The spatial distribution of Cu, Cr, Cd, Pb, Ni and Co in the Jiaozhou Bay seawater and their distribution among different size fractions were investigated. The distribution mechanism of trace metals and the influence of environmental factors such as plankton activity and salinity during the distribution process were also discussed. The results showed that the highest values for most trace metals were distributed along north and northeast coast, while Cd and Pb also presented high value areas in the mouth and middle of the bay respectively. The trace metals in the Jiaozhou Bay seawater were mostly partitioned in the <1 kDa fraction with an average value of 70.1%, of which the percentages of Cu and Cd were up to 79.0% and 77.6% respectively, while Pb was only 58.2%. Similarly, the bulk dissolved organic carbon was also mostly partitioned in the <1 kDa size fraction with an average value of 73.1%. Spectroscopic properties indicated that low molecular weight (LMW, <1 kDa) fractions which mainly composed of humic-like organic matters contained more effective functional groups like hydroxyl and carboxyl groups and had higher complexing capacities with trace metals. There were significant positive correlations between chlorophyll a concentrations and high molecular weight (HMW, >1 kDa) proportions, indicating that primary production by phytoplankton in the euphotic zone was the major source of HMW dissolved organic matters in seawater and influenced complexation between trace metals and dissolved organic matters. The top area of the Jiaozhou Bay with lower salinity was characterized with higher proportions of large size components, which may be resulted from the combined effects of biological activity, terrestrial input and salinity.

Based on the data of pH and environmental parameters from 2011 to 2017, using the method of grid statistics and time-space matrix, contrastive analysis of pH in each environmental unit and the correlation of pH and environmental factors were studied. Furthermore, the differences of relevant factors affecting different seasons, regions and water levels were analyzed. The results showed that: (1) during from 2011 to 2017, the spatial distribution of pH was relatively stable in the Bohai Sea, the average value of surface pH in environmental units was from 7.95 to 8.38, the bottom was from 7.89 to 8.35, the absolute variation of average value was 1−1.5 standard deviations; (2) the time series of pH in each environmental unit tend to change synchronously, but there were differences among the units due to the different spatial distribution, the distribution characteristic of surface pH in winter was consistent with the saline; (3) there was a significant positive correlation between pH and chlorophyll a content in the Bohai Sea, and the surface pH varied seasonally, which was obviously consistent with distribution and variation characteristics of chlorophyll a, therefore, biological factor played an important role in regulating the pH of surface water; (4) the low value region of pH in Bohai Sea bottom in August was consistent with the formation of hypoxic zones by regional water stratification, and it was found that the bottom pH was positively correlated with dissolved oxygen; (5) the characteristic information of acidification indicators was further displayed by gridding processing technology and time-space matrix analysis method, which provided a good technical support for long-time scale analysis and research under climate change.

Neon flying squid Ommastrephes bartramii is a cephalopod species of economically importance distributed in the North Pacific Ocean. Because of short lifespan, their abundances mainly depend on the recruitments and the marine environment during their early life stages will directly affect the recruitments. Using fishery data collected by Chinese squid-jigging fleets in the Northwest Pacific Ocean from 2004 to 2015 and the sea surface temperature (SST) of spawning and feeding grounds, which were divided into different numbers of subareas, correlation analysis and random forest model were used to screen out the subareas that CPUE has significant relationships with Ps (the proportion of favorable-SST in spawning grounds) of spawning grounds and Pf (the proportion of favorable-SST in feeding grounds) of feeding grounds during spawning and feeding periods. The Ps and Pf were used as input variables of the neural network model to forecast recruitments based on spawning ground and feeding ground, respectively, and the advantages and disadvantages of the model and forecast accuracy were analyzed. The results show that the schemes of dividing spawning ground into 5°×5° and feeding field into 2.5°(longitude)×4°(latitude) were optimal. The ranges of subareas selected by random forests are largely consistent with those selected by correlation analysis, both random forests and correlation analysis can identify potential subareas associated with CPUE, and both have forecasting accuracy of >90%. However, the subareas selected by the random forest are better and the forecast accuracy is higher than those selected by correlation analysis. In addition, the model based on the spawning ground is more accurate and stable than that based on feeding ground.

Observations were carried out at Nanliu River, Dafeng River, Qinjiang River, Maoling River and Fangcheng River in the Beibu Gulf to analyze the distribution characteristics and fluxes of nutrient in February (dry season) and August (flood season) 2018. The results showed that significantly variations of nutrient concentration were observed, and the nutrient concentrations in the Fangcheng River, Maoling River and Qinjiang River in the dry season were higher than that in the flood season, while the nutrient concentrations in the Dafeng River and Nanliu River in the flood season were higher than that in the dry season. Nitrate (${\rm {NO}}_3^- $) was the predominant species of dissolved inorganic nitrogen (DIN) during the flood season, while the ${\rm {NH}}_4^+ $ content in the Fangcheng River and Dafeng River increased during the dry season. Based on the runoff data and nutrient concentration, the fluxes of nitrogen and phosphorus into the Beibu Gulf were calculated to be 1014607 tons and 47929 tons respectively in 2018, of which DIN accounted for 77% of total nitrogen and ${\rm {PO}}_4^{3-} $ accounted for 40% of total phosphorus. During the flood river, higher nutrient fluxes were found in the Nanliu River, followed by Dafeng River, Fangcheng River, Maoling River and Qinjiang River. While in the dry season, the flux of nutrients from rivers to the coastal gulf changed significantly due to the influence of regional pollution. Compared with the historical data, the fluxes of nutrient into the coastal gulf increased significantly, which may be responsible for the increase of water eutrophication in the coastal Beibu Gulf. High and different terrestrial inputs transported by the rivers in northern Beibu Gulf may lead to an extensive impact on the ecological system of the Beibu Gulf.

In recent years, the water quality of the Liaohe Estuary has been declining, and a large input of nitrogen has increased the burden on the environment. The denitrification process releases nitrogen from sediments into the atmosphere in the form of N₂O and N₂, which reduces the nitrogen load in the estuarine ecosystem. In this study, quantitative PCR was used to determine the levels of four denitrification functional genes narG, nirK, norB and nosZ present in the surface sediments of the Liaohe Estuary. The narG gene, which dominates nitrate reduction, was found to be the most abundant. The nirK-type denitrification functional gene was sequenced by high-throughput sequencing. The results showed that the genus of denitrifying bacteria in the Liaohe Estuary was mainly Devosia, Phaeobacter, Alcaligenes, Pseudomonas. The abundance of denitrification function genes is mainly affected by sediment properties, except that norB gene is significantly related to many environmental factors. The community structure and diversity of nirK type denitrifying bacteria are mainly affected by salinity, pH, dissolved oxygen and ${\rm {NO}}_2^- $ contents. The effects of environmental factors on the abundance and community structure of denitrifying bacteria were studied. The results provided a theoretical basis for alleviating the fate of nitrogen elements in the eutrophication of Liaohe Estuary.

Mangrove growing on the tidal flat is of important value for the estuarine plant community compositions and coastal protection against wind and wave. This study aims to explore the spatial distribution pattern and associated influencing factors of estuarine mangrove based on the soaking and sinking experiment of aboriginal Aegiceras corniculatum embryo and observations on water salinity, plant community structure and geomorphology of the tidal flat along the estuaries of Nanliujiang River and Dafengjiang River. Our results show that the distribution pattern of mangrove along Nanliuujiang River and Dafengujiang River estuaries exhibits a mode of “pure mangrove (e.g. mixture of Aegiceras corniculatum, Kandelia candel, Sonneratia apetala)→mixture of mangrove and semi-mangrove (Hibiscus tiliaceus, Clerodendrum inerme Gaertn)→mixture of mangrove, semi-mangrove and non-mangrove→mangrove mosaic→sparse mangrove seedlings” from sea to land. However, mangrove at the landward limitation of the Dafeng River estuary is characterized by a mixture of mangrove, mangrove seedlings and semi-mangrove. Besides, the time length of mangrove socking dominates the spatial distribution pattern of the estuarine mangrove while the time length of landward transport of tidal current affects the extreme location of the mangrove landward growth. A suitable tidal flat is an essential condition for the mangrove development and growth.

Using fishery data of Scomber japonicus from Chinese light-purse seine fishing on the high seas of the Northwest Pacific Ocean from May to November during 2014 to 2017, and the environmental remote sensing data, the habitat suitability index (HSI) model of Scomber japonicus was constructed based on fish catch and nos of hauls, respectively. Applying sea surface temperature, sea level anomaly, chlorophyll a concentration, the suitability index model of each environmental variable was established by one-dimensional exponential regression fitting. The weight of each environmental factor was determined by linear programming method to improve the prediction precision of HSI model for fishing ground. The prediction accuracy of the HSI model was verified with the actual fishing data from May to November in 2018, and the results showed that in the sea areas with HSI values over 0.7, the fishing catches accounts for 77.29% for HSI model based on fish catch and 76.79% for HSI model based on nos of hauls respectively, which indicates that the HSI model based on different environmental factor weights can better predict the central fishing ground of Scomber japonicus on the high seas of the Northwest Pacific Ocean.

Volatile halocarbons (VHCs) produced in the oceans are important carriers for chlorine, bromine, and iodine to enter into the atmosphere. Marine algae can produce VHCs that have an ozone-depleting potential. Marine microalgae in particular have been shown to be major contributors of VHCs in the atmosphere. However, little is known about the influences of environmental factors on the production of VHCs by marine microalgae. In this study we examined the influence of different light intensities (20 μmol/(m²·s), 70 μmol/(m²·s) and 140 μmol/(m²·s)) and nitrate concentrations (1 mg/L, 5 mg/L, 10 mg/L and 50 mg/L) on the growth of Prorocentrum donghaiense and Phaeodactylum tricornutum and the releases of four VHCs (CH₃I, CH₂Br₂, CHBr₂Cl and C₂HCl₃) by these two microalgae. Unialgal cultures of these two kinds of microalgae were conducted in axenic and sealed glass vessels. The VHCs were extracted and analyzed by gas chromatography coupled to purge-and-trap preconcentration system. The releases of VHCs by these two microalgae were affected by light intensity and nitrate concentration, while their influences on different VHCs were various. The release of CH₃I was significantly affected by light intensity and nitrate concentrations. Within a certain range, the amount of CH₃I released from the two microalgae raised with the increase of light intensity. Moreover, our results showed that increasing the nitrate level above 5 mg/L could promote the production of CH₃I by these two microalgae.

The photosynthetic active radiation (PAR) plays a significant role in regulating ocean primary productivity, so it may indirectly affect the abundance and spatial distribution of cephalopods. In this study, we examined the relationship between photosynthetic active radiation and Ommastrephes bartramii stocks in the Northwest Pacific Ocean, and evaluated the impacts of the anomalous climatic environments on the squid stocks, based on the fishery data during 2006−2015 obtained from the squid-jigging Science and Technology Group of Shanghai Ocean University and the remotely satellite data of PAR. The results indicated that catch per unit effort (CPUE), latitudinal gravity center (LATG), PAR and its spatial distribution exhibited significant monthly variation. From July to November, the suitable range of PAR was 36−39 E/(m²·d) in July, 33−36 E/(m²·d) in August, 24−27 E/(m²·d) in September, 18 E/(m²·d) in October and 12 E/(m²·d) in November. The most favorable PAR was 36 E/(m²·d), 33 E/(m²·d), 27 E/(m²·d), 18 E/(m²·d), 12 E/(m²·d), respectively, from July to November. The results showed that a significant positive relationship (p<0.05) was found between CPUE and PAR, and further a significantly positive correlation (p<0.05) was found between CPUE and the monthly percentages of suitable PAR accounting for the whole fishing ground. Meanwhile, the LATG varied with the mean latitude of the most preferred PAR in each month. Finally, under the anomalous climatic environments, the CPUE in the La Niña years is higher than that in the El Niño years, which may be caused by the higher PAR in the La Niña years. Our findings indicated that the PAR strongly affected the abundance and spatial distribution of O.bartramii in the Northwest Pacific Ocean.

Using the two-dimensional non-static numerical model, which neglect the submarine topography but consider the pycnocline and background shear flow, the numerical experiment was made on the generation and evolution of linear and nonlinear symmetric ocean internal waves in the unstable downward shear background flow. After analyzing and comparing the results, the main conclusions are as follows: the linear internal wave strength is exponentially growing with integral time, and there’s symmetric instability of the wave, while nonlinear internal wave strength is growing quasi-linearly in the development stage, and finally enters the stabilization stage. The linear growing is much faster than the nonlinear growing and the latter has a stabilizing effect. For linear and nonlinear symmetric internal waves, there are maximum value of potential density perturbation, which is captured by the pycnocline. This is consistent with actual observations. The stream function and potential density perturbation are well coordinated, which is reflected in the positive and negative centers of the potential density perturbation corresponding to the rising and sinking movements of the stream function, respectively. This shows that there is a slantwise convection occurred from the bottom of the sea and the pycnocline is the top cover. For linear internal waves, with the increase of integral time, its waveform is basically the same and the positive and negative amplitude is also about the same. There are two slantwise circulations that grow in opposite signs and between them is a strong slantwise upwelling. The waveform of nonlinear internal wave changes with the integration time and the number of slantwise circulations is also increasing, resulting in the stronger negative circulations and a sharp increase in the horizontal gradient of stream function and potential density perturbation. The sharp increase can be regarded as an interruption.