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The ecological effects of eutrophication on estuaries and coastal ecosystems are significant worldwide. Based on data collected in 2019 from Hangzhou Bay and adjacent waters, this study employed biological traits analysis and RLQ/fourthcorner analysis methods to investigate the distribution patterns of macrobenthic assemblages along a eutrophication gradient and reveal the response patterns of their biological traits to eutrophication stress. The results showed that eutrophication had a significant structuring effect on the spatial distribution of macrobenthic community structure. As the level of eutrophication increased, the community abundance and number of macrobenthic biological traits decreased. The composition of macrobenthic community biological traits changed in response to eutrophication. In areas with high levels of eutrophication, larger body sizes became more dominant, reflecting a shift in dominant traits similar to the eutrophication gradient. Furthermore, the predominant species in this region were burrowers and tube dwellers, which preferred muddy sand and sandy mud substrates. The AMBI ecological group accurately reflects the degree of eutrophication disturbance, with tolerant species and second-order opportunistic species being common in eutrophic areas. [ABSTRACT FROM AUTHOR]

Asymmetric tidal dynamics are of great significance for material transport and morphological evolution in estuaries. The tidal dynamics of the macro-tidal Hangzhou Bay (HZB) are characterized by flood-ebb asymmetries, spring-neap asymmetries, surface-bottom asymmetries, and up-downstream asymmetries. The mechanisms of spatio-temporal asymmetric tides and lateral flows in HZB were studied through a fully calibrated three-dimensional numerical model. The results show that tidal tides, tidal currents, and tidal asymmetry in HZB varied specially and temporally. In general, the bay was mostly flood-dominant. Temporally, tidal duration asymmetry in the bay fluctuated between spring and neap tides, with larger skewness during spring tides and smaller skewness during neap tides. The locally produced overtides are the primary sources of shallow-water tides in the bay, and the interaction between the lunar semi-diurnal tide M2 and the solar semi-diurnal tide S2 generates shallow-water overtides and deforms tidal asymmetries. The dissipated tidal energy may consumed by the bottom friction, with less passed to the generated shallow water overtides M4 and M6 tides (AM4 = 12.07 cm, AM6 = 3.91 cm) when comparing with the experiments that open boundary is purely forced by M2 tide (AM4 = 13.63 cm, AM6 = 6.31 cm). The increased depth reduces the bottom friction and the convergence of volume, resulting in skewness values close to zero (γTDA = 0.220, γM2-M4 = 0.141, γM2-M4-M6 = −0.002, γM2-S2-MS4 = 0.105). The changes of tidal duration asymmetry caused by the increased channel convergence, reduced bay width, and reclaimed intertidal zone spatially vary in different parts. The bottom friction contributed to the generation of the shallow-water tides and asymmetries in the bay (the RVRs for M4 and M6 are −73.5% and −92.5%), while the Coriolis force (the RVRs for M4 and M6 are 4.8% and 8.9%) and nonlinear advection (the RVRs for M4 and M6 are −17.3% and − 21.8%) are minor factors. The findings of the study provide hydrodynamic foundations for the research of sediment transport and estuarine evolution in similar macro-tidal turbid estuaries worldwide. [ABSTRACT FROM AUTHOR]

The Changjiang Estuary and Hangzhou Bay system has experienced river damming and estuarine engineering in the last decades. However, few studies focused on the shifts in its sediment dynamics due to such human activities. In this study multi-decadal development of sediment dynamics in the transitional zone of the two large estuaries was analyzed, based on the synchronous hydrographic data in the winter of 2023, 2014 and 1983. The results revealed significant changes in regional hydrodynamics and suspended sediment transport, despite the continuous good correlations between the current velocity, suspended sediment concentration (SSC), water/sediment fluxes and tidal range. Specifically, the current velocity has been decreased by 8 - 21% after 2014, mainly due to the land reclamation (implemented around 2016) with several groins stretching into deep water and altering alongshore hydrodynamics. The SSC has decreased further by 29 - 38% in addition to the significant decrease during 1983 - 2014. The SSC changes are related to the combination of river damming which induced sediment load reduction and land reclamation which enclosed a large amount of sediment. Furthermore, the sediment transport from Changjiang Estuary to Hangzhou Bay decreased by 36% - 53%, explaining the observed bed erosion in the northern bay mouth in recent years. The findings are also relevant for studies on sediment dynamics in other large estuaries worldwide. [ABSTRACT FROM AUTHOR]

Aiming at the problems of siltation promotion and siltation return in the beach area of Hangzhou Bay, a numerical calculation model of hydrodynamic and scour and siltation in the south bank of Ningbo Bay was constructed, and the reliability of the short-term scour and siltation numerical calculation model was verified by combining with the field measured scour and siltation data, so as to obtain the natural siltation situation in this area under a longer time scale in the future. Meanwhile, the siltation promotion scheme was selected by comparing with artificial embankment construction. The research results show that the restoration effect of natural silt beach under the action of excavation diversion is remarkable, and the construction of barrier has a significant effect on the retention and sedimentation of sediment in the trench. After the construction of the barrier with a height of -2.22m, the average thickness of sediment promotion in the low-lying area reaches 0.22m, and the elevation of seabed in the low-lying area can reach about 2.5m. Therefore, it is particularly effective for the sediment deposition in low-lying areas in the high sediment content sea area to adopt the method of natural diversion and separation embankment.

Eutrophication caused by inputs of excess nitrogen (N) has become a serious environmental problem in Hangzhou Bay (China), but the sources of this nitrogen are not well understood. In this study, the August 2019 distributions of salinity, nutrients [nitrate (NO3−), nitrite, ammonium, and phosphate], and the stable isotopic composition of NO3− (δ15N and δ18O) were used to investigate sources of dissolved inorganic nitrogen (DIN) to Hangzhou Bay. Spatial distributions of nitrate, salinity, and nitrate δ18O indicate that the Qiantang River, the Changjiang River, and nearshore coastal waters may all contribute nitrate to the bay. Based on the isotopic compositions of nitrate in these potential source waters and conservative mixing of nitrate in our study area, we suggest that the NO3− in Hangzhou Bay was likely derived mainly from soils, synthetic N fertilizer, and manure and sewage. End-member modeling indicates that in the upper half of the bay, the Qiantang River was a very important DIN source, possibly contributing more than 50% of DIN in the bay head area. In the lower half of the bay, DIN was sourced mainly from strongly intruding coastal water. DIN coming directly from the Changjiang River made a relatively small contribution to Hangzhou Bay DIN in August 2019. [ABSTRACT FROM AUTHOR]

Ocean fronts play important roles in nutrient transport and in the shaping ecological patterns. Frontal zones in small bays are typically small in scale, have a complex structure, and they are spatially and temporally variable, but there are limited data on how biological communities respond to this variation. Hangzhou Bay, a medium-sized estuary in China, is an ideal place in which to study the response of plankton to small-scale ocean fronts, because three water masses (Qiantang River Diluted Water, Changjiang River Diluted Water, and the East China Sea current) converge here and form dynamic salinity fronts throughout the year. We investigate zooplankton communities, and temperature, salinity and chlorophyll a (Chl a) in Hangzhou Bay in June (wet period) and December (dry period) of 2022 and examine the dominant environmental factors that affect zooplankton community spatial variability. We then match the spatial distributions of zooplankton communities with those of salinity fronts. Salinity is the most important explanatory variable to affect zooplankton community spatial variability during both wet and dry periods, in that it contributes >60% of the variability in community structure. Furthermore, the spatial distributions of zooplankton match well with salinity fronts. During December, with weaker Qiantang River Diluted Water and a stronger secondary Changjiang River Plume, zooplankton communities occur in moderate salinity (MS, salinity range 15.6 ± 2.2) and high salinity (HS, 22.4 ± 1.7) regions, and their ecological boundaries closely match the Qiantang River Diluted Water front. In June, different zooplankton communities occur in low salinity (LS, 3.9 ± 1.0), MS (11.7 ± 3.6) and HS (21.3 ± 1.9) regions. Although the LS region occurs abnormally in the central bay rather than its apex because of the anomalous influence of rising and falling tides during the sampling period, the ecological boundaries still match salinity interfaces. Low-salinity or brackish-water zooplankter taxa are relatively more abundant in LS or MS regions, and the biomass and abundance of zooplankton is higher in the MS region. [ABSTRACT FROM AUTHOR]

Tidal flat plays an important role in coastal development because of its ecological and spatial resources. We take the southern tidal flat in the macro-tidal turbid Hangzhou Bay as an example to study the long-term (1990–2020) evolution of the muddy tidal flat, using remote sensing data and field observational data. The detailed bathymetric elevation of the tidal flat is obtained, using remote sensing images of Landsat and Sentinel-2, combined with the real-time kinematic (RTK) data. The correlation coefficient between the remote sensing data and the RTK data is 0.73. The tidal flat and vegetation areas are affected by reclamation. The total tidal flat area decreased by 467.78 km2. The vegetation area declined from 64.98 km2 in 2000 to 13.41 km2 in 2015 and recovered to 41.62 km2 in 2020. The largest change in tidal flat slope occurs in the eastern and western sides of the tidal flat, compared with the wide middle part. The total length of tidal creeks decreased to 45.95 km in 2005 and then increased to 105.83 km in 2020. The middle- and low-grade tidal creeks accounted for 91.4%, with a curvature slightly larger than 1 in 2020. High-grade tidal creeks occur inside the vegetation areas, with less bending and fewer branch points. Vegetation promotes the development of tidal creeks but limits the lateral swing and bifurcation. These results provide a basis for the management of global tidal flat resources and ecosystems. [ABSTRACT FROM AUTHOR]

Marine water quality significantly impacts human livelihoods and production such as fisheries, aquaculture, and tourism. Satellite remote sensing facilitates the predictions of large-area marine water quality without the need for frequent field work and sampling. Prediction of diffuse attenuation coefficient (Kd), which describes the speed at which light decays as it travels through water, obtained from satellite-derived ocean color products can reflect the overall water quality trends. However, current models inadequately explore the complex nonlinear features of Kd, and there are difficulties in achieving accurate long-term predictions and optimal computational efficiency. This study innovatively proposes a model called Remote Sensing-Informer-based Kd Prediction (RSIKP). The proposed RSIKP is characterized by a distinctive Multi-head ProbSparse self-attention mechanism and generative decoding structure. It is designed to comprehensively and accurately capture the long-term variation characteristics of Kd in complex water environments while avoiding error accumulation, which has a significant advantage in multi-dataset experiments due to its high efficiency in long-term prediction. A multi-dataset experiment is conducted at different prediction steps, using 70 datasets corresponding to 70 study areas in Hangzhou Bay and Beibu Gulf. The results show that RSIKP outperforms the five prediction models based on Artificial Neural Networks (ANN, Convolutional Neural Networks (CNN), Gated Recurrent Unit (GRU), Long Short-Term Memory Recurrent Neural Networks (LSTM-RNN), and Long Short-Term Memory Networks (LSTM)). RSIKP captures the complex influences on Kd more effectively to achieve higher prediction accuracy compared to other models. It shows a mean improvement of 20.6%, 31.1%, and 22.9% on Mean Absolute Error (MAE), Mean Square Error (MSE), and Mean Absolute Percentage Error (MAPE). Particularly notable is its outstanding performance in the long time-series predictions of 60 days. This study develops a cost-effective and accurate method of marine water quality prediction, providing an effective prediction tool for marine water quality management. [ABSTRACT FROM AUTHOR]

The correlation between the amount of organic carbon (OC) and sulfur (S) in sediments has been widely used as a paleosalinity indicator to distinguish between marine and freshwater environments. However, whether the ratio of total OC to total S (TOC/TS) can be used to identify unsteady or dynamic marine environments across sedimentary strata is still contended. An HZW1907 sediment core of 80 m in length was successfully collected in the middle of Hangzhou Bay (HZB), serving as one of the few boreholes that are crucial for the study of geologic and geo-environment changes in the coastal regions of eastern China since the Last Glacial Maximum (LGM). Total OC (TOC), stable carbon isotope, and TS of 82 subsamples from the HZW1907 core were analyzed to reconstruct the history of the shallow water biological pump and sulfur preservation record in the bay since the Late Pleistocene. Our results indicate that the samples had low concentrations of TOC (0.21%) and total nitrogen (TN) (0.02%), high mass ratio of TOC/TN (10.8), low δ13C (-24.9%0), low TS content (0.06%), and a high ratio of TOC/TS (9.1) from 33.6 ka BP to 12.3 ka BP, implying that freshwater organic matter (OM), algae, and C3 plant fragments were the main sources of OM in a relatively cold environment. The abundances of TOC, TN, and TS increased to 0.56%, 0.07%, and 0.4%, respectively, while δ13C (-23.9%) increased and TOC/TS (2.7) decreased in the Holocene sediments, suggesting that seawater began to influence the composition of the sediments of HZB. Climate warming, which is likely to have impacted the results, was experienced from 12.3 ka BP. An OC isotope mixing model indicated that since the Mid-late Holocene, more than 70% of riverine OM accounted for the total OM. The TOC/TS ratio was identified as an effective indicator of seawater intrusion, with C/S ratios of 1-6 being considered to indicate a "sea-land transitional zone" sedimentary environment, a C/S >6 indicating freshwater, and a C/S<1 indicating normal marine facies. These findings provide crucial evidence for using TOC/TS to distinguish freshwater from marine environments and enhance our understanding of past climate changes. Therefore, these geochemical indicators can be used in conjunction with other sedimentary records to obtain accurate results about sedimentary evolution. [ABSTRACT FROM AUTHOR]

With sea level rise (SLR), tidal nuisance flooding has become a growing threat, especially around estuaries with large tidal amplitudes. This study investigated how sea level change affects tides in Hangzhou Bay, a macro-tidal estuary with high SLR rate. By downscaling climate projections to a regional hydrodynamic model, the amplitude of primary tidal constituent (M2) was predicted to increase by 0.25 m in the upper bay, where the amplitude of major diurnal tide (K1) was also predicted to increase by 15%. In addition, the sensitivity of tidal amplitude to mean sea level was examined by a set of numerical simulations with different SLR. It was found that the increase of tidal amplitude is nonlinear to SLR, and the tidal amplitudes almost cease to increase when SLR is over 1.5 m. Although predictions show less amplitude changes in the lower bay, Zhoushan Archipelago around the bay mouth strongly modulates the incoming tidal energy, thus affecting the tidal amplitude in the upper bay. Energy budget analysis revealed that the complex topography, such as narrow channels, in the archipelago area leads to strong horizontal shear, which dissipates approximately 25% of total tidal energy in the bay. On the other hand, around 60% of the energy is dissipated in the bottom boundary layer. However, the bottom dissipation decreases by 4% due to reduced friction, while horizontal dissipation increases by 10% due to enhanced horizontal shear with SLR. This suggests that the strong horizontal shear in the Zhoushan archipelago region can play a more important role in the tidal energy budget in the future. [ABSTRACT FROM AUTHOR]

Locust plagues and tidal disasters are primary natural hazards in China's eastern coastal regions, yet their interrelationship remains unclear. This study, drawing on historical documents from the Ming and Qing dynasties (1368–1911 AD), focuses on Zhejiang Province and its Hangzhou Bay coastline, areas typically affected by tidal disasters. Employing advanced quantitative analysis and spatiotemporal models, the research aims to reveal the mechanisms behind tidal disasters and their impact on locust population dynamics. The findings indicate a limited spatiotemporal correlation between locust plagues and tidal or drought disasters but a significant association with flooding. The relationship between locust infestations and floods is notably strong in the unique geographical context of Hangzhou Bay's northern shore. The 'hydromarginal' nature of the north coast creates an ideal habitat for locusts. This study pioneers in identifying flooding as a crucial mediator between tidal disasters and locust plagues, shedding light on the 'typhoon-tidal-flood-locust' disaster sequence and offering new insights into understanding and mitigating natural disasters in the region. In this study, we primarily employ a quantitative methodology, utilizing advanced data analysis and sophisticated spatiotemporal modeling to investigate the interplay between locust plagues and tidal disasters. Although some progress has been made in the study of historical natural disasters, systematic studies of the relationship between tidal floods and locust breeding sites along the east coast of China during the Ming and Qing dynasties are still scarce. This study fills this gap by employing advanced GIS and time series analysis techniques, combining traditional historical documentary studies with modern scientific methods and providing a new methodological approach to the analysis of historical disaster patterns. [ABSTRACT FROM AUTHOR]

With rapid urbanization and industrialization, Hangzhou Bay faces significant pressure in water environment governance. This study, based on panel data from 2011 to 2021 in Zhejiang's Hangzhou, Jiaxing, Shaoxing, and Ningbo, employs the Super-Efficiency DEA model to assess water environment governance performance. The Tobit model analyzes external environmental factors. Findings reveal fluctuating water governance efficiency during the study period, with inefficiencies from 2012 to 2019, followed by significant improvement from 2019 to 2021. Key factors impacting governance include urban water environment performance in Hangzhou, urban residents' disposable income, population density, and secondary industry GDP development. A higher urban income enhances environmental awareness and governance performance, while population density and industrial GDP intensify resource use, energy consumption, and wastewater discharge, worsening governance pressures and performance. This research offers insights for enhancing water environment governance in Hangzhou Bay, aiding in the formulation of protection plans and management policies. Additionally, it provides valuable experiences for watershed governance globally. [ABSTRACT FROM AUTHOR]

Based on the water quality monitoring data of 12 voyages in Hangzhou Bay from 2017 to 2019, the distribution characteristics of petroleum in the water quality survey project were analyzed. It was found that the content range of petroleum in the waters of Hangzhou Bay were 0.008~0.042 mg/L, 0.011~0.046 mg/L, 0.007~0.094 mg/L respectively, from 2017 to 2019, and the annual average content were 0.023 mg/L, 0.023 mg/L and 0.016 mg/L, all met the Class I sea water quality standard. In terms of seasonal change, the petroleum indicators in water quality were not obvious due to the influence of physical factors such as tidal current, sediment content and wind force, and they all belonged to fluctuations at low contents. In terms of interannual changes, the petroleum pollutants content were generally the same in 2017 and 2018, compared with the first two years, there was a significant decrease in 2019, with a certain downward trend. In terms of plane distribution, it mainly presented multipoint source distribution, and high value areas mainly appeared in coastal waters of Jiaxing and the south coast of Hangzhou Bay. Through correlation analysis and research, it was found that the content of petroleum was significantly negatively correlated with the suspended solids. The suspended solids in seawater had adsorption effect on petroleum pollutants, Thus the greater the mass of suspended solids in seawater, the lower the content of petroleum.

The Jiayong Channel sea area, where the Hangzhou Bay Railway Sea-Crossing Bridge is located, has frequent typhoons. It is of great significance to study and clarify the characteristics of wind, wave and current parameters during typhoons to ensure the safety of cross-sea bridges. First, the typhoon disasters and topographic information in the area are investigated. Then, based on the parametric wind field and wave-current coupling model, the wind, wave and current parameters of 47 historical typhoons that seriously impacted the sea area are calculated. The distribution of the wind, wave, current fields, and the relationship between wind-wave, wind-current, and wave-current are discussed. Similar distributions of wind and wave fields in the sea area are observed during the typhoon. There are differences in the wind-wave relationship fitted by different sample selection methods. Under the same wind environment, the closer the open sea, the greater the water depth and the higher the wave height. Clayton copula can better describe the joint distribution of wind-current and wave-current. When the probability density is 0.01, the maximum wind speed and current speed considering the dependency of wind-current parameters are 34.75 m/s and 1.87 m/s respectively. Considering the dependency of wave-current parameters, the maximum wave height and current speed are 6.43 m/s and 2.08 m/s respectively. Studies have shown that to obtain more realistic environmental parameters, the correlation between environmental variables should be fully considered in the design. [ABSTRACT FROM AUTHOR]

As a class of persistent organic pollutants, polycyclic aromatic hydrocarbons (PAHs) are widely present and accumulate in multimedia environments. The pollution characteristics, spatiotemporal distribution, potential sources, influencing factors, and ecological risks of 16 PAHs were investigated in the water–sediment system of the Hangzhou Bay and outer bay area (HZB and OBA, respectively). The total concentrations of 16 PAHs (∑PAHs) were 220 ± 97.0 and 130 ± 36.0 ng/L in the seawater and 343 ± 179 and 505 ± 415 μg/kg (dry weight) in the sediments of the HZB and OBA, respectively. The pollution level of PAHs in the HZB seawater was higher than that in the OBA seawater, but the opposite result was found in the sediments. Moreover, ∑PAHs exhibited high temporal variability in the HZB seawater (rainy season > dry season), whereas ∑PAHs in the sediments showed no significant difference between seasons. The molecular diagnostic ratio method was used to identify pollution sources and showed that the PAHs in seawater came from different pollution sources (fuel combustion and petroleum), whereas the PAHs in the sediments originated from coincident sources (mixed combustion). Correlation analysis revealed that temperature was positively related to ∑PAHs, whereas salinity was negatively related to seawater ∑PAHs values. Ecological risk assessment demonstrated that the potential for adverse ecological effects was low to moderate in seawater but moderate to high in the sediments. [ABSTRACT FROM AUTHOR]

The Geostationary Ocean Color Imager (GOCI) provided images at hourly intervals up to 8 times per day with a spatial resolution of 500 m from 2011 to 2021. However, in the typical sediment-laden turbid water of Hangzhou Bay, valid ocean color parameters in operational data products have been extensively missing due to failures in atmospheric correction (AC) and bio-optical retrieval procedures. In this study, the seasonal variations in chlorophyll a (Chl-a) concentrations in Hangzhou Bay derived using GOCI data in 2020 were presented. First, valid remote sensing reflectance data were obtained by transferring neighboring aerosol properties of less to more turbid water pixels. Then, we improved a regionally empirical Chl-a retrieval algorithm in extremely turbid waters using GOCI-derived surface reflectance and field Chl-a measurements and proposed a combined Chl-a retrieval scheme for both moderately and extremely turbid water in Hangzhou Bay. Finally, the seasonal variation in Chl-a was obtained by the GOCI, which was better than operational products and in good agreement with the buoy data. The method in this study can be effectively applied to the inversion of Chl-a concentration in Hangzhou Bay and adjacent sea areas. We also presented its seasonal variations, offering insight into the spatial and seasonal variation of Chl-a in Hangzhou Bay using the GOCI. [ABSTRACT FROM AUTHOR]

The continuous monitoring of the dynamic changes in coastlines is crucial to ascertaining the change patterns and evolution characteristics of coastlines. Long - time - series coastline datasets allow for the detailed description of the dynamic changes in coastlines from the spatio - temporal dimensions and further reflect the effects of human activities and natural factors on coastal areas. Therefore, they are conducive to the scientific management and sustainable development of the spatial resources in coastal wetlands. Based on the Google Earth Engine (GEE), this study analyzed the change in the coastline of Hangzhou Bay during 1990-2019 based on long - time-series Landsat TM/ETM +/OLI images. Using the pixel - level modified normalized difference water index (MNDWI) time series reconstruction technology, this study achieved the automatic information extraction of long-time - series coastlines and the analysis of spatio - temporal changes by combining the Otsu algorithm threshold segmentation and the Digital Shoreline Analysis System. The results show that the total coastline length of Hangzhou Bay increased by about 20.69 km during 1990-2019, corresponding to an increase in the land area by about 764.81 km, with an average annual increase rate of 0.35%. In addition, the average end point rate (EPR) and linear regression rate (LRR) of the coastline were 110.07 m/a and 119.06 m/a, respectively. The analysis of the spatio - temporal evolution of the coastline in Hangzhou Bay over 30 years will provide a basis for the sustainable development and comprehensive management of resources along the coastline in Hangzhou Bay. [ABSTRACT FROM AUTHOR]

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Hangzhou Bay is a world-famous strong tidal estuary with an irregular coastline, unique topography, numerous human activities, and complex hydro-sedimentological environment. The Daishan-Yangshan Sea-Crossing Transport Corridor (DSTC) project is located at the mouth of Hangzhou Bay, which is composed of multiple sea-crossing bridges, an underground tube tunnel, and several man-made islands. The large-scale engineering of DSTC fully connects the cities of Shanghai, Yangshan, Daishan, Zhoushan, and Ningbo. This article discusses the morphodynamic responses due to the construction of the DSTC based on a state-of-art numerical model system from the perspective of its impacts on the hydro-sedimentological environment of Hangzhou Bay, as well as on adjacent projects. This study proved that the variation range of tide level in Hangzhou Bay is mostly within 2 cm after the implementation of the DSTC, while that of the man-made island and piers is only within 6 cm. The tidal prism decrease percentage of Hangzhou Bay is less than 0.5%. It does not significantly change the current field and underwater topography in Hangzhou Bay, except near the man-made islands and the bridge. The effect of the DSTC on surrounding ports and channels is small and limited. That is, the proposed DSTC engineering is feasible from the perspective of morphodynamic responses. The conclusions provide a useful reference for similar large-scale estuary construction projects. [ABSTRACT FROM AUTHOR]

Locust plagues and tidal disasters are primary natural hazards in China’s eastern coastal regions, yet their interrelationship remains unclear. This study, drawing on historical documents from the Ming and Qing dynasties (1368–1911 AD), focuses on Zhejiang Province and its Hangzhou Bay coastline, areas typically affected by tidal disasters. Employing advanced quantitative analysis and spatiotemporal models, the research aims to reveal the mechanisms behind tidal disasters and their impact on locust population dynamics. The findings indicate a limited spatiotemporal correlation between locust plagues and tidal or drought disasters but a significant association with flooding. The relationship between locust infestations and floods is notably strong in the unique geographical context of Hangzhou Bay’s northern shore. The ‘hydromarginal’ nature of the north coast creates an ideal habitat for locusts. This study pioneers in identifying flooding as a crucial mediator between tidal disasters and locust plagues, shedding light on the ‘typhoon-tidal-flood-locust’ disaster sequence and offering new insights into understanding and mitigating natural disasters in the region. In this study, we primarily employ a quantitative methodology, utilizing advanced data analysis and sophisticated spatiotemporal modeling to investigate the interplay between locust plagues and tidal disasters. Although some progress has been made in the study of historical natural disasters, systematic studies of the relationship between tidal floods and locust breeding sites along the east coast of China during the Ming and Qing dynasties are still scarce. This study fills this gap by employing advanced GIS and time series analysis techniques, combining traditional historical documentary studies with modern scientific methods and providing a new methodological approach to the analysis of historical disaster patterns.

Nowadays estuarine deltas are threatened by factors such as insufficient terrigenous sediment supply and rising sea levels. The Changjiang Estuary is adjacent to Hangzhou Bay, characterized by high turbidity waters, and the suspended sediment exchange between the two will inevitably affect the erosion and deposition of subaqueous delta in the future. Based on in situ observation data and numerical model, we found that suspended sediment is transported from the Changjiang Estuary into Hangzhou Bay during spring tides, while from Hangzhou Bay into the Changjiang Estuary during neap tides. The key driving mechanisms for the difference during spring-neap tides were expounded by momentum analysis and numerical sensitivity experiments. The barotropic pressure gradient force during spring tides is the key force that drives the suspended sediment from the Changjiang Estuary into Hangzhou Bay. Conversely, the baroclinic pressure gradient force during neap tides is the key force that drives the suspended sediment from Hangzhou Bay into the Changjiang Estuary. This study can provide valuable scientific evidence for erosion and deposition in estuaries and adjacent seas, as well as the sustainable utilization of regional coastal sediment resources. • Suspended sediment is transported from the Changjiang Estuary into Hangzhou Bay during spring tides, while the opposite occurs during neap tides. • During spring tides, the suspended sediment from the Changjiang Estuary into Hangzhou Bay is driven by the barotropic pressure gradient force. • During neap tides, the suspended sediment from Hangzhou Bay into the Changjiang Estuary is driven by the baroclinic pressure gradient force. [ABSTRACT FROM AUTHOR]

Coastal systems are continuously reshaped by rapid anthropogenic disturbance globally. However, the awareness of how coastal systems adapt to rapid anthropogenic disturbance remains inadequate. Thus, this study assessed the spatial response of coastal systems to rapid anthropogenic disturbances, and a typical coastal system (Hangzhou Bay) was selected for a case study. Three environmental indicators (i.e., coastline change rate, accretion/erosion grade, and the displacement of the center of gravity) were selected to measure the morphological changes in the coastal system between 1990 and 2020. The results showed that the coastal waters of Hangzhou Bay decreased by 432 km2, and the coastal morphology became structured driven by increasing artificial coastlines. Moreover, the accretion–erosion equilibrium of underwater elevation transitioned northwest, which derived the shift of geometric center of gravity toward the northwestern part of the coast. These fluctuating signals provided us with a macroscopic perception of coastal system changes, which is expected to provide local decision-makers with sites where coastal systems are adaption loss to assist coastal protection.

Coastal wetlands provide essential ecosystem services, while usually experiencing land transformation or degradation mainly due to intense anthropogenic activities and climate changes. Understanding the changes in wetlands ecosystem services is essential to decision makers for generating sound coastal planning. Hangzhou Bay is rich in wetland resources, and the urbanization of Hangzhou Bay in the past three decades has caused fundamental changes in the wetlands in the region. Based on the remote sensing images of the Hangzhou Bay area from 1990 to 2020, this paper analyzes the land use situation of the Hangzhou Bay area in seven periods. This paper calculates the area transfer matrix of various types of wetlands. It uses the InVEST model to evaluate the changes in the function of wetland ecosystem services in the Hangzhou Bay area. Hangzhou Bay wetlands show a trend of transferring natural wetlands to artificial and non-wetlands from 1990 to 2020. Carbon stocks fell by 14.24%. The annual water production decreased by 33.93% and then returned to the original level. The area of habitat degradation increased by 79.94%. The main influencing factors are paddy field degradation, increase in non-wetland area, and decrease in sea area. This paper proposes that the development and construction of farmland in the “red line” area and established wetland reserves are prohibited, and to strengthen the training of wetland management personnel, establish a sound decision-making consultation mechanism, and increase the scientific research expenditure on wetlands in the region. [ABSTRACT FROM AUTHOR]

The tidal asymmetry under the action of sea level rise in Hangzhou Bay. Coastlines dominated by the tide are not only directly affected by the rise of the mean sea level but also by the tidal dynamics. The computational domain of the hydrodynamic model covers the entire Hangzhou Bay and takes into account the feedback between the tidal motion and the erodible bottom. Its main application fields include: the simulation of different sea level rise (SLR) rates, the interaction between tidal duration and skewness and the interaction between tidal range and astronomical tide. The results on tidal asymmetry in Hangzhou Bay is a systematic process consisting of four aspects: Firstly, the tide increase, which is affected by the sea level rise, is between 25% and 50%. Secondly, the value of the sea level rise is about two times the added value of the tidal range, and the tidal range increased to the left side of the tidal wave propagation direction, which accelerated the propagation velocity. Thirdly, the sea level rise amplified the M2 tidal amplitude and delayed the M2 tidal phase in the inner bay, which reduced about 50%. Finally, the change of the tidal range caused by tide level had the same magnitude as the change caused by the mean sea level rise. The purpose of this study was to emphasize the importance of the predictions of the response area affected by tidal asymmetry based on the action of the sea level rise in Hangzhou Bay. [ABSTRACT FROM AUTHOR]

Hangzhou Bay, one of the fastest economy and population growth region in China, was heavily polluted by a large amounts of industrial waste water and domestic sewage containing harmful heavy metal pollutants. To investigate the status of heavy metals pollution and assess the ecological risks in Hangzhou Bay, seven heavy metals (Cu, Zn, Pb, Cd, Cr, Hg and As) concentrations of water and sediments were analyzed. Heavy metals concentrations in sediments close to the estuarine coast and nearshore area were higher than that in other areas. Cu, Zn, Pb, Cd, Cr and As in sediments might have extensive homologies and originate from the petroleum industry. The pollutions of Cu, Zn, Pb, Cd, Cr and As in seawater and sediment were very light or no pollution. Both in seawater and sediments, the Hg contamination was the most serious among the measured seven heavy metals and should be paid more attention., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Water quality in Hangzhou Bay is inferior (grade 5) because of discharged from Yangtze River and Qiantang River, and from factories around the bay. This study analyzed relationships between the environment and macrobenthic communities at 44 stations throughout Hangzhou Bay, based on samples collected in 2006, from 2016–2018, and in 2021. Long-term spatial and temporal changed in macrobenthos, and the influence of secondary water fronts on community composition, were discussed. Macrobenthos in Qiantang River Estuary was numerically, primarily dominated by crustaceans, and elsewhere by polychaetes. Species that differ most in abundance between four identified regions in the bay were the amphipod Corophium sinensis, clam Potamocorbula laevis, and polychaete Amaeana occidentalis. The abundance and biomass of macrobenthos in different regions differs significantly. Taxa were allocated to six feeding guilds: filter feeders and omnivores predominate in Qiantang River Estuary and south of Hangzhou Bay, while surface and subsurface deposit feeders predominate in sediments north of Hangzhou Bay and in the bay mouth area. Negative correlations were apparent between the abundances of polychaetes Nephtys polybranchia, Magelona japonica, Heterospio sinica, Sabella sp. and A. occidentalis and salinity and pH, while positive correlations were apparent between those of Sternaspis chinensis and Capitellidae indet. Fine-grained fraction (silt and clay) and mid-salinity were more suitable for macrobenthos. The numbers and biomasses of macrobenthic species in the Hangzhou Bay frontal area increased significantly relative to values in adjacent areas. The difference of each area near the front was more than 94%, and the main difference species were polychaetes and mollusks. Our baseline data for this region might ultimately contribute towards improved conservation of regional macrobenthos, and a better understanding of ecosystem health in this highly polluted bay.

Hangzhou Bay is a large, high-turbidity shallow bay located on the southern side of the Changjiang Estuary, China. The process and dynamic mechanisms of water and sediment transport in the bay are not yet clear. An improved three-dimensional sediment numerical model that combined various dynamic factors was established to simulate and analyze these mechanisms. The residual current cannot properly represent the net water and sediment transport, and the residual unit width water flux (RUWF) and residual unit width sediment flux (RUSF) were used to explain the water and sediment transport. The results of numerical simulations indicate that in summer, the surface RUWF from the Changjiang Estuary near Nanhui Cape flows westward along the coast, in which the major part flows southward to the Zhenhai area, and the small part flows further westward along the north coast and then turns to the south coast and eastward, forming the water transport pattern of north-landward and south-seaward, which is stronger in the spring tide than in the neap tide. The bottom RUWF near Zhenhai flows northward to Nanhui Cape in the neap tide, which is larger in the neap tide than in the spring tide. In the middle and western parts of the bay, the RUWF has the same pattern as the surface water transport and is stronger in the spring tide than in the neap tide. The pattern of RUSF is roughly similar to the water flux transport. During the spring tide, the water and sediment transport fluxes near Nanhui Cape are from the Changjiang Estuary into Hangzhou Bay, but from Hangzhou Bay into the Changjiang Estuary during the neap tide. In the winter, the distributions of RUWF, RUSF, and suspended sediment concentration (SSC) are similar to those in the summer. In addition, the distance of surface water transport westward along the north coast is shorter than that in the summer, the magnitude of the bottom RUWF is smaller than that in the summer due to the weaker salinity gradient, and the bottom RUSF near Nanhui Cape is weaker than that in the summer during the neap tide. The net transect water flux (NTWF) and the net transect sediment flux (NTSF) near Nanhui Cape are from the Changjiang Estuary into Hangzhou Bay during the spring tide; during the neap tide, the NTWF is still from the Changjiang Estuary into Hangzhou Bay, but the NTSF is from Hangzhou Bay into the Changjiang Estuary because the SSC is much higher in the bottom layer than in the surface layer. The dynamic reason for the temporal and spatial variation in RUWF and RUSF is that the barotropic pressure gradient force is larger than the baroclinic pressure gradient force during the spring tide and is the opposite during the neap tide. [ABSTRACT FROM AUTHOR]

Sea level rise (SLR) due to climate change is expected to alter tidal processes and energy transport, disproportionately affecting coastal communities. Utilizing a nested hydrodynamics model, we provided an integrated investigation of tidal responses to SLR in the Hangzhou Bay (HZB). The scenarios of SLR in the next hundred years count for both non-uniform trends based on historical altimetry data and uniform trends from the latest IPCC projections. In a comparison of model results under different SLR scenarios, we found that the tidal range is amplified by SLR in HZB with stronger amplification at the shallow southern coast. Tidal range change generally increases with the SLR scale; however, neglecting the heterogeneities in the spatial distribution of SLR tends to overestimate the SLR effects. The harmonic analysis illustrates that SLR exaggerates the dominated semidiurnal tides (M2 and S2) but dampens their overtides and compound tides (M4, M6, and MS4), of which M2 amplitude amplification explains 71.2–90.0% of tidal range change. SLR tends to promote tidal energy entering HZB through the Zhoushan Archipelago (ZA) compared to the prototype, while dampened sea-bed roughness and reduced tidal velocity come with a less dissipative environment in HZB, resulting in 6–18% more tidal energy exported upstream. Numerical experiments indicate ZA has significant effects on tidal responses and energy flux generation, therefore, its quantitative influences and physical mechanism are also discussed in this paper. [ABSTRACT FROM AUTHOR]

The suspended sediment in water infers water quality, and directly reflects optical properties such as water transparency, turbidity, and water color. Thus, these physical properties provide a viable basis to rigorously retrieve for suspended sediment concentration (SSC) using satellite remote sensing water color measurements in estuaries. The contemporary Ocean and Land Color Instrument (OLCI) on Sentinel-3A, provides more waveband options for remote sensing of water color and an opportunity for retrieval of suspended sediment in estuarine coast. Yet, accurate retrieval of SSC in high turbid waters from OLCI is still challenging due primarily to the high uncertainty of atmospheric correction. Here, we use OLCI images to measure water quality in Hangzhou Bay, and construct a retrieval model of SSC, and cross-validated using Geostationary Ocean Color Imager (GOCI) data. The study shows that: (1) the atmospheric correction algorithm based on ultraviolet wavelengths (UV-AC) can achieve better results for both OLCI and GOCI data, and the overall correction accuracy for OLCI is higher than that for GOCI data; (2) the multi-band index model constructed by using Rrs(Oa16)/Rrs(Oa5) of OLCI data has higher retrieval accuracy and model stability, with R2 is 0.96, MRE is 17.52%, and RMSE is 69.10 mg/L; (3) the spatial distribution of SSC in the study area is complex, mainly showing that the SCC in the top of the bay is larger than the mouth of the bay, and the south shore is larger than the north shore; (4) whe distribution of SSC obtained from retrieving OLCI and GOCI data in general is consistent, with the OLCI SSC estimates with higher accuracy than GOCI data, and the numerical difference between the two retrieval results is more obvious in the ocean with high SSC; and (5) with appropriate atmospheric corrections and retrieval models, OLCI data can be used to estimate improved SSC observables in Hangzhou Bay. We conclude that the SSC retrieval models proposed here provide a good reference method for retrieval of water color observable in Hangzhou Bay coastal estuary.

The hydrodynamics and sediment characteristics of muddy estuaries and coasts during typhoons are closely related to the geomorphic evolution, ecological environment, and economic development of coastal zones. Taking the macro-tidal turbid Hangzhou Bay (HZB) as an example, the sediment characteristics and effects of wave-current interactions on sediment dynamics during Typhoon Mitag were studied using a fully-calibrated numerical model. The model considered tide-wave sediment interactions and the reconstructed typhoon wind field. Net sediment fluxes were controlled by residual currents and suspended sediment concentration (SSC). The combined interactions of currents and waves led to a high SSC during the typhoon. Under calm weather conditions, the impact of wave-current interactions (wave dissipation, form drag, wave radiation stress, mean current advection and refraction) was small, except for the combined bottom stresses. The combined bottom stress was the primary wave-current interaction that changed sediment resuspension and increased SSC, particularly in shallow waters or during storms. The advection term, which played an essential role in reducing SSC in HZB, mainly affected SSC by increasing the velocity. The wave dissipation term enhanced vertical mixing, which involved the vertical exchange of suspended sediment and currents. In the shallow waters of the southern bay, the wave dissipation term mostly led to decreased bottom stresses, increased currents, decreased SSC, and increased SSC in deep waters. The effects of form drag, wave radiation stress, and refraction terms on the suspended sediment dynamics were relatively small. These findings provide a theoretical foundation for the study of dynamic geomorphology in macro-tidal estuaries.

The Geostationary Ocean Color Imager (GOCI) provided images at hourly intervals up to 8 times per day with a spatial resolution of 500 m from 2011 to 2021. However, in the typical sediment-laden turbid water of Hangzhou Bay, valid ocean color parameters in operational data products have been extensively missing due to failures in atmospheric correction (AC) and bio-optical retrieval procedures. In this study, the seasonal variations in chlorophyll a (Chl-a) concentrations in Hangzhou Bay derived using GOCI data in 2020 were presented. First, valid remote sensing reflectance data were obtained by transferring neighboring aerosol properties of less to more turbid water pixels. Then, we improved a regionally empirical Chl-a retrieval algorithm in extremely turbid waters using GOCI-derived surface reflectance and field Chl-a measurements and proposed a combined Chl-a retrieval scheme for both moderately and extremely turbid water in Hangzhou Bay. Finally, the seasonal variation in Chl-a was obtained by the GOCI, which was better than operational products and in good agreement with the buoy data. The method in this study can be effectively applied to the inversion of Chl-a concentration in Hangzhou Bay and adjacent sea areas. We also presented its seasonal variations, offering insight into the spatial and seasonal variation of Chl-a in Hangzhou Bay using the GOCI.

The Hangzhou Bay (HZB) is an important part of the Zhoushan fishing ground, the most productive region in the Eastern China Seas. Although HZB remains eutrophication all year round, its chlorophyll a (Chl) and primary productivity (PP) are usually significantly lower than those in the adjacent waters. In the present study, we presented the Chl and PP distributions in the HZB and analyzed their correlations with environmental factors in four seasons. The field observation showed that Chl and PP had significant seasonal variations, and was highest in the summer (1.66 ± 0.61 mg·m−3 and 12.11 ± 12.25 mg C·m−3·h−1, respectively). Total suspended matters (TSM) concentration was the key environmental factor that constrains PP in the study area. High concentration of TSM reduced light exposure (LE, the annual mean value was 0.92 ± 0.81 Einstein·m−2·day−1) in the mixed layer of the HZB, which was much lower than the saturated light intensity of phytoplankton growth, and thus caused a strong light limitation in the HZB. However, the seasonal variations in the photosynthesis rates (PB) and Chl did not coincide. This fact suggested that the growth rate was not the only factor controlling seasonal variations of phytoplankton biomass. In winter, the very high TSM and strong mixing might reduce the zooplankton grazing rate, and lead to a relatively high concentration of Chl during the very low LE and PB period. These results implied that, in the HZB, the extremely turbid water could affect both phytoplankton growth and loss, which was probably the major mechanism responsible for the complex phytoplankton spatial and temporal variations. [ABSTRACT FROM AUTHOR]

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Waves characteristics of the developing windfarm in the semi-enclosed Hangzhou Bay are distinctive due to the East Asian monsoon and frequent typhoons. In this paper, statistical analysis is performed to study the wave parameters in central Hangzhou Bay using 3-year-long wave datasets and the companion wind data. The monsoonal pattern has a significant impact on both annual and seasonal distribution of wave parameters. Compared with mild southeasterlies in summer, the NW-NE winds prevailing in winter tend to produce more extreme waves with large height and spectral energy, and especially in the south of the bay due to the extended fetch. Most waves are generated by local winds and have single-peak spectra. During extreme weather, most large waves had a peak frequency of around 0.2 Hz, i.e., the characteristic frequency. The wave generation processes observed during different extreme events had similar growth-decay tendencies and wave magnitudes. The occurrence probability of significant wave height and mean period can be well represented by both the Weibull and the Rayleigh distribution, and large waves ( H 1 / 3 > 1.0 m, T mean > 4 s) occur rarely (2.38% of the time). The correlations between key wave parameters are also examined. In general, this study highlights the typical wind wave patterns and provides practical guidance for future offshore development. [ABSTRACT FROM AUTHOR]

The tidal asymmetry under the action of sea level rise in Hangzhou Bay. Coastlines dominated by the tide are not only directly affected by the rise of the mean sea level but also by the tidal dynamics. The computational domain of the hydrodynamic model covers the entire Hangzhou Bay and takes into account the feedback between the tidal motion and the erodible bottom. Its main application fields include: the simulation of different sea level rise (SLR) rates, the interaction between tidal duration and skewness and the interaction between tidal range and astronomical tide. The results on tidal asymmetry in Hangzhou Bay is a systematic process consisting of four aspects: Firstly, the tide increase, which is affected by the sea level rise, is between 25% and 50%. Secondly, the value of the sea level rise is about two times the added value of the tidal range, and the tidal range increased to the left side of the tidal wave propagation direction, which accelerated the propagation velocity. Thirdly, the sea level rise amplified the M2 tidal amplitude and delayed the M2 tidal phase in the inner bay, which reduced about 50%. Finally, the change of the tidal range caused by tide level had the same magnitude as the change caused by the mean sea level rise. The purpose of this study was to emphasize the importance of the predictions of the response area affected by tidal asymmetry based on the action of the sea level rise in Hangzhou Bay.

Ji, Y. and Yin, Y., 2021. Water quality maintenance approaches and on-site monitoring results of an artificial bathing beach. Journal of Coastal Research, 37(4), 793–799. Coconut Creek (Florida), ISSN 0749-0208. The construction of artificial beaches on the muddy coasts involves water purification and long-term maintenance. In the paper, based on the investigation of tidal current, sediment distribution, water quality, and background creatures, a technical scheme of "building submerged breakwater enclosure and accelerating sediment deposition" to form a transparent water body and a long-term water quality maintenance scheme of "diversion, drainage, and self-purification of ecology" are proposed. Through sand precipitation test, water exchange feasibility, and facility scale demonstration, biological purification measures research and on-site practice, as well as long-term water quality monitoring and analysis, the conclusions are as follows: (1) The construction of submerged breakwater for water enclosure promotes the sediment deposition process. The experiment results indicate that after two-day static settlement, 93% of the suspension is precipitated and the concentration of total phosphorus decreased by more than 70%. (2) Water from artificial beaches can be diverted by harnessing tide or pumping facilities. The scale of the pump station and sluice should be determined according to the filling or drainage capability of water in a tidal cycle. (3) The ecological self-purification should be established on the basis of background investigation. The aquatic animals, such as fish, shrimp, crab, shell, and algae m (4) The water quality tends to deteriorate and changes with seasons with the increase of tourists. Finally, it is suggested renovating the current water diversion system, enhancing the monitoring of ecosystem, limiting the number of tourists in summer and increasing the frequency of water exchange. [ABSTRACT FROM AUTHOR]

Coastal estuaries are often heavily subject to riverine influences by the inputs of sediment from terrestrial sources. Hangzhou Bay (HZB) is threatened by the riverine derived trace metals from two large rivers of Qiantang River (QTR) and Yangtze River (YZR). However, previous studies mainly focused on the incidental transport from the largest river in China (YZR) and failed to simultaneously evaluate the contributions of these two rivers, especially the directly flowing river of QTR, by their trace elemental geochemical composition and distribution. Herein, a comprehensive study identified the river-derived sources of multiple trace metals in surface sediments which transported from both of the rivers. The sampling stations were separated into three regions of YZR, HZB, and QTR based on their spatial distributions of sediment grain size and components. The significant variations for most of the trace metals concentrations, except for Cd, Th, and U, were found among three regions (χ 2 ≥ 8.22, p ≤ 0.016). The highest concentrations in HZB were mainly resulted from the grain size effect (68.82% of the total variance), while the highest concentrations of Sr, Cd, and Ba in YZR and Zr and Hf in QTR were attributed to the anthropogenic source (11.90%) and mineral composition (6.21%) of river basins. After normalized the diversity of multiple trace metals concentrations and the influence of grain size by ratios of I geo and EF Li , three regions were effectively distinguished. It was indicated that As, Cd, and Sb were enriched in the sediments of rivers by anthropogenic source (EF Li > 1.5 and/or I geo > 1). The results evidenced that, after removing the influence of grain size, elemental geochemical composition of the surface sediments confidently identified the river-derived anthropogenic sources of the enriched trace metals from two major rivers, and largely from YZR. [Display omitted] • Regions of YZR, QTR, and HZB were separated by sediment grain size and components. • Most trace metals varied significantly in the surface sediments of three regions. • More enrichment of trace metals were found in two rivers after normalized by EF Li. • Anthropogenic trace metals in sediment of HZB were identified as riverine sources. • YZR was regarded as the main river-derived sources of trace metals in HZB. [ABSTRACT FROM AUTHOR]

Hangzhou Bay is a large, high-turbidity shallow bay located on the southern side of the Changjiang Estuary, China. The process and dynamic mechanisms of water and sediment transport in the bay are not yet clear. An improved three-dimensional sediment numerical model that combined various dynamic factors was established to simulate and analyze these mechanisms. The residual current cannot properly represent the net water and sediment transport, and the residual unit width water flux (RUWF) and residual unit width sediment flux (RUSF) were used to explain the water and sediment transport. The results of numerical simulations indicate that in summer, the surface RUWF from the Changjiang Estuary near Nanhui Cape flows westward along the coast, in which the major part flows southward to the Zhenhai area, and the small part flows further westward along the north coast and then turns to the south coast and eastward, forming the water transport pattern of north-landward and south-seaward, which is stronger in the spring tide than in the neap tide. The bottom RUWF near Zhenhai flows northward to Nanhui Cape in the neap tide, which is larger in the neap tide than in the spring tide. In the middle and western parts of the bay, the RUWF has the same pattern as the surface water transport and is stronger in the spring tide than in the neap tide. The pattern of RUSF is roughly similar to the water flux transport. During the spring tide, the water and sediment transport fluxes near Nanhui Cape are from the Changjiang Estuary into Hangzhou Bay, but from Hangzhou Bay into the Changjiang Estuary during the neap tide. In the winter, the distributions of RUWF, RUSF, and suspended sediment concentration (SSC) are similar to those in the summer. In addition, the distance of surface water transport westward along the north coast is shorter than that in the summer, the magnitude of the bottom RUWF is smaller than that in the summer due to the weaker salinity gradient, and the bottom RUSF near Nanhui Cape is weaker than that in the summer during the neap tide. The net transect water flux (NTWF) and the net transect sediment flux (NTSF) near Nanhui Cape are from the Changjiang Estuary into Hangzhou Bay during the spring tide; during the neap tide, the NTWF is still from the Changjiang Estuary into Hangzhou Bay, but the NTSF is from Hangzhou Bay into the Changjiang Estuary because the SSC is much higher in the bottom layer than in the surface layer. The dynamic reason for the temporal and spatial variation in RUWF and RUSF is that the barotropic pressure gradient force is larger than the baroclinic pressure gradient force during the spring tide and is the opposite during the neap tide.

Sea level rise (SLR) due to climate change is expected to alter tidal processes and energy transport, disproportionately affecting coastal communities. Utilizing a nested hydrodynamics model, we provided an integrated investigation of tidal responses to SLR in the Hangzhou Bay (HZB). The scenarios of SLR in the next hundred years count for both non-uniform trends based on historical altimetry data and uniform trends from the latest IPCC projections. In a comparison of model results under different SLR scenarios, we found that the tidal range is amplified by SLR in HZB with stronger amplification at the shallow southern coast. Tidal range change generally increases with the SLR scale; however, neglecting the heterogeneities in the spatial distribution of SLR tends to overestimate the SLR effects. The harmonic analysis illustrates that SLR exaggerates the dominated semidiurnal tides (M2 and S2) but dampens their overtides and compound tides (M4, M6, and MS4), of which M2 amplitude amplification explains 71.2–90.0% of tidal range change. SLR tends to promote tidal energy entering HZB through the Zhoushan Archipelago (ZA) compared to the prototype, while dampened sea-bed roughness and reduced tidal velocity come with a less dissipative environment in HZB, resulting in 6–18% more tidal energy exported upstream. Numerical experiments indicate ZA has significant effects on tidal responses and energy flux generation, therefore, its quantitative influences and physical mechanism are also discussed in this paper.

The interaction of various environmental triggers on phytoplankton communities of an artificial lagoon of Hangzhou Bay China, was studied during a Microcystis bloom in summer 2016. Forty-two phytoplankton genera (six phyla) were defined, with Bacillariophyta accounting for half of all phytoplankton genera. It was determined that Melosira, Chlorella, Cyclotella, Microcystis, Merismopedia, Anabaena and Selenastrum, which were identified and counted by an inverted microscope, were the dominant genera. In addition, a series of environmental indicators were analyzed, including salinity, seawater temperature, dissolved inorganic nitrogen, soluble reactive phosphorus (PO4-P), ammonium (NH4-N), nitrate nitrogen (NO3-N), nitrite (NO2-N), silicate (SiO4-Si), and chemical oxygen demand of the water samples, as well as zooplankton community. The results of variance partitioning by R language revealed that the most influential factor driving the change in the phytoplankton community was the environment (49.7%), and zooplankton grazing represented only 7.9%. The results of redundancy analysis indicated that the change and composition of the phytoplankton community correlated significantly with the interaction of salinity, PO4-P, transparency, seawater temperature, and the dominant zooplankton species. Notably, salinity and temperature fluctuation were the key factors inducing the rapid succession of the plankton community in artificial lagoons such as within the Jinshan City Beach (Shanghai, China). [ABSTRACT FROM AUTHOR]

It is an important development plan of national tourism construction in the new era to develop rural tourism towns with regional characteristics and special ethnic features and to construct a group of famous tourism towns and villages with distinctive landscape. This study took the Greater Bay Area around Hangzhou Bay as the research area and adopted the evaluation method of tourist's perceived value to study and analyze the construction and development status of seven representative rural tourist attractions in the Greater Bay Area around Hangzhou Bay from the perspectives of ecological environment, social environment, cultural environment and tourism products and services. The result of the research showed that at the present stage, the main problems of rural tourism scenic spots in the Greater Bay Area around Hangzhou Bay included poor humanistic environment, insufficient cultural heritage of rural tourism, serious homogenization of scenic spot tourism projects and products, single tourist structure, low professional quality of scenic spot practitioners, poor service attitude, etc. In view of the existing problems, this study put forward corresponding optimization strategies from three aspects: cultural and social environment, market expansion and operation, scenic spot products and tourism services. [ABSTRACT FROM AUTHOR]

Soil bacterial successional trajectories under frequently disturbed circumstances (such as agricultural practice) are less known due to the complexity and uncertainty of disturbance. Here, a reclaimed coastal soil chronosequence spanning over a millennium was studied to understand the variation in soil microorganisms. We used 16S rRNA gene-based quantitative PCR to determine bacterial number and Illumina Sequencing to analyse bacterial community composition and diversity. Despite 10-fold higher 16S rRNA gene copy number, coastal sediments showed the lowest bacterial phylogenetic diversity, demonstrating that bacteria acclimatised in the destination environment with low nutrient and high salinity. Among the reclaimed soil, regular variation in microbial distribution (abundance and diversity) and the “disturbance climax” theory can explain the dynamics of bacterial succession. Consistent with soil physicochemical variables, bacterial community varied in an orderly way and changed more drastically at initial stage (early 60 years) but only slightly fluctuated thereafter. The soil variables soil organic matter (SOM), total nitrogen (TN), and electrical conductivity (EC) were confirmed to be the main factors affecting bacterial succession, among which SOM played a dominant role in initial and long-term reclamation stage (500 ~ 1000 years), while TN was more important in mid-term reclamation (5 ~ 280 years).

The tidal flat evolution law is an important basis for protecting and developing tidal flat resources. The complex flow-sediment conditions and high intensity of human activities in Hangzhou Bay have led to complex tidal flat evolution mechanisms. The tidal flat evolution law and its mechanism on the south bank of Hangzhou Bay under the influence of flow-sediment variation and human activities in the past 60 years were analyzed based on the hydrographic and bathymetrical monitoring data of Hangzhou Bay in the period of 1959—2019,combined with the process of deposit-promoting and reclamation. The results show that the tidal flat on the south bank of Hangzhou Bay has been deposited since 1959,with a deposition rate of approximately 6.70 cm/a during 1959—2003,and increased to 12.59 cm/a during 2003—2019. Large-scale reclamation projects and the increased tidal range are the main reasons for the increase in the slope gradient of the tidal flat profile. The periodic evolution of the plane morphology of the Andong tidal flat is related to the cycle of high and low runoff, showing the increased/decreased curvature in wet/dry years. The reduction of incoming sediment from the Yangtze River has not significantly affected the deposition of the tidal flat on the south bank of Hangzhou Bay. The reclamation project is the main reason for the increased deposition rate and decreased tidal flat width of the south bank of Hangzhou Bay. [ABSTRACT FROM AUTHOR]

Coastal ecosystem is vulnerable to heavy metal contamination. The northern Hangzhou Bay is under intensifying impact of anthropogenic activities. To reveal the heavy metal pollution status in the coastal environment of the Hangzhou Bay, a long-term investigation into the heavy metal contamination during 2011 to 2016 was initiated. Seawater and sediment samples of 25 locations depending on the sewage outlet locations in the northern Hangzhou Bay were collected to analyze the concentrations and temporal and spatial distribution of Cu, Pb, Zn, Cd, Hg, and As. Pollution condition, ecological risk, and potential sources were additionally analyzed. Results show that the annual mean concentrations of Cu, Pb, Zn, Cd, Hg, and As were 2.13–4.59, 0.212–1.480, 7.81–20.34, 0.054–0.279, 0.026–0.090, and 1.08–2.57 μg/L in the seawater, and were 16.34–28.35, 16.25–26.33, 67.32–97.61, 0.084–0.185, 0.029–0.061, and 6.09–14.08 μg/L in the sediments. A decreasing trend in Cu, Pb, Zn, Cd, and Hg concentrations and an increasing trend in As of the seawater were observed. However, in the sediment, the heavy metals demonstrated a rising trend, except for Hg. The single-factor pollution index showed an increasing trend in Cd and As in the seawater, depicting an enhanced pollution of Cd and As, while in the sediments, Cu, Pb, and As were in pollution-free level (average Geo-accumulation index (Igeo) values below 0) in general, and only occasional slight pollution occurred in individual years, e.g., As with 0.403 in 2016. The mean Igeo values of Cd ranged from − 0.865 to 0.274 during 2011 to 2016, indicating that the pollution level of Cd was slight, but is likely to increase in the forthcoming years. The level of heavy metal contamination in sediments was low in 2011 (5.853) and 2012 (5.172), and moderate during 2013 to 2016 (in the range of 6.107 to 7.598), while the degree of potential ecological risk was low in the study period, except moderate in 2013 (125.107). The highest contamination degree and potential ecological risk appeared in 2013 (Cd = 7.598; RI = 125.107), while Cd and Hg contributed over 75% of the ecological risk. Overall, the results show low pollution level and low potential ecological risk in the northern Hangzhou Bay; however, more attention should be paid to the potential ecological risk due to Hg and Cd. [ABSTRACT FROM AUTHOR]