RESUMO
Volatile sulfur compounds, such as dimethyl sulfide (DMS), carbonyl sulfide (OCS), and carbon disulfide (CS2), have significant implications for both atmospheric chemistry and climate change. Despite the crucial role of oceans in regulating their atmospheric budgets, our comprehension of their cycles in seawater remains insufficient. To address this gap, a field investigation was conducted in the western North Pacific to clarify the sources, sinks, and biogeochemical controls of these gases in two different marine environments, including relatively eutrophic Kuroshio-Oyashio extension (KOE) and oligotrophic North Pacific subtropical gyre. Our findings revealed higher concentrations of these gases in both seawater and the atmosphere in the KOE compared to the subtropical gyre. In the KOE, nutrient-rich upwelling stimulated rapid DMS biological production, while reduced seawater temperatures hindered the removal of OCS and CS2, leading to their accumulation. Furthermore, we have quantitatively evaluated the relative contribution of each pathway to the source and sink of DMS, OCS, and CS2 within the mixed layer and identified vertical exchange as a potential sink in most cases, transporting substantial amounts of these gases from the mixed layer to deeper waters. This research advances our understanding of sulfur gas source-sink dynamics in seawater, contributing to the assessment of their marine emissions and atmospheric budgets.
RESUMO
Halogenated organic contaminants, such as chlorinated and brominated polycyclic aromatic hydrocarbons (Cl/Br-PAHs), are some of the most important emerging environmental pollutants. However, empirical data on Cl/Br-PAHs in estuarine and marine ecosystems are limited, rendering assessments of Cl/Br-PAH contamination in estuarine and offshore environments uncertain. Here the occurrence, sources, and ecological risks of 7 Cl-PAHs and 18 Br-PAHs were determined in surface sediments of the Yangtze River Estuary (YRE), a highly urbanized and industrialized area, and its adjacent marine area. The concentrations of Cl-PAHs ranged from 4.50 to 18.38 ng g-1 (average 7.19 ng g-1), while those of Br-PAHs ranged from 4.80 to 61.18 ng g-1 (average 14.11 ng g-1). The dominant Cl-PAH and Br-PAH in surface sediment were 9-chlorofluorene (17.79%) and 9-bromofluorene (58.49%), respectively. The distributions and compositions of Cl/Br-PAHs in the surface sediments varied considerably due to complex hydrodynamic and depositional conditions in the YRE and its adjacent marine area, as well as differences in physicochemical properties of different Cl/Br-PAHs. Positive matrix factorization revealed that the primary sources of Cl/Br-PAHs in the study area were e-waste dismantling (33.6%), waste incineration (23.2%), and metal smelting (11.0%). According to the risk quotient, the Cl/Br-PAHs in sediments posed no toxic risk to aquatic organisms.
Assuntos
Monitoramento Ambiental , Estuários , Sedimentos Geológicos , Hidrocarbonetos Policíclicos Aromáticos , Rios , Poluentes Químicos da Água , Sedimentos Geológicos/análise , Sedimentos Geológicos/química , Poluentes Químicos da Água/análise , China , Rios/química , Hidrocarbonetos Policíclicos Aromáticos/análise , Água do Mar/química , Água do Mar/análiseRESUMO
Nitric oxide (NO) is an atmospheric pollutant and climate forcer as well as a key intermediary in the marine nitrogen cycle, but the ocean's NO contribution and production mechanisms remain unclear. Here, high-resolution NO observations were conducted simultaneously in the surface ocean and the lower atmosphere of the Yellow Sea and the East China Sea; moreover, NO production from photolysis and microbial processes was analyzed. The NO sea-air exchange showed uneven distributions (RSD = 349.1%) with an average flux of 5.3 ± 18.5 × 10-17 mol cm-2 s-1. In coastal waters where nitrite photolysis was the predominant source (89.0%), NO concentrations were remarkably higher (84.7%) than the overall average of the study area. The NO from archaeal nitrification accounted for 52.8% of all microbial production (11.0%). We also examined the relationship between gaseous NO and ozone which helped identify sources of atmospheric NO. The sea-to-air flux of NO in coastal waters was narrowed by contaminated air with elevated NO concentrations. These findings indicate that the emissions of NO from coastal waters, mainly controlled by reactive nitrogen inputs, will increase with the reduced terrestrial NO discharge.
Assuntos
Poluentes Atmosféricos , Poluição do Ar , Água do Mar , Óxido Nítrico , Poluentes Atmosféricos/análise , Oceanos e Mares , China , Monitoramento AmbientalRESUMO
The Pacific Ocean plays an important role in regulating the budget of climatically active gases and the burden of sulfate aerosols. Here, a field investigation was conducted to clarify the key processes and factors controlling climatically active gases, including dimethyl sulfide (DMS), carbonyl sulfide (OCS), carbon disulfide (CS2), and carbon dioxide (CO2), in both surface seawater and the lower atmosphere of the western Pacific. In addition, the relative contributions of different sources to atmospheric sulfate aerosols were quantitatively estimated, and their causes were explored. The maximum concentrations of DMS, OCS and CS2 and the minimum partial pressure of CO2 (pCO2) were observed in the Kuroshio-Oyashio Extension. Kuroshio-induced mesoscale eddies brought abundant nutrients and organic matter from the subsurface layer of Oyashio into the euphotic layer, thus enhancing primary productivity and accelerating the photoreaction of organic matter. These processes led to higher concentrations of DMS, OCS and CS2 and lower pCO2. However, the oligotrophic subsurface layer in the subtropical gyre and the strong barrier layer in the equatorial waters suppressed the upward fluxes of nutrients and organic matter, resulting in lower surface concentrations of DMS, OCS, and CS2 in these areas. Being far from the continents, atmospheric concentrations of DMS, OCS and CS2 and pCO2 in the western Pacific generally were observed to depend on the local sea-to-air exchange and may be regulated by atmospheric oxidation and mixing of air masses. In general, oceanic DMS emissions played an important role in the formation of sulfate aerosols in the western Pacific (accounting for â¼19.5% of total sulfate aerosols), especially in the Kuroshio-Oyashio Extension (â¼32.3%). These processes in seawater may also determine the variations and emissions of other climatically active gases from biogenic and photochemical sources.
Assuntos
Dióxido de Carbono , Gases , Sulfatos , Oceano Pacífico , AerossóisRESUMO
Understanding the control mechanisms of carbon dioxide (CO2) emissions in intertidal wetland sediments is beneficial for the concern of global carbon biogeochemistry and climate change. Nevertheless, multiple controls on CO2 emissions from intertidal wetland sediments to the atmosphere still need to be clarified. This study investigated the effect of tidal action on CO2 emissions from salt marsh sediments covered by Spartina alterniflora in the Jiaozhou Bay wetland using the static chamber method combined with an infrared CO2 detector. The results showed that the CO2 emission fluxes from the sediment during ebb tides were higher than those during flood tides. The whole wetland sediment acted as a weak source of atmospheric CO2 (average flux: 24.44 ± 16.80 mg C m-2 h-1) compared to terrestrial soils and was affected by the cycle of seawater inundation and exposure. The tidal influence on vertical dissolved inorganic carbon (DIC) transport in the sediment was also quantitated using a two-end member mixing model. The surface sediment layer (5-15 cm) with maximum DIC concentration during ebb tides became the one with minimum DIC concentration during flood tides, indicating the DIC transport from the surface sediment to seawater. Furthermore, aerobic respiration by microorganisms was the primary process of CO2 production in the sediment according to 16 S rDNA sequencing analysis. This study revealed the strong impact of tidal action on CO2 emissions from the wetland sediment and provided insights into the source-sink pattern of CO2 and DIC at the land-ocean interface.
Assuntos
Dióxido de Carbono , Áreas Alagadas , Dióxido de Carbono/análise , Metano/análise , Água do Mar , Solo/químicaRESUMO
Oceanic emissions are a major source of atmospheric, very short-lived, ozone-depleting, brominated substances. These substances can be produced by marine microalgae, estimates of their current and future emissions are imperfect, because the processes by which marine microalgae respond to environmental changes are rarely account for environmental pollutants. Here, concurrent measurements of the potential effects of polystyrene (PS) microplastics with concentrations of 25-100 mg/L on the growth of Phaeodactylum tricornutum and their volatile halocarbons (VHCs) production were made over a 20-day culture period. The maximum inhibition rates (IR) due to 0.1 µm and 0.5 µm PS microplastics on cell density were 40.11 % and 32.87 %, on Chl a content were 25.89 % and 20.73 %, and on Fv/Fm were 9.74 % and 9.00 %, respectively. All IR showed dose-dependent effects with maxima occurring in the logarithmic phase. However, in the stationary phase, P. tricornutum exposed to PS microplastics exhibited improved attributes. Enhanced biogenesis of VHCs was induced by the excess reactive oxygen species in algal cells due to microplastics exposure, and their production rates were higher in the logarithmic phase than stationary phase. This represents that oxidative stress to cells plays a dominant role in determining the release of CHBrCl2, CHBr2Cl, and CHBr3. Hence, we suggest that the widespread microplastics in the ocean may be partly responsible for the increase in the emission of VHCs by marine phytoplankton, thereby affecting the ozone layer recovery in the future.
Assuntos
Diatomáceas , Microalgas , Poluentes Químicos da Água , Microplásticos/toxicidade , Poliestirenos/toxicidade , Plásticos/toxicidade , Poluentes Químicos da Água/toxicidadeRESUMO
Monomethylamine (MMA) is an important climate-active oceanic trace gas and ubiquitous in the oceans. γ-Glutamylmethylamide synthetase (GmaS) catalyzes the conversion of MMA to γ-glutamylmethylamide, the first step in MMA metabolism in many marine bacteria. The gmaS gene occurs in â¼23% of microbial genomes in the surface ocean and is a validated biomarker to detect MMA-utilizing bacteria. However, the catalytic mechanism of GmaS has not been studied because of the lack of structural information. Here, the GmaS from Rhodovulum sp. 12E13 (RhGmaS) was characterized, and the crystal structures of apo-RhGmaS and RhGmaS with different ligands in five states were solved. Based on structural and biochemical analyses, the catalytic mechanism of RhGmaS was explained. ATP is first bound in RhGmaS, leading to a conformational change of a flexible loop (Lys287-Ile305), which is essential for the subsequent binding of glutamate. During the catalysis of RhGmaS, the residue Arg312 participates in polarizing the γ-phosphate of ATP and in stabilizing the γ-glutamyl phosphate intermediate; Asp177 is responsible for the deprotonation of MMA, assisting the attack of MMA on γ-glutamyl phosphate to produce a tetrahedral intermediate; and Glu186 acts as a catalytic base to abstract a proton from the tetrahedral intermediate to finally generate glutamylmethylamide. Sequence analysis suggested that the catalytic mechanism of RhGmaS proposed in this study has universal significance in bacteria containing GmaS. Our results provide novel insights into MMA metabolism, contributing to a better understanding of MMA catabolism in global carbon and nitrogen cycles.
Assuntos
Carbono-Nitrogênio Ligases/metabolismo , Glutamatos/metabolismo , Trifosfato de Adenosina/metabolismo , Catálise , Escherichia coli/metabolismo , Ácido Glutâmico/metabolismo , Magnésio/metabolismo , Metilaminas/metabolismo , Microscopia Eletrônica , Rhodovulum/metabolismoRESUMO
Most marine copiotrophic bacteria can produce extracellular enzymes to degrade biopolymers into bio-available smaller solutes, while oligotrophic bacteria usually cannot. Bacterial extracellular enzymes and enzymatic products can be a common resource that could be utilized by both copiotrophs and oligotrophs; when present, oligotrophs may outcompete the enzyme-producing copiotrophs. However, copiotrophs and oligotrophs consistently coexist in the ocean. How they maintain coexistence has still not been experimentally studied. In this study, the interaction and coexistence of a copiotroph and an oligotroph, isolated from the same surface seawater sample and utilizing the same proteinaceous substrate, were experimentally investigated. The copiotroph could secrete extracellular proteases to degrade and then utilize the proteinaceous substrate. The oligotroph was unable to utilize the proteinaceous substrate by itself, but could grow by using the hydrolysate amino acids. The copiotroph outcompeted the oligotroph by adsorbing the amino acids quickly and having a higher growth rate in the rich medium. The oligotroph survived by adapting to low concentration of nutrients. The copiotroph and oligotroph were able to maintain long-term (up to 142 days) coexistence in the laboratory. This study indicates that differences in the utilization of different concentrations of nutrients can drive the coexistence of marine copiotrophs and oligotrophs.
Assuntos
Bactérias/crescimento & desenvolvimento , Interações Microbianas , Água do Mar/microbiologia , Aminoácidos/análise , Aminoácidos/metabolismo , Bactérias/metabolismo , Meios de Cultura/química , Meios de Cultura/metabolismo , Nutrientes/análise , Nutrientes/metabolismo , Água do Mar/químicaRESUMO
Nitric oxide (NO) is a short-lived intermediate of the oceanic nitrogen cycle, and it is produced by biological and photochemical processes in the ocean. Nitrogen dioxide (NO2) is a reactive atmospheric compound which has not been determined in the ocean so far. Here, we present the setup and validation of a novel continuous underway measurement system to measure dissolved NO and NO2 in the surface ocean. The system consists of a seawater/gas equilibration component coupled to a chemiluminescence detector. It was successfully deployed during a 12 day cruise to the East China Sea in May 2018. Dissolved NO and NO2 surface concentrations ranged from Assuntos
Óxido Nítrico
, Dióxido de Nitrogênio
, China
, Medições Luminescentes
, Oceanos e Mares
, Água do Mar
RESUMO
Microbial production and catabolism of dimethylsulfoniopropionate (DMSP), generating the climatically active gases dimethyl sulfide (DMS) and methanethiol (MeSH), have key roles in global carbon and sulfur cycling, chemotaxis, and atmospheric chemistry. Microorganisms in the sea surface microlayer (SML), the interface between seawater and atmosphere, likely play an important role in the generation of DMS and MeSH and their exchange to the atmosphere, but little is known about these SML microorganisms. Here, we investigated the differences between bacterial community structure and the distribution and transcription profiles of the key bacterial DMSP synthesis (dsyB and mmtN) and catabolic (dmdA and dddP) genes in East China Sea SML and subsurface seawater (SSW) samples. Per equivalent volume, bacteria were far more abundant (~ 7.5-fold) in SML than SSW, as were those genera predicted to produce DMSP. Indeed, dsyB (~ 7-fold) and mmtN (~ 4-fold), robust reporters for bacterial DMSP production, were also far more abundant in SML than SSW. In addition, the SML had higher dsyB transcripts (~ 3-fold) than SSW samples, which may contribute to the significantly higher DMSP level observed in SML compared with SSW. Furthermore, the abundance of bacteria with dmdA and their transcription were higher in SML than SSW samples. Bacteria with dddP and transcripts were also prominent, but less than dmdA and presented at similar levels in both layers. These data indicate that the SML might be an important hotspot for bacterial DMSP production as well as generating the climatically active gases DMS and MeSH, a portion of which are likely transferred to the atmosphere.
Assuntos
Bactérias/isolamento & purificação , Microbiota/fisiologia , Água do Mar/microbiologia , Compostos de Sulfônio/metabolismo , Bactérias/classificação , Fenômenos Fisiológicos Bacterianos , ChinaRESUMO
The microbial cleavage of dimethylsulfoniopropionate (DMSP) generates volatile DMS through the action of DMSP lyases and is important in the global sulfur and carbon cycles. When released into the atmosphere from the oceans, DMS is oxidized, forming cloud condensation nuclei that may influence weather and climate. Six different DMSP lyase genes are found in taxonomically diverse microorganisms, and dddQ is among the most abundant in marine metagenomes. Here, we examine the molecular mechanism of DMSP cleavage by the DMSP lyase, DddQ, from Ruegeria lacuscaerulensis ITI_1157. The structures of DddQ bound to an inhibitory molecule 2-(N-morpholino)ethanesulfonic acid and of DddQ inactivated by a Tyr131Ala mutation and bound to DMSP were solved. DddQ adopts a ß-barrel fold structure and contains a Zn(2+) ion and six highly conserved hydrophilic residues (Tyr120, His123, His125, Glu129, Tyr131, and His163) in the active site. Mutational and biochemical analyses indicate that these hydrophilic residues are essential to catalysis. In particular, Tyr131 undergoes a conformational change during catalysis, acting as a base to initiate the ß-elimination reaction in DMSP lysis. Moreover, structural analyses and molecular dynamics simulations indicate that two loops over the substrate-binding pocket of DddQ can alternate between "open" and "closed" states, serving as a gate for DMSP entry. We also propose a molecular mechanism for DMS production through DMSP cleavage. Our study provides important insight into the mechanism involved in the conversion of DMSP into DMS, which should lead to a better understanding of this globally important biogeochemical reaction.
Assuntos
Alphaproteobacteria/metabolismo , Sulfetos/química , Compostos de Sulfônio/química , Sequência de Aminoácidos , Carbono/química , Ciclo do Carbono , Liases de Carbono-Enxofre/química , Catálise , Domínio Catalítico , Dicroísmo Circular , Cristalografia por Raios X , Análise Mutacional de DNA , Metais/química , Simulação de Dinâmica Molecular , Dados de Sequência Molecular , Oceanos e Mares , Oxigênio/química , Ligação Proteica , Dobramento de Proteína , Estrutura Secundária de Proteína , Enxofre/química , Microbiologia da Água , Zinco/químicaRESUMO
Dimethylsulfoniopropionate (DMSP) and nitric oxide (NO) in marine microalgae are considered as two important compounds involved in a variety of physiological functions. We examined the NO responses and the growth of Isochrysis galbana Parke and Gymnodinium sp. when supplemented with different concentrations of DMSP solutions in the cultures. Production of DMSP and dimethylsulfide (DMS) in Amphidinium carterae and Emiliania Huxleyi was investigated after the addition of NO donor sodium nitroprusside (SNP) and NO solution to algal media. The release peaks of NO were observed in cell suspensions of I. galbana Parke and Gymnodinium sp. immediately after the injection of DMSP solutions. The growth of these two microalgae was found to be significantly promoted or inhibited caused by exogenous DMSP. There was a decrease of DMSP concentrations in algal cultures within 24 h, accompanied with an increase in DMS, due to the effect of NO. The results provided direct evidence to confirm that there exist mutual effects of DMSP and NO during the growth of marine microalgae, which is speculated to be related to their roles as signaling molecules in planktonic communities.
Assuntos
Biologia Marinha , Microalgas/crescimento & desenvolvimento , Óxido Nítrico/farmacologia , Compostos de Sulfônio/farmacologiaRESUMO
The distributions and toxicities of the pollutants benzothiazoles (BTHs), benzotriazoles (BTRs), and benzotriazole ultraviolet stabilizers (BUVs) have attracted much attention, but most research has focused on freshwater environments and few have examined their levels in marine environments. This study, for the first time, investigated the spatial and temporal variability and ecological risks of BTHs, BTRs and BUVs in the Yangtze River estuary and its adjacent area, and further elucidated how environmental factors influence the transport of these contaminants. The concentrations of BTHs, BTRs, and BUVs in seawater showed significant seasonal variability, with the highest concentrations in summer, followed by autumn, and then winter-spring. The spatiotemporal variability in BTHs, BTRs and BUVs in the seawater and sediments samples showed decreasing trends from nearshore to offshore, reflecting the influence of river discharge. Marine debris and continuous discharge from cities were responsible for the high detection frequency of these contaminants in the YRE and its adjacent area. Furthermore, the moderate risk from the presence of BTHs, BTRs, and BUVs as they accumulate in sediments should not be ignored. Our study provides new insights into the fate and ecological risk of BTHs, BTRs, and BUVs in the estuary.
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An integrated observation of NOx that included coastal cities and oceanic cruises covering the Qingdao coastal waters sites (QDCW) and the Yellow Sea and East China Sea sites (YECS) was conducted in spring. The average concentrations of the coastal cities, the QDCW, and the YECS were 5.4 ± 4.1, 4.2 ± 3.5, and 2.9 ± 6.8 ppb for NO while 18.5 ± 7.2, 9.4 ± 5.2, and 4.9 ± 6.4 ppb for NO2, depicting lowest levels in the open seas. Atmospheric NO and NO2 showed similar spatial variations over the seas, the stations where the air masses originated from land or nearshore regions showed higher levels, but the decisive influencing factors were not the same in the different study areas. The calculated NOx flux value in the YECS (-8.7 × 10-17 mol N cm-2) indicated that the sea surface was a net sink of atmospheric NOx.
Assuntos
Poluentes Atmosféricos , Água do Mar , Poluentes Atmosféricos/análise , Dióxido de Nitrogênio , Monitoramento Ambiental , Oceanos e Mares , Óxidos de Nitrogênio , ChinaRESUMO
Dimethyl sulfide (DMS) is a prevalent volatile organic sulfur compound relevant to the global climate. Ecotoxicological effects of nano- and microplastics (NPs and MPs) on phytoplankton, zooplankton, and bacteria have been investigated by numerous studies. Yet, the influences of NPs/MPs on dimethylated sulfur compounds remains understudied. Herein, we investigated the impacts of polystyrene (PS) NPs/MPs (80 nm, 1 µm, and 10 µm) on zooplankton grazing, chlorophyll a (Chl a) concentration, bacterial community, dimethylsulfoniopropionate (DMSP), and DMS production in the microcosms. Our findings revealed that rotifer grazing increased the production of DMS in the absence of NPs/MPs but did not promote DMS production when exposed to NPs/MPs. The ingestion rates of the rotifer and copepod exposed to NPs/MPs at high concentrations were significantly reduced. NPs/MPs exposure significantly decreased DMS levels in the treatments with rotifers compared to the animal controls. In the bacterial microcosms, smaller NPs/MPs sizes were more detrimental to Chl a concentrations compared to larger sizes. The study revealed a stimulatory effect on Chl a concentrations, DMSPd concentrations, and bacterial abundances when exposed to 10 µm MP with low concentrations. The effects of NPs/MPs on DMS concentrations were both dose- and size-dependent, with NPs showing greater toxicity compared to larger MPs. NPs/MPs led to changes in bacterial community compositions, dependent on both dosage and size. NPs caused a notable decrease in the alpha diversities and richness of bacteria compared to MPs. These results provide insights into the influences of NPs/MPs on food webs, and subsequently organic sulfur compounds cycles.
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The sorption behavior of phosphorus on marine sediments in the presence of black carbon derived from fly ash (FC) was studied. For both the FC and sediment samples, the kinetic curves could be described by a two-compartment first order equation, and the isotherms fit the Freundlich and Langmuir models well. The high specific surface area with abundant acidic functional groups of FC promoted the sorption and make this process more irreversible. The effects were more significant with higher amount of FC added. After sorption, more significant increase in Ex-P, Fe/Al-P and CaP was found in the sediment with FC added, while the organic groups in FC rarely react with phosphorus to form OP. The pH of medium influenced the sorption character, and FC promoted the process significantly at pH < pHPZNPC. The sorption was endothermic with an increase in randomness. The presence of FC had little effects on the thermodynamic parameters.
Assuntos
Cinza de Carvão , Sedimentos Geológicos , Fósforo , Poluentes Químicos da Água , Sedimentos Geológicos/química , Fósforo/química , Fósforo/análise , Cinza de Carvão/química , Adsorção , Poluentes Químicos da Água/química , Poluentes Químicos da Água/análise , Cinética , Fuligem/química , Carbono/química , TermodinâmicaRESUMO
Sea-to-air emissions of very short-lived brominated halocarbons (VSLBrHs) are known to contribute to 30 % of stratospheric and tropospheric ozone depletion. However, empirical data on their occurrence in open ocean are scarce, which makes it difficult to estimate the significant contribution of open ocean releases to the global budget of halocarbons. This study was conducted in 2022 to explore the spatial variations of VSLBrHs and their controlling factors in the western tropical Pacific Ocean (WTPO). The findings highlighted that high biological productivity and the resulting dissolved organic matter (DOM) as well as upwelling dynamics significantly influenced the distribution and production of VSLBrHs in seawater, with atmospheric levels primarily governed by oceanic emissions. Based on the simultaneous observation of seawater and atmospheric concentrations, the mean sea-to-air fluxes of CH2Br2, CHBr3, CHBrCl2, and CHBr2Cl were estimated to be 1.01, 6.65, 9.31, and 7.25 nmol m-2 d-1, respectively. Sea-to-air fluxes of these gases in the upwelling regions were 9.0, 4.6, 2.9, and 6.8 times those in the non-upwelling regions, respectively. Additionally, in-situ incubation experiments revealed that the enzymatic mediated biosynthesis pathways of VSLBrHs were enhanced under temperature and light-induced stress and in waters rich in humus-like substances. Therefore, we tentatively concluded that abundant photothermal conditions and the existence of upwelling in the WTPO made it a potential hotspot for the emission of VSLBrHs. This study offers critical insights into the environmental dynamics of VSLBrHs emissions and underscores the importance of regional oceanic conditions in influencing atmospheric greenhouse gas compositions.
RESUMO
The carbonate chemistry in river-dominated marginal seas is highly heterogeneous, and there is ongoing debate regarding the definition of atmospheric CO2 source or sink. On this basis, we investigated the carbonate chemistry and air-sea CO2 fluxes in a hotspot estuarine area: the Changjiang Estuary during winter and summer. The spatial characteristics of the carbonate system were influenced by water mixing of three end-members in winter, including the Changjiang freshwater with low total alkalinity (TA) concentration, the less saline Yellow Sea Surface Water with high TA, and the saline East China Sea (ECS) offshore water with moderate TA. While in summer with increased river discharge, the carbonate system was regulated by simplified two end-member mixing between the Changjiang freshwater and the ECS offshore water. By performing the end-member mixing model on DIC variations in the river plume region, significant biological addition of DIC was found in winter with an estimation of -120 ± 113 µmol kg-1 caused by wintertime organic matter remineralization from terrestrial source. While this biological addition of DIC shifted to DIC removal due to biological production in summer supported by the increased nutrient loading from Changjiang River. The pCO2 dynamics in the river plume and the ECS offshore were both subjected to physical mixing of freshwater and seawater, whether in winter and summer. In the inner estuary without horizontal mixing, the pCO2 dynamics were mainly influenced by biological uptake in winter and temperature in summer. The inner estuary, the river plume, and the ECS offshore were sources of atmospheric CO2, with their contributions varying seasonally. The Changjiang runoff enhanced the inner estuary's role as a CO2 source in summer, while intensive biological uptake reduced the river plume's contribution.
Assuntos
Dióxido de Carbono , Carbonatos , Monitoramento Ambiental , Estuários , Rios , Estações do Ano , Água do Mar , Dióxido de Carbono/análise , Carbonatos/análise , China , Rios/química , Água do Mar/química , Poluentes Químicos da Água/análise , Poluentes Atmosféricos/análiseRESUMO
Protozoa play a pivotal role in the microbial cycle, and ciliated protozoan grazing habits are associated with dimethyl sulfide (DMS) cycle. Many studies have explored the impacts of nanoplastics (NPs) and microplastics (MPs) on ecotoxicological effects of ciliates. However, limited research exists on NPs and MPs influences on the production of organic sulfur compounds. The impact of NPs and MPs on the production of dimethyl sulfoxide (DMSO) and carbonyl sulfide (COS) remains unclear. Therefore, we examined the impacts of three concentrations (1 × 105, 5 × 105, and 1 × 106 items/mL) of polystyrene (PS) NPs (50 nm) and MPs (1 and 5 µm) on the ecotoxicology and DMS/dimethylsulfoniopropionate (DMSP)/DMSO/COS production in the ciliate Uronema marinum. NPs and MPs exposure were found to reduce the abundance, growth rate, volume, and biomass of U. marinum. Additionally, NPs and MPs increased the superoxide anion radical (O2Ëâ) production rates and malondialdehyde (MDA) contents (24 h), leading to a decline in glutathione (GSH) content and an ascend in superoxide dismutase (SOD) activity to mitigate the effects of reactive oxygen species (ROS). Exposure to PS NPs and MPs decreased the ingestion rates of algae by 7.5-14.4%, resulting in decreases in DMS production by 56.8-85.4%, with no significant impact on DMSO production. The results suggest a distinct pathway for the production of DMSO or COS compared to DMS. These findings help us to understand the NPs and MPs impacts on the marine ecosystem and organic sulfur compound yield, potentially influencing the global climate.
RESUMO
Due to the potential impacts of microplastics (MPs) and nanoplastics (NPs) on algal growth and thereby affect the climate-relevant substances, dimethylsulfoniopropionate (DMSP) and dimethyl sulfide (DMS), we studied the polystyrene (PS) MPs and NPs of 1 µm and 80 nm impacts on the growth, chlorophyll content, reactive oxygen species (ROS), antioxidant enzyme activity, and DMS/DMSP production in Emiliania huxleyi. E. huxleyi is a prominent oceanic alga that plays a key role in DMS and DMSP production. The results revealed that high concentrations of MPs and NPs inhibited the growth, carotenoid (Car), and Chl a concentrations of E. huxleyi. However, short-time exposure to low concentrations of PS MPs and NPs stimulated the growth of E. huxleyi. Furthermore, high concentrations of MPs and NPs resulted in an increase in the superoxide anion radical (O2.-) production rate and a decrease in the malondialdehyde (MDA) content compared with the low concentrations. Exposure to MPs and NPs at 5 mg L-1 induced superoxide dismutase (SOD) activity as a response to scavenging ROS. High concentrations of MPs and NPs significantly inhibited the production of DMSP and DMS. The findings of this study support the potential ecotoxicological impacts of MPs and NPs on algal growth, antioxidant system, and dimethylated sulfur compounds production, which maybe potentially impact the global climate.