Influence of the community assemblage on sulfur distributions in the South China sea.

Marine distribution of dimethylsulfoniopropionate (DMSP) and its cleavage product dimethyl sulfide (DMS) is greatly affected by the community structures of bacteria, phytoplankton, and zooplankton. Spatial distributions of dissolved and particulate DMSP (DMSPd,p), and DMS were measured and their relationships with DMSP lyase activity (DLA), abundance of DMSP-consuming bacteria (DCB), and the community structures of phytoplankton, zooplankton, and bacteria were determined during summer in the South China Sea (SCS). The depth distributions of DMSPd,p exhibited a similar trend with Chl a, reaching their maxima in the mixing layer. The DMS concentration was positively correlated with DCB abundance and DLA, indicating that DCB and DMSP lyase had a significant effect on DMS production. High DMS concentrations in the horizontal distribution coincided with high DCB abundance and DLA and may be due to the rapid growth of phytoplankton resulting from the high dissolved inorganic nitrogen concentration brought by the cold vortices. Moreover, the highest copepod abundance at station G3 coincided with the highest DMS concentrations there among stations B4, F2, and G3. These results suggest that copepod may play an important role in DMS production. The bacterial SAR11 clade was positively correlated with DLA, indicating its significant contribution to DMSP degradation in the SCS. These findings contribute to the understanding of the effect of the community assemblage on DMSP/DMS distributions in the SCS dominated by mesoscale vortices.

Emission of CO2 and its related carbonate system dynamics in a hotspot area during winter and summer: The Changjiang River estuary.

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.

Occurrence of halogenated organic contaminants in surface sediments of the Yangtze River estuary and its adjacent marine area.

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.

Revealing the Marine Cycles of Volatile Sulfur Compounds and Their Biogeochemical Controls: A Case of the Western North Pacific.

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.

Distribution and influencing factors of atmospheric nitrogen oxides (NOx) over the east coast of China in spring: Indication of the sea as a sink of the atmospheric NOx.

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.

Effects of nanoplastics exposure on ingestion, life history traits, and dimethyl sulfide production in rotifer Brachionus plicatilis.

Microplastics (MPs) and nanoplastics (NPs) have gained global concern due to their detrimental effects on marine organisms. We investigated the effects of 80 nm polystyrene (PS) NPs on life history traits, ingestion, and dimethyl sulfide (DMS) and dimethylsulfoniopropionate (DMSP) production in the rotifer Brachionus plicatilis. Fluorescently labeled 80 nm PS NPs were ingested by the rotifer B. plicatilis and accumulated in the digestive tract. The lethal rates of B. plicatilis exposed to NPs were dose-dependent. High concentrations of PS NPs exposure had negative effects on developmental duration, leading to prolonged embryonic development and pre-reproductive periods, shortened reproductive period, post-reproductive period, and lifespan in B. plicatilis. High concentrations of PS NPs exposure inhibited life table demographic parameters such as age-specific survivorship and fecundity, generation time, net reproductive rate, and life expectancy. Consequently, the population of B. plicatilis was adversely impacted. Furthermore, exposure to PS NPs resulted in a reduced ingestion rate in B. plicatilis, as well as a decreased in DMS, particulate DMSP (DMSPp) concentration, and DMSP lyase activity (DLA), which exhibited a dose-response relationship. B. plicatilis grazing promoted DLA and therefore increased DMS production. PS NPs exposure caused a decline in the increased DMS induced by rotifer grazing. Our results help to understand the ecotoxicity of NPs on rotifer and their impact on the biogeochemical cycle of dimethylated sulfur compounds.

Spatiotemporal variation, partitioning, and ecological risk assessment of benzothiazoles, benzotriazoles, and benzotriazole UV absorbers in the Yangtze River Estuary and its adjacent area.

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.

Physiological responses and altered halocarbon production in Phaeodactylum tricornutum after exposure to polystyrene microplastics.

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.

Driving force of tidal pulses on denitrifiers-dominated nitrogen oxide emissions from intertidal wetland sediments.

Intertidal wetland sediments are an important source of atmospheric nitrogen oxides (NOx), but their contribution to the global NOx budget remains unclear. In this work, we conducted year-round and diurnal observations in the intertidal wetland of Jiaozhou Bay to explore their regional source-sink patterns and influence factors on NOx emissions (initially in the form of nitric oxide) and used a dynamic soil reactor to further extend the mechanisms underlying the tidal pulse of nitric oxide (NO) observed in our investigations. The annual fluxes of NOx in the vegetated wetland were significantly higher than those in the wetland without vegetation. Their annual variations could be attributed to changes in temperature and the amount of organic carbon in the sediment, which was derived from vegetated plants and promoted the carbon-nitrogen cycle. Anaerobic denitrifiers had advantages in the intertidal wetland sediment and accounted for the major NO production (63.8 %) but were still limited by nitrite and nitrate concentrations in the sediment. Moreover, the tidal pulse was likely a primary driver of NOx emissions from intertidal wetlands over short periods, which was not considered in previous investigations. The annual NO exchange flux considering the tide pulse contribution (8.93 ± 1.72 × 10-2 kg N ha-1 yr-1) was significantly higher than that of the non-pulse period (4.14 ± 1.13 × 10-2 kg N ha-1 yr-1) in our modeling result for the fluxes over the last decade. Therefore, the current measurement of NOx fluxes underestimated the actual gas emission without considering the tidal pulse.

[Effects of Polyethylene Microplastics on Growth and Halocarbon Release of Marine Microalgae].

Volatile halocarbons (VHCs) are important trace greenhouse gases and ozone-destroying substances and play an important role in global climate change. As an important producer of VHCs, the release of VHCs by marine microalgae is affected by marine environmental factors. Microplastics are an important pollutant in the ocean; however, there are few studies on VHCs release from marine microalgae under the influence of microplastics. This study aimed to explore the effects of different concentrations of polyethylene (PE) microplastics on the growth, photosynthesis, oxidative stress, and release of VHCs by diatoms and dinoflagellates by measuring the density of algae, maximum photoquantum efficiency (Fv/Fm), reactive oxygen species (ROS), and concentration of VHCs. The results revealed that PE microplastics mainly inhibited the growth of Nitzschia closterium f. minutissima and promoted the growth of Prorocentrum donghaiense. The addition of 50 µm PE microplastics had a shielding effect on the growth of the two microalgae, resulting in the inhibition of Fv/Fm of two kinds of microalgae, and the inhibition effect of PE microplastics on P. donghaiense was more significant. Compared with that in the control group, PE microplastic stress stimulated the increase in ROS production in algal cells, which caused an oxidative stress response in these microalgae, thereby promoting the release of three types of volatile brominated halocarbons.

The sulfate assimilation and reduction of marine microalgae and the regulation of illumination.

To examine the sulfate assimilation and reduction process and the regulation of illumination, diatom Phaeodactylum tricornutum and dinoflagellate Amphidinium carterae were selected for continuous simulation incubation under different photon flux densities (PFDs) (54, 108 and 162 µmol photons m-2 s-1), and concentration variations of related sulfur compounds sulfate, dimethylsulfoniopropionate (DMSP), dimethylsulfide (DMS) and acrylic acid (AA) in the culture system were observed. The optimal PFD for the growth of two microalgae was 108 µmol photons m-2 s-1. However, the maximum sulfate absorption occurred at 162 µmol photons m-2 s-1 for P. tricornutum and at 54 µmol photons m-2 s-1 for A. carterae. With the increase of PFD, the release of DMSP by P. tricornutum decreased while A. carterae increased. The largest release amount of DMS was 0.59 ± 0.05 fmol cells-1 for P. tricornutum and 2.61 ± 0.89 fmol cells-1 for A. carterae under their optimum growth light condition. The sulfate uptake of P. tricornutum was inhibited by the addition of amino acids, cysteine had a greater inhibitory effect than methionine, and the absorption process was controlled by light. The intermediate products of sulfur metabolism had an up-control effect on the sulfate uptake process of P. tricornutum. However, the addition of amino acids had no obvious effect on the sulfate absorption of A. carterae.

Tidal effects on carbon dioxide emission dynamics in intertidal wetland sediments.

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.

Sulfur hexafluoride in the marine atmosphere and surface seawater of the Western Pacific and Eastern Indian Ocean.

Sulfur hexafluoride (SF6) is a powerful greenhouse gas with a high global warming potential. While SF6 emissions from urban areas have been extensively studied, our knowledge about SF6 concentrations in the oceanic atmosphere and its air-sea exchange remains limited. Herein, the concentrations of SF6 in the atmosphere and surface seawater of the WPO (Western Pacific Ocean) and EIO (Eastern Indian Ocean) were comprehensively characterized from 2019 to 2022 in the first long-term study. The mean mixing ratios of SF6 over the WPO and EIO during 2019-2020 (2021-2022) were 10.9 (11.2) and 10.9 (11.1) ppt, respectively. The atmospheric SF6 concentration over the WPO and EIO increased at rates of 0.40 ± 0.06 and 0.58 ± 0.28 ppt yr-1, respectively, surpassing previously reported annual growth rates. The faster growth was primarily attributed to the influence of polluted air masses originating from eastern Asian countries, particularly Japan, Northeast China, and India. This might explain why the radiative forcing caused by SF6 in the study region was higher than the global average. The concentrations of SF6 in the surface seawater of the WPO and EIO ranged from 0.33 to 2.54 fmol kg-1, and the distribution was affected by atmospheric concentrations and ocean currents. Estimated air-sea fluxes revealed that the ocean acted as a significant sink of atmospheric SF6, and the preliminary estimation suggested oceanic uptake accounts for about 7% of annual global SF6 emissions. Based on these findings, we tentatively suggest that the strength of the ocean as a sink of SF6 may warrant reassessment. The global oceanic uptake of SF6 has the potential to reduce its global abundance and environmental impacts.

Spatiotemporal distributions and oceanic emissions of short-lived halocarbons in the East China Sea.

Coastal waters are important sources of volatile halocarbons, which are important in atmospheric chemistry. Here, in May (spring) and October (autumn) 2020, we studied the surface, bottom, and sediment-pore seawater concentrations, atmospheric mixing ratios, and sea-to-air fluxes of the three primary short-lived atmospheric halocarbons (CH3I, CH2Br2, and CHBr3) in the East China Sea (ECS). The highest concentrations of the three short-lived halocarbons occurred in coastal waters, such as the Changjiang estuary and Zhejiang coastal waters, reflecting the influence of excessive anthropogenic inputs on the distributions of these gases. Interestingly, the aqueous levels of these gases seemed to be lower compared to previous measurements in this oceanic region, probably due to reduced contributions from local anthropogenic emission sources. The concentrations of CH3I, CH2Br2, and CHBr3 in pore water were significantly higher than those in bottom water, suggesting that sediment could be a source of these short-lived halocarbons. Additionally, the atmospheric mixing ratios of these gases occasionally increased in coastal areas. An air-mass back trajectory analysis showed this was due to continental anthropogenic sources and emissions from enriched waters. The atmospheric mixing ratios of these halocarbons exhibited significant seasonal variability, with significant correlations among atmospheric CH3I, CH2Br2, and CHBr3 in spring, but not in autumn. The sea-to-air fluxes of CH3I, CH2Br2, and CHBr3 indicated that the ECS is a source of these gases. Seasonal differences in CH3I and CH2Br2 fluxes were driven by changes in wind speed and sea surface temperature, while CHBr3 flux changes were associated with changes in its surface seawater concentration.

Emissions of Nitric Oxide from Photochemical and Microbial Processes in Coastal Waters of the Yellow and East China Seas.

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.

Biogeochemical controls on climatically active gases and atmospheric sulfate aerosols in the western Pacific.

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 ∼19.5% of total sulfate aerosols), especially in the Kuroshio-Oyashio Extension (∼32.3%). These processes in seawater may also determine the variations and emissions of other climatically active gases from biogenic and photochemical sources.

Simultaneous determination of benzothiazoles, benzotriazoles, and benzotriazole UV absorbers by solid-phase extraction-gas chromatography-mass spectrometry.

Benzotriazoles (BTRs), benzothiazoles (BTHs), and benzotriazole ultraviolet absorbers (BUVs) are common products in plastic rubber and personal care products. Due to their toxicity and bioaccumulation, they have been identified as emerging contaminants (ECs) in the environment. Solid-phase microextraction (SPME) and solid-phase extraction (SPE) combined with gas chromatography-mass spectrometry (GC-MS) were used for the enrichment and detection of the contaminants in seawater and sediment, respectively. The conditions of SPE and SPME were optimized in terms of material, temperature, time, pH, ionic strength, extraction solvent, and elution solvent. Although SPME requires a small sample volume, it is not reliable for the extraction efficiency and reproducibility of BTHs, BTRs, and BUVs in seawater. However, the precision of SPE-GC-MS for the determination of BTHs, BTRs, and BUVs was around 10%, with recoveries of 67.40-102.3% and 77.35-101.8% in seawater and sediment, respectively. The limits of detection of 14 contaminants in seawater and sediment were 0.03-0.47 ng/L and 0.01-0.58 ng/g, respectively. Secondly, BTHs, BTRs, and BUVs were detected with low ecological risk when SPE-GC-MS was applied to the analysis of seawater and sediment samples from the Yangtze estuary and its adjacent areas. The SPE-GC-MS was highly precise with lower detection limits relative to previous studies and thus was able to meet the requirements for the detection of BTHs, BTRs, and BUVs in seawater and sediments.

Aerobic oxidation of methane significantly reduces global diffusive methane emissions from shallow marine waters.

Methane is supersaturated in surface seawater and shallow coastal waters dominate global ocean methane emissions to the atmosphere. Aerobic methane oxidation (MOx) can reduce atmospheric evasion, but the magnitude and control of MOx remain poorly understood. Here we investigate methane sources and fates in the East China Sea and map global MOx rates in shallow waters by training machine-learning models. We show methane is produced during methylphosphonate decomposition under phosphate-limiting conditions and sedimentary release is also source of methane. High MOx rates observed in these productive coastal waters are correlated with methanotrophic activity and biomass. By merging the measured MOx rates with methane concentrations and other variables from a global database, we predict MOx rates and estimate that half of methane, amounting to 1.8 ± 2.7 Tg, is consumed annually in near-shore waters (<50 m), suggesting that aerobic methanotrophy is an important sink that significantly constrains global methane emissions.

Sorption and distribution performance of organophosphorus compound (Adenosine 5'-monophosphate)on marine sediments.

In this paper, the kinetics and thermodynamics of Adenosine 5'-monophosphate (AMP) sorption on the sediments obtained from the Yangtze River Estuary and adjacent areas were studied, in combination with the effects of the sediments' properties and media conditions. The kinetics curves could be described by a two-compartment first-order equation, and the equilibrium isotherms fitted well with the modified Langmuir and Freundlich models. The analysis of organic phosphorus (OP) fractions changes after sorption indicated that the contents of exchangeable or loosely sorbed PO increased most significantly. Higher organic matter (OM) of the sediments were favorable for the sorption ability. It was also found that the content of OP and OM in the sediments showed an obvious positive correlation, indicating that organic matter rather than Fe/Al oxides played an important role in the migration of OP in the Yangtze River estuary and its adjacent area. Temperature, salinity and pH of the media influenced the sorption of AMP significantly. Increase of temperature was of benefit to the sorption of AMP, which was a spontaneous and exothermic process according to the calculations of the thermodynamic parameters. The sorption capacity was higher at a moderate salinity in the range of our study. With the pH changing from 3 to 10, the sorption capacity exhibited as a "U-trend" curve.

Changes in dissolved organic pool and regulation of associated nutrients during green tides: A case study of Ulva prolifera bloom in the southern Yellow Sea.

To explore the spatial and temporal distributions of dissolved organic matter (DOM) affected by Ulva prolifera bloom and the regulation of DOM released by the addition of nitrate (NO3-N) nutrients, the variation in DOM was analyzed by three cruises in the coastal waters of the southern Yellow Sea (SYS) off Qingdao during a 2018 U. prolifera bloom. A mesocosm experiment was conducted during the decay of U. prolifera. The U. prolifera bloom resulted in higher concentrations of the bulk DOM except for total dissolved amino acids (TDAA), compared with levels recorded during non-bloom periods. Three different fluorescent substances of chromophoric dissolved organic matter (CDOM) were identified, which were also affected by the bloom. Concentrations of total dissolved carbohydrates (TCHO), monosaccharides (MCHO), and polysaccharides (PCHO) peaked during the late bloom, with average levels of 49.78 ± 9.73, 14.23 ± 3.32, and 35.55 ± 9.19 µmol C L-1, respectively, accompanied by an increase of DOC, indicating release of DOM with U. prolifera decay. In contrast, the concentrations of CDOM and TDAA declined during the late bloom, with averages of 0.10 ± 0.10 m-1 and 1.16 ± 0.82 µmol L-1, suggesting that the yields of CDOM and TDAA were regulated by the U. prolifera bloom and other mechanism. These findings were confirmed by the mesocosm experiment. DOM production was obviously improved by NO3-N addition except for TDAA and CDOM. The release of protein-like CDOM was primarily regulated by NO3-N nutrients, however, it was not obvious with humic-like CDOM. Our findings provide evidence supporting the role of U. prolifera blooms in the coastal DOM pool and its significant effect on the marine carbon cycle.