As a famous plateau lake and a place rich in biodiversity located at the Hengduan Mountains, there is little research on microbial diversity and community composition in Erhai. In this study, 770,425 16S rRNA sequences had obtained at different depth samples. The abundance-based coverage estimates (ACE), Chao1, and Shannon indices indicated the high abundance and diversity of Erhai sediment microorganisms. And they were obviously affected by human disturbance.Gammaproteobacteria,Deltaproteobacteria,Bacteroidia,Anaerolineae,Phycisphaerae, andMethanomicrobiawere dominant bacteria and existed in almost all samples. The content of total nitrogen (TN) in sediments had a significant positive correlation betweenSyntrophus,Deltaproteobacteria,Desulfatiglans,Oxyphotobacteria,Clostridiales,Burkholderiaceae,Geobacter,Crenothrixspecies richness.Desulfobacca,Syntrophus,Deltaproteobacteria,Desulfatiglans,Gammaproteobacteria,Oxyphotobacteria, andClostridialeswere positively correlated with the nitrates in sediments. And the species richness ofDesulfatiglanswas correlated with NO2-. The RDA analysis was shown that dbRDA1 was affected mainly by the depth of lake, while the content of TN, NO3-, NO2-, and NH(4)(+)had the largest effect on dbRDA2. The results indicated the great relations between the diversity and composition of microbial communities and different forms of sediment nitrogen in Erhai lake sediments.

Flood control of the Yangtze River is an important part of China's national water security. In July 2020, due to continuous heavy rainfall, the water levels along the middle-lower reaches of the Yangtze River and major lakes constantly exceeded the warning levels, in which Taihu Lake exceeded its highest safety water level and some stations of Poyang Lake reached their highest water levels in its history. In August 2020, another huge flood occurred in the Minjiang River and the Jialing River in the upper Yangtze River, and some areas of Chongqing Municipality and other cities along the rivers were inundated, resulting in great pressure on flood control and high disaster losses. The 2020 Yangtze River flood has received extensive media coverage and raised concerns on the roles of the Three Gorges Dam and other large reservoirs in flood control. Here we analyze the changes in the pattern of the Yangtze River flood control by comparing the strategies to tackle the three heavy floods occurring in 1954, 1998, and 2020. We propose that the overall strategy of the Yangtze River flood control in the new era should adhere to the principle of "Integration of storage and drainage over the entire Yangtze River Basin, with draining floods downstream as the first priority" by using both engineering and non-engineering measures. On the basis of embankments, the engineering measures should use the Three Gorges Dam and other large reservoirs as the major regulatory means, promote the construction of key flood detention areas, keep the floodways clear, and maintain the ecosystem services of wetlands and shoals. In terms of non-engineering measures, we should strengthen adaptive flood risk management under climate change, standardize the use of lands in flood detention areas, give space to floods, and promote the implementation of flood risk maps and flood insurance policies. The ultimate goal of this new flood control system is to enhance the adaptability to frequent floods and increase the resilience to extreme flood disasters.

Erhai is a famous tectonic rift lake in China. In this study, the distribution of nitrogen and phosphorus species in Erhai sediment cores and their ecology risk were evaluated. The total nitrogen (TN) in the sediment cores ranged from 1583.3 to 8018.5 mg/kg. Nitrogen (N) was still accumulating in the sediment. For depths of 0 to 25 cm, the TN decreased dramatically and for deeper depths the TN got stabilized. The proportions of various N fractions in the sediments of the study areas ranked as follows: the strong oxidation extractable N (SOEF-N) > the weak acid extractable N (WAEF-N) > the strong alkali extractable N (SAEF-N) > the ion-exchangeable N (IEF-N). The total phosphorus (TP) ranged from 814.9 to 1442.3 mg/kg. The vertical distribution of each fraction of phosphorus showed that there were different sources of sediment phosphorus around the Erhai Lake. The results of nitrogen and phosphorus pollution evaluation in sediments by single pollution standard index method showed that the standard index of the TN (STN) ranged from 4.29 to 14.01, and the standard index of the TP (STP) ranged from 1.69 to 2.18. It illustrated that N and P in the sediments were the serious ecological pollution risks in Erhai Lake.

分析长江源区生态保护工程和气候变化对植被变化的影响程度,对于长江源区生态工程的生态效益评估,以及区域植被适应性生态管理政策的制定具有重要意义.因此,本文基于1982-2015年的归一化植被指数数据(Normalized Difference Vegetation Index,NDVI)和气象数据,分析长江源区植被NDVI的时空变化规律,构建预测植被NDVI对气候因子响应的人工神经网络模型,在此基础上,在年和季节尺度上量化气候变化和生态保护工程对长江源区植被变化的影响程度.结果表明:①在长江源区气候条件变化和生态保护工程影响下,长江源区植被退化得到遏制,植被生长呈好转趋势;②海拔相对较低的通天河附近植被NDVI增加幅度较大,高海拔的沱沱河和当曲流域的植被NDVI增加幅度相对较小;③长江源区植被NDVI对气候因子响应存在1～2月的滞后性.构建的人工神经网络模型的拟合优度参数人工神经网模型具有较高的预测精度,可以用来模拟植被NDVI对气候因子的响应;④年尺度的植被NDVI增加受到生态保护工程的影响程度(58.5％)大于气候变化的影响程度(41.5％).生长季生态保护工程对NDVI的影响程度(63.3％)大于气候变化对NDVI的影响程度(36.7％),而非生长季气候变化是影响长江源区植被生长的关键要素(52.8％).研究结果有助于为长江源区植被生态系统恢复、管理和利用战略的科学制定提供决策依据.

Changes of hydro-meteorological factors in the source region of the Yangtze River are a global concern.Pervious research focused on the temporal and spatial variation characteristics in hydro-meteorological factors.Research on the relationships between hydrometeorological factors and large-scale circulation in the source region of the Yangtze River is scarce.Based on the hydro-meteorological factors and large-scale atmospheric circulation factors in the source region of the Yangtze River,trends,volatilities and periodic changes of hydro-meteorology factors (precipitation,evapotranspiration and streamflow) during 1957-2012 were explored by using Mann-Kendall method,detrended fluctuation analysis method and wavelet analysis method.The relationships between hydro-meteorological factors and largescale atmospheric circulation factors were further studied.Meanwhile,the driving mechanism of large-scale atmospheric circulation on hydro-meteorological factors was disclosed by analyzing the water vapor flux in the source region of the Yangtze River.The results showed that climatic situations in the source region of the Yangtze River were basically characterized by warm and dry during 1990s.Since 2000s,the climatic turned to warm and wet.Time series of hydrometeorological factors in the source region of the Yangtze River had positive long-rang correlations.Climatic situation in the source region of the Yangtze River will keep warm and wet in the future.There were 1-5 year,10-24 year and 25-45 year periods of hydrometeorological factors in the source region of the Yangtze River.South Asian monsoon (SAM) is a relative important large-scale atmospheric circulation that can influence the precipitation and streamflow in the source region of the Yangtze River.It is mainly because the southwest vapor fluxes driven by the SAM are dominant source of vapor fluxes in the source region of the Yangtze River.

In order to comprehensively and objectively assess water resources carrying status and to provide a theoretical support for regional socio-economic development, this study reviewed existing researches on carrying capacity of water resources, analyzed the conceptual meaning and assessment indicator system. It is indicated that red-line indexes are allocated based on the regional economic development statement, which cannot reflect water resources characteristics and the deficiency in the development of water conservancy development in that place. From the perspective of regional characteristics, this paper focused on the choice of evaluation indexes, and an assessment method was proposed based on water resources carrying potential factors such as water resources endowment, degree of development and utilization and water supply capacity of projects. Based on Cannikin Law, the evaluation system with potential indexes was proposed in this study. Taking Lijiang city in Yunnan province as example, two evaluation systems, the present one and the assessment indicator system using quantity red line and quality red line, were used to evaluate the water resources carrying capacity in Lijiang city to test all the factors and to verify the rationality and feasibility of assessment method proposed. The results revealed that the demand of regional social economic development is the main factor considered in red-line indexes allocation. While the old town district is assigned to a relatively high value in Lijiang city because it is the most developed area, the other districts can only get enough water to meet their need and further constrained their development. It is a problem for water resources management that the water use indexes only allocated in administrative regions but not in water resources regions. The results of potential indexes considering water resource endowment condition and water supply project can better reflect the real condition. In fact, Lijiang water resources condition is not bad, but it lacks of water conservancy projects and has the difficulty in water resources allocation, which causes engineering water shortage, a common problem in southwest China. Measures and suggestions for managing water resources were proposed based on the analysis of overloading causes.

In this research, characteristics of summer runoff variations during monsoon season in the Yangtze River basin and their connections with Asian summer monsoons were detected by using continuous wavelet transform and wavelet coherence analysis methods. The following results were obtained: (i) The periodic character of summer runoff along the mainstream of the Yangtze River basin has distinct differences upstream and downstream of Yichang station. (ii) Summer runoff of the source and upper regions of the Yangtze River basin is mainly influenced by the South Asian summer monsoons. Summer runoff of the midstream and downstream regions of the Yangtze River basin are controlled by the East Asian summer monsoons. (iii) An in-phase relationship between summer runoff and South Asian summer monsoon intensity indices is detected in the source region of the Yangtze River basin, and an anti-phase relationship between summer runoff and East Asian summer monsoon intensity indices dominates in the midstream and downstream regions of the Yangtze River basin.

When predicting dam-break floods and the associated risk zones for the flood risk management of dams, the breach size must be determined by considering the complex structure of the dam body under the effects of different loads. To predict the breach size quantitatively, this article proposes the concept of an element group, comprising a group of elements through the dam body. The dam-body safety status is simulated by using the three-dimensional (3D) finite element model ANSYS and is quantified by the element reliability index beta for various loads such as hydraulic and earthquake loads. A new structural reliability method for calculating the breach size was developed to quantitatively predict the failure likelihood of a dam. This new method is more intuitive and reasonable than the point safety factor k. It allows for a more accurate and quantitative prediction of the breach size of new or existing dams. An existing Roller Compacted Concrete arch dam was taken as an example to demonstrate the applicability of the new method.

To mitigate possible negative impacts of cascade dams in the Lower Jinsha River and maintain the natural flow regime of national natural reserve areas of rare and special fishes of the upper Yangtze River, environmental flow (e-flow) demands need to be considered in the cascade dams operation. Due to lack of regular ecological observation data, multiple hydrology-based e-flow methods including Tennant, minimum monthly flow, 7Q10 and Q90 are applied to provide specific e-flow prescripts to guide the reservoir release. A joint operation optimization model is developed for the cascade dams in the Lower Jinsha River for maximal hydropower generation under various e-flow constraints. The economic and ecological performances of cascade dams operation are evaluated by total hydropower outputs and hydrological alteration degree of downstream river individually. The operation results are analyzed and discussed, and some questions on the tradeoff relationship between ecology and hydropower generation, inherent relationship between ecological constrains and hydrological alteration, and rationality criteria of e-flow are further addressed. The conclusions indicate : (1) optimal operation for ecological considerations under e-flow constrains only reduce hydropower outputs slightly, no more than 2.4%; (2) e-flow constrains help lower hydrological alteration induced by hydropower dams, among the four e-flow methodologies Tennant is best in term of ecology; (3) there is a limitation for hydrology-based e-flow methodologies, and it is necessary to stress ecological foundation and ecological relevance for e-flow methodology. The paper will provide technical references for future ecological re-operation of the cascade dams.

The response of Changjiang delta to river sediment declination has attracted more and more attention in recent years. The present paper analyses radiometric210 Pb and137Cs and grain size of the core on the north of the subaqueous delta and extracts sensitive grain size population,which help explore the response of the delta to channel regime evolution and river sediment declination. The radioactive nuclear results show mean sedimentation rate of 3.28 cm / yr for the whole core by210 Pb. This rate is much higher than 1.78 ~ 1.90 cm /yr by137 Cs for the upper core section( 104 cm),mainly because of different deposit environments in the two sections. Combined with the results of210 Pb,137Cs and spherical carbon particle in the previous study,sedimentation rate of the upper core section is about 1.85 cm /yr. Grain size results show that from finer sediments with the same feature as surface sediments of mud region in the Changjiang estuary control the lower core section before 1954,which implies the northern boundary of mud region beyond this core at that time. The sediments become coarsening upward the core after 1954,which feature are close to shelf sediments. The above environmental change might be closely related to the block of north branch in the estuary after 1954,when it was away from influence of Changjiang freshwater and sediments became coarser due to reformation and join of continental material by marine dynamics. However,in terms of sediment composition,we did not find an obvious response to significant sediment supply decline of the Changjiang after 1980's. Therefore,besides sediment supply declination,coarsening due to estuarine channel regime evolution might be a contributor to western retreat of clay-sand boundary off the Changjiang estuary in the recent studies.

This research presents a detailed study which was performed to infer the quantity of metal (Cd, Cr, Pb, Zn, Cu and Fe) contents in sediments of Daye Lake, Central China. The geo-accumulation ( I geo ) and potential ecological risk (PER) of these metals were assessed. The results reveal that: (1) the mean value of I geo ranked an order of Fe (class 6) > Cd (class 5) > Pb (class 3) > Zn (class 2) > Cr (Class 1) > Cu (Class 0); (2) Potential ecological risk (PER) values calculated for all these metals at different sampled points in Daye Lake exceeded the value of very high risk. Multivariate statistical analyses were carried out to determine the relationship between these six metals and to identify the possible pollution sources, with the results suggesting that the metal content in the sediments has three patterns: the first pattern includes Pb, Cd and Cr which were mainly present due to discharged water by smelting industries; second pattern contains Zn and Cu which mainly originated from the waste residue of the copper mining industry; the third pattern is Fe which is mainly related to mine tailing leaches. This study indicates very high metal content levels in the sediments, which may have adverse risks (average PER = 7,771.62) for the lake’s ecosystem and human beings associated with Daye Lake.

Emergency management of landslide lake hazard has attracted wide attention in China since the 2008 Wenchuan Earthquake. This paper illustrated the emergency management process by analyzing the causes and evolving features of landslide lake hazard and then discussed emergency management strategies according to the principles of classified management, graded response and phased disposal. It is suggested that the emergency management system for landslide lake hazard should be a part of the current flood and drought management system. The emergency management should focus on mitigating the original hazard, and risk mapping, monitoring and information sharing network construction should be completed above all.

The problems of seasonal uneven distribution of water resources and continuous drought in recent yeats in the Poyang Lake are analyzed.Based on the assessment on the potentiality of floodwater resources,an idea from the view point of giving attention both to flood prevention and drought fighting is suggested.The core of this suggestion is to reasonably utilize the floodwater by means of engineering and non-engineering measures,since the floodwater of the lake is abundant.Under the conditions of flood prevention is ensured and the waterways linking the lake and rivers will not be blocked.By establishing and effective controlling adjustable spillways at the inlets and outlets of the lake,the floodwater can be reasonably detained in the lake for mitigating the problem of seasonal drought and fulfill the need of eco-environment.

The cumulative environmental impact is one of the most important components in the environment research.The essence content of defining cumulative environmental impacts is put forward based on the review of the connotation including the cumulative environmental impacts sort and the concept's generation and development;the research in cumulative environmental impacts is conducted abroad for a long time and there are some problems,such as the concept inconsistency,the poor quantity of method and the lack of recognization.In China research in cumulative environmental impacts concentrates more on the analysis methods,but less on the definition and examples since 1990s.Then several analysis methods are classfied by the different application conditions.Especially,the research status of cumulative environmental impact assessment in water resource subject and the cumulative environmental impacts' characteristic in cascade hydropower exploitation are introduced in this paper.And four research trends are proposed.