Marine mesoscale eddies significantly influence the vertical transport of dissolved organic matter (DOM), yet their role in DOM production and transformation in the oligotrophic open ocean remains poorly constrained. Here, we investigated DOM dynamics associated with an anticyclonic-cyclonic eddy (AE-CE) pair in the oligotrophic central South China Sea through analysis of high-resolution profiles of dissolved organic carbon (DOC), optical DOM properties, and related biogeochemical parameters such as NO3 (-), chlorophyll-a (Chl-a), Chl-a-derived pheopigments (Pheo-a), and microbial community composition. Three fluorescent components were identified with parallel factor analysis: two humic-like, and one protein-like. The CE uplifted humic-rich low-DOC subsurface water, whereas the AE transported protein-rich high-DOC surface water downward. In the CE, net DOC production was coupled well with Chl-a distribution, indicating DOM production promoted by enhanced primary production due to upwelled nutrients. Concurrently, the net consumption of protein-like FDOM, production of humic-like FDOM, and high abundance of heterotrophs indicated microbial transformation of labile DOM into refractory compounds. The AE exhibited higher net DOC production, primarily protein-like. A higher ratio of Pheo-a to Chl-a in the inventory suggested that DOC production in the AE was likely derived from the release of dead phytoplankton cells, a process associated with the downwelling of oligotrophic surface waters. This study reveals that the open-ocean eddy pairs reshape microbial community structure and directly modulate the production and transformation of DOM, thereby significantly influencing carbon cycling and food web dynamics in the oligotrophic ocean.

Dissolved organic matter (DOM) derived from plant litter frequently regulates the generation and migration of carbon in coastal wetlands and its transport to adjacent waters. To understand the role of salt marsh in regulating organic carbon cycling in coastal wetlands, laboratory incubation was conducted on litter from one woody plant (Tamarix chinensis) and two herbaceous plants (Phragmites australis, Suaeda salsa) from the Yellow River Delta wetland. The net increment of dissolved organic carbon (ΔDOC) and the net total fluorescence intensity (ΔFt) in soil DOM rapidly peaked within 1 week after burial of the plant litter, and then quickly decreased to much lower values and fluctuated with a slightly increasing trend. A large percentage of tryptophan-like proteins in soil DOM were detected in the early stage of incubation, whereas a high percentage of humic-acid-like organics was observed after litter decomposition for 3 months. Leaf litter of T. chinensis with the higher initial quality (e.g., low carbon/nitrogen (N), cellulose/N, and lignin/N ratios), released the maximum amount of DOM, suggesting that woody plant leaf litter has greater potential for releasing organic matter than herbaceous plant litter. This study highlights the significant impacts of salt marsh plant litter decomposition on soil DOM characteristics and its potential contribution to coastal ecosystem.

Environmental context External nutrients giving rise to critical ecological issues of the coastal seawater. We investigated the nearshore nutrient concentrations and their sources in Xiamen Bay during 2013–18. Our results could provide theoretical support for controlling nearshore nutrient pollution. Rationale External nutrients greatly increase the critical ecological risks of the coastal seawater. Therefore, it is important to understand the sources and variation characteristics of nitrogen (N) and phosphorus (P) in the coastal area. Methodology The dissolved inorganic nitrogen (DIN) and phosphate (PO4–P) in coastal Xiamen were monitored from 2013 to 2018. The input of nitrogen from runoff in the coastal Xiamen was calculated from the runoff flow amount collected by Xiamen Marine and Fisheries Bureau. Atmospheric dry deposition of DIN was simulated using Williams model to analyse the potential sources of nutrients in the coastal Xiamen. Results High DIN and PO4–P levels occurred in the inner bay and decreased dramatically outside Xiamen Bay. The lowest values of DIN and PO4–P were observed in summer, which is consistent with the temporal variation in nutrient inputs from the surface runoff and atmospheric deposition. The nutrient input of Jiulong River is the main source of eutrophication for Xiamen Bay, providing more than 4 × 104 tonnes (Mg) of N input per year. The atmospheric N dry deposition provided more than 2.2 × 103 Mg of DIN input per year, which accounts for ~3.4–6.3% of the Jiulong River DIN input in the coastal Xiamen. Discussion The ratio of atmospheric nitrogen deposition to nitrogen enrichment from Jiulong River varied from 0.21 to 0.40, indicating that atmospheric nitrogen deposition was an important contributor to the coastal nutrient in Xiamen. This study provides an insight into the major sources of N and P and highlights the importance of atmospheric nitrogen deposition to the DIN in the coastal city Xiamen.

Atmospheric nitrogen deposition in coastal areas has a significant impact on water nutrients, with increasing emission of atmospheric nitrogen-containing pollutants. Clarifying the characteristics, source, and nutrient impact of atmospheric inorganic N deposition is therefore critical for targeted eutrophication control in coastal areas. Dry and wet atmospheric nitrogen deposition samples were collected and integrated into the atmospheric deposition model to analyze the influence of the deposition flux and source on coastal water nutrients. The results showed that inorganic nitrogen in the atmosphere over Xiamen’s coast was mainly composed of NH4+-N and NO3−-N. A high concentration of nitrogen was found in the cold season. Source apportionment analysis revealed that NH4+-N mainly originated from agricultural sources, while NO3−-N was primarily derived from traffic sources (24%) and secondary sources (25%). The wet deposition flux of NH4+-N and NO3−-N was significantly larger than the dry deposition flux. The NO3−-N wet deposition flux was elevated during winter and summer, whereas the dry deposition flux peaked in spring and winter. A high NH4+-N wet deposition flux was also found in spring and summer. Spatially, the inorganic nitrogen deposition flux was higher in offshore areas than in the inner bay, which was attributed to the higher wind speed in the offshore region. The atmospheric inorganic nitrogen input accounted for only 0.9% to 1.8% of the inorganic nitrogen input from the Jiulong River to Xiamen Bay; however, the NO3− concentration in Xiamen Bay showed a significant positive correlation with the dry deposition flux of atmospheric nitrogen (p < 0.05). Atmospheric nitrogen deposition directly affects coastal water nutrients without estuarine filtration. This study clarifies the different sources of atmospheric inorganic nitrogen deposition and their contribution to coastal water nutrients, providing an important basis for eutrophication in coastal areas, as well as pollutant control and emission reduction efforts.

The East China Sea (ECS) is among the most important and highly dynamic shelf seas, where the coupling of physical and biogeochemical processes is distinctive and may play a crucial role in regulating nutrient conditions and the pattern of primary production. Based on field observations during the late summer of 2019, the physical controls of nutrient supply and the subsequent influences on phytoplankton chlorophyll-a (Chl-a) regime were investigated in the ECS. The coastal upwelling originating from the Kuroshio Subsurface Water (KSSW) intrusion serves as a nutrient source on the inner East China Sea (ECS) shelf, and this inshore upwelling combined with the coastal water largely governs the surface Chl-a patterns. The halocline, thermocline and nutricline exhibit a vertically synchronous fluctuating phenomenon, and the coexistence of several subsurface cold rings/patches was significantly observed on the middle-outer ECS shelf, indicating intense vertical advection and the occurrence of upwelling. The subsurface cold rings greatly regulate the vertical hydrodynamics, constituting unique upward pathways of the onshore intruded KSSW on the middle-outer shelf. Nutrients can be upwelled within these cold rings to support primary production, thus partially leading to the spatial variability of subsurface Chl-a maximum in terms of intensity and depth. Our findings would considerably contribute to our understanding of the physical-biogeochemical-ecological processes on the ECS shelf. The East China Sea (ECS) is one of the most important continental shelves in the world. Exploring the physical-biogeochemical processes is of great significance for the in-depth understanding of ecosystem in this shelf sea. Here, specific attention was paid to the physical controls on the nutrient supply and the associated influences on phytoplankton chlorophyll-a (Chl-a) regime in the ECS. We show that the coastal/inshore upwelling originating from the nearshore branch of the Kuroshio Subsurface Water (KSSW) intrusion serves as a nutrient source on the inner ECS shelf. The co-occurrence of several subsurface cold rings clearly indicates the upward transport of the onshore intruded KSSW on the middle-outer ECS shelf. The subsurface cold rings may play a role in modulating the vertical hydrodynamics and related biogeochemical-ecological processes, leading to the upward delivery of nutrients and enhanced Chl-a levels. Our results would provide a sound scientific basis for the studies of biogeochemical and ecological dynamics in the ECS. The coexistence of several subsurface cold rings indicating upwelling on the middle-outer East China Sea shelf was observed Subsurface cold rings and coastal upwelling constituted unique upward pathways of the onshore intruded Kuroshio Subsurface Water Nutrients could be upwelled within the cold rings and potentially modulated the associated biogeochemical-ecological processes

The relationships among sea ice melting, phytoplankton assemblages, and the production of climate-relevant trace gases in the Southern Ocean are gaining increasing attention from the scientific community. This is particularly true for dimethyl sulfide (DMS), which plays an important role in atmospheric chemistry by influencing the formation of sulfated aerosols with radiative impacts and constituting cloud condensation nuclei. In the current study, chlorophyll a (Chl a), DMS and its precursors dimethylsulfoniopropionate (DMSP), were quantified in the Weddell-Scotia Confluence (WSC) during the 2018 record ice extent minimum period. Mixed layer changes were found to be generally associated with spatial variation in sea ice melt, with the depth being six times deeper in ice-free, well-mixed regions than in seasonal ice-melting zones. The surface Chl a concentration increased from ice-free to ice-melting regions with elevated sea ice meltwater percentages and drawdown surface nutrient concentrations. The concentrations of surface and depth-integrated Chl a in the upper 150 m reached maxima in the ice-melting region with the highest fraction of sea ice meltwater, illustrating that sea ice melting promoted the occurrence of phytoplankton blooms. The DMS and DMSP concentrations in the vicinity of the ice-melting zone were approximately three times higher than those in the ice-free waters. The observations of this study show that the regions of ice melting in the WSC were a zone of particularly high sea-air fluxes of DMS, which could significantly contribute to the atmospheric budget of DMS in the polar regions.

Ophiuroids, as an important group of echinoderms, are widely distributed in marine benthic habitats. Previous studies have identified two primary feeding types of ophiuroids in the Yellow Sea, including carnivorous (Ophiura sarsii vadicola and Stegophiura sladeni) and suspension feeders (Ophiopholis mirabilis). Despite their ecological role in the benthic food webs, little is known about their accumulation of trace metal elements (TMEs). In this study, the content of TMEs (Pb, As, Cd, Hg, Cr, Cu, Zn), methylmercury (MeHg) and δ15N value of three ophiuroids species from the North Yellow Sea were determined. Our results showed that the contents of some TMEs (As, Cd, Cr, Cu and Zn) and MeHg were significantly different in three species of ophiuroid (p < 0.05). There were significant correlations between the accumulations of trace metal elements (Pb, Cd and Zn) and the δ15N value of the ophiuroids (p < 0.05). Additionally, As and Zn exhibited opposite correlations in ophiuroid with two feeding types, which may be related to their host species and different feeding habits. This study provided fundamental data for understanding the distribution of trace metal elements in echinoderms.

基于2019年春末所获取的东海调查资料,通过分析温度、盐度、营养盐和叶绿素a(Chl-a)等理化参数的分布特征和空间格局,重点对东海北部冷涡区水文环境特征、营养盐动力过程及藻华发生机制进行了探讨.研究表明:济州岛西南海域的低温区清晰显示了春末东海北部冷涡的位置,且冷涡边缘锋面区冷水的抬升指示了上升流的存在.冷涡区的营养盐来源于冬季南下的黄海西部沿岸流的水平输运,冷涡边界锋区的上升流在一定程度上控制着营养盐的垂向输送.春末济州岛西南的Chl-a高值区(最高Chl-a含量为5.69μg/dm3)预示了藻华的发生,其与东海北部冷涡和营养盐高值区位置总体相吻合.较高的营养盐水平、良好的光照和增强的水体稳定度是春末东海北部冷涡区藻华形成的有利因素,同时该冷涡与南部高温、高盐水交汇形成的西北-东南向锋面对Chl-a高值区的空间格局与位置也具有重要影响.济州岛西南海域水体浊度较低,满足浮游植物生长所需光照条件所能达到的垂向深度较大,导致冷涡藻华区存在次表层Chl-a高值.该研究为进一步深入认识东海北部初级生产过程的调控机制和开展区域生态系统动力学研究等提供了重要科学依据.

The spatial distribution and seasonal variations of the hypoxic zone in the eastern equatorial Indian Ocean were investigated using survey data collected from four cruises from 2013 to 2018. Results showed that hypoxic zone occurred all year round in the eastern equatorial Indian Ocean, and it spread southward in the shape of a double tongue at two depths with one at subsurface centered at a depth of 150 m and the other in intermediate water centered at a depth of 800 m. The southward expansion and maximum thickness of the hypoxic zone were greatest in the spring inter-monsoon and least in the summer monsoon. The hypoxic zone originated from the southward expansion of the hypoxic water in the Bay of Bengal and its spatial distribution was driven by southward output flux of mid-deep (100–1000 m) hypoxic water from the Bay of Bengal. The hypoxia southward expansion was blocked near the equator in the subsurface layer, because of mixing with multiple zonal circulations (e.g., Wyrtki Jets and the equatorial undercurrent), which meant that the hypoxic zone extended over a smaller area than in the intermediate water. These new findings will contribute to an improved understanding of the hypoxic zone and will contribute to circulation research, particularly about intermediate circulation in the eastern equatorial Indian Ocean.

Using historical data, long-term variations in pollutant sources and water quality in China's coastal waters over the last three decades are reviewed. The results show that the total area of non-clean water, which reflects state of total water quality, increased rapidly before 2000, but then underwent two stages of decline, with a modest decline by one-quarter between 2001 and 2015, followed by a sharp decline of more than half of that in 2015 since then. Consequently, water quality at present is better than it was at the beginning of the 1990s. The total area of polluted water fluctuated without any trend from the end of the 1990s until 2015, but has declined sharply by nearly two-thirds since 2015, indicating that the water quality in China's coastal seas has improved substantially. Geographically, the Bohai Sea was the first to see a turning point in water quality, followed by the Yellow Sea and East China Sea, while the South China Sea was the last. The main pollutants that govern the water quality grade and area are dissolved inorganic nitrogen and phosphate as well as petroleum hydrocarbons. As a response to variations in water quality, changes in both the frequency and total area affected by harmful algal blooms were similar to those of water quality over the last three decades, albeit with a slight lag. Analysis showed that variations in water quality were closely related to the land- and sea-sourced pollutant inputs. The combination of shift in the mode of economic growth from high-speed growth to high-quality development and the enforcement of the new, strictest ever Environmental Protection Law resulted in a significant decline of pollutant emissions, inducing a turning point in the water quality in the coastal seas of China in the mid-2010s.

BACKGROUND Lignin is an important component of marine organic carbon. It is also an important biomarker for extracting information on the evolution of the land and marine environment and tracking the source of organic marine matter. However, the existing analytical techniques are difficult to determine lignin directly. So, the content of phenolic compounds in the decomposition products of lignin in marine sediments were generally determined to indicate the content of lignin and the source of organic matter. The content of phenolic compounds in the decomposition products of lignin in marine sediments is often used to reflect the content of lignin. In addition, by calculating the diagnostic ratio of individual phenolic compounds, it also provides important information about the classification, source, and diagenesis of terrestrial organic matter in marine sediments. However, phenolic compounds in the decomposition products of lignin have the characteristics of strong polarity and low volatility, so they cannot be directly detected by gas chromatography and need to be derivatized first, which makes the sample processing complicated and often results in incomplete derivatization. Therefore, it is of great significance to develop a simple and reliable method for determination of phenolic compounds of the lignin decomposition products in marine sediments to explore the source of organic matter and understand the environmental evolution process. OBJECTIVES To establish a simple and reliable method for the determination of phenolic compounds of lignin decomposition products in marine sediments using solid phase extraction (SPE) combined with ultra-high performance liquid chromatography-high resolution mass spectrometry, and to trace the content level and source of lignin in the sediments of Laizhou Bay in China. METHODS Marine sediment samples were first decomposed with oxidative-alkaline CuO and extracted by solid phase extraction. Briefly, the oxidation was carried out in a polytetrafluoroethylene digestion tank. 1.00g of sediment sample, 500mg of copper oxide, and 100mg of ammonium ferrous sulfate were accurately weighed and placed in the tank. The components were thoroughly mixed with the sample and then the digestion tank was transferred to a glove box filled with nitrogen. 8.0mL of aqueous sodium hydroxide solution with a concentration of 8.0% (bubbled with N2 to remove dissolved oxygen) was added to the tank. The digestion tank was covered tightly and transferred to an oven heating to 150℃ for reaction, which was terminated after 3h. After the digestion tank cooled to room temperature, it was carefully unscrewed, and an internal standard (ethyl vanillin) solution was added. Subsequently, the hydrolysate was transferred to a centrifuge tube, spun at 8000r/min for 10min, and the supernatant and reaction residue was separated. 2.0mL of 1.0% sodium hydroxide solution was added to rinse the residue, and centrifuged at 8000r/min for 10min. Combining the centrifuged supernatant obtained twice, the solution was acidified to pH=1 with hydrochloric acid. After the solution was left to stand for 30 minutes, solid phase extraction was performed. The SPE procedure was as follows: A hydrophilic-lipophilic balance (HLB) SPE cartridge (200mg, 6mL) was conditioned with 5mL of methanol and 5mL of ultrapure water. Sample solution was passed through the cartridge in a flow rate 1.0mL/min, and then the cartridges were rinsed with 10mL water, and dried under vacuum for about 3min. Phenolic compounds were eluted with 10mL ethyl acetate, and were evaporated by a rotary evaporator, reconstituted with sample solvent. Then, ultra-high performance liquid chromatography using ZORBAX Eclipse XDB-C18 column with packing particle size of 1.8μm was used to directly separate all target compounds at 28℃, with gradient elution. The mobile phase was composed of ultrapure water with 0.1% formic acid (V/V) and acetonitrile/methanol (9:1, V/V) , and the flow rate was set to 0.25mL/min. Electrospray ionization (in positive) time of flight mass spectrometry was applied to detect target compounds in full scan mode, and quantification was performed using an internal standard determination. RESULTS Firstly, chromatographic conditions and solid phase extraction conditions were systematically optimized. Ultra-high performance liquid chromatography was used for the chromatographic separation of phenolic compounds from lignin decomposition products in marine sediments. The separation effects of three mobile phase systems, namely, water-acetonitrile, water- methanol, and water-methanol-acetonitrile, were compared. When using a water-methanol -acetonitrile ternary mobile phase system, the resolution of various phenolic compounds was superior to the commonly used water-acetonitrile or water-methanol binary mobile phase systems in the literature. In addition, the effects of mobile phase acidity (trifluoroacetic acid, formic acid, and acetic acid were added into the mobile phase) on the separation of various phenolic compounds were investigated. The results showed that adding a certain concentration of all three acids to the mobile phase provided better separation results. Considering the compatibility with mass spectrometry, it was finally determined that adding 0.1% formic acid into the mobile phase achieved good peak patterns and resolution. In order to determine the ionization mode suitable for the analysis of phenolic compounds from lignin decomposition products in marine sediment, electrospray ionization (ESI) mass spectrometry was performed on each target phenolic compound in ESI+ and ESI− mode, respectively. Under ESI+ mode, various target phenolic compounds were less affected by interfering substances in the sample matrix, and the MS response value for most of the phenolic compounds was higher than that found in ESI− mode. Hence, ESI-TOF/MS in positive mode was selected to determine phenolic compounds of lignin decomposition products in marine sediment. Subsequently, the fragmentation voltage was optimized to obtain the highest sensitivity for all target phenolic compounds, which was the main mass spectrometric condition that affected the quantification accuracy and sensitivity. The effect of fragmentation voltage on the MS response signal of each target phenolic compound was investigated in the range of 80V to 200V. Overall, considering the detection sensitivity of the [M+H]+ ion peak of each target compound, 130V was selected as the optimal fragmentation voltage to determine phenolic compounds of lignin decomposition products in marine sediment. The effect of pH (1.0-2.5) of the loading solution for solid phase extraction on the extraction efficiency of various target phenolic compounds was systematically investigated, to ensure that the phenolic compounds of lignin decomposition products in marine sediments have a good recovery rate during the SPE process. When the pH of the loading solution was 1.0 and 1.5, the recovery rate of various phenolic compounds by using HLB solid phase extraction column was significantly higher than that of the loading solution adjusted pH to 2.0 and 2.5. When the pH of the sample solution was 1.0 and 1.5, although the recoveries of syringaldehyde and acetovanillone were relatively similar, the recoveries of other phenolic compounds were the highest at a pH of 1.0. Considering the recovery rate of all the target phenolic compounds and applicability of the method, the pH of the sample solution was confirmed to adjust to 1.0. In this study, HLB SPE column with 200mg of packing material was used to enrich phenolic compounds in sample extraction solution. Generally, 5-10mL of eluting solvent can ensure the full elution of all target phenolic compounds adsorbed on the SPE column. Therefore, based on the results of literature research, ethyl acetate was finally selected as the eluting solvent, with a dosage of 10mL. Under the optimum experimental conditions, the 11 main decomposition phenol compounds of lignin in marine sediments were well separated within 20 minutes. The proposed method had good precision (RSD was less than 9.0%), the correlation coefficient (R2) was not less than 0.9989 in the linear range, and the recovery rate of all spiked phenol compounds in blank marine sediment was in the range of 86.8%-93.2%, thereby indicating that the developed method would be suitable to determine the target decomposition phenol compounds of lignin in marine sediment. Subsequently, the method was used to determine the phenolic compounds of lignin decomposition products in the surface sediments of Laizhou Bay. The detection rate of 11 target phenolic compounds in 12 surface sediment samples was 100%, and the concentration of Σ8 in 12 surface sediment samples ranged from 0.001mg/10gds to 0.019mg/10gds. The value of C/V was between 0.18 and 0.81, with an average of 0.38; the value of S/V was between 0.18 and 0.45, with an average of 0.26; PON/P value was between 0.01 and 0.07, with an average of 0.03; P/(V+S) value was between 0.55 and 3.77, with an average of 1.44; (Ad/Al)v value was between 0.12 and 1.07, with an average of 0.48; the value of (Ad/Al)s was between 0.15 and 1.26, with an average of 1.02. CONCLUSIONS The above diagnostic ratios indicate that the lignin in the surface sediments of Laizhou Bay originate mainly from the herbaceous tissue of angiosperms, while the proportion of organic matter in vascular plants is relatively low. The degradation degree of terrestrial organic matter in most sampling stations is medium or high, but there is still a small amount of fresh plant debris. The proposed method has the advantages of high efficiency, simple for sample pretreatment, and is a powerful technique for the determination of main decomposition product phenolic compounds of lignin in marine sediments.

基于 2017年 5月所获取的温度、盐度、营养盐和叶绿素a(Chl a)等调查资料,本文从多学科交叉的视角分析了春季东海营养盐的空间分布格局及其与水文动力状况的关系,探讨了黑潮次表层水涌升和跨陆架输运对营养盐与Chla分布的影响.结果表明:浙江近海和调查海域东北部为2个营养盐高值区,且浙江近海的Chl a质量浓度较高;调查海域东南部上层总体具有低营养盐、低Chl a的特征,而该海域底层水体中的磷酸盐(PO4-P)浓度较高.调查海域的水团格局对营养盐浓度和分布具有重要的调控作用,其中浙闽沿岸水和黄海沿岸流的南下输运对应形成了 2个营养盐高值区;受黑潮次表层水入侵的影响,调查海域东南部底层呈现出高PO4-P的特征.春季黑潮次表层水由台湾东北部向东海陆架的入侵和涌升不仅显著影响了研究海域的温、盐度场和流场格局,同时也是实现营养盐跨陆架输运的重要通道和途径.受浙闽沿岸水和黑潮次表层水对营养盐输运的影响,在杭州湾东南—浙江近海对应形成了 Chl a高值区;富PO4-P且具有适宜N/P值的黑潮次表层水向陆架入侵所形成的上升流对维持近海的初级生产具有潜在的重要作用.本研究揭示了春季东海营养盐的空间分布格局及其与相关水文、生态过程的关系,为阐释该海域营养盐的控制机制和生态影响等提供了科学依据.

Lipophilic marine algal toxins (LMATs) are produced by some toxigenic microalgae, which pose a serious threat to marine ecosystem and even human health. The occurrence and environmental control factors of LMATs in the surface seawater and phytoplankton in spring in Laizhou Bay in which Huanghe (Yellow) River estuary is included, in Shandong, East China were investigated. Okadaic acid (OA), pectenotoxin-2 (PTX2), dinophysistoxin-1 (DTX1), pectenotoxin-2 seco acid (PTX2 SA), DTX2, 7-epi-PTX2 SA, PTX11, and 13-desmethyl spirolide C (SPX1) were detected from the surface seawater samples, and PTX2, 7-epi-PTX2 SA, OA, DTX2, DTX1, PTX2 SA, and PTX11 were discovered in the phytoplankton samples showed a decreasing trend. The concentrations of ∑LMATs in the seawater and phytoplankton ranged 2.03–74.38 ng/L on average of 13.72 ng/L and 0.98–479.27 pg/L on average of 50.20 pg/L, respectively. The joint influence of terrigenous input and internal circulation could promote the growth, toxin production, and toxin release of toxin-producing algae, leading to a higher content of LMATs in the bay nearby the Huanghe River estuary in both seawater and phytoplankton. The concentration of LMATs in spring was higher than that in summer, showing obvious seasonal variation. In addition, no significant correlation between most of the physiochemical parameters and LMAT contents in seawater was revealed by correlation analysis except for the positive correlation between DTX2 and chlorophyll a, OA and NH4-N. However, the increase of dissolved inorganic nitrogen content in seawater could enhance the production of OA, DTX1, and DTX2 in phytoplankton due probably to that the inorganic N input could benefit the growth and stimulate toxin production of toxin-producing algae. The result also proved that some PTX2 may be originated from Procentrum spp. and OA, DTXs and part of PTX2 may be originated from Dinophysis spp.

We studied the spatial variations of six volatile halocarbons (VHCs), namely, iodomethane (CH3I), chloroform (CHCl3), tetrachloroethylene (C2Cl4), bromodichloromethane (CHBrCl2), dibromomethane (CH2Br2), and carbon tetrachloride (CCl4), and the environmental influencing factors involved in the cycling of VHCs in the upper ocean (0-500 m) off the Northern Antarctic Peninsula (NAP) during the summer of 2018. About 5%-10% of the total biogenic VHCs in the upper ocean were accumulated in the assemblage layer (AL) with high chlorophyll a. However, higher VHCs levels were observed in the dicothermal layer (DL) compared with the AL because of the preservation from winter and production from dinoflagellates and chlorophytes. Owing to the co-existence occurrence of sharp seasonal pycnocline and thick permanent pycnocline, DL could be an important VHCs reservoir in the upper water column during summer. In response to melting of sea ice and glacier, decreased salinity was responsible for ca. 50% of the variation in the CH2Br2 and CCl4 concentrations, which corresponded with increased CH2Br2 and CCl4 concentrations in the less saline water mass. Anthropogenic CCl4 was found with an average concentration of 44.9 pmol/ L, and there was a strong positive relationship between CCl4 and CHCl3 in the upper water, indicating their similar source of pollutant transport caused by anthropogenic activities. Calculated sea- to-air fluxes of CCl4, C2Cl4, CHBrCl2, and CH2Br2 averaged 478.7, 93.7, 33.7, and 61.8 nmol/(m(2).d) in summer, respectively, indicating that the waters off the NAP are important sources of VHCs for the atmosphere and exert potentially adverse impacts on the Antarctica ozone depletion. (C) 2020 Elsevier B.V. All rights reserved.

Identifying trophic status shift and developing nutrient criteria were considered important for controlling coastal eutrophication. Based on data from 1980 to 2018, we used sequential t-test analysis of regime shifts and assessment of coastal trophic status models to detect regime shifts in trophic status in Bohai Bay (China). We identified four distinct periods: unimpaired (1980-1984), minimally impacted (1985-1994), tipping point (1995-1999) and severely degraded (2000-2018). Using the reference conditions at different trophic status, a frequency distribution analysis was performed to develop candidate nutrient criteria. By considering other factors, such as the quantity and quality of data and long-term nutrient variations, we determined recommended criteria for dissolved inorganic nitrogen (15.3 mu mol L-1) and phosphorus (0.42 mu mol L-1) in Bohai Bay. This study provides a novel and feasible approach to determine reference conditions for the determination of nutrient criteria for coastal waters.

To understand the current community structure and diversity of macrobenthos in Jiaozhou Bay, a survey was conducted at eight sampling stations in April, July, and October 2018, as well as January 2019. Eighty-two macrobenthos species were collected, including 30 of Annelida, 21 of Mollusca, 20 of Crustacea, 8 of Echinodermata, and 3 classified as "Others". Ruditapes philippinarum was a common dominant species in summer, autumn, and winter. The annual average abundance and biomass were 280 ind./m2 and 446.45 g/m2, respectively. Shannon-Wiener diversity varied from 0.09 to 2.45 with an average value of 1.14. Margalef richness was 0.17-2.32 with an average value of 0.89. Pielou evenness was 0.14-1.00 with an average value of 0.71. The seasonal variation patterns of all tested indices were largely the same, with the highest in spring, next highest in winter, and lower in summer and autumn. The diversity at different survey stations varies greatly.

The occurrence, spatiotemporal variations, influence factors and environmental risks of eight common neonicotinoids (NEOs), fipronil, and three fipronil metabolites (fipronil and its metabolites are collectively referred to as FIPs) in different seasons from the estuary to the inner area of Jiaozhou Bay, China were comprehensively investigated. First- and second-generation NEOs were found to be the predominant pesticides in this area. The average contents of ∑NEOs and ∑FIPs from the estuary to the inner bay decreased from 12.99 ng/L to 0.82 ng/L and from 1.10 ng/L to 0.17 ng/L, respectively. NEO and FIP concentrations were higher in summer and autumn. High ∑NEO content is distributed in main inflow rivers, such as Dagu River and Licun River, which are influenced by pesticide application. NEO concentrations in all rivers were high upstream and low downstream because of the influence of heavy rainfall and seawater dilution in summer. NEO concentrations were high along the coast and low at the mouth and center of Jiaozhou Bay in summer and autumn and evenly distributed in winter and spring. Temperature has a great influence on most NEOs and FIPs owing to its effect on their degradation. Nitrogen-containing nutrients have an important influence on the distribution of fipronil and acetamiprid, which may be due to the activity of nitrogen-containing functional groups in their structure. Only Licun River, Dagu River and Haibo river sewage treatment plant in summer posed a certain risk of chronic toxicity for NEOs using the new threshold established by the species sensitive distribution (SSD) method for Chinese native aquatic lives. These findings should arouse people's attention.

基于2012年和2014年中国北极科学考察航次白令海现场调查数据,分析白令海东陆架区二甲基硫(DMS)及其前体物质β-二甲基硫巯基丙酸内盐(DMSP)的空间分布特征和年际变化.结果显示,白令海东部陆架区DMS浓度呈自西向东递减的趋势,浓度平均值由2012年0.80 nmol·L-1(范围为0.11～2.27 nmol·L-1)增加至2014年1.33 nmol·L-1(范围为0.07～4.49 nmol·L-1).DMSP浓度的空间变化与DMS不一致,高值区位于断面东部,主要受近岸阿拉斯加沿岸流以及育空河淡水输入的影响.2012—2014年,溶解态DMSP(DMSPd)和颗粒态DMSP(DMSPp)浓度平均值分别从4.21 nmol·L-1、16.83 nmol·L-1提高至14.94 nmol·L-1、49.77 nmol·L-1,应是冷水团范围缩减以及浮游植物群落变化所引起的.DMS浓度同温度、cPO3-4、cSiO2-3显著相关,而DMS和DMSP浓度同无机氮浓度、盐度均存在显著相关性.表层海水DMS和DMSPd的生物生产速率均高于消费速率,且呈现出东高西低的趋势,原因是温度影响了微生物代谢活动.2014年的生产和消费速率均高于2012年的,主要由于表层海水DMS和DMSPd浓度升高和水团的年际变化.2012年和2014年表层海水中DMS微生物消耗速率平均值分别为13.66 nmol·L-1·d-1和33.87 nmol·L-1·d-1,海-气通量平均值分别为3.66μmol·m-2·d-1和5.33μmol·m-2·d-1,表层海水DMS通过海气扩散去除的周转时间分别是微生物消费的7.4和5.7倍.白令海东部陆架区表层水体中微生物消费是比海气释放更重要的DMS去除途径.