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.

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.

Chub mackerel (Scomber japonicus) is a major target species in the Northwest Pacific fishery. Understanding changes in its fishing grounds is of great significance for assessing population size, resource, utilization, and management of the fishery. Based on catch data of high sea light purse seine fishery of China from 2014 to 2019, the spatial and temporal patterns of chub mackerel fishing grounds in the Northwest Pacific using the global Moran index, the local hot spot analysis, center of gravity migration trajectory model, and standard deviation ellipse are analyzed in this study. The results show that: (1) catches of chub mackerel mainly concentrates in the area between 39°−44°N and 147°−155°E, the annual catches show a trend of first increase and then decrease, the annual CPUE decrease year by year, the monthly catches show a trend of first increase and then decrease, which maintaines at a high level from June to October, and the monthly CPUE increases with month. (2) The spatial autocorrelations of annually and monthly chub mackerel catches are significant, and the monthly autocorrelations are stronger than annually ones, indicated highly aggregated distribution of the fishing grounds. (3) The distributions of chub mackerel hot spots and cold spots show a certain spatial agglomeration, but their distribution patterns and the areas cover varied apparently with years and months. (4) The gravity center of fishing ground generally show northwest shift from year to year, and in term of seasonal changes, moves northwest from April to August, and then turnes back to the southwest. (5) The annual and monthly shifts in directions of fishing grounds are consistent, showing an southwest-northeast pattern with strong directivity and aggregation. The spatial correlation models used in this analysis present a new look at spatial and temporal patterns of the chub mackerel fishing grounds, which may provide useful information for the rational development and utilization of the chub mackerel resource.

Based on the investigations of surface sediments at six sampling stations of nine cruises carried out in the sea around the Yongxing Island of Xisha from 2009 to 2017, the background values of seven heavy metals are determined through the process of mathematical statistics, the contents and inter-annual variations of heavy metals are analyzed, and the contents of the heavy metals are evaluated by means of single factor standard index and potential ecological risk index. The results show that the background values of heavy metals in the sediments of the study area are low, the average level of them meet the first class of marine sediment quality, and the quality of sediment is excellent. The inter-annual variations of seven heavy metals in the sediments of the study area are slightly different and generally significant and affected obviously by the development activities on the Yongxing Island. From 2009 to 2017, the contents of Zn, Cd, Cu, Cr, As and Hg are to increase first and then decrease, while the content of Pb is to increase. The assessment by means of potential ecological risk index shows that the multi year average of potential ecological risk indexes are in the order of Cd, Hg, As, Cu, Pb, Cr, Zn, and Cd and Hg are the main potential ecological risk factors of the study area.

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%.

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.

The distribution and diffusion of suspended particulate matter (SPM) in coastal waters play an important role on ecological environment, coastal geomorphic evolution, aquaculture and coastal engineering. The northern Yellow River Delta is a strong coastal erosion area due to the diversion of Diaokou course. Revealing the variation characteristics and laws of SPM concentration in this area is the basis for maintaining the safety of protection projects. Using the well-validated model to retrieve the SPM concentration in the coastal waters, the cross validation results of Landsat-8 and Sentinel-2 satellite sensors show that the SPM concentrations retrieved by the two sensors have strong consistency, and the two kinds of satellite data can be used together. The seasonal variation of SPM concentration in the study area is obvious. The concentration of SPM is higher in spring and winter, and lower in summer. Autumn is the season when SPM concentration changes from low to high. In winter and spring, the wind and waves are large in this area. Under the combined action of waves and current, strong sediment resuspension occurs, which is the main source of SPM. The construction of spur dike group altered the spatial and temporal distribution of SPM to a certain extent.

The waterline method is an important method for remote sensing inversion of intertidal terrain. Aiming at the problems in the digital elevation model (DEM) construction with variable topography, which the waterlines intersect and lack of representation of micro-topography for the tidal creek in the conventional waterline method, an enhanced terrain remote sensing construction method was proposed in this paper. First, the waterlines with the correct trend of elevation change and spatial separation were selected through tidal level sorting. Second, the images group with similar waterlines position in the screening process were combined according to the mean of a sequence of the modified normalized difference water index values in each pixel, and the boundary line of land-sea was obtained. These two methods worked together to construct the initial intertidal DEM. Then, the tidal creek DEM was generated by using the boundary and centerline of the tidal creek in the low tide period. Through the mosaic processing, the tidal flat DEM that can express the undulating micro-topography of the beach surface was constructed. Comparing with the measured terrain, the results in the central core area of the radial sand ridges off the coast of Jiangsu showed that the mean absolute error of the 4 measured sections was 0.43 m, the root mean square error was 0.54 m, and the average correlation (r) was 0.75. The simulation results and the measured results were in good agreement with the changes in beach undulations. Furthermore, the spatial fragmentation of the simulated DEM was small and can reflect more detailed terrain features. This method can provide a new idea for constructing high-precision DEM of intertidal zone considering micro terrain changes by using multi-source remote sensing data.

The information on sediment flux (Q_s) from continental shelf islands is an important supplement to the study of accurate records interpretation of continental shelf sedimentary systems. Aiming at the scientific problem of how to estimate the Q_s of continental islands, this paper proposes a solution to calculate their Q_s based upon the empirical formula of small and medium-sized rivers in adjacent continent, taking the 8227 continental islands in Southeast China as examples. Two preconditions are set up to perform the calculation. That is, the Q_s rule of the continental islands follows the rule of the small and medium-sized rivers in adjacent continent, and a continental island can be treated as a river basin to calculate its Q_s. The results show that: (1) the Q_s calculated by empirical formula is the minimum estimated value; if the actual basins of the continental island are taking into considered, the Q_s value will slightly increase, but the increase will not exceed n^0.13 (n is the number of basins); (2) the empirical formula give the approximate magnitude information of Q_s for continent islands; the total area of the continental islands is 4418.49 km², and the corresponding order of magnitude of Q_s is 10⁶ t/a; (3) during the completion of the estuarine filling stage, the continental island sediment is one of the main source for the inner continental shelf areas. Therefore, more attentions and researches are expected to the role play by the continental shelf islands to the formation and evolution of continental shelf depositional systems.