Associated impact mechanism of heavy rain and floods in the middle and lower reaches of the Yangtze river basin based on ocean-atmosphere anomaly patterns.

Heavy rainfall and flooding disasters are increasing due to global warming. A clear understanding of the mechanism of heavy rain and floods is the basic premise of disaster risk management. However, most previous studies emphasized more on the single anomalous signal from the average state in the whole season, which may neglect the combined influence of multiple signals in the ocean-atmosphere and differential characteristics of anomalous signals at different periods. Here, our study aimed to reveal the possible influence mechanism of heavy rain and floods in the middle and lower reaches of the Yangtze River Basin (MLRYRB) by systematically analyzing the monthly-scale and daily-scale ocean-atmosphere anomaly patterns in the preceding periods of heavy rainfall and flooding events. The results showed that heavy rainfall and flooding events were highly likely to occur in the region one month after El Niño decayed, with the flooding intensity in June having the negative correlation with the sea ice concentration anomaly in the Arctic with a lag of about 5 months (150 days). Besides, North Atlantic Oscillation, Western Pacific subtropical high, blocking, East Asian subtropical westerly jet, and the water vapor fluxes from the Arabian Sea and western Pacific Ocean could be used as the anomalous signals inducing heavy rain and floods. The daily-scale conceptual model inducing heavy rainfall and flooding events was built based on the patterns of all anomalous signals, which detailed the possible impact mechanism of heavy rain and floods in the region. By making targeted forecasts of anomalous signals and using this information in water resources planning and management based on climate mechanisms, it will have a significant impact on water management in the country.

Evaluating a river's ecological health: A multidimensional approach.

Evaluating the health of river surface water is essential, as rivers support significant biological resources and serve as vital drinking water sources. While the Water Quality Index (WQI) is commonly employed to evaluate surface water quality, it fails to consider biodiversity and does not fully capture the ecological health of rivers. Here we show a comprehensive assessment of the ecological health of surface water in the lower Yangtze River (LYR), integrating chemical and biological metrics. According to traditional WQI metrics, the LYR's surface water generally meets China's Class II standards. However, it also contains 43 high-risk emerging contaminants; nitrobenzenes are found at the highest concentrations, representing 25-90% of total detections, while polycyclic aromatic hydrocarbons present the most substantial environmental risks, accounting for 81-93% of the total risk quotient. Notably, the plankton-based index of biological integrity (P-IBI) rates the ecological health of the majority of LYR water samples (59.7%) as 'fair', with significantly better health observed in autumn compared to other seasons (p < 0.01). Our findings suggest that including emerging contaminants and P-IBI as additional metrics can enhance the traditional WQI analysis in evaluating surface water's ecological health. These results highlight the need for a multidimensional assessment approach and call for improvements to LYR's ecological health, focusing on emerging contaminants and biodiversity rather than solely on reducing conventional indicators.

Channel-forming discharge based on the extreme value identification of sediment-carrying capacity index.

Channel-forming discharge (Dcf) is an important parameter in river management and reservoir flood regulation. Applying the methods for calculating Dcf to reaches downstream reservoirs characterized by drastic changes in water and sediment conditions and long-term scouring status is difficult. Based on the riverbed-shaping principle of sediment-laden water flow, while simultaneously considering the active action of water flow and response of the riverbed, this study proposes a new method for calculating Dcf by identifying the extreme value of the suspended sediment-carrying capacity index. The application of this method to the middle and lower reaches of the Yangtze River showed that after the impoundment of the Three Gorges Reservoir, Dcf in this section was reduced by an amplitude between 2500 and 4700 m3/s. The results can be used to guide the operation of the Three Gorges Reservoir and the management of the middle and lower reaches of the Yangtze River, thus providing reference for other river channels downstream of the reservoir.

Research on the coupling coordination and driving role of urbanization and ecological resilience in the middle and lower reaches of the Yangtze River.

Background: The growth of urbanization in the 20th and 21st centuries has resulted in unprecedented ecological security issues. The imbalance between urban development and internal ecological security is a growing concern. Methods: Based on the urban development process and the characteristics of ecosystem resilience, the corresponding urbanization evaluation system ("scale-structure-benefit") and ecosystem resilience assessment model ("resistance-adaptability-restoring") were constructed to explore the changes in each dimension as well as to analyze the spatial and temporal changes and driving effects of the coupled coordination level of urbanization and ecological resilience using the coupled coordination degree (CCD) model and geographically and temporally weighted regression (GTWR). Results: (1) From 2005 to 2020, urbanization levels increased (from 0.204 to 0.264, respectively), whereas the level of ecological resilience gradually decreased (from 0.435 to 0.421, respectively). The spatial distribution of urbanization is rather steady, with a "high-northeast low-southwest" pattern of regional distribution; however, the spatial distribution pattern of ecological resilience is essentially the reverse. (2) During the study period, there was an improvement in the level of coordination between urbanization and ecological resilience, with an increase from 0.524 to 0.540. However, the main coordination type remained the same, with over 46% being at the basic coordination stage. The relative development type was dominated by the lagging urbanization stage, with the lagging ecological resilience and synchronous development stages accounting for a smaller proportion, and the space was distributed in a block-like cluster. (3) The running results of the GTWR show that the core dimensions of the whole region are scale, benefit, and structure, and the impact of each dimension shows obvious spatial heterogeneity. Cities with different levels of relative development also have different central dimensions. This research will provide support for the coordination of urban development in areas where economic construction and ecological resilience are not coordinated, and will contribute to the sustainable development of urban areas.

Spatiotemporal distribution of oncomelania hupensis snail habitats in the Middle and Lower Reaches of the Yangtze River / 公共卫生与预防医学

Schistosomiasis is one of the major communicable diseases, which seriously impacts human health, Oncomelania hupensis snail is unique intermediate host of Schistosoma japonicum as well as posts significant influence on schistosomiasis transmission. The long-term serial data of oncomelania snail area in the Middle and Lower Reaches of the Yangtze River in the Schistosomiasis situation in People's Republic of China ,were collected from 1999 to 2018. The spatial and temporal variation characteristics of oncomelania hupensis area in five provinces were analyzed by Manner-Kendall test. In the spatial change, the area composition ratio of lake-and-marshland regions in Hunan increased, while that in Hubei and Jiangxi showed a slight decline. The lake-and-marshland snails in Anhui showed a significant downward trend, while Jiangsu showed no stable trend. In the spatial change, the area of lake-and-marshland snails in Jiangsu, Anhui, and Hubei showed a downward trend, among which the downward trend in Hubei was not obvious, while the upward trend in Jiangxi and Hunan had an upward trend but the trend was not obvious. the year of the sudden change in the area of the lake and marshes in in Jiangsu and Hubei were 2010 and 2017 ; There was no significant mutation in Anhui Province; the mutation point of the lake-and-marshland snails in Hunan was between 2001 and 2002; the mutation year of the lake-and-marshland snails in Jiangxi was 2002.This paper studies the temporal and spatial changes of the snail breeding area in the middle and lower Yangtze River, and the results can provide a basis for the elimination of snails in different types of distribution areas.

[Temporal and Spatial Characteristics of Total Phosphorus in the Middle and Lower Yangtze River Mainstem Under New Water and Sediment Conditions].

After the completion of the Three Gorges Reservoir and the upstream reservoir group of the Yangtze River, new water and sediment conditions appeared in the middle and lower reaches of the Yangtze River, and its influence on the phosphorus concentrations in water has attracted much attention. Therefore, the spatial and temporal distributions of total phosphorus (TP) concentrations in the middle and lower reaches of the mainstem under the new water and sediment conditions were studied. The results show that:① after the construction of the Three Gorges Reservoir, the concentrations of TCP (samples were allowed to settle for 30 min) in the middle and lower reaches of the Yangtze River fluctuates between 0.10 and 0.15 mg·L-1, and generally increased during 2004-2010 and then decreased during 2014-2019, and increases along the flow direction. The concentrations of dissolved total phosphorus (TDP) have slowly increased with time. ② The settleable solids influence the phosphorus content to varying degrees. The median values of TCP/TP ratio in Nanjinguan, Hankou, and 23 km below Wusongkou, are 0.900, 0.720, and 0.609, respectively, which decreases successively from upstream to downstream. The proportion of TPP (total particulate phosphorus)/TP shows an increasing trend along the flow direction. The median values of TPP/TP ratios in Nanjinguan, Hankou, and 23 km below Wusongkou were 0.439, 0.567, and 0.738, respectively. ③ According to the "Environmental quality standard for surface water GB 3838-2002", the water quality was assessed using TCP concentrations, and the assessment results showed that the water quality of the middle and lower reaches of the Yangtze River was generally good. However, considering the influence of settleable solids, the water quality categories assessed based on TP concentrations would be worse, especially near estuaries. ④ In the middle and lower reaches of Yangtze River, there is little difference in the phosphorus concentration of different monitoring sites in the upper section of main stream; however, the difference is obvious near the estuary. ⑤ The concentration of TCP in the coastal waters of the urban river section of the middle and lower reaches of the Yangtze River is significantly higher than that of the main channel, and there are obvious coastal pollution zones in the coastal waters of the urban river section.

Vulnerability Analysis to Drought Based on Remote Sensing Indexes.

A vulnerability curve is an important tool for the rapid assessment of drought losses, and it can provide a scientific basis for drought risk prevention and post-disaster relief. Those populations with difficulty in accessing drinking water because of drought (hereon "drought at risk populations", abbreviated as DRP) were selected as the target of the analysis, which examined factors contributing to their risk status. Here, after the standardization of disaster data from the middle and lower reaches of the Yangtze River in 2013, the parameter estimation method was used to determine the probability distribution of drought perturbations data. The results showed that, at the significant level of α = 0.05, the DRP followed the Weibull distribution, whose parameters were optimal. According to the statistical characteristics of the probability density function and cumulative distribution function, the bulk of the standardized DRP is concentrated in the range of 0 to 0.2, with a cumulative probability of about 75%, of which 17% is the cumulative probability from 0.2 to 0.4, and that greater than 0.4 amounts to only 8%. From the perspective of the vulnerability curve, when the variance ratio of the normalized vegetation index (NDVI) is between 0.65 and 0.85, the DRP will increase at a faster rate; when it is greater than 0.85, the growth rate of DRP will be relatively slow, and the disaster losses will stabilize. When the variance ratio of the enhanced vegetation index (EVI) is between 0.5 and 0.85, the growth rate of DRP accelerates, but when it is greater than 0.85, the disaster losses tend to stabilize. By comparing the coefficient of determination (R2) values fitted for the vulnerability curve, in the same situation, EVI is more suitable to indicate drought vulnerability than NDVI for estimating the DRP.

Subfossil cladocerans as quantitative indicators of past ecological conditions in Yangtze River Basin lakes, China.

Cladocerans (Crustacea: Branchiopoda) are an essential component of the food webs of shallow lakes. However, their potential significance as sentinels of environmental change in subtropical regions of South-East Asia, is not well elucidated. In this study, we examined the distribution pattern of cladoceran subfossils in the surface sediments of 64 shallow lakes located in the middle and lower reaches of the Yangtze River Basin (MLYB). Using constrained ordination and multivariate regression trees (MRT), we explored the relationships between the distribution of cladocerans and contemporary environmental variables. The results indicated that macrophyte abundance is the most important regulator, followed by chlorophyll a and total phosphorus that all were important drivers of cladoceran community dynamics. Despite intensive aquaculture in the MLYB lakes over the past decades, fish predation did not have a significant influence on the cladoceran community, likely because the fish predation pressure was generally high. The MRT analysis showed distinct variations in the composition of cladoceran communities and was able to identify the key indicator species of various stressors, including Bosmina coregoni, small Alona (A. intermedia, A. rectangula) and Leydigia acanthocercoides, Leydigia leydigi and Chydorus sphaericus. Boosted Regression Tree (BRT), a novel numerical model, was employed to establish the quantitative relationship between cladoceran composition and environmental variables. The model was used to reconstruct historical macrophyte coverage over the past 60 years in a typical Yangtze lake, Liangzi Lake, based on sedimentary cladoceran records. The BRT-inferred macrophyte coverage was validated well by the macrofossil records in the same lake. Using subfossil cladocerans as indicator of the past environmental change in MLYB lakes is potentially useful given their key ecological roles. However, caution should be taken due to species-specific differences in preservation in the sediment and confounding environmental processes that to some extent may bias the conclusions.

Genetic diversity and differentiation of Daphnia galeata in the middle and lower reaches of the Yangtze River, China.

Mitochondrial 16S rDNA and CO I gene were used as molecular markers for the analysis of the genetic diversity and differentiation of Daphnia galeata populations in nine water bodies in the middle and lower reaches of the Yangtze River. In the combined 16S rDNA and CO I gene sequences, 54 variable sites and 44 haplotypes were observed among 219 individuals belonging to nine D. galeata populations. Average haplotype diversity and nucleotide diversity were, respectively, 0.72% and 0.56%. The F-statistics (F ST) value of the D. galeata populations was 0.149. According to the results of the neutral test, D. galeata in the middle and lower reaches of the Yangtze River had experienced a bottleneck effect in the history. Molecular variance analysis indicated that the genetic differentiation of the D. galeata populations mainly occurred within populations (85.09%). Greater genetic differentiations of D. galeata among individuals within populations appeared in the populations from the Huaihe River basin, whereas smaller genetic differentiations occurred in the populations from the middle reaches of the Yangtze River. Strong gene flows were all observed between Group I (four populations from the middle reaches of the Yangtze River) and Group ΙΙ (three populations from the middle and lower reaches of the Yangtze River), and Group ΙΙΙ (two populations from the Huaihe River basin). The effective migration rates (M) were 851.49 from Group I to Group ΙΙ and 685.96 from Group I to Group ΙΙΙ, respectively. However, no significant relationship was observed between the genetic differentiation and geographical distance of the nine populations (r = .137, p > .05). Results suggested that the genetic differentiation of D. galeata in the water bodies in the middle and lower reaches of the Yangtze River resulted mainly from geographical isolation.

Interdecadal changes of summer aerosol pollution in the Yangtze River Basin of China, the relative influence of meteorological conditions and the relation to climate change.

Winter is a season of much concern for aerosol pollution in China, but less concern for pollution in the summertime. There are even less concern and larger uncertainty about interdecadal changes in summer aerosol pollution, relative influence of meteorological conditions, and their links to climate change. Here we try to reveal the relation among interdecadal changes in summer's most important circulation system affecting China (East Asian Summer Monsoon-EASM), an index of meteorological conditions (called PLAM, Parameter Linking Air Quality and Meteorological Elements, which is almost linearly related with aerosol pollution), and aerosol optical depth (AOD) in the middle and lower reaches of the Yangtze River (M-LYR) in central eastern China during summertime since the 1960's. During the weak monsoon years, the aerosol pollution load was heavier in the M-LYR and opposite in the strong monsoon years mainly influenced by EASM and associated maintenance position of the anti-Hadley cell around 115°E. The interdecadal changes in meteorological conditions and their associated aerosol pollution in the context of such climate change have experienced four periods since the 1960's, which were a relatively large decreased period from 1961 to 1980, a large rise between 1980 and 1999, a period of slow rise or maintenance from 1999 to 2006, and a relatively rapid rise between 2006 and 2014. Among later three pollution increased periods, about 51%, 25% and 60% of the aerosol pollution change respectively come from the contribution of worsening weather conditions, which are found to be greatly affected by changes in EASM.

Study on distribution and countermeasures of Oncomelania snails in beach wetlands of Runzhou section of lower reaches of Yangtze River / 中国血吸虫病防治杂志

Objective To understand the distribution of the river beach wetlands and Oncomelania snails in the lower reach-es of the Yangtze River,and explore the countermeasures of snail control. Methods The river beach wetlands outside the Yang-tze River levee were investigated and classified according to the hierarchical and classification system of wetlands of China. The snail survey was carried out in the beach wetlands of Runzhou section of lower reaches of the Yangtze River from 2004 to 2013. The change trend of snail areas and the densities was analyzed in the wetlands. Results The river beach of Runzhou section of lower reaches of the Yangtze River belongs to the riverine wetland. There was Oncomelania snail breeding except the permanent wa-ter area. At present,there were natural wetlands of 1 303.0 hm2,human-made wetlands of 1 479.0 hm2 and wetland function chang-es of 1 059.0 hm2 in the river beach of Runzhou section. There was the snail area of 181.4 hm2 in the natural wetland in 2013. The area of snail control by the molluscicide and environmental modification was 4 624.55 hm2 from 2004 to 2013. The decline rates of snail areas and densities were 66.53%and 77.66%respectively. The existing Oncomelania snails were distributed in the natural wetlands. Conclusion The human-made wetland is helpful to snail control. The snail control in the river beach wetlands should attach a great importance to the protection of wetland ecology.