Dissimilatory nitrate reduction in marine sediment is one of the key nitrogen loss processes in the ocean. Dissimilatory nitrate reduction to ammonium (DNRA), unlike denitrification and anammox by which nitrate is reduced to N₂ and removed from the environment eventually, directly reduce nitrate to ammonium, could lead to eutrophication and water hypoxia afterwards. ¹⁵N labeled technique is the main method to investigate dissimilatory nitrate reduction processes in sediments. Accurate determination of ¹⁵${\rm {NH}}_4^+ $ in isotope enrichment samples is primarily required to evaluate the potential rate of DNRA. The commonly used method for the determination of ¹⁵${\rm {NH}}_4^+ $ at present is the hypobromite iodine oxidation-membrane inlet quadrupole mass spectrometer determination method. However, ³⁰N₂ as the final analyte of the method has two problems which lead to an analysis error: firstly, ³⁰N₂ determined can be significantly overestimated due to the O₂ interference; secondly, the low equilibrium rate of ³⁰N₂ in the detector could influence the precision of the method and low down the analysis speed. To solve the problems mentioned, a sodium hypobromite oxidation-sulfamic acid reduction method by which ¹⁵${\rm {NH}}_4^+ $ is transformed to ²⁹N₂ only and detected using membrane inlet quadrupole mass spectrometer afterwards (Redox-MIMS method) is reported in this article. The results indicate that the optical concentration of sulfamic acid is 80−100 mmol/L; the detection limit is 0.5 μmol/L and the precision (RSD) is 0.8%; the dynamic range of standard curve is 0−150 μmol/L. Comparing with the hypobromite iodine oxidation method, the Redox-MIMS method not only has the advantages of mild reaction conditions and easily obtained reagents, the memory effect of ³⁰N₂ in the detector can also be solved effectively for most of the produced ¹⁵N₂ is ²⁹N₂ which improves detection efficiency (2 min per sample) meanwhile. Determination results of rates of DNRA and the contribution of DNRA to all dissimilatory nitrate reduction processes in the Laizhou Bay sediments using both hypobromite iodine oxidation and Redox-MIMS methods shows no significant difference. These make the Redox-MIMS method an accurate and high-efficient method for determination of ¹⁵${\rm {NH}}_4^+ $ in isotope enrichment samples.

The Bohai Sea and Yellow Sea are continental shelf areas with high production of dimethyl sulfide (DMS). Field investigation of DMS in this area is helpful to accurately assess its amount released from the ocean and its negative feedback on global climate change. Both model-based and direct measurement methods are based on DMS concentration in surface seawater and lower atmosphere, respectively, so advanced detection technology plays a decisive role in the accurate flux estimation. Gas chromatography, mass spectrometry, chemiluminescence and satellite remote sensing are commonly used observation techniques. At this paper, a method based on benzene-assisted photoionization positive ion mobility spectrometry (BAPI-PIMS) for in-situ observation of DMS in seawater is proposed. Combined with dynamic gas stripping and on-line water removal Nafion tube sampling system, the interference of environmental water vapor is eliminated. Under the optimal conditions, the linear range based on the two DMS product ions is 0.10−120 nmol/L, and the detection limit is as low as 0.065 nmol/L. Then the demonstrated method is applied to field detect DMS in the Bohai Sea and northern Yellow Sea, and the concentration of DMS in surface seawater ranged from 0.08 nmol/L to 0.96 nmol/L, while the air-sea exchange flux ranged from 0.12 μmol/(m²·d) to 17.75 μmol/(m²·d). Lastly, the difference between DMS detected on field and in lab and the main impact factors are discussed via the correlation analysis and canonical correspondence analysis, and results show that nutrients and phytoplankton community are the main factors during the seawater preservation, indicating the important significance of field observation method established currently for accurate evaluation of DMS release from the ocean.

The wetland vegetation is an important part of coastal wetlands, and its dynamic changes affect the structures and functions of wetland ecosystem. Therefore, it is of great significance to monitor and evaluate the long-term changes of wetland vegetation by remote sensing technology for the management of coastal resources and ecological protection. In this paper, we used multi-temporal Landsat satellite images as data sources, combined object-oriented method and random forest algorithm to achieve accurate classification of typical wetland vegetation in the Current Huanghe River Estuary Reserve, and revealed the spatiotemporal variation characteristics of Phragmites australis, Suaeda salsa and Spartina alterniflora in the study area from 2000 to 2020. It has been verified that the overall accuracy of wetland vegetation mapping is between 84.74% and 92.39%, and the Kappa coefficient is between 0.81 and 0.91. The results of long time series classification show that Phragmites australis is the dominant species in the Current Huanghe Estuary Reserve, and its distribution area is maintained at more than 6% and the overall growth is steady. The area of Suaeda salsa shows a decreasing trend since 2006. The dominance degree of Suaeda salsa is decreasing continuously and the degree of fragmentation is severe. The area of Spartina alterniflora increased year by year from 211.85 hm² in 2002 to 5267.79 hm² in 2020. The expansion process of Spartina alterniflora in the reserve could be divided into three stages: in the initial expansion period before 2008, the growth of Spartina alterniflora was unstable; from 2008 to 2014, there was a rapid expansion stage, with an average annual expansion rate of 54%, which showed that the seaward expansion invaded the plain and the landward expansion invaded the habitat of Suaeda salsa in space; since 2014, Spartina alterniflora has been growing slowly, entering a stable growth period, and the annual average expansion rate is only 9%.

To examine the benthos food web structure in the Xiaoqing River Estuary adjacent sea area, four potential food sources, including sediment organic matter (SOM), suspended particulate organic matter (POM), zooplankton and phytoplankton, and 35 aquatic organisms are collected in October 2020. Carbon and nitrogen stable isotope technique and Bayesian mixing model (MixSIAR) are used to analyze the food web structure and the trophic relationship of benthos. The results show that the δ¹³C and δ¹⁵N values of potential food sources varies from −25.56‰ to −17.91‰ and 2.43‰ to 10.33‰, respectively. Moreover, the δ¹³C and δ¹⁵N values of benthos varies from −23.48‰ to −18.31‰ and 8.79‰ to 18.01‰, respectively. The trophic levels of the main consumers rang from 1.65 (Arcuatula senhousia) to 3.54 (Ctenotrypauchen chinensis). Trophic relationship analysis showes that there are two main energy transfer pathways in the Xiaoqing River Estuary adjacent sea area. One is the planktonic food chain with plankton as the major energy source, in which bivalves (except Solen brevissimus), small shrimps, and polychaetes are the main primary consumers. The other is the benthic food chain with SOM as the major energy source, in which Solen brevissimus and gastropods are the main primary consumers. On the whole, there is a certain degree of niche overlap and fierce competition among species in the Xiaoqing River Estuary adjacent sea area.

Based on the fish survey data of the offshore waters of southern Zhejiang in August 2016 (summer), November 2016 (Autumn), March 2017 (winter) and May 2017 (spring), the relationship between dominant fish species is determined by niche breadth, niche overlap, cluster analysis, variance ratio (VR) method, chi-square test, association coefficient (AC) and species pair common percentage (PC). The results show that: (1) 169 species of fish are collected, including 26 major species; (2) in the spatial dimension, the niche breadth of Scomber japonicus is the largest (2.83); the niche overlap between Sardinella zunasi and Thryssa chefuensis is the largest (0.97); in the temporal dimension, the niche breadth of Harpadon nehereus is the largest (1.34); the niche overlap of six groups is equal to 1.00; in the spatial and temporal dimension, the niche breadth of Harpadon nehereus is the largest (3.08); the niche overlap between Sardinella zunasi and Thryssa chefuensis is the largest (0.97); (3) the variance ratio analysis showed that the VR deviation is significant, and the overall positive association of the major fish is significant, among which 170 groups of species pair association reached a significant level (χ²≥3.841). The results of the AC and the PC showed that the interspecific connection tended to be positive.

In order to mine single nucleotide polymorphism (SNP) sites relates to hypoxia stress and study the function of the gene SNP-Unigene from Rachycentron canadum. SOAPsnp software is mainly used to detect the SNP of the intestinal transcriptome sequencing results of cobia juveniles under hypoxia stress conditions, and then annotation of them in the databases of GO, KOG, and KEGG are compared. The results show that the transcriptome SNP locus are distributed on 26 120 SNP-Unigene, with a total of 431 845 SNP sites are detected, the average frequency of SNP occurrence is about 1/171 bp. SNP-Unigene functional annotation showes that the cobia is mainly involved in signal transduction, infectious disease, cancer and endocrine system under hypoxia stress. Further, 3 417 SNP-Unigene are annotated to 35 immune-related pathways including MAPK signaling pathway. Based on the transcriptome differential gene analysis, the distribution of SNP sites of 18 immune-related genes in 7 important immune pathways is examined. At the same time, the distribution of SNP sites of 8 differential genes such as PIK3CA in the HIF-1 signaling pathway is also detected. The research results will lay the foundation for further mining of the molecular genetic markers of immune and hypoxia-related SNPs, and provide a scientific reference for the in-depth study of cobia’s hypoxia adaptation mechanism.

Based on the investigation data of zooplankton in the sea area near the north operation area in the Lanshan Port of Rizhao Port in May (spring) and October (autumn) 2015, the community structure characteristics of zooplankton was analysed in this paper. The results showed that 20 species and 7 taxa of zooplankton were found in the two seasons, including 12 species and 4 taxa in spring and 19 species and 6 taxa in autumn, the average abundance of zooplankton were 128.1 ind./m³ in spring and 103.3 ind./m³ in autumn, the average biomass (wet weight) were 1 129.9 mg/m³ and 954.3 mg/m³, the average Shannon-Wiener diversity index (H'), Margalef’s species richness diversity (D) and Pielou’s evenness index (J) were 2.39, 0.85, 0.87 in spring, respectively, and 2.01, 1.21, 0.62 in autumn, respectively. In spring, the dominant species were Sagitta crassa, Calanus sinicus, Labibocera euchaeta, Acartia pacifica, Pleurobrachia globosa, while in autumn, the dominant species were Acartia pacifica, Doliolum denticulatum, Sagitta crassa, Labibocera euchaeta. Cluster analysis showed that the zooplankton in the investigation area could be divided into three groups. This study could provide important basic data for further study of zooplankton community structure in the coastal waters of Rizhao.

The characteristics of the maximum shear force in the boundary layer were studied based on the wave attenuation experiment of nearshore plants considering the influence of roots. The maximum shear force characteristics of the boundary layer under two plant models, root alone and combination of roots and stems, were investigated by using the formula of boundary layer velocity calculation with plant water flow under regular waves proposed by predecessors. The shear force variation along the path and the effect of plants on the shear force attenuation characteristics of the two models were analyzed, and the formulas of the attenuation coefficients were fitted. Studies have shown that when waves pass through the plant zone, the shear force increases to a certain extent and then decreases gradually. The reduction effect of plant on shear force increases with the increase of incident wave height, and the stem contributes to the reduction effect of root group on the maximum shear force of boundary layer, and the reduction coefficient ranges from 0.06 to 0.61. The fitted formula is more suitable for shallow water.

Based on the 141 surface sediments collected from the Yazhou Bay, Hainan Island, the distribution characteristics of grain size components, grain size parameters and sediment types were analyzed. The results indicate that the samples can be classified into 6 types as argillaceous arenaceous gravel, gravelly argillaceous sand, sand, silty sand, arenaceous silt and silt in the study area. In particular, the arenaceous silt is most widely distributed. The grain size diameters increase and then decrease, showing a banding distribution from north to south. The separation coefficient is generally high, which indicates the complex sediment sources and hydrodynamic conditions in this area. Base on Flemming ternary diagram, combined with sediment sources, hydrodynamic conditions and topographic features, the study area is divided into three sedimentary districts from north to south: the nearshore zone which showing the characteristics of wave-controlled deposition is mostly impacted by wave winnowing and transport, and the grain size is relatively small; the central Yazhou Bay zone is a high-energy coarse grained sand area, mainly controlled by the combined action of runoff, wave and tidal current; relatively, the southern zone is mainly affected by tidal current load, where the wave action is weakened, the sediment is the finest and deposited in a lower energy environment. In addition, the analysis of sediment transport trend shows that the midwest part of the study area is a depositional center, the silt of coastal erosion, Ningyuan River and offshore tidal current transport are carried to this area.

The global climate and environment have changed significantly upon the development of the Northern Hemisphere glaciation (NHG) during the Pliocene/Pleistocene. The Pacific meridional overturning circulation (PMOC) plays an important role on the distribution of heat in the global ocean and atmospheric CO₂ sequestration in the deep ocean, however, the relationship between PMOC and the formation of NHG is poorly studied. In this paper, we collected the available Nd isotope data of seamount Fe-Mn crusts from the Pacific. By comparing the Nd isotopic records from different water depths and different regions of the Pacific, considering the influences of water mass evolution and dust input on the Nd isotope records, we discuss the evolution of the PMOC and its relationship with the global climate change. It is suggested that the stagnation of the deep water formation in the North Pacific and the increase of the Asian dust input may be the reasons for the decline of the εNd of the North Pacific deep water since 3～4 Ma, and the increase of CO₂ sequestration in the deep ocean caused by the weakening of the deep water ventilation in the North Pacific contribute to the global cooling and the formation of NHG.