Seawater Layer Research Articles

Evaluation of the efficiency of sorbents for accidental oil spill response in the Arctic waters

The development and operation of new oil fields on the Arctic shelf increases the risks of oil spills, which require the use of oil spill response tools and materials that are efficient in harsh climatic conditions. The question of actual efficiency of sorbents for reducing the level of oil pollution in the conditions of the Arctic and subarctic waters is relevant. The work is aimed at a comparative study of the efficiency of sorbents of mineral and organic origin used by coastal enterprises in the Kola Bay as well as a sorbent based on chitin in model systems simulating real conditions in sea waters. The characteristics of sorption agents were determined applying ASTM F716-18 procedure. Sorption capacity was evaluated in respect of ARCO grade oil, diesel fuel and marine oil. The efficiency of sorbents was estimated in model systems “sea water – oil” at water temperature corresponding to the average annual surface temperature in the Barents Sea. Actual data on sorption capacity of commercial sorbents “Lessorb”, “Novosorb”, a sorbent based on vermiculite and chitin sorbent in relation to potential pollutants of waters were obtained. The dynamics of sea water saturation with oil products at –0.5 (±1) and 10 (±1) °С was determined. It is shown that at higher temperature the concentration of oil products in sea water column (in the presence of an oil film on the surface) is on average four times higher than at low temperature. Kinetic dependences were obtained that describe the content of oil products in water column and near-surface layer of sea water in the presence of the studied sorbents at 5 (±1) °C, corresponding to the average annual temperature in the Kola Bay of the Barents Sea. A method is proposed for evaluating the efficiency of sorbents from the values of regression coefficients characterizing the dependence of oil products content in sea water on the character of sorbent and duration of its action.

Retracted] Analysis of VLF Wave Field Components and Characteristics Based on Finite Element Time‐Domain Method

Most traditional sound field calculation methods regard the seabed as the horizontal stratified liquid sea bottom and conduct simulation analysis based on the frequency domain. Hence, the generality of the above research methods is limited to varying degrees. To accurately clarify the propagation characteristics and mechanism of very low‐frequency (VLF, ≤100 Hz) sound waves in the shallow sea, a numerical calculation model is established using the finite element time‐domain method (FETD) based on the three‐dimensional cylindrical coordinate system. Using this model, the effects of sea‐bottom topographies and geoacoustic parameters on the composition and characteristics of VLF sound fields in the shallow sea and their corresponding mechanism are investigated through the comparative analysis of various numerical simulation examples. The simulation results demonstrate that the low‐frequency sound field in the full waveguide of the shallow sea is composed of normal mode waves in the seawater layer, Scholte waves at the liquid‐solid interface, and elastic waves at the sea bottom. Compared with the soft sea bottom, which has a more negligible elastic impedance, the hard sea bottom is more conducive to the long‐distance propagation of normal mode waves and the excitation of Scholte waves. The Scholte waves on the hard sea bottom are significantly stronger than those on the soft sea bottom. Compared with the horizontal sea bottom, the uphill topography enhances the sound energy leakage to the sea bottom. It is more favorable to receive Scholte waves at shallow depths, whereas the influence laws of downhill topography are the opposite.

Analysis on the seismic wave caused by low frequency sound source in shallow sea based on multi-transmitting formula artificial boundary

The elastic waves propagating in seabed caused by sailing ships are called ship seismic waves, which can be used to identify ship targets. The wave components and the influences of source frequency, source depth and depth of seawater to the seismic waves are important to the application of seismic wave to detect ship targets. Thus, a forward numerical simulation of seismic waves in shallow sea excited by low frequency sources in time domain was carried out with finite element method based on the Multi-Transmitting Formula artificial boundary. The numerical results show that the body waves and conical waves decay faster in space, but the interface wave decays relatively slow. Multi-transmitting Formula (MTF) artificial boundary has achieved good transmitting effect for longitudinal wave, upstream and downstream acoustic wave and transverse wave. When the source frequency is very low and the seawater layer is shallow, due to the effect of low-frequency cutoff, there is no normal mode wave which can propagate without attenuation in the seawater waveguide, and only the interface wave is propagating near the sea bottom surface. When the frequency of the source or the depth of the seawater layer increases, the effect of low frequency cutoff in the shallow water waveguide is weakened, and the normal mode waves propagating in seawater layer are gradually excited. The intensity of the interface wave caused by low-frequency point sound source mainly depends on the distance between the source and the seafloor.

Evolutions of upwelling and terrestrial organic matter input in the inner shelf of the East China Sea in the last millennium revealed by long-chain alkyl diols proxies

Long-chain alkyl diols (LCDs) can be used as organic geochemical proxies for paleoceanographic change, especially in marginal sea areas where large volumes of sediments are deposited rapidly and continuously. However, little is known about the applicability and response on a millennium scale in relation with existing records in those sediments. We reconstruct changes in upwelling and terrestrial organic matter (OM) input in core sediments from the Zhejiang Fujian coastal station (T08) and Yangtze River Estuary station (T06) in the inner shelf of the East China Sea (ECS) over the last millennium, using the LCD based proxies: diol index 2 (DI-2), and FC321,15-diol. Our results show that DI-2 values ([(C28+C30)1,14-diols]/([(C28+C30)1,13-diols]+[(C28+C30)1,14-diols])) at T08 decrease significantly during 600–400 yr BP but increase gradually after 400 yr BP. The FC321,15-diol proxy ([C321,15-diol]×100/([(C28+C30)1,13-diols]+[(C30+C32)1,15-diols])) at T06 shows marked fluctuations during 1000–800 yr BP, followed by a significant decline during 800–500 yr BP but a subsequent increase from 500 to 300 yr BP. We find that variations in DI-2 values are broadly consistent with changes in the strength of the East Asian Summer Monsoon (EASM) and the Kuroshio Current and are likely linked to changes in the frequency and intensity of the El Niño-Southern Oscillation (ENSO). The increased strength of the EASM causes greater offshore movement of the upper layer of seawater, which in turn triggers upwelling of bottom waters formed by Kuroshio subsurface waters. We find that variations in FC321,15-diol proxy are controlled mainly by the East Asian Winter Monsoon (EAWM) and the Yangtze River discharge. By increasing the strength of the EAWM, southward transportation of material deposited in the estuary of the Yangtze River by the ECS coastal currents is promoted. In addition, we synthesize records of other organic geochemical indicators nearby core sediments in the ECS; these records emphasize the importance of reconstructing the evolutionary history of upwelling and subdividing the relative inputs of terrestrial OM. Our study provides a new means for reconstructing the evolution of upwelling and terrestrial OM input in the inner shelf of the ECS over the last millennium.

Modeling geomagnetic induction in submarine cables

Submarine cables have become a vital component of modern infrastructure, but past submarine cable natural hazard studies have mostly focused on potential cable damage from landslides and tsunamis. A handful of studies examine the possibility of space weather effects in submarine cables. The main purpose of this study is to develop a computational model, using Python, of geomagnetic induction on submarine cables. The model is used to estimate the induced voltage in the submarine cables in response to geomagnetic disturbances. It also utilizes newly acquired knowledge from magnetotelluric studies and associated investigations of geomagnetically induced currents in power systems. We describe the Python-based software, its working principle, inputs/outputs based on synthetic geomagnetic field data, and compare its operational capabilities against analytical solutions. We present the results for different model inputs, and find: 1) the seawater layer acts as a shield in the induction process: the greater the ocean depth, the smaller the seafloor geoelectric field; and 2) the model is sensitive to the Ocean-Earth layered conductivity structure.

Numerical Imaging of the Seabed and Acoustic Flares with Topography and Velocity Variance

During seabed mapping, anomalous acoustic events in the seawater layer often degrade bathymetric quality. Acoustic-flare-like events that are induced by gas seepage occur accompanied by small seabed depressions known as pockmarks. In this study, we performed numerical imaging to verify whether acoustic flares are related to changes in the topography of the seabed. The input models assumed convex or concave upward structures which differ based on aperture size. The imaging study determined that acoustic flares appear because the sensing instrument measures the velocity changes in the water layer regardless of the seabed topography. Changes in the velocity of the seawater column can be caused by the concentration of suspended particles and the wave current above the seabed, but further quantification research is required.

Analytical and Numerical Analyses on Vertical Site Responses of Submarine Permafrost in Polar Ocean

Submarine permafrost is widely distributed in polar ocean, which has an important impact on polar engineering and subsea energy exploitation. According to the frozen porous medium theory, an analytical solution of the one-dimensional vertically dynamic response of the submarine permafrost is derived by using the Laplace transform and the separation variable method. Using the general forms of partial differential equations and the pressure acoustics module in COMSOL software, a finite element model of submarine permafrost overlying a seawater layer is established. The results show that the degraded solution agrees well with the existing results of the vertically dynamic response of the saturated soil layer in the seabed, and the analytical and numerical solutions are in good agreement. The water depth, saturation and temperature have important effects on the dynamic responses of submarine permafrost. When the soil layer is fully saturated, the water depth has a weak effect on resonance frequency. However, if not fully saturated, even a small amount of air bubbles will have a significant impact on the resonance frequency of the soil layer, and this effect increases with the increase of water depth. The effect of temperature on the nearly saturated permafrost layer is also significantly higher than that on the saturated permafrost layer.

Magnetotelluric Sounding in the Arctic Using a Drifting Station on an Ice Floe (Numerical Experiment)

Abstract —The magnetotelluric sounding (MTS) method implemented on drifting ice floes in the Arctic is suitable for detection of 3D inhomogeneities in crustal conductivity while recording the transverse magnetic (TM) mode potential of the electromagnetic field. Highconductivity layers of seawater and sediments shield the underlying 3D inhomogeneity. Their presence virtually does not affect changes in the standard responses of the medium used in MTS but is quite noticeable in the characteristics of the TM mode. To register them, one can use a circular electric dipole (CED) located at the surface of an ice floe. During the drift, the electric field can be measured on the ice floe using electrodes in seawater. We propose to lower the magnetic sensors beneath the ice, in seawater, because ice deformations interfere with the magnetic-field component measurements. The coordinates of the observation station during MT soundings on the ice floe in the Arctic (similarly to earlier observations at the North Pole stations) can change significantly. To take into account the effect of horizontal movements of the drifting station, we propose to complement all the recorded time series with the coordinates of measurement points. We have developed a technique for processing such data to take into account nonplane-wave effects, which can occur in the Arctic because of the proximity of ionospheric current jets. We carry out the synchronization of all observations in the investigated area, using a model of spatial and temporal field variations and data accumulation. To test our approach, we use the synthetic experimental data for the model that considers the existence of seawater, sediment, resistive crust, crustal object, and underlying mantle. We determine the crustal 3D object parameters with account of the TM-mode potential distributions at the seawater surface restored from the synthetic experimental data obtained at the drifting station during the drift. We use the Nelder–Mead method for optimization of the object characteristics. The parameters of the object become highly similar to their test values if the trajectory of the drifting station passes through an object, covering it most fully.

Stochastic processes shape the aggregation of free‐living and particle‐attached bacterial communities in the Yangtze River Estuary, China

An estuary plays an important role in material and energy exchange between the land and sea, where complex physical, chemical, and biological processes occur. Here, we investigated the assembly processes of free-living (FL) and particle-associated (PA) bacterial communities in two seawater layers at five stations in the Yangtze River Estuary (YRE) by using 16S rRNA sequencing methods. The results indicated that Proteobacteria was the most abundant phylum in the YRE. The α-diversity of PA community was significantly higher than FL community, and analysis of similarity showed significantly different (Global R = 0.2809, p < 0.005). RDA revealed that phosphate (PO4 3- ) was significantly correlated with PA bacterial community abundance (p < 0.05). An ecological null model showed that both PA and FL bacterial communities were mainly influenced by stochastic processes (PA: 100%, FL: 70%), which PA attached to nutrient particles and are less affected by environmental filtration. Dispersal limitation (50%) was the main assembly process of the PA community, while homogeneous selection (30%) and drift (30%) were important processes in the FL community assembly. The available substrate for colonization limits the transformation from FL to PA bacteria. This study would improve our understanding of FL and PA bacterial community structure and factors affecting assembly process in estuarine environments.

A Potential Energy Analysis of Ocean Surface Mixed Layers

AbstractTurbulent mixing in the ocean surface boundary layer leads to the presence of a surface mixed layer. This mixed layer is important for many phenomena including large‐scale ocean dynamics, ocean‐atmosphere coupling, and biological and biogeochemical processes. Analysis of the ocean mixed layer requires one to estimate its vertical extent, for which there are various definitions. Correspondingly, there are uncertainties on how to best identify an ocean surface mixed layer for a given application. We propose defining the mixed layer depth (MLD) from energetic principles through the potential energy (PE). The PE based MLD is based on the concept of PE anomaly, which measures the stratification of a layer of seawater by estimating its energetic distance from a well‐mixed state. We apply the PE anomaly to diagnose the MLD as the depth to which a given energy could homogenize a layer of seawater. We evaluate the MLD defined by common existing methods and demonstrate that they contain a wide range of PE anomalies for the same MLD, particularly evident for deep winter mixed layers. The MLD defined from the PE anomaly ensures a more consistent MLD identified for a large range of stratifications. Furthermore, the PE method relates to the turbulent kinetic energy budget of the ocean surface boundary layer, which is fundamental to upper ocean mixing processes and parameterizations. The resulting MLD is more representative of active boundary layer turbulence, and is more robust to small anomalies in seawater properties.

Trace Metal Partitioning in the Salinity Gradient of the Highly Stratified Estuary: A Case Study in the Krka River Estuary (Croatia)

A size partitioning of several trace metals (Zn, Cd, Pb, Cu, Ni, Co, Mn, Fe and Al) between five size fractions (&lt;3 kDa, 3 kDa–0.1 µm, 0.1 µm–1.2 µm, 1.2 µm–5 µm and &gt;5 µm) was studied in the vertical salinity gradient of the highly stratified Krka River estuary. The results indicated a dominant river source for Zn, Co, Mn, Fe and Al and a diluting effect on Cd, Pb and Ni. The truly dissolved fraction (&lt;3 kDa) dominated the Zn, Cd, Cu, Ni and Co pool, and a large part of Pb, Mn, Fe and Al was present in &gt;5 µm particles. Pb, Mn, Fe and Al were closely related, showing a precipitation and colloidal aggregation in the surface layers and dissolution in the seawater layer. The highest percentage (30–37%) of colloids (3 kDa–0.1 µm) in the dissolved pool was found for Pb, Cu, Fe and Al. Differences in size distribution between low and high river flow periods revealed that Zn, Pb, Co, Mn, Fe and Al are introduced by the river mostly in the 3 kDa–5 µm size range. Therefore, a low percentage of colloidally bound metals compared to other coastal areas can be explained by a limited riverine input of terrigenous material, characteristic for this estuary. Correlation with PARAFAC components revealed associations of Cu with protein-like substances and Co with humic-like substances. The accumulation of Cu at the freshwater-seawater interface coupled with an increase of its colloidal fraction was observed, apparently governed by biologically produced organic ligands.

Design and Depth Control of a Buoyancy-Driven Profiling Float.

This paper presents the design and fabrication of a profiling float primarily used for thermocline observations and tracking, with an emphasis on depth control performance. The proposed float consists of a frame-type electronic chamber and a variable buoyancy system (VBS) actuator chamber. Components or sensors can be added or removed according to specific requirements. All components were off the shelf, which lowered the cost of the float. In addition, a segment PD control method is introduced. Simulink results showed that there was no need to change any parameter when carrying out tasks at different depths. This method is superior to the traditional PD control and sliding mode control (SMC). In the process of diving, the speed could be well controlled to less than 0.2 m/s. We completed depth determination and control method validation in Qiandao Lake. The final results were consistent with the simulation results, and the maximum depth retention error was less than 0.3 m. Field tests also demonstrated that the prototype float can be used for thermocline observations in the upper layer of seawater or lake water.

Seismic responses of sea-crossing isolated continuous beam bridges considering seabed–pile–seawater–bridge interaction

To consider the multiple interactions between offshore sites and sea-crossing bridges under seismic actions, a seabed–pile–seawater–bridge interaction model is established by the ADINA software [1]. This study uses seismic fluctuation analysis as an input to bedrock ground motion. It reflects the influence of submarine sites and seawater layers on ground motion characteristics through the fluid-solid coupling of seawater to the seabed. It was found that the whole bridge piers considering the coupling effect are in an elastic state. The yielding of the isolated bearings occurs. Also, the seismic response of the bridge structure under the seabed-pile-seawater-bridge interaction is significantly higher than those under the direct input of the ground motions from the fixed basement assumption. In addition, when the pile cap is above the seabed, the average seismic response of the bridge structure is 1.2–1.3 times the response when the pile cap is below the seabed. Therefore, the seismic design of marine structures should take full account of the influence of the submarine site and the seawater layer. Otherwise, it will result in greater seismic risks for marine structures such as sea-crossing bridges. In addition, this study also suggests the influence of the pile cap location on the seismic response of the bridge.

Thermal–Structural Coupling Analysis of Subsea Connector Sealing Contact

Taking a subsea collet connector as an example, the contact characteristics of the sealing structure of the subsea connector under thermal–structural coupling were studied. Considering the heat transfer problem of the subsea connector in deep water, the heat transfer model of seawater layer between sealing structures was established, and the relationship between equivalent thermal conductivity, composite heat transfer coefficient, and temperature was determined. The steady-state temperature field distribution of the connector under the action of the internal high-temperature oil and gas and external low-temperature seawater was obtained. Considering the stress and deformation of the subsea connector under the thermal load, the thermal–structural coupling analysis model of the steady-state temperature field was established, and the thermal stress theoretical analysis and numerical simulation of the key sealing structures of the connector were compared and verified. Analysis of coupled stress calculation, for example, under a steady-state temperature field, was carried out on the sealing structure of the subsea connector. At the same time, the pressure shock mode under a steady temperature field was analyzed, which showed that the lenticular sealing gasket is sensitive to high pressure under high-temperature conditions.

Solar chimney power plant combined with membrane distillation (SCPPMD), part I: Principle and operation characteristics

In this paper, a novel solar chimney power plant combined with membrane distillation (SCPPMD) was proposed. SCPPMD could not only achieve power output but also product more freshwater, by installing a novel air gap membrane distillation module vertically in the disc distiller. A transient heat and mass model was established to predict the system performance. Then, the operation laws of SCPPMD under unsteady weather conditions and the effect of seawater thickness were explored. The results show that the peak power generation is about 4p.m. and the peak water yield lags two hours. The hourly water yield of the membrane is much higher than that of the disc distiller and its valley value reaches 11.55 t/h, 14.26 times the valley value of the disc distiller and 0.875 times its peak value. Membrane distillation still has considerable freshwater output even when the water production of disc distiller is weak. As the seawater layer thickens, the peak-valley difference of power generation is reduced and the daily power generation drops; The peak hourly water yield of disc distiller drops, the valley value increases and its daily water yield drops; Both the peak and valley value of membrane hourly water yield increase, and its daily water yield rises; The change of the system water yield is basically the same as that of membrane.

Dissolution of Silver Nanoparticles in Stratified Estuarine Mesocosms and Silver Accumulation in a Simple Planktonic Freshwater Trophic Chain

The increasing presence of nanomaterials in consumer products has led the scientific community to study the environmental fate of these contaminants of emerging concern. Silver nanoparticles, used mainly for their antibacterial properties, are among the most common nanomaterials. Understanding their transformations and interactions with living organisms, especially under environmentally relevant conditions that can modify metal bioavailability, is a crucial step in the study of their impacts on aquatic ecosystems. In the present study, citrate-coated silver nanoparticles (20 nm; 10 µg/L) were added to the surface freshwater layer of mesocosms simulating a stratified estuary. The investigation by dialysis of the nanoparticle dissolution showed that a large amount of total silver was found in the freshwater layer (and a very low amount in the seawater layer) and that 5–15% was in the form of dissolved silver. These results indicate that the halocline, separating fresh water from seawater, acted as a strong density barrier limiting the sedimentation of the nanoparticles. A simple trophic chain, composed of the freshwater alga Chlamydomonas reinhardtii and the invertebrate Daphnia magna, was used to determine silver bioavailability. This study suggests that citrate-coated silver nanoparticles do not significantly contribute to Ag accumulation by algae but may do so for invertebrates.

New Insight Into the Mechanism of Ecological Effects of Artificial Habitats: Elucidating the Relationship Between Protists Associated With Artificial Reefs and Adjacent Seawater

Artificial habitat deployment can restore natural habitats or supplement existing natural habitats. The effect of resource proliferation and protection is obvious. However, few reports have addressed the biological community association between artificial habitats and adjacent environments. Here, Illumina sequencing of 18S rDNA was performed, and the diversity, community structure, and co-occurrence networks of protists in different layers of artificial reefs (ARs) and adjacent seawater (WAR) were described to verify that constructing ARs in Bailong Pearl Bay improves local spatial heterogeneity and functional diversity. In terms of the degree of species interaction, the protist communities were ranked as follows: surface and bottom of WAR &amp;gt; ARs and WAR &amp;gt; different layers of ARs. The α-diversity of protists associated with ARs and WAR decreased with an increase in depth. Protist diversity was greater in WAR than in ARs. β-Diversity analysis revealed significant differences in protist community structure between WAR and ARs (P &amp;lt; 0.05), and the upper layers of ARs and the middle or bottom layers of ARs differed. The key topological features of protist networks showed more positive interspecific interactions in the AR-associated protist community, a higher degree of niche differentiation, and higher complexity and stability. The keystone protists in the bottom seawater layer displayed community functions that were biased toward initial fixation in the ocean carbon cycle. The AR-associated protist community tended to participate in carbon transfer in the food chain and decomposition and utilization of dissolved organic matter (DOM). This study revealed significant differences in protist community structure between ARs and the adjacent environment, and the ecological functions of the key phyla were found to be related. In conclusion, protist communities in WAR may provide food sources for AR-associated heterotrophic protists. A variety of key phyla associated with ARs have biological roles in the carbon pump via their ecological characteristics.

A hybrid grid-based finite-element approach for three-dimensional magnetotelluric forward modeling in general anisotropic media

Magnetotelluric (MT) forward modeling often requires the consideration of the deviation generated by anisotropic structures to avoid misleading the detection results, which is implemented by the flexible unstructured finite-element (FE) method based on tetrahedrons. However, the unstructured FE method needs a large number of small elements near the sharp boundary of the electrical structure to produce sufficiently stable grids, and this leads to a sharp increase in the degrees of freedom (DoFs) of the FE system. To this end, we develop an FE approach based on a hybrid grid. It uses the stretched prismatic elements to divide the regions around the abrupt interfaces, which can significantly reduce the number of elements needed to capture the corresponding changes of the physical fields compared to using tetrahedrons. The remaining regions are still divided with tetrahedrons in this hybrid grid in order to keep the total elements needed for the entire computational region at a minimum. By showing numerical examples of the sea- and land-based electrical anisotropy models, as well as a real anisotropic inversion model, the advantages of our method are tested by evaluating the MT response curves, the number of elements, the DoFs, the computational time, and the consumed memory. The results show that the prismatic elements are suitable for discretizing the near-surface region, seawater layer, and electrical anisotropic blocks. This approach can maintain the high accuracy of the numerical solution and reduce the number of elements required for discretizing these regions and the DoFs, thus requiring less computer memory. With this hybrid grid, the computational efficiency of the FE method can be improved for MT forward modeling for a complicated model, which combined with the lower memory consumption is very suitable to implement inversion.

Variability of the oceanographic structures of the Southern Ocean by the FerryBox data

During Antarctic summers in the 2018—2021 period, physical, chemical, and biological parameters of the upper layer of seawater were continuously recorded using the FerryBox (FB) software and measuring system installed on-board the Ukrainian krill fishing trawler F/V More Sodruzhestva. The main hydrological fronts of the South Atlantic and the Southern Ocean were crossed from Cape Town to the Antarctic Peninsula. About 800,000 one-minute FB measurements were used in this research to determine and identify marine structures. The paper aims to estimate the spatial-temporal variability of oceanographic parameters of the surface layer of water in the Southern Ocean based on the FB data analysis. We use classical methods of analysis of hydrological structures, graphical, comparative, and statistical types of analysis of the field data, as well as data from the Copernicus Marine Environment Monitoring Service (CMEMS). Trawling areas were considered as hydrological landfills. We found a decrease in the total number of front crosses: from 8.6% in the 2018—2019 season to 3.9% in the 2020—2021 season. Analysis of the quality of information obtained from the FB showed that after adjustment the measurements allow solving various oceanographic problems, such as identifying frontal zones and detailing their hydrological structure, determining surface water masses and variability of their distribution limits, highlighting significant cycles in time of the measured parameters, studying the gas component of the upper sea layer water. A comparative analysis of the results of the FB observations with the CMEMS data showed their qualitative consistency.

中国东海微型鞭毛虫群落的分布特征及其环境影响因子

PDF HTML阅读 XML下载 导出引用 引用提醒 中国东海微型鞭毛虫群落的分布特征及其环境影响因子 DOI: 10.5846/stxb202103010554 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（41676131，41876155） Distribution of the microbial flagellates' community and the key affecting environmental factors in the East China Sea Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:海洋微型鞭毛虫是海洋原生生物中一类高度异质化的类群，物种多样性高，具有多种营养方式，在全球海洋生态系统中占据广阔的生态位，在生物地球化学循环中发挥着关键作用。然而关于其生物多样性和群落结构的认识十分有限，特别是有关环境因子与其生物地理分布关系的研究更为罕见。为了探究微型鞭毛虫群落多样性、群落结构以及影响其生物地理分布格局的环境因素，将高通量测序技术与传统的显微镜观测方法相结合，全面调查了中国东海春季和秋季微型鞭毛虫的群落特征，并深入探讨了与环境因子之间的关系。结果表明：东海微型鞭毛虫的丰度平均为2.27×103个/mL，表现为近岸处较高、随离岸距离的增加而下降的趋势；Shannon多样性指数呈现表层低于底层、近岸区低于陆架区的特征，反映了生物群落的稳定程度以及对环境条件的适应程度；不同类群的鞭毛虫具有各自独特的营养模式和相对固定的粒级，表现出对温度、盐度、溶解氧等环境因素的不同响应，从而使群落的物种组成和分布模式呈现明显的季节变化和生境差异。研究结果可为深入认识东海海洋微型鞭毛虫的群落结构、分布格局以及环境影响因素提供理论依据。 Abstract:Marine microbial flagellates are a highly heterogeneous group of protists with high biodiversity and multiple trophic modes. They occupy broad niches in global marine ecosystem and play essential roles in the biogeochemical cycles. However, little is known about the distribution of the diversity and community structure of the microbial flagellates in a regional marine area, especially the relationship between their biogeographic distribution and the environmental factors. The East China Sea (ECS) is a marginal sea with sloping topography, leading to a wide coastal area and its adjacent open continental shelf area. The hydrological conditions display gradient changing patterns from the coastal area to the shelf area in the ECS, which could affect the microbial flagellates' communities differently, but is so far understudied. Thus, the ECS region provides a suitable system for the study of the relationship between environmental conditions and microbial flagellates' communities. In order to adequately describe the diversity and community structure of the microbial flagellates, as well as the environmental factors that shape and drive their biogeographic distribution patterns, a comprehensive investigation on the microbial flagellates' communities using combined methods of high-throughput sequencing of eukaryotic 18S rRNA gene V4 region and traditional microscopic observation was conducted in the ECS in spring and autumn, 2019. Intensive exploration also attempted using multiple statistical analyses on interpretation of the relationships between environmental factors and structure of microbial flagellates' communities. The main findings are as follows:Firstly, the average abundance of the nano-sized flagellates in the ECS was 2.27×103 cells/mL, which decreased with increasing distance from the shore. The heterotrophic nano-sized flagellates were dominant at the bottom layer of seawater while the surface seawater was dominated by the pigmented ones. Secondly, the community alpha diversity reflected the community stability and adaptability to environmental conditions, with higher Shannon diversity index both at the bottom seawater and in the shelf area than those at the surface seawater and in the coastal area, respectively. This indicated that the relatively stable environmental characteristics and environmental heterogeneity among different patches in the bottom layer and shelf area might cause sufficient competition and niche differentiation of the community, and thus led to higher biodiversity. Thirdly, different taxa groups of microbial flagellates owned unique nutritional modes and relatively fixed size fractions. The relative richness[numbers of the Operational taxonomic units (OTUs)] and relative abundance (numbers of the sequencing reads) of various taxa were different. Alveolata were the most abundant and diverse taxa in the studied area. Archaeplastida, Hacrobia, and Stramenopiles displayed high relative abundance and richness in the pico-sized flagellates' community, while Rhizaria showed high relative richness mostly in the nano-sized community. Lastly, the potential correlation between the microbial flagellates' communities and environmental factors depended on the degree to which the biological community matched with or adapted to the changing environmental conditions. Different taxa showed different responses to the environmental factors such as temperature, salinity, and dissolved oxygen, etc. This led to the obviously seasonal dynamics and biogeographic distribution patterns of the community composition. Moreover, the geographic distances had an impact on the dispersal limitation of the microbial flagellates' community, which might also result in spatial difference of the community. Specifically, the similarity of the community composition was greatly reduced with the increasing of the environmental heterogeneity and geographical distance. Overall, the findings of this study contribute to improve our understanding of the diversity, community structure, and affecting factors of marine microbial flagellates in the ECS, and to promote the research of marine flagellates from the phenomenon to the process and the mechanism. 参考文献 相似文献 引证文献