Heterosigma akashiwo is one of the species of harmful algal blooms (HABs) threatening marine ecosystems and the fishing industry across coastal waters worldwide. With increasing global levels of atmospheric CO2 and global warming, HABs have increased in prevalence, duration, and geographic span; this phenomenon has been further stressed by intensified anthropogenic influences, such as eutrophication. Through controlled experiments with different nutrients, CO2 concentrations, and temperatures, our study aimed to understand the response of H. akashiwo to different nutrients with changes in climate. In all simulated CO2 and temperature scenarios, both cell density and the specific growth rate of H. akashiwo in the low phosphorus groups were significantly lower than those in the high phosphorus groups. Furthermore, the maximum cell density and specific growth rate of H. akashiwo were significantly enhanced by increased CO2, while the specific growth rate was accelerated by the dual effect of increased CO2 levels and temperature. The growth response of H. akashiwo to CO2 and temperature was similar between different nutrient treatments. Taken together, the results indicate that phosphorus concentration could be the major factor controlling the growth of H. akashiwo, and the intensity and risk of H. akashiwo blooming in the future is increasing. Hence, controlling the increase of nutrients, particularly phosphate, could be a critical pathway to decrease the occurrence of H. akashiwo blooms. In summary, our case study provides scientific support for marine ecological management of HABs.
Yingwuzhou Wetland is an artificially restored coastal salt marsh wetland aimed at improving ecosystem services. Development of the wetland has restored the original damaged coastal ecosystem through comprehensive coastline ecological engineering measures. The birds in the study site have been investigated and researched using the route survey method since 2018, and changes in the bird population and species diversity have been analyzed to evaluate the effectiveness of coastal zone ecological restoration projects and the impact of different wetland habitat types on bird diversity. The results showed that 67 bird species were recorded in the wetland, belonging to 13 orders and 32 families, with the largest number of birds belonging to Passeriformes, including 42 species belonging to 18 families. There were 35 species of resident birds, 24 species of winter migratory birds, 10 species of summer migratory birds, and 8 species of migratory birds. Among these, one species of national class I and seven species of class II are in the List of Key Protected Wild Animals in China, respectively. Remiz consobrinus, Gallinula chloropus, Acridotheres cristatellus, Tachybaptus ruficollis, Spodiopsar cineraceus, Hirundo rustica, and Passer montanus were the dominant species. The number of wetland bird species increased annually. There were significant differences in the bird species, quantity, and Shannon–Wiener indexes among different seasons. The declining trends of bird species, quantity, and Shannon–Wiener index were in the orders of fall > winter > spring > summer, fall > winter > summer > spring, and fall > spring > winter > summer, respectively. The bird numbers and species were the highest in the natural wetland complex area. Declining trends of the Shannon–Wiener index in different habitat areas were observed for the natural wetland complex area, salt marsh wetland restoration area, clear water conservation area, lawn activity area, and wetland purification exhibition area. The ecological restoration of the coastline has enriched the bird diversity of the wetland. Habitats with rich patch types and high patch mosaic have a markedly positive impact on bird diversity. The results of this study can provide a scientific basis for the coastal ecological restoration and sustainable development of coastline wetlands.
To understand the metabolic potential and environmental adaptation mechanisms of Nitrospira in tidal flat wetlands, 14 high-quality Nitrospira genomes were constructed from five tidal flat wetlands along the coast of China using metagenomic binning and assembly methods. Phylogenetic analysis showed that among these genomes, three belonged to Comammox (complete ammonia oxidizer), nine belonged to lineage II and IV of Nitrospira, and two belonged to lineage III, which has yet to be discovered; taken together, this data suggests that abundant and diverse Nitrospira are present in China’s tidal flat wetlands. Metabolic reconstruction revealed that these Comammox and Nitrospira contained cyanase, urease, and other enzymes involved in the degradation of nitrile compounds and amide compounds; hence, they may utilize the organic nitrogen as energy by coupling with ammonia-oxidizing microorganisms. In addition, Nitrospira possessed flexible strategies to resist environmental stresses such as viral attack and osmotic changes. These results provide insights on the diversity, ecological function, and environmental adaptation mechanisms of Nitrospira from tidal wetlands.
Under the dual influence of human activities and natural factors, the coastal zone patterns are prone to rapid changes which can directly or indirectly affect the structure, function, and sustainable development of the coastal ecosystem. Using the coastal zone of Nanhui Dongtan in Shanghai as a typical research area, we used remote sensing interpretation, sea chart digitization, and field investigation to analyze changes in spatial patterns and changes in coastal zones over the last 20 years (from 2000 to 2020). In addition, the effects of coastal engineering (including reclamation engineering and siltation promotion engineering) and S. alterniflora invasion on coastal pattern dynamics were analyzed. The results showed that: ① Since 2000, under the influence of coastal engineering and biological invasion, the land use types of Nanhui Dongtan coastal zone changed from a simple pattern dominated by coastal wetlands to a complex pattern which included multiple land use types (i.e. coastal wetlands, inland wetlands, constructed wetlands, farmland, and construction land). ② Coastal reclamation engineering decreased 11894.7 hm2 of coastal wetlands in the Nanhui Dongtan coastal zone from 2000 to 2005. The reclaimed coastal wetlands were transferred into land use types such as rice fields, ponds, and farmland due to human activities; the reclamation engineering promoted deposition of sediment in the estuary and tidal mudflat (above 0 m) and the intertidal salt marsh developed with increased rates of 320.5 hm2/a and 110.9 hm2/a, respectively; meanwhile, the siltation rate decreased to 286.8 hm2/a and 15.7 hm2/a, respectively, after 2015. After 10 years (2005—2015) of natural recovery, the area of coastal wetlands did not reach the levels seen before reclamation in Year 2000. ③ Two types of siltation promotion engineering—hard siltation promotion engineering and biological siltation promotion engineering—have both significantly promoted the rapid development of coastal wetlands in Nanhui Dongtan. Hard silting promotion engineering with propagation rates of 516.9 hm2/a in tidal mudflats (above 0 m) and 915.7 hm2/a in intertidal salt marshes, respectively, was 5.4 times and 13.9 times higher than rates observed in non-siltation areas; hence, the effects were more significant than biological siltation promotion engineering which only resulted in pattern changes in a limited area between the seawall and the wave dissipation dike by planting S. alterniflora. ④ After introducing S. alterniflora in Nanhui Dongtan, it became the most dominant plant in the Nanhui Dongtan salt marsh, accounting for 56% of the total area; this significantly changed the ecological structure and function of coastal wetlands in 2020. Coastal engineering and biological invasion have a great impact on coastal zone patterns. Although the coastal ecosystem showed a certain resilience to coastal human activities, changes in the wetland type, area, and function were difficult or impossible to recover at a great cost in the future. How to integrate the ecological functions of coastal wetlands and inland wetlands through the implementation of coastal zone restoration, ecological protection, and other measures to achieve the sustainable and healthy development of coastal zones is an important problem for future land and sea planning.
This study analyzed the spatial and temporal variations of depth-averaged residual currents of Eulerian, Lagrangian, and Stokes during a tidal cycle in the eastern waters of Macao. Data were collected for 15 days during the summer from two field stations using a method specifically designed to deal with stratified residual flow. Our findings revealed similar dynamical characteristics during flood and ebb tides in the southeast and northeast waters of Macao, with currents being more pow-erful in the southeast. We found that the material carried by the tidal current tends to travel northwest at the station A6 and southeast at A7, with Lagrange residuals being around 2.2 cm/s and 5.1 cm/s, respectively, which is slightly smaller than Eulerian residuals. Influenced by the southwest monsoon, the directions of Euler, Lagrangian, and Stokes surface residual currents on the surface generally pointed northeast. Furthermore, our results showed that the depth-averaged residuals during a tidal cycle pointed towards the open sea during upstream flooding, towards nearshore in northeast waters, and towards the east in southeast waters under non-flooding conditions. The intensity of Stokes drift in southeast waters was primarily influenced by wind on the water surface, while the effect of wind on the northeast waters was limited and weakened by enhanced runoff. The intensity and direction of transportation in both southeast and northeast waters were related to wind speeds on the sea surface. During summer, analysis of net tidal flux indicated a relatively stable counterclockwise residual current circulation in the waters downstream to the outlet of the Macao waterway. This circulation was driven by the strong northeast littoral current outside the Pearl River Estuary, leading to the formation of an east-west flowing structure compensated in the east waters of Macao. During this season, part of the tidal sediment was intercepted by this unique dynamic structure discharged by east four mouths in the Lingdingyang Estuary upstream and re-entered the Macao waters with rising tidal water, which leaded to sedimentation of beaches and troughs and poor water exchange.
In the context of rising sea-levels under global warming and fluvial sediment load decline, the risk of coastal erosion is increasing in global deltas. Evaluating the delta morphological change and its vulnerability to erosion in the future and analyzing land use exposure to coastal erosion, is of great significance for spatial planning, disaster prevention and mitigation, and the sustainable development of coastal regions. In this study, Pudong New Area of Shanghai, which is located in the Yangtze River Delta, was selected to compare its coastal erosion vulnerability in 2016 and 2035 using bathymetry of 2016 and modelled bathymetry of 2035 under a scenario of fluvial sediment load of 125 Mt/a and a cumulative sea-level rise of 16.5 cm. A comparison of land use exposure is made between the pattern in 2019 and the pattern projected for 2035 by the government. The results show that the spatial pattern of coastal erosion vulnerability is controlled by the morphological evolution of the delta over the last 1000 years. Coastal sections with high and very high categories of land use exposure and erosion vulnerability in the recent past (2016—2019) total 32.3 km in length, which accounts for 31.1% of the coast of the Pudong New Area. These figures are projected to be 47.5 km and 45.8%, respectively, in 2035, under the condition of reduced fluvial sediment load and planned land usage. In 2035, coastal sections along the Pudong Airport and Luchaogang will face an increase of erosion vulnerability category. According to the current plan, these two sections also show an increase in land use exposure due to airport expansion and new city development. The results suggest that these sections require erosion monitoring and erosion management during implementation of the plan. The methods used in this study can provide references for exposure assessment of coastal erosion and the formulation of territorial planning in coastal regions elsewhere.
In February 2014, a persistent and strong northerly wind caused an extremely severe saltwater intrusion event in the Changjiang Estuary, which posed a threat to the safety of water intake from this source. Increasing river discharge from upstream reservoirs in the river basin is a method to combat severe saltwater intrusion. To simulate and analyze the effects of various river discharges on saltwater intrusion, we used the Unstructured quadrilateral grid, Finite-differencing, Estuarine and Coastal three-dimensional Ocean numerical Model (UnFECOM). By taking into account realistic river discharge and wind conditions, the model accurately reproduced the extremely severe saltwater intrusion process that occurred in February 2014. Our findings indicated that the net water flux (NWF) across the section at the upper reaches of the North Channel (NC) remained landward during the most critical period of saltwater intrusion from February 10 to 13, 2014, despite the increase in river discharge. However, the magnitude of NWF tended to decrease with increasing river discharge. The net water diversion ratio (WDR), NWF (Net Water Flux), and salt flux increased with the increase in river discharge. Under realistic river discharge conditions, WDR was –29% (the negative sign indicates that the NWF is landward), NWF was –2300 m 3/s, and the net salt flux (NSF) was –68 t/s, indicating that the NWF and NSF were landward due to the landward Ekman transport effect induced by the persistent severe northly wind. When the river discharge increased by 3000 m 3/s, WDR and NWF across the section were nearly zero, and NSF was –34 t/s. When the river discharge increased by 8000 m 3/s, WDR was 21.5% and NWF was seaward, at 3550 m3/s. NSF was –6 t/s and landward. At the water intake of Qingcaosha Reservoir, the longest continuous unsuitable water intake time decreased slightly when the river discharge increased by less than 4000 m 3/s. When the river discharge increased to 5000 m3/s, the longest continuous unsuitable water intake time decreased significantly to 10.5 days. It may be challenging to achieve the necessary value and duration of river discharge increase required for the actual operation of the Three Gorges Reservoir. To ensure the safety of water intake, implementing an early warning and forecasting system for saltwater intrusion and storing water into the reservoir at a high level before the intrusion occurs are recommended as effective methods.
The process of change and factors influencing dissolved CH4 concentration and flux in the coastal wetlands of Jiuduansha (JDS) and Xisha (XS) in the Yangtze Estuary were explored. The concentration of dissolved CH4 varied significantly during the sampling period, with the highest in JDS wetland being (0.30±0.19) μmol·L–1 during autumn, while that in XS wetland being (1.16±1.52) μmol·L–1 during summer. The average dissolved CH4 concentration in XS wetland ((0.56±0.91) μmol·L–1) was slightly higher than that in JDS wetland ((0.18±0.17) μmol·L–1). Principal component analysis revealed that the temporal and spatial variations in CH4 were mainly related to seasonal variation and tidal cycling in coastal wetlands. The CH4 emission under low-temperature, high-salinity, and oxygen-rich water environments was limited. The fluxes of dissolved CH4 also showed seasonal and regional variations. The water-to-air diffusion of CH4 was the largest in autumn in JDS wetlands ((0.45±0.43) nmol·m–2·s–1) and in summer in XS wetlands ((3.34±5.21) nmol·m–2·s–1). The lateral fluxes of dissolved CH4 were maximum in autumn in JDS wetlands ((2.32±9.32) nmol·m–2·s–1) and in summer in XS wetlands ((1.66±5.06) nmol·m–2·s–1). Use of water quality parameters and dissolved CH4 concentration to fit a multiple regression equation produced a high-frequency and continuous CH4 concentration. The annual average lateral transport flux (JDS wetland: 1.46 mg·m–2·d–1; XS wetland: 0.34 mg·m–2·d–1) and annual average vertical diffusion flux (JDS wetland: 1.85 mg·m–2·d–1; XS wetland: 2.90 mg·m–2·d–1) of dissolved CH4 was calculated. The results show that dissolved CH4 in coastal wetlands is an important sources of CH4 in the atmosphere and coastal waters.
中国综合性科技类核心期刊(北大核心)
