The interactions between host genome and gut microbiome increase the risk of psychiatric disorders: Mendelian randomization and biological annotation.

BACKGROUND: The correlation between human gut microbiota and psychiatric diseases has long been recognized. Based on the heritability of the microbiome, genome-wide association studies on human genome and gut microbiome (mbGWAS) have revealed important host-microbiome interactions. However, establishing causal relationships between specific gut microbiome features and psychological conditions remains challenging due to insufficient sample sizes of previous studies of mbGWAS. METHODS: Cross-cohort meta-analysis (via METAL) and multi-trait analysis (via MTAG) were used to enhance the statistical power of mbGWAS for identifying genetic variants and genes. Using two large mbGWAS studies (7,738 and 5,959 participants respectively) and12 disease-specific studies from the Psychiatric Genomics Consortium (PGC), we performed bidirectional two-sample mendelian randomization (MR) analyses between microbial features and psychiatric diseases (up to 500,199 individuals). Additionally, we conducted downstream gene- and gene-set-based analyses to investigate the shared biology linking gut microbiota and psychiatric diseases. RESULTS: METAL and MTAG conducted in mbGWAS could boost power for gene prioritization and MR analysis. Increases in the number of lead SNPs and mapped genes were witnessed in 13/15 species and 5/10 genera after using METAL, and MTAG analysis gained an increase in sample size equivalent to expanding the original samples from 7% to 63%. Following METAL use, we identified a positive association between Bacteroides faecis and ADHD (OR, 1.09; 95 %CI, 1.02-1.16; P = 0.008). Bacteroides eggerthii and Bacteroides thetaiotaomicron were observed to be positively associated with PTSD (OR, 1.11; 95 %CI, 1.03-1.20; P = 0.007; OR, 1.11; 95 %CI, 1.01-1.23; P = 0.03). These findings remained stable across statistical models and sensitivity analyses. No genetic liabilities to psychiatric diseases may alter the abundance of gut microorganisms.Using biological annotation, we identified that those genes contributing to microbiomes (e.g., GRIN2A and RBFOX1) are expressed and enriched in human brain tissues. CONCLUSIONS: Our statistical genetics strategy helps to enhance the power of mbGWAS, and our genetic findings offer new insights into biological pleiotropy and causal relationship between microbiota and psychiatric diseases.

Nitrifier adaptation to low energy flux controls inventory of reduced nitrogen in the dark ocean.

Ammonia oxidation to nitrite and its subsequent oxidation to nitrate provides energy to the two populations of nitrifying chemoautotrophs in the energy-starved dark ocean, driving a coupling between reduced inorganic nitrogen (N) pools and production of new organic carbon (C) in the dark ocean. However, the relationship between the flux of new C production and the fluxes of N of the two steps of oxidation remains unclear. Here, we show that, despite orders-of-magnitude difference in cell abundances between ammonia oxidizers and nitrite oxidizers, the two populations sustain similar bulk N-oxidation rates throughout the deep waters with similarly high affinities for ammonia and nitrite under increasing substrate limitation, thus maintaining overall homeostasis in the oceanic nitrification pathway. Our observations confirm the theoretical predictions of a redox-informed ecosystem model. Using balances from this model, we suggest that consistently low ammonia and nitrite concentrations are maintained when the two populations have similarly high substrate affinities and their loss rates are proportional to their maximum growth rates. The stoichiometric relations between the fluxes of C and N indicate a threefold to fourfold higher C-fixation efficiency per mole of N oxidized by ammonia oxidizers compared to nitrite oxidizers due to nearly identical apparent energetic requirements for C fixation of the two populations. We estimate that the rate of chemoautotrophic C fixation amounts to ∼1 × 1013 to ∼2 × 1013 mol of C per year globally through the flux of ∼1 × 1014 to ∼2 × 1014 mol of N per year of the two steps of oxidation throughout the dark ocean.

Metaproteomics of marine viral concentrates reveals key viral populations and abundant periplasmic proteins in the oligotrophic deep chlorophyll maximum of the South China Sea.

Viral concentrates (VCs), containing bioinformative DNA and proteins, have been used to study viral diversity, viral metagenomics and virus-host interactions in natural ecosystems. Besides viruses, VCs also contain many noncellular biological components including diverse functional proteins. Here, we used a shotgun proteomic approach to characterize the proteins of VCs collected from the oligotrophic deep chlorophyll maximum (DCM) of the South China Sea. Proteins of viruses infecting picophytoplankton, that is, cyanobacteria and prasinophytes, and heterotrophic bacterioplankton, such as SAR11 and SAR116, dominated the viral proteome. Almost no proteins from RNA viruses or known gene transfer agents were detected, suggesting that they were not abundant at the sampling site. Remarkably, nonviral proteins made up about two thirds of VC proteins, including overwhelmingly abundant periplasmic transporters for nutrient acquisition and proteins for diverse cellular processes, that is, translation, energy metabolism and one carbon metabolism. Interestingly, three 56 kDa selenium-binding proteins putatively involved in peroxide reduction from gammaproteobacteria were abundant in the VCs, suggesting active removal of peroxide compounds at DCM. Our study demonstrated that metaproteomics provides a valuable avenue to explore the diversity and structure of the viral community and also the pivotal biological functions affiliated with microbes in the natural environment.

Human perturbation increases the fluxes of dissolved molybdenum from land to ocean - The case of the Jiulong River in China.

Rivers contribute a substantial amount of trace metals including molybdenum (Mo) into the oceans. The driving forces controlling the riverine fluxes of dissolved metals still remain not fully understood. Our study then investigated the spatial variations of dissolved metals including molybdenum in a typically human perturbed river, the Jiulong River (JR), China. The aim of the study is to elucidate the relevance of anthropogenic perturbation on the fluxes of dissolved metals such as molybdenum from land to ocean. Our study shows a large spatial variability of dissolved Mo across tributary to main stream of the JR. Particularly, dissolved Mo was generally low (average: 5 ± 1 nM) in the "pristine" JR headwaters, and elevated (19 ± 6 nM) along the lower river continuum. Sporadically high levels of dissolved Mo occurred in the upper North River (77 ± 19 nM), as a result of mining activities locally. Significant correlations of dissolved Mo with total dissolved solids (TDS) and dissolved strontium (Sr) were observed in the whole JR (Mo = 1.4* TDS -1.7, R2 = 0.86, p < .01; Mo = 1.2*Sr - 2.2, R2 = 0.70, p < .01, logarithmic scales). This indicates that dissolved Mo is mobilized mainly along with other major ions such as Sr during similar mineral dissolution processes. From the "pristine" headwaters to the mouth of the JR, riverine Mo fluxes at the mouth of the JR has elevated by at least 3 times due to human perturbation. Compiled historic data regarding metal fluxes from world rivers further confirmed that small and medium rivers are relatively more sensitive to human perturbation.

Eutrophication-Driven Hypoxia in the East China Sea off the Changjiang Estuary.

Coastal hypoxia is an increasingly recognized environmental issue of global concern to both the scientific community and the general public. We assessed the relative contributions from marine and terrestrially sourced organic matter that were responsible for oxygen consumption in a well-studied seasonal coastal hypoxic zone, the East China Sea off the Changjiang Estuary. Our fieldwork was conducted in August 2011 during reinstatement of a subsurface hypoxia, when we observed a continuous decline of dissolved oxygen along with production of dissolved inorganic carbon resulting from organic carbon remineralization. On the basis of a three end-member mixing model and determinations of the stable isotopic compositions of dissolved inorganic carbon (δ(13)CDIC), the end product of particulate organic carbon (POC) degradation, we quantified the δ(13)C value of the remineralized organic carbon (δ(13)COCx), which was -18.5 ± 1.0‰. This isotopic composition was very similar to the δ(13)C of marine sourced POC produced in situ (-18.5 ± 0.3‰) rather than that of the terrestrially sourced POC (-24.4 ± 0.2‰). We concluded that marine-sourced organic matter, formed by eutrophication-induced marine primary production, was the dominant oxygen consumer in the subsurface hypoxic zone in the East China Sea off the Changjiang Estuary.

Drivers shaping the diversity and biogeography of total and active bacterial communities in the South China Sea.

To test the hypothesis that different drivers shape the diversity and biogeography of the total and active bacterial community, we examined the bacterial community composition along two transects, one from the inner Pearl River estuary to the open waters of the South China Sea (SCS) and the other from the Luzon Strait to the SCS basin, using 454 pyrosequencing of the 16S rRNA and 16S rRNA gene (V1-3 regions) and thereby characterizing the active and total bacterial community, respectively. The diversity and biogeographic patterns differed substantially between the active and total bacterial communities. Although the composition of both the total and active bacterial community was strongly correlated with environmental factors and weakly correlated with geographic distance, the active bacterial community displayed higher environmental sensitivity than the total community and particularly a greater distance effect largely caused by the active assemblage from deep waters. The 16S rRNA vs. rDNA relationships indicated that the active bacteria were low in relative abundance in the SCS. This might be due to a high competition between active bacterial taxa as indicated by our community network models. Based on these analyses, we speculate that high competition could cause some dispersal limitation of the active bacterial community resulting in a distinct distance-decay relationship. Altogether, our results indicated that the biogeographic distribution of bacteria in the SCS is the result of both environmental control and distance decay.

Coastal acidification induced by tidal-driven submarine groundwater discharge in a coastal coral reef system.

We identified a barely noticed contributor, submarine groundwater discharge (SGD), to acidification of a coastal fringing reef system in Sanya Bay in the South China Sea based on time-series observations of Ra isotopes and carbonate system parameters. This coastal system was characterized by strong diel changes throughout the spring to neap tidal cycle of dissolved inorganic carbon (DIC), total alkalinity, partial pressure of CO2 (pCO2) and pH, in the ranges of 1851-2131 µmol kg(-1), 2182-2271 µmol kg(-1), 290-888 µatm and 7.72-8.15, respectively. Interestingly, the diurnal amplitudes of these parameters decreased from spring to neap tides, governed by both tidal pumping and biological activities. In ebb stages during the spring tide, we observed the lowest salinities along with the highest DIC, pCO2 and Ra isotopes, and the lowest pH and aragonite saturation state. These observations were consistent with a concurrent SGD rate up to 25 and 44 cm d(-1), quantified using Darcy's law and (226)Ra, during the spring tide ebb, but negligible at flood tides. Such tidal-driven SGD of low pH waters is another significant contributor to coastal acidification, posing additional stress on coastal coral systems, which would be even more susceptible in future scenarios under higher atmospheric CO2.

Isotopic composition and distribution of plutonium in northern South China Sea sediments revealed continuous release and transport of Pu from the Marshall Islands.

The (239+240)Pu activities and (240)Pu/(239)Pu atom ratios in sediments of the northern South China Sea and its adjacent Pearl River Estuary were determined to examine the spatial and temporal variations of Pu inputs. We clarified that Pu in the study area is sourced from a combination of global fallout and close-in fallout from the Pacific Proving Grounds in the Marshall Islands where above-ground nuclear weapons testing was carried out during the period of 1952-1958. The latter source dominated the Pu input in the 1950s, as evidenced by elevated (240)Pu/(239)Pu atom ratios (>0.30) in a dated sediment core. Even after the 1950s, the Pacific Proving Grounds was still a dominant Pu source due to continuous transport of remobilized Pu from the Marshall Islands, about 4500 km away, along the North Equatorial Current followed by the transport of the Kuroshio current and its extension into the South China Sea through the Luzon Strait. Using a simple two end-member mixing model, we have quantified the contributions of Pu from the Pacific Proving Grounds to the northern South China Sea shelf and the Pearl River Estuary are 68% ± 1% and 30% ± 5%, respectively. This study also confirmed that there were no clear signals of Pu from the Fukushima Daiichi Nuclear Power Plant accident impacting the South China Sea.

Monetizing shipping emission reduction: Environmental benefit analysis of domestic emission control areas 2.0 policy in China.

Shipping is a major contributor to anthropogenic emissions, exerting complex effects on both the environment and climate. To improve the air quality of coastal areas, China adopted an upgraded policy on domestic emission control areas (DECA 2.0) for shipping in December 2018, which expanded the geographical scope of ECAs from three designated heavy-traffic coastal regions to the entire 12 nautical mile-territorial seas and also introduced more stringent ship emission requirements. Based on data from the Automatic Identification System, this study first evaluates the environmental effects of ship emissions' reduction brought by DECA policy 2.0. Results reveal that implementation of DECA policy 2.0 has resulted in a cumulative reduction (2019-2021) of 8.43 × 105 tons, 1.3 × 105 tons, and 1.49 × 105 tons of sulfur dioxide (SO2), particulate matter <2.5 µm diameter (PM2.5) and PM <10 µm (PM10) emissions, respectively. Based on the external cost method, we further monetize the environmental benefits arising from reduction of air pollution emissions, averaging $3.6 billion USD per year. This number equates to ca. 4 % of the total output value of China's marine transportation industry over the three-year period. Finally, we calculated the fuel replacement cost arising from the implementation of DECA policy 2.0 in 2019, which was approximately $1.86 billion USD. This indicates that the environmental benefits of DECA policy 2.0 equate nearly double the associated costs.

The interactions between olivine dissolution and phytoplankton in seawater: Potential implications for ocean alkalinization.

Ocean alkalinity enhancement, one of the ocean-based CO2 removal techniques, has the potential to assist us in achieving the goal of carbon neutrality. Olivine is considered the most promising mineral for ocean alkalinization enhancement due to its theoretically high CO2 sequestration efficiency. Olivine dissolution has been predicted to alter marine phytoplankton communities, however, there is still a lack of experimental evidence. The olivine dissolution process in seawater can be influenced by a range of factors, including biotic factors, which have yet to be explored. In this study, we cultivated two diatoms and one coccolithophore with and without olivine particles to investigate their interactions with olivine dissolution. Our findings demonstrate that olivine dissolution promoted the growth of all phytoplankton species, with the highly silicified diatom Thalassiosira pseudonana benefiting the most. This was probably due to the highly silicified diatom having a higher silicate requirement and, therefore, growing more quickly when silicate was released during olivine dissolution. Based on the structural characteristics and chemical compositions on the exterior surface of olivine particles, T. pseudonana was found to promote olivine dissolution by inhibiting the formation of the amorphous SiO2 layer on the surface of olivine and therefore enhancing the stoichiometric dissolution of olivine. However, the positive effects of T. pseudonana on olivine dissolution were not observed in the coccolithophore Gephyrocapsa oceanica or the non-silicate obligate diatom Phaeodactylum tricornutum. This study provides the first experimental evidence of the interaction between phytoplankton and olivine dissolution, which has important implications for ocean alkalinization research.

Automated spectrophotometric analyzer for rapid single-point titration of seawater total alkalinity.

An automated analyzer was developed to achieve fast, precise, and accurate measurements of seawater total alkalinity (AT) based on single-point titration and spectrophotometric pH detection. The single-point titration was carried out in a circulating loop, which allowed the titrant (hydrochloric acid and bromocresol green solution) and a seawater sample to mix at a constant volume ratio. The dissolved CO2 in the sample-titrant mixture was efficiently removed by an inline CO2 remover, which consists of a gas-permeable tubing (Teflon AF2400) submerged in a sodium hydroxide (NaOH) solution. The pH of the mixture was then measured with a custom-made spectrophotometric detection system. The analyzer was calibrated against multiple certified reference materials (CRMs) with different AT values. The analyzer features a sample throughput time of 6.5 min with high precision (±0.33-0.36 µmol kg(-1); n = 48) and accuracy (-0.33 ± 0.99 µmol kg(-1); n = 10). Intercomparison to a traditional open-cell AT titrator showed overall good agreement of 0.88 ± 2.03 µmol kg(-1) (n = 22). The analyzer achieved excellent stability without recalibration over 11 days, during which time 320 measurements were made with a total running time of over 40 h. Because of its small size, low power consumption requirements, and its ability to be automated, the new analyzer can be adapted for underway and in situ measurements.

An empirical comparison of the harmful effects for randomized controlled trials and non-randomized studies of interventions.

Introduction: Randomized controlled trials (RCTs) are the gold standard to evaluate the efficacy of interventions (e.g., drugs and vaccines), yet the sample size of RCTs is often limited for safety assessment. Non-randomized studies of interventions (NRSIs) had been proposed as an important alternative source for safety assessment. In this study, we aimed to investigate whether there is any difference between RCTs and NRSIs in the evaluation of adverse events. Methods: We used the dataset of systematic reviews with at least one meta-analysis including both RCTs and NRSIs and collected the 2 × 2 table information (i.e., numbers of cases and sample sizes in intervention and control groups) of each study in the meta-analysis. We matched RCTs and NRSIs by their sample sizes (ratio: 0.85/1 to 1/0.85) within a meta-analysis. We estimated the ratio of the odds ratios (RORs) of an NRSI against an RCT in each pair and used the inverse variance as the weight to combine the natural logarithm of ROR (lnROR). Results: We included systematic reviews with 178 meta analyses, from which we confirmed 119 pairs of RCTs and NRSIs. The pooled ROR of NRSIs compared to that of RCTs was estimated to be 0.96 (95% confidence interval: 0.87 and 1.07). Similar results were obtained with different sample size subgroups and treatment subgroups. With the increase in sample size, the difference in ROR between RCTs and NRSIs decreased, although not significantly. Discussion: There was no substantial difference in the effects between RCTs and NRSIs in safety assessment when they have similar sample sizes. Evidence from NRSIs might be considered a supplement to RCTs for safety assessment.

Satellite-estimated air-sea CO2 fluxes in the Bohai Sea, Yellow Sea, and East China Sea: Patterns and variations during 2003-2019.

The Bohai Sea (BS), Yellow Sea (YS), and East China Sea (ECS) together form one of the largest marginal sea systems in the world, including enclosed and semi-enclosed ocean margins and a wide continental shelf influenced by the Changjiang River and the strong western boundary current (Kuroshio). Based on in situ seawater pCO2 data collected on 51 cruises/legs over the past two decades, a satellite retrieval algorithm for seawater pCO2 was developed by combining the semi-mechanistic algorithm and machine learning method (MeSAA-ML-ECS). MeSAA-ML-ECS introduced semi-analytical parameters, including the temperature-dependent seawater pCO2 (pCO2,therm) and upwelling index (UISST), to characterise the combined effect of atmospheric CO2 forcing, thermodynamic effects, and multiple mixing processes on seawater pCO2. The best-selected machine learning algorithm is XGBoost. The satellite-derived pCO2 achieved excellent performance in this complicated marginal sea, with low root mean square error (RMSE = 20 µatm) and mean absolute percentage deviation (APD = 4.12 %) for independent in situ validation dataset. During 2003-2019, the annual average CO2 sinks in the BS, YS, ECS, and entire study area were 0.16 ± 0.26, 3.85 ± 0.68, 14.80 ± 3.09, and 18.81 ± 3.81 Tg C/yr, respectively. Under continuously increasing atmospheric CO2 concentration, the BS changed from a weak source to a weak sink, the YS experienced interannual fluctuations but did not show significant trend, while the ECS acted as a strong sink with CO2 absorption increased from ∼10 Tg C in 2003 to ∼19 Tg C in 2019. In total, CO2 uptake in the entire study area increased by 85 % in 17 years. For the first time, we present the most refined variation in the satellite-derived pCO2 and air-sea CO2 flux dataset. These complete ocean carbon sink statistics and new insights will benefit further research on carbon fixation and its potential capacity.

Active degradation-nitrification microbial assemblages in the hypoxic zone in a subtropical estuary.

In 2017 summer, we observed widespread bottom hypoxia at the lower estuary of the Pearl River estuary (PRE). Our previous study noticed that AOA and bacteria were highly abundant and clustered within the hypoxia zone. Moreover, nitrification and respiration rates were also evidently higher in these hypoxic waters. These observations prompt us to investigate whether these two oxygen-consuming microorganisms have symbiotic relationships and whether specific groups consistently coexist and form ecological-meaningful associations. In this study, we use network analysis to investigate the presence and active communities (DNA-RNA) based on bacterial and AOA communities sequencing (inferred from the 16S rRNA and amoA gene, respectively) to gain more insight into ecological-meaningful associations. We observed a highly diverse and active bacterial community in the hypoxia zone. The RNA networks were more modulized than the corresponding DNA networks, indicating that the active communities were better parsed into functional microbial assemblages. The network topology revealed that Gammaproteobacteria, Bacteroidetes (Flavobacteriales), Alphaproteobacteria (Rhodobacterales and Rhodospirillales), Marinimicrobia, Cyanobacteria (Synechococcales), and AOA sublineages were module hubs and connectors, indicating that they were the keystone taxa of the microbial communities. The hub-subnetwork further showed robust co-occurrence between Gammaproteobacteria, Bacteroidetes (Flavobacteriales), Alphaproteobacteria (Rhodobacterales and Rhodospirillales), Marinimicrobia with AOA sublineages, and Nitrospinae (presumably NOB) reflecting the formation of Degradation-Nitrification (sequential oxidation of Organic matter degradation to ammonia, then nitrate) microbial assemblage in the hypoxia zone. The subnetworks revealed AOA ecotype-specific modularization and niche partitioning of different AOA sublineages. Interestingly, the recurring co-occurrence of nitrifiers assemblage in the RNA subnetworks (SCM1-like-II (AOA) and Nitrospinae OTUs (NOB) suggests an active interaction via nitrite exchange. The Degradation-Nitrification microbial assemblage may contribute substantially to the oxygen consumption in the hypoxia formation in PRE. Our results provide new insight into the functional microbial assemblages, which is worth further investigation on their ecological implication in estuarine waters.

Association between childhood trauma and white matter deficits in first-episode schizophrenia.

OBJECTIVE: This study aimed to investigate the relationship between childhood trauma (ChT) and white matter (WM) deficits in first-episode schizophrenia (FES). METHODS: A total of 103 individuals with FES and 206 healthy control individuals (HCs) were enrolled and assessed based on ChT Questionnaire (CTQ) and Positive and Negative Symptoms Scale (PANSS). Diffusion tensor imaging was acquired on a Signa 3.0 T scanner. Map of fractional anisotropy (FA) was analyzed using Tract-Based Spatial Statistics. Hierarchical logistic regression analyses were used to examine associations of sociodemographic characteristics, total CTQ scores, and WM deficits. RESULTS: Compared with the HCs group, the FES group showed significantly lower FA in several WM bundles (left anterior thalamic radiation, left inferior frontal-occipital fasciculus, left cingulum, forceps major, and forceps minor), and the mean FA value in these WM bundles was inversely related to the total CTQ score. In addition, a higher CTQ score may increase the risk of schizophrenia, while higher FA values may decrease the risk of schizophrenia. CONCLUSION: This study demonstrates that individuals with FES evince widespread cerebral WM abnormalities and that these abnormalities were associated with ChT. These results provide clues about the neural basis and potential biomarkers of schizophrenia.

Reduced nitrite accumulation at the primary nitrite maximum in the cyclonic eddies in the western North Pacific subtropical gyre.

Nitrite, an intermediate product of the oxidation of ammonia to nitrate (nitrification), accumulates in upper oceans, forming the primary nitrite maximum (PNM). Nitrite concentrations in the PNM are relatively low in the western North Pacific subtropical gyre (wNPSG), where eddies are frequent and intense. To explain these low nitrite concentrations, we investigated nitrification in cyclonic eddies in the wNPSG. We detected relatively low half-saturation constants (i.e., high substrate affinities) for ammonia and nitrite oxidation at 150 to 200 meter water depth. Eddy-induced displacement of high-affinity nitrifiers and increased substrate supply enhanced ammonia and nitrite oxidation, depleting ambient substrate concentrations in the euphotic zone. Nitrite oxidation is more strongly enhanced by the cyclonic eddies than ammonia oxidation, reducing concentrations and accelerating the turnover of nitrite in the PNM. These findings demonstrate a spatial decoupling of the two steps of nitrification in response to mesoscale processes and provide insights into physical-ecological controls on the PNM.

Nitrogen isotope constraint on the zonation of multiple transformations between dissolved and particulate organic nitrogen in the Changjiang plume.

Information on the sources and transformations of particulate organic N (PN) and dissolved organic N (DON) at the coastal interface remains insufficient due to technological difficulties and complicated features of intensive physical mixing and rapid biological activities. Here, we investigated the spatial distribution of concentrations and isotopic compositions of PN and DON in the Changjiang plume during the summer flood period. In average, DON and PN accounted for 25.6 ± 12.1% and 8.1 ± 9.1% (n = 55), respectively, of the total N pool, with the remaining N primarily in the form of nitrate (NO3-). Mean δ15N values were the lowest for DON (-0.1 ± 2.7‰, n = 58) and slightly higher for PN (2.0 ± 1.6‰, n = 101), and the highest for NO3- (6.5 ± 2.2‰, n = 67), suggesting multiple transformations had occurred to differentiate isotopic characteristics among the three N pools. By applying a conservative mixing model, we found DON deficits (-3.5 ± 3.7 µmol L-1, n = 43) and negative shift in δ15NDON (-3.6 ± 2.2‰, n = 43) in the Changjiang plume, revealing nonconservative DON behaviors. In the offshore surface plume where Chlorophyll a was high, the most likely cause is the DON uptake by phytoplankton with a strong inverse isotope effect (around -40‰). This DON assimilation by phytoplankton contributed to ~16 ± 12% of the PN production, with the remaining supported by NO3- assimilation, producing an overall isotope effect of 4-9‰. However, in waters near the river mouth and at the bottom of the offshore plume where total suspended matter concentrations were high (>5 mg L-1), the DON deficit was most likely induced by the selective adsorption of 15N enriched moieties of DON onto particulate surfaces (with an isotope effect of -20‰ to -5‰). Unlike dissolved organic carbon to behave conservatively in most estuaries, our results show that active transformations had occurred between the DON and PN pools in the Changjiang plume.

[Advances and Prospect of Sampling Techniques and Analytical Methods for Trace Elements in the Ocean: Progress of Trace Element Platform Construction in Xiamen University].

Trace elements, which are important chemical components in the ocean, generally refer to those chemical elements with concentrations below 10 µmol·kg-1in seawater. Some trace elements, such as Fe and Zn, serve as essential micronutrients for marine organisms, which regulate marine primary productivity and are closely related to the biogeochemical cycle of carbon and nitrogen and therefore affect the global environment and climate change. In contrast, some elements, such as Pb, are anthropogenic pollutants largely released by human activities. In addition, some trace elements and their isotopes can be used as tracers for oceanographic processes and proxies for paleoceanography. However, the high saline matrix and extremely low trace element concentrations in seawater, as well as the contamination from research vessels, sampling equipment, and the surrounding environment during the process of sample collection, pretreatment, and analysis, have restricted researchers from obtaining reliable trace element data in the ocean for a long period of time. Nevertheless, high quality samples and accurate data are prerequisites for investigating the biogeochemical and environmental behavior of marine trace elements. This paper reviews the development of sampling techniques and analytical methods for trace elements in seawater, introduces the research history and platform construction activities in Xiamen University in this field, summarizes the advantages and disadvantages of various sampling and analytical techniques and methods, and presents the perspectives on future developments in the research on trace elements in the ocean.

Sedimentary processes dominate nitrous oxide production and emission in the hypoxic zone off the Changjiang River estuary.

Coastal oceans, known as the major nitrous oxide (N2O) source to the atmosphere, are increasingly subject to eutrophication and concurrent near-bottom hypoxia. The natural nitrogen cycle is likely to be altered markedly in hypoxic coastal oceans. However, the processes responsible for N2O production and emission remain elusive because of lacking field rate measurements simultaneously conducted in the water column and sediment. Here, we quantified N2O production rates using a 15N-labeled technique in the water-column and surface sediments off the Changjiang (Yangtze) River estuary, the largest hypoxic zone in the Pacific margins. Our results showed that the estuarine surface sediments were the major source for N2O production, accounting for approximately 90% of the total water-column accumulation and consequent efflux of N2O in the hypoxic zone, whereas the water-column nitrification and denitrification combined only contributed <10%. More importantly, the coupling of nitrification and denitrification at the presence of abundant supply and remineralization of labile organic matter was the main driver of the N2O release from the sediment-water interface in this region. This study highlights the dominant role of benthic processes occurring at the sediment-water interface controlling the coastal N2O budget, as the anthropogenic eutrophication and hypoxia are expanding in coastal oceans.