilization of Three Gorges Project, the Chenglingji control engineering at the outlet of Dongting Lake and the dredging of four-inlet river system are car- ried out. Thus the roles of flood control （1.67x101~ m3） and water amount regulation （2.3~101~ m3） of Dongting Lake are fully played. The Dongting Lake plays compen- sating and scheduling roles in the flood control and water storage of the Three Gorges Reservoir. It can reduce a volume of 4.0x109 m3 of excess flood around Chenglingji. In addition, it can also provide a water supply of 5 000 m3/s to the lower reaches of Yangtze River during the dry season for about 30 d. The Dongt- ing Lake plays an important role in the stabilization of ecological environment in the watershed, the regional water resources security and the protection of Dongting Lake and Yangtze River.

Analysis on the Area of Dongting Lake Before and After Building Three Gorges Dam Based on MODIS Image Sequences

[Objective] This study aimed to analyze the changes in the area of Donting Lake before and after building Three Gorges Dam based on MODIS image sequences. [Method] Based on the MODIS image sequences of 2000-2010, the change in the area of Dongting Lake in dry season and wet season before and after building Three Gorges Dam was analyzed, and the correlation between the change of the lake area in flood season and drought season and the record of Chenglingji Hydrological Observation Station was studied. [Result] The construction of Three Gorges Dam greatly influenced the area of Dongting Lake in dry season and wet season that in dry season, the linear relationship between the lake area and the waterline of Chenglingji was weak, while it was strong in wet season. [Conclusion] This study can estimate the changes of the area of Dongting Lake through the analysis on the waterline changes in Chenglingji, providing basis for the study on the changes in the area of Dongting Lake.

Landscape ecological assessment and eco-tourism development in the South Dongting Lake Wetland, China

As an important resource and the living environment of mankind, wetland has become gradually a highlight, strongly concerned and intensively studied by scientists and sociologists. The governments in the world and the whole society have been paying more and more attention on it. The Dongting Lake of China is regarded as an internationally important wetland. For a rational development and protection of the wetland, an investigation and studied on its resources and its value to tourism in the South Dongting Lake was conducted, to create an assessment system of the ecological landscapes, and to evaluate qualitatively and quantitatively the value of wetland landscape to the eco-tourism. The results showed that the scenic value of the South Dongting Lake Wetland satisfied the criterion of AAAA grade of China national scenic attraction. The eco-tourism value of the landscape cultures in the South Dongting Lake Wetland was discussed with emphasis. It were formulated that a principle and frame of sustainable exploitation of the wetland landscapes and it was proposed as well that establishing a Wetland Park and developing eco-tourism in the South Dongting Lake. Wetland is a fragile ecosystem with low resistance to the impact of the exploitation. Thus, we must pay intensively attention to the influence of exploitation on the landscape, take the ecological risk in account to employ a right countermeasure and avoid the negative affection.

Eco-compensation effects of the wetland recovery in Dongting Lake area

Eco-compensation is an environmental economic instrument for internalization of external cost. Returning farmland to lake is one of the important parts of restoring wetland ecosystem function in the Yangtze River Valley of China. Whether the project of lake recovery can be successful depends on the compensation to the farmers who have lost their original benefits and contributed to the wetland ecosystem recovery by returning farmland to lake. Aiming at the wetland recovery of the Dongting Lake, the practical implementation of pro- grams of the lake recovery and flood control in this area has been challenged by the heavy task of population resettlement, so it is an ideal area for case studies to reach the academic objectives proposed as the above. Based on field survey and experimentation, this research evaluated the benefit losses of the resettled farmers and the increased values of ecosystem service functions caused by wetland recovery, and furthermore, the value of eco-compensation for relocated farmers was calculated by considering the combination of the farmers＇ compensation appeal. The value of eco-compensation for relocated farmers in the Dongting Lake area was 6084.5 yuan per household by synthetic analysis of the effects on wetland ecosystem restoration. Moreover, this article took Dongting Lake area as a case to study and explore the basic issues of the eco-compensation by returning farmland to lake, that was who should pay, who should be paid, how much the payment was and what the payment means was, which sought the mechanisms of wetland restoration eco-compensation and prompted the people＇s enthusiasms for ecological restoration.

Flood management of Dongting Lake after operation of Three Gorges Dam

Full operation of the Three Gorges Dam(TGD) reduces flood risk of the middle and lower parts of the Yangtze River Basin. However,Dongting Lake, which is located in the Yangtze River Basin, is still at high risk for potentially severe flooding in the future. The effects of the TGD on flood processes were investigated using a hydrodynamic model. The 1998 and 2010 flood events before and after the operation of the TGD, respectively, were analyzed. The numerical results show that the operation of the TGD changes flood processes, including the timing and magnitude of flood peaks in Dongting Lake. The TGD can effectively reduce the flood level in Dongting Lake, which is mainly caused by the flood water from the upper reach of the Yangtze River. This is not the case, however, for floods mainly induced by flood water from four main rivers in the catchment. In view of this, a comprehensive strategy for flood management in Dongting Lake is required. Non-engineering measures, such as warning systems and combined operation of the TGD and other reservoirs in the catchment, as well as traditional engineering measures, should be further improved. Meanwhile, a sustainable philosophy for flood control, including natural flood management and lake restoration, is recommended to reduce the flood risk.

Comparison between BCR sequential extraction and geo-accumulation method to evaluate metal mobility in sediments of Dongting Lake, Central China

The form in which a metal exists strongly influences its mobility and thus, the effects on the environment. Operational methods of speciation analysis, such as the use of sequential extraction procedures, are commonly applied. The Dongting Lake, the second largest fresh-water lake in China, contains three China wetlands of international importance, the East Dongting Lake, South Dongting Lake, and West Dongting Lake. In this work, an optimized BCR sequential extraction procedure was used to assess the environmental risk of Cd, Cr, Cu, Ni, Pb and Zn in contaminated sediment of the Dongting Lake. The procedure was evaluated by using a certified reference material, BCR701. The results of the partitioning study indicated that in the lake sediments, more easily mobilized forms (acid exchangeable) were predominant for Cd, particularly in the samples from the East Dongting Lake. In contrast, the largest amount of Pb was associated with the iron and manganese oxide fractions and Cu, Zn, Cr, and Ni analyzed were mainly distributed in residual phase at an average percentage greater than 60% of the total metals. The potential risk to the lake's water contamination was highest in the East Dongting Lake based on the calculated contamination factors. On the other hand, the total metal content was determined as well by inductively coupled plasma and mass spectrometry (ICP-MS) and assessed by using geo-accumulation index. The assessment results using geo-accumulation index were compared with the information on metal speciation. Both were correspondent with each other.

Environmental Assessments of Trace Metals in Sediments from Dongting Lake, Central China

To examine the degree of contamination in the Dongting Lake （洞庭湖） area, surface sediments samples were collected and investigated in this study. This lake lies in the south of the middle Yangtze River, and it is the second largest fresh-water lake in China. These samples were analyzed for the concentrations of the following 6 elements （CA, Cr, Cn, Ni, Ph and Zn） collected from 46 locations. The index of geo-accumulation was used to assess the degree of contamination of the total trace elements and the assessments showed that the contamination of Cd reached strong to very strong pollution. The speciation of metal in sediments was analyzed using the modified BCR （Community Bureau of Reference） sequential extraction technology and the water column-contamination risk was evaluted by the calculated contamination factors. The results of the speciation of metal indicated that more easily mobilized forms （exchangeable, water soluble, and acid soluble） were predominant for CA, especially in the samples from East Dongting Lake. In contrast, the largest amount of lead was associated with the iron and manganese oxide fractions, and Cn, Zn, Cr, and Ni analyzed were mainly distributed in residual phase at an average percentage higher than 60 % of the total metals. The potential risk to the lake＇s water contamination was the highest in East Dongting Lake based on the calculated contamination factors. The assessment results using geo-accamnlation index were compared with the information obtained by trace metal speciation and both results were consistent.

Assessment on soil fertility of Dongting Lake wetland area (China) based on GIS and fuzzy evaluation

Using soil data of the Second National Field Survey,the soil fertility of wetland ecosystem of Dongting Lake was evaluated by using the technology of GIS and method of fuzzy evaluation.Integrated with the wetland actuality of Dongting Lake and particularity of paddy,seven factors (including soil organic matter,total nitrogen,total phosphorus,total potassium,available phosphorus,available potassium,and pH value),closely related with soil fertility,were chosen to establish the index system of synthetical evaluation.Based on the effect degree of each selected index on soil fertility,a judgment matrix was built,and the weight coefficient was determined by the method of correlation coefficient.Finally,under the support of the spatial analysis module of GIS (Geographic Information System),the spatial distribution properties of soil fertility in wetland ecosystem of Dongting Lake were studied.The results show that the soil fertility of Dongting Lake wetland ecosystem is not very good,and the area of type III and type IV achieves 69.8%.As a result,many countermeasures should be taken to improve the soil fertility.As for the spatial properties,the soil fertility level of central and west Dongting Lake is much higher than that of north and south part.The soil fertility of paddy field surpasses that of red soil,and the contents of soil organic matter and total nitrogen in paddy field are large.

Discussion on the Green Tax Stimulation Measure of Nitrogen Fertilizer Non-Point Source Pollution Control-Taking the Dongting Lake Area in China as a Case

A study on designing the tax of nitrogen fertilizer can provide a new method for controlling nitrogen fertilizer non-point source pollution. The tax design of nitrogen fertilizer was discussed by utilizing the external theory and the demand elasticity theory. The results indicated that the coefficient of price elasticity of nitrogen fertilizer demand is -0.21, which instructed that the market demand is in lack of elasticity in the short period and the impact of nitrogen fertilizer manufacturers is subtle. The 11 counties （cities and boroughs） in the Dongting Lake area in China, where the farmland nitrogen application surpassed the average ecological fertilization dosage, is listed to the taxation scope of nitrogen fertilizer tax. The environment loss will reduce 0.07 hundred million RMB yuan and the revenue will increase 0.89 hundred million RMB yuan in the country after levying on nitrogen fertilizer. The loss, which was brought by the decreasing food supplies production, will be 0.58 hundred million RMB yuan and the net social benefit will be 0.38 hundred million RMB yuan following revenue collection. The variation scope of the increasing expenditure of farmers will range from 0.95 to 1.49%. The variation scope of the income of farmers will range from -8.41 to 6.44%. The 5 areas, Yunxi Borough, Junshan Borough, Hanshou County, Jinshi City, and Ziyang Borough, had an increase in food supplies production after the revenue collection. The environment loss will reduce 0.01 hundred million RMB yuan and the revenue will increase 0.16 hundred million RMB yuan in the country after levying on nitrogen fertilizer. The economic benefits, which was brought by the increasing cereals production, will be 0.67 hundred million RMB yuan and the net social benefit will be 0.84 hundred million RMB yuan after revenue collection. The variation scope of the increasing expenditure of farmers will range from 0.95 to 1.06%. The variation scope of the increasing income of farmers will range from 0.69 to 6.44%. Considering the entire social welfare, taxation of nitrogen fertilizer will have more advantages than disadvantages in the Dongting Lake area.

THE PRELIMINARY STUDY ON LANDSCAPE CULTURE ORIENTATION AND EXPLOITATION OF THE SOUTH DONGTING LAKE WETLAND

Dongting Lake is internationally a n important wetland.We studied and s ummarized the conception,func-tion,classification and current situation of the wetland-landscape cu lture in this region.The results showed that the cul-ture of Dongting Lake wetland was ric h in diversity,which are the Rice Cul tivation Culture,high-balustrade dwelling,Nuo Culture,Ship Culture,Dragon Bo at Culture,Chu Culture,Ancient Arc hitecture Landscape,Wetland Foodstuff and Cuisine Culture,Civil Art,Historic Heritage and Cultural Relics,Revolutionary Sites and Ruins,and Production and Living Culture,etc.We also evaluated the eco-tourism value of wetland l andscape culture,and analyzed its f eatures and orientation.The results revealed t hat the south Dongting Lake wetland p lays a key role on the Changjiang(Yangtze)River reaches civilization and Chinese civilization,even has great influence on the global civilization.We summ arized that the soul of the south Dongting Lake Cultu re was Wetland Culture,Water Cultur e,Rice Cultivation and Chu Culture.The thoughts,principles and approaches of sustainable exploitation and ut ilization of the wetland landscape c ulture were formulat-ed and suggested.

Application of Bayesian regularized BP neural network model for analysis of aquatic ecological data—A case study of chlorophyll-a prediction in Nanzui water area of Dongting Lake

Bayesian regularized BP neural network（BRBPNN） technique was applied in the chlorophyll-α prediction of Nanzui water area in Dongting Lake. Through BP network interpolation method, the input and output samples of the network were obtained. After the selection of input variables using stepwise/multiple linear regression method in SPSS i1.0 software, the BRBPNN model was established between chlorophyll-α and environmental parameters, biological parameters. The achieved optimal network structure was 3-11-1 with the correlation coefficients and the mean square errors for the training set and the test set as 0.999 and 0.000？8426, 0.981 and 0.0216 respectively. The sum of square weights between each input neuron and the hidden layer of optimal BRBPNN models of different structures indicated that the effect of individual input parameter on chlorophyll- α declined in the order of alga amount 〉 secchi disc depth（SD） 〉 electrical conductivity （EC）. Additionally, it also demonstrated that the contributions of these three factors were the maximal for the change of chlorophyll-α concentration, total phosphorus（TP） and total nitrogen（TN） were the minimal. All the results showed that BRBPNN model was capable of automated regularization parameter selection and thus it may ensure the excellent generation ability and robustness. Thus, this study laid the foundation for the application of BRBPNN model in the analysis of aquatic ecological data（chlorophyll-α prediction） and the explanation about the effective eutrophication treatment measures for Nanzui water area in Dongting Lake.

Relationship between community type of wetland plants and site elevation on sandbars of the East Dongting Lake,China

Plant communities on sandbars were important, and restoration of degraded wetland were significant to biological conservation in the East Dongting Lake region. In this study, typical wetland community types on sandbars and their site elevation were surveyed to explore relationship between community distribution and site elevation. Results show that eight major communities in this region were wetland communities dominated by Juncus effusus, Carex brevicuspis, Polygonum hydropiper, Salix triandra, Oenanthe Javanica, Phalaris arundinacea, Miscanthus sacchariflorus and Phragmites communis respectively. These communities had obvious constructive species and companion species, while site elevation could affect community composition and their species diversity. On sandbars in the East Dongting Lake, vegetation was largely composed of hygrophytes companied with a few mesophytes. The higher the site elevation was, the nearer the site was to the water, and the lower community diversity became. Except soil humidity and site elevation, growth period of plants after inundation could also affect species richness in the communities.

The spatial-temporal changes of the land use/cover in the Dongting Lake area during the last decade

The research on the land use/cover change is one of the frontiers and the hot spots in the global change research. Based on the Chinese resource and environment spatial-temporal database, and using the Landsat TM and ETM data of 1990 and 2000 respectively, we analyzed the spatial-temporal characteristics of land use/cover changes in the Dongting Lake area during the last decade. The result shows that during the last ten years there were three land-use types that had changed remarkably. The cultivated land decreased by 0.57% of the total cultivated land. The built-up land and water area expanded, with an increase of 8.97% and 0.43% respectively. The conversion between land use types mostly happened among these three land-use types, especially frequently between cultivated land and water area. The land-use change speed of land-use type is different. Three cities experienced the greatest degree of land-use change among all the administrative districts, which means that the land use in these cities changed much quickly. The following changed area was the west and south of the Dongting Lake area. The slowest changed area is the north and east area.

Ichthyoplankton recruitment from mainstream of the Changjiang River into the Dongting Lake, the second largest freshwater lake in China

Floodplains are important and distinctive ecosystems around the world,and the recruitment of ichthyoplankton from river to floodplain lakes is crucial to maintain this unique ecosystem.However,this process has not been well documented.In this study,ichthyoplankton were sampled to investigate the details of ichthyoplankton recruitment from the Changjiang(Yangtze)River to the Dongting Lake via a floodway channel,the Songzi River,from May to July in 2013 and 2014.During the study period,41 species of eggs and larvae were sampled.Among the samples,16 were river-lake migratory species(RL),representing 23.5%of the species in the Dongting Lake.In 2013,an estimated 130 million eggs and 3180 million larvae drifted through the sampling section,and in 2014,an estimated 1 060 million eggs and 1040 million larvae drifted through the sampling section.The amount of eggs and larvae of RL reached 3 210 million in 2013 and 1 850 million in 2014,respectively.These results demonstrated the importance of ichthyoplankton recruitment from the river to the lake,as species diversity will decrease sharply without this recruitment.Canonical correspondence analysis(CCA)showed that water temperature and water flow are the two most important factors influencing the spawning activities of fish.To maintain the high fish diversity in the Changjiang floodplain,we suggest to irrigate the channel to increase water discharge and increase the transport of ichthyoplankton from the Changjiang mainstream into the Dongting Lake.

Study on the Water Quality and Protection Measures of Dongting Lake

From nitrogen and phosphorus,chemical oxygen demand,phytoplankton,and eutrophication,this article analyzes the current situation of water quality in the Dongting Lake area,and discusses the factors influencing the water quality of Dongting Lake. Based on the actual production,geographic characteristics and outstanding problem of grim water pollution situation in the Dongting Lake area,some specific proposed measures are put forward in order to provide the basis and reference for the future pollution control in the Dongting Lake area,such as strengthening the industrial pollution control,developing ecological agriculture,and enhancing ecological restoration and water quality early warning.