Search Results (127)

The focus of pK_a calculations has primarily been on stable molecules, with limited studies comparing radical cations and stable cations. In this study, we comprehensively investigate models with implicit solvent and explicit water molecules, direct and indirect calculation approaches, as well as methods for calculating free energy, solvation energy, and quasi-harmonic oscillator approximation for para-substituted aniline radical cations (R-PhNH₂^•+) and anilinium cations (R-PhNH₃⁺) in the aqueous phase. Properly including and positioning explicit H₂O molecules in the models is important for reliable pK_a predictions. For R-PhNH₂^•+, precise pK_a values were obtained using models with one or two explicit H₂O molecules, resulting in a root mean square error (RMSE) of 0.563 and 0.384, respectively, for both the CBS-QB3 and M062X(D3)/ma-def2QZVP methods. Further improvement was achieved by adding H₂O near oxygen-containing substituents, leading to the lowest RMSE of 0.310. Predicting pK_a values for R-PhNH₃⁺ was more challenging. CBS-QB3 provided an RMSE of 0.349 and the M062X(D3)/ma-def2QZVP method failed to calculate pK_a accurately (RMSE > 1). However, by adopting the double-hybrid functional method and adding H₂O near the R substituent group, the calculations were significantly improved with an average absolute difference (ΔpK_a) of 0.357 between the calculated and experimental pK_a values. Our study offers efficient and reliable methods for pK_a calculations of R-PhNH₂^•+ (especially) and R-PhNH₃⁺ based on currently mature quantum chemistry software. Full article

Accurately mapping the surface water bodies through remote sensing technology is of great significance for water resources management, flood monitoring, and drought monitoring. At present, many scholars at home and abroad carry out research on deep learning image recognition algorithms based on convolutional neural networks, and a variety of variant-based convolutional neural networks are proposed to be applied to extract water bodies from remote sensing images. However, due to the low depth of convolutional layers employed and underutilization of water spectral feature information, most of the water body extraction methods based on convolutional neural networks (CNNs) for remote sensing images are limited in accuracy. In this study, we propose a novel surface water automatic extraction method based on the convolutional neural network (CRAUnet++) for Sentinel-2 images. The proposed method includes three parts: (1) substituting the feature extractor of the original Unet++ with ResNet34 to enhance the network’s complexity by increasing its depth; (2) Embedding the Spatial and Channel ‘Squeeze and Excitation’ (SCSE) module into the up-sampling stage of the network to suppress background features and amplify water body features; (3) adding the vegetation red edge-based water index (RWI) into the input data to maximize the utilization of water body spectral information of Sentinel-2 images without increasing the data processing time. To verify the performance and accuracy of the proposed algorithm, the ablation experiment under four different strategies and comparison experiment with different algorithms of RWI, FCN, SegNet, Unet, and DeepLab v3+ were conducted on Sentinel-2 images of the Poyang Lake. The experimental result shows that the precision, recall, F1, and IoU of CRAUnet++ are 95.99%, 96.41%, 96.19%, and 92.67%, respectively. CRAUnet++ has a good performance in extracting various types of water bodies and suppressing noises because it introduces SCSE attention mechanisms and combines surface water spectral features from RWI, exceeding that of the other five algorithms. The result demonstrates that CRAUnet++ has high validity and reliability in extracting surface water bodies based on Sentinel-2 images. Full article

Due to the joint influence of climate change and human activities, the hydrological rhythm of Poyang Lake has changed in recent years, leading to an increasingly severe drought problem during autumn and winter in this region. Notably, the extreme drought that occurred in 2022 had profound impacts on shipping, water supply and the ecological environment of the wetlands in the Poyang Lake Delta, sparking widespread concern. Based on the historical hydrometeorological data of Poyang Lake, we used statistical models (such as Chow test, correlation analysis, etc.) to analyze the cause of the extreme drought in the Poyang Lake Delta from the perspectives of natural factors and human activity. Through correlation analysis, we found that the water level, discharge, and drought duration of the Poyang Lake Delta were all significantly affected by climate change, particularly rainfall in the Poyang Lake basin. Furthermore, combining the results of Chow test and correlation analysis, we also found that the operation of the Three Gorges Reservoir had a notable impact on the water level of the Poyang Lake Delta. Based on remote sensing images, ecological and environmental sampling monitoring, the damage inflicted by the extreme drought event on the Poyang Lake Delta was analyzed. The results show that the inundated area of the delta wetlands in the extreme-drought year (2022) decreased by 45.75% compared with that in a normal year (2017). In addition, the ecological environment of the wetlands deteriorated significantly. The water quality parameters (TN, TP, NH₄⁺-N) increased by 50.2%, 240% and 64.7%, respectively. The concentrations of TN and TP were 3.8 mg/L and 0.17 mg/L, respectively, while the context values in the delta were 1.2 mg/L and 0.075 mg/L. The density and biomass of algae increased by 87.2% and 557.9%, respectively. In contrast, the density and biomass of benthos decreased by 59.9% and 78.5%, respectively. The control strategy for the Poyang Lake Delta under extreme drought was studied through an experiment on the operation of hydraulic controllers. The results show that under extreme drought conditions, the newly built hydraulic controllers could raise the water level of the delta from 9.1 ± 0.7 m to 14.2 ± 1.8 m, thus effectively solving the water cut-off problem in the four branches of the delta. Furthermore, by adjusting the distributive ratio of the main, north, middle and south branches of the delta to 50%, 4%, 24% and 22% through newly built hydraulic controllers, the water area can be increased by 56%. Full article

Agricultural cultural heritage is crucial in advancing comprehensive rural revitalization. The Yangtze River Basin is rich in biodiversity and abundant in fishery cultural resources. The cultural resources not only reflect the ecological wisdom of harmonious coexistence and the human–land relationship between humans and nature but also provide critical cultural support for rural revitalization and watershed sustainable development. This study investigates the spatial distribution, influencing factors, and historical evolution of fishery cultural resources in the Yangtze River Basin. The highest proportions of significant resources are found in fishery engineering and landscapes, culinary flavors, fishery customs, dances, fishery gear, and poetry. By analyzing 14 categories of fishery cultural resources and 157 national and provincial intangible cultural heritage items, this study reveals a significant geographical clustering of these resources in the mid-lower reaches, particularly around the middle reaches of the Yangtze River and Poyang Lake Basin, Wuhan and Dongting Lake, and the lower reaches of the Taihu Lake Basin. This study underscores the role of natural geographical conditions, aquatic biodiversity, socio-economic factors, and historical–cultural backgrounds in the distribution and evolution of fishery cultural resources, with these factors interacting dynamically. By advocating for a comprehensive approach to coordinating fishery culture preservation with rural revitalization, this study outlines a multidimensional strategy for the preservation and sustainable development of fishery cultural resources. Full article

The Yangtze River floodplain is an area with an extremely rich diversity of fish species. Poyang Lake, as an important part of this river–floodplain system, is a crucial habitat for the survival of fish. However, prolonged human activities, such as environmental pollution and hydroelectric development, have degraded the habitat in the Poyang Lake Basin, posing threats to fish populations. Understanding genetic diversity is crucial for maintaining fish populations and understanding their dynamics. The genetic diversity of Hemiculterella wui, an economically endemic species in China of subfamily Cultrinae (Cypriniformes: Cyprinidae), has been understudied. This study investigated the genetic diversity and structure of H. wui populations from the Ganjiang, Xinjiang, Fuhe, and Raohe rivers in the Poyang Lake Basin using mitochondrial Cytb gene analysis. Results showed high haplotype diversity but low nucleotide diversity in H. wui’s Cytb sequences. Analysis of molecular variance (AMOVA) showed no significant geographic genetic structure among populations. Haplotype network analysis revealed no clear geographical clustering. Neutrality tests and haplotype nucleotide mismatch distribution indicated that all populations had experienced expansion events. These findings suggest that H. wui in Poyang Lake does not show a distinct geographic structure. However, it is still necessary to monitor the genetic characteristics of H. wui to maintain the genetic diversity of fishes in Poyang Basin, considering the threat of habitat loss and fragmentation to the population. Full article

The conflict between biodiversity conservation and economic development is intense in developing countries. With the decline in biodiversity, the Chinese government imposed a 10-year fishing ban in the priority waters of the Yangtze River Basin, which resulted in many fishermen losing their livelihood. However, a compensation policy was subsequently introduced. To investigate the impact of the ban, we conducted a two-year study using balanced panel data and the PSM-DID model for 365 households in the Poyang Lake area and introduced fixed effects to discuss the impact of the Yangtze River fishing ban compensation policy on the income of returning fishermen and their choices for alternative income. We also explored the interactive effects of fishing ban compensation and other biodiversity conservation policies on their income. The results showed that the fishing ban negatively impacted the agricultural income of households but not the total household income, and the compensation somewhat subsidized the fishermen’s loss of income. Moreover, this was an opportunity for farmers to adjust their livelihood strategies. These findings improve our understanding of the impact of this fishing ban and compensation policy on the household incomes of returning fishermen and their adaptive strategies for alternative income. Full article

Plain lakes play a crucial role in the hydrological cycle of a watershed, but their interactions with adjacent rivers and downstream water bodies can create complex river–lake relationships, often leading to frequent flooding disasters. Taking Poyang Lake as an example, this paper delves into its interaction with the Yangtze River, revealing the spatiotemporal patterns of flood propagation within the lake and its impact on surrounding flood control measures. The aim is to provide insights for flood management in similar environments worldwide. This study employs a comprehensive approach combining hydrological statistical analysis and two-dimensional hydrodynamic modeling, based on extensive hydrological, topographic, and socio-economic data. The results indicate that the annual maximum outflow from Poyang Lake is primarily controlled by floods within the watershed, while the highest annual lake water level is predominantly influenced by floods from the Yangtze River. The peak discharge typically reaches the lake outlet within 48 h, with the peak water level taking slightly longer at 54 h. However, water storage in the lake can shorten the time that it takes for the peak discharge to arrive. When converging with floods from the Yangtze River, the peak water level may be delayed by up to 10 days, due to the top-supporting interaction. Furthermore, floods from the “Five Rivers” propagate differently within the lake, affecting various lake regions to differing degrees. Notably, floods from the Fu River cause the most significant rise in the lake’s water level under the same flow rate. The top-supporting effect from the Yangtze River also significantly impacts the water surface slope of Poyang Lake. When the Yangtze River flood discharge significantly exceeds that of the “Five Rivers” (i.e., when the top-supporting intensity value, f, exceeds four), the lake surface becomes as flat as a reservoir. During major floods in the watershed, the water level difference in the lake can increase dramatically, potentially creating a “dynamic storage capacity” of up to 840 million cubic meters. Full article

Nanling Mountain region is a typical southern hilly region, which plays an important ecological and environmental protection role in China’s overall land protection pattern. Based on the remote sensing image data of Longnan City in Nanling Mountain region in 2013, 2018 and 2023, this paper interpreted the land use type and analyzed the land use transfer situation by using land use transfer flow, and a land use transfer matrix. At the same time, based on the remote sensing ecological index (RSEI) model, the ecological environmental quality of Longnan City from 2013 to 2023 was retrieved. The temporal and spatial response model of the ecological environmental quality to land use transfer in Longnan City from 2013 to 2023 was discussed based on spatial autocorrelation and a geographical detector. The results show that from 2013 to 2023, the decrease of forest land (16.23 km²) and the increase of construction land (13.25 km²) were the main land use transfers in Longnan City. The ecological environment indexes of Longnan City in 2013, 2018 and 2023 were 0.789, 0.917 and 0.872, respectively, showing a trend of “first rising and then decreasing”. The ecological environmental quality in the north of Longnan City was significantly lower than that in the south, and the poor ecological quality area appeared in and around the northern main urban area, showing a trend of “inward contraction”. Forest land, garden land, grassland, cultivated land and water area have a positive impact on ecological environmental quality, while traffic land, construction land and other land have a negative impact on ecological environmental quality. The response of ecological environmental quality to different land use transfer modes is related to the change of the overall ecological environmental quality. The interaction between land use and land cover change (LUCC) and other factors had a great impact on the evolution of ecological environmental quality in Longnan City. Full article

Investigating the effects of natural rainfall on the soil moisture for sloping farmland is extremely important for comprehending a variety of hydrological processes. Rainfall regimes can elicit different responses to soil moisture at the depth of soil layers, and the responses may differ depending on the landscape position of the sloping farmland. This paper utilized the surface runoff natural rainfall and soil moisture measured on sloping farmland with conventional tillage and contour tillage in the red soil area of China to investigate the influence of natural rainfall events on soil moisture content and to evaluate if the response results were consistent across the four rainfall regimes. Natural rainfall events were classified into different four regimes in line with rainfall duration, rainfall amount, and the maximum 30 min rainfall intensity (I₃₀) by the k-means clustering method, including advanced, intermediate, uniform and delayed regimes. The result showed that the advanced regime was the predominant one in the study area, which represented 45.9% of the total rainfall events. The rainfall regimes influenced the surface runoff coefficient and runoff depth on sloping farmland for conventional and contour tillage, with the uniform regime generating the highest runoff coefficient (5.20% and 5.82%) and runoff depth (2.00% and 2.05%), respectively. For the conventional tillage, soil moisture at a depth of 0–20 cm increased appreciably when the rainfall amount was larger than 20 mm and larger than 30 mm for the advanced regime. For the contour tillage, soil moisture in 20–40 cm layer increased for the advanced regime when the rainfall amount was larger than 15 mm and 30 mm, while the values were modified with rainfall duration and the antecedent dry day (ADD). A longer rainfall duration had a more obvious effect on soil moisture increasing in deep soil. At a depth of 20 cm, the ADD showed an appreciably positive correlation with the increment in soil moisture, which means that a brief ADD produces a compounding effect for a natural rainfall event. The present results underline the complexity of the effect of the rainfall events on soil moisture under two tillage measures for different rainfall regimes and suggest that the advanced regime significantly affects the distinction of soil moisture and the contour tillage can effectively reduce soil water loss and enhance water storage on the sloping farmland with red soil, presenting a theoretical basis for local soil and water conservation research and sloping farmland conservation tillage management. Full article

Global warming is exacerbating flood hazards, making the robustness of flood risk management a critical issue. Without considering future scenarios, flood risk analysis built only on historical knowledge may not adequately address the coming challenges posed by climate change. A comprehensive risk analysis framework based on both historical inundations and future projections to tackle uncertainty is still lacking. In this view, a scenario-based, data-driven risk analysis framework that for the first time integrates recent historical floods and future risk trends is here presented, consisting of flood inundation-prone and high-risk zones. Considering the Poyang Lake Eco-Economic Zone (PLEEZ) in China as the study area, we reproduced historical inundation scenarios of major flood events by using Sentinel-1 imagery from 2015 to 2021, and used them to build the risk baseline model. The results show that 11.7% of the PLEEZ is currently exposed to the high-risk zone. In the SSP2-RCP4.5 scenario, the risk would gradually decrease after peaking around 2040 (with a 19.3% increase in high-risk areas), while under the traditional fossil fuel-dominated development pathway (SSP5-RCP8.5), the risk peak would occur with a higher intensity about a decade earlier. The attribution analysis results reveal that the intensification of heavy rainfall is the dominant driver of future risk increase and that the exploitation of unused land such as wetlands induces a significant increase in risk. Finally, a hierarchical panel of recommended management measures was developed. We hope that our risk analysis framework inspires newfound risk awareness and provides the basis for more effective flood risk management in river basins. Full article

Due to underlying surface changes (USCs), the changes in the Taojiang River Basin’s flood generation conditions could impact the flooding process in the basin. However, most studies have typically focused on either land-use changes (LUCs) or soil and water conservation measures (SWCMs) to assess the impact of the USCs on floods, which may not provide a more comprehensive understanding of the response of floods to the USCs. To investigate how the USCs have altered the floods in the Taojiang River Basin, located upstream of Poyang Lake, China, the HEC-HMS model, which incorporates the influence of the USCs into the parameter calibration, is established in this study to investigate the flood processes on an hourly scale. The flood peak and the maximum 72 h flood volume are selected as two indexes and are applied to analyze the changes in floods caused by the USCs. The 1981–2020 period is divided into three sub-periods (i.e., 1981–1992, 1993–2007, and 2008–2020) based on the conditions of the USCs. It is found that the two indexes have exhibited decreasing trends, mainly due to the USCs during 1981–2020. Benchmarked against the baseline period of 1981–1992, the two indexes decreased by 3.06% (the flood peak) and 4.00% (the maximum 72 h flood volume) during 1993–2007 and by 5.92% and 7.58% during 2008–2020. Moreover, the impacts of the LUCs and SWCMs are separated through parameter adjustments in the model, revealing that the SWCMs played a dominant role in the USCs in the Taojiang River Basin. The quantification and assessment of the impact of the USCs on floods of different magnitudes revealed that the influence decreases with increasing flood magnitude. The results of this study improve our understanding of how USCs affect the flooding process and therefore provide support for flood control management under changing environments. Full article

Dredging, adsorbent inactivation, and phytoremediation are commonly used to control internal nitrogen and phosphorus sediment loads in eutrophic still-water ecosystems, such as lakes and ponds. However, the effectiveness of these remediation techniques has not been verified for rivers, lakes, and reservoirs with large disturbances. In this study, a calcium-loaded clay granular adsorbent (CRB) was prepared as an alternative to commercial adsorbents, and an experiment was conducted on the ecological restoration effects of both dredging and adsorbent single treatments as well as combined treatments on eutrophic flowing water. The enhancement effect of phytoremediation on the above restoration techniques was investigated. The results indicated that CRB inactivation treatment reduced the phosphorus and turbidity of the water by 63% and 80%, respectively and increased the total nitrogen and permanganate index (COD_Mn) by 25% and 101% before phytoremediation, respectively compared to the control group. There were no significant differences in the nutrient indexes of the sediment and water between the dredging treatment and the control group, but dredging enhanced the effect of the CRB treatment. Compared with the CRB treatment, the total nitrogen and COD_Mn of water in the dredging and combined CRB treatments decreased by 13% and 15%, respectively. Phytoremediation significantly improved the effectiveness of the dredging and adsorbent treatments, both individually and in combination. Additionally, there were notable differences in the growth rates of the submerged plants and the contents of different phosphorus speciation among the plant species. Selecting suitable plant species is recommended when implementing phytoremediation methods. This study highlights that the combination of multiple restoration techniques is effective for eutrophic flowing water. The results provide a guide for the ecological restoration of flowing water. Full article

Poyang Lake, the largest freshwater lake in China, is an important regional water resource and a landmark ecosystem. In recent years, it has experienced a period of prolonged drought. Using appropriate drought indices to describe the drought characteristics of the Poyang Lake Basin (PLB) is of great practical significance in the face of severe drought situations. This article explores the applicability of four drought indices (including the precipitation anomaly index (PJP), standardized precipitation index (SPI), China Z-index (CPZI), and standardized precipitation evapotranspiration index (SPEI)) based on historical facts. A systematic study was conducted on the spatiotemporal evolution patterns of meteorological drought in the PLB based on the optimal drought index. The results show that SPI is more suitable for the description of drought characteristics in the PLB. Meteorological droughts occur frequently in the summer and autumn in the PLB, with the frequency of mild drought being 17.29% and 16.88%, respectively. The impact range of severe drought or worse reached 22.19% and 28.33% of the entire basin, respectively. The probability of drought occurrence in the PLB shows an increasing trend in spring, while in most areas, it shows a decreasing trend in other seasons, with only a slight increase in the upper reaches of the Ganjiang River (UGR). One of the important factors influencing drought in the PLB is atmospheric circulation. The abnormal variation of the Western Pacific Subtropical High was one of the key factors contributing to the severe drought in the PLB in 2022. This study is based on a long-term series of meteorological data and selects the drought index for the PLB. It describes the spatiotemporal distribution characteristics and evolution patterns of drought and investigates the developmental path and influencing factors of drought in typical years. This study provides a reliable scientific basis for similar watershed water resource management. Full article

Accurate mapping of vegetation in the coexisting area of paddy fields and wetlands plays a key role in the sustainable development of agriculture and ecology, which is critical for national food security and ecosystem balance. The phenology-based rice mapping algorithm uses unique flooding stages of paddy rice, and it has been widely used for rice mapping. However, wetlands with similar flooding signatures make rice extraction in rice–wetland coexistence challenging. In this study, we analyzed phenology differences between rice and wetlands based on the Sentinel-1/2 data and used the random forest algorithm to map vegetation in the Poyang Lake Basin, which is a typical rice–wetland coexistence zone in the south of China. The rice maps were validated with reference data, and the highest overall accuracy and Kappa coefficient was 0.94 and 0.93, respectively. First, monthly median composited and J-M distance methods were used to analyze radar and spectral data in key phenological periods, and it was found that the combination of the two approaches can effectively improve the confused signal between paddy rice and wetlands. Second, the VV and VH polarization characteristics of Sentinel-1 data enable better identification of wetlands and rice. Third, from 2018 to 2022, paddy rice in the Poyang Lake Basin showed the characteristics of planting structure around the Poyang Lake and its tributaries. The mudflats were mostly found in the middle and northeast of Poyang Lake, and the wetland vegetation was found surrounding the mudflats, forming a nibbling shape from the lake’s periphery to its center. Our study demonstrates the potential of mapping paddy rice in the rice–wetland coexistence zone using the combination of Sentinel-1 and Sentinel-2 imagery, which would be beneficial for balancing the changes between paddy rice and wetlands and improving the vulnerability of the local ecological environment. Full article

Phosphate-solubilizing bacteria (PSB) offer an eco-friendly approach to boost plant growth in soils low or deficient in phosphorus (P). In this study, we isolated 97 PSB strains from the soil around moso bamboo roots in Jiangxi Province, China. The RW37 strain was identified as Enterobacter soli through its physical characteristics and genetic sequencing. Our experiments revealed that RW37 could dissolve phosphate at levels exceeding 400 mg L⁻¹ across a wide range of environmental conditions, including temperature (25–35 °C), pH levels (3.5–7.2), salinities (0–2.0%), and volumes of medium (1/5–3/5 of flask volume), showcasing its adaptability. Furthermore, RW37 showed remarkable phosphate-solubilizing abilities at various pH levels using different phosphate sources, with the highest capacity observed in a medium containing CaHPO₄. This study also found a negative correlation between P-solubilizing capacity and fermentation broth pH, indicating that RW37 likely secretes organic acids to dissolve phosphate sources. Pot experiments demonstrated that applying RW37 significantly improved the plant height, biomass, root growth, and P uptake of moso bamboo seedlings in red soil. Our results highlight the potential of RW37 as an eco-friendly biofertilizer for subtropical bamboo forests. Full article