Spatiotemporal dynamics of bacterioplankton communities in the estuaries of two differently contaminated coastal areas: Composition, driving factors and ecological process.

Seasonal variations of environmental parameters usually lead to considerable changes in microbial communities. Nevertheless, the specific response patterns of these communities in coastal areas subjected to different levels of contamination remain unclear. Our results revealed notable fluctuations in the bacterioplankton community both seasonally and spatially, with seasonal variations being particularly significant. The diversity and composition of bacterioplankton communities in the estuaries varied significantly across seasons and between seas. Some bacterial phyla that were highly abundant in the dry season (e.g., Patescibacteria and Epsilonbacteraeota) were almost absent in the wet season. Furthermore, the network analysis revealed that the bacterioplankton networks were more complex during the wet season than in the dry season. In the wet season, the estuarine bacterioplankton network in the Yellow Sea region was more complex and stable, while the opposite was true in the dry season. According to the neutral community model, stochastic processes played a more significant role in the formation of bacterioplankton communities during the wet season than during the dry season. Estuarine bacterioplankton communities in the Yellow Sea region were more affected by stochastic processes compared to those in the Bohai Sea. In summary, in the estuaries of two differently contaminated coastal areas, the seasonal increase in nutrient levels enhanced the deterministic processes and network complexity of the bacterioplankton communities.

Sediment nitrogen mineralization and immobilization affected by non-native Sonneratia apetala plantation in an intertidal wetland of South China.

The mineralization and immobilization of nitrogen (N) are critical biogeochemical transformations in estuarine and coastal sediments. However, the biotic and abiotic mechanisms that regulate the two processes in different aged mangrove sediments remain poorly understood. Here, we used 15N isotope dilution method to investigate the changes in sediment N mineralization (GNM) and NH4+ immobilization (GAI) of different aged mangrove habitats (including 0, 10, and 20 years Sonneratia apetala, as well as >40 years mature native Kandelia obovata) in Qi'ao Island, Guangdong Province, China. Measured GNM and GAI rates ranged from 2.69 to 17.53 µg N g-1 d-1 and 2.29-21.38 µg N g-1 d-1, respectively, which varied both spatially and seasonally. The ratio of GNM to total N (PAM%, 0.24-0.86%) also varied spatially and seasonally, but the ratio of GAI to GNM (RAI, 0.79-1.54) only varied spatially. Mangrove restoration significantly increased the N mineralization and immobilization rates, but remained lower than those of mature native Kandelia obovata habitat. The sediment bacterial abundance, labile organic matter and temperature are the dominant factors in controlling N mineralization and immobilization. Our findings suggested that exotic mangrove Sonneratia aperale plantation can enhance sediment N mineralization and immobilization rates and improve N stability through accumulated biomass rapidly. Overall, these results provide new insights into sediment N transformation processes and associated influencing mechanisms in such intertidal wetlands profoundly influenced by human activities.

Responses of the macrobenthic community to the Dalian Bay oil spill based on co-occurrence patterns and interaction networks.

On July 16, 2010, a pipeline explosion spilled 1500 tons of crude oil into the Port of Dalian, China. To identify taxa responses to the spill, we exploited seven years of monitoring data to examine the co-occurrence of taxon pairs and the variation of the macrobenthic community. Non-parametric correlation analysis was used to construct interaction networks of relationships between oil spill contaminants and macrobenthic taxa. We observed that the impacted macrobenthic community not restored before 2016. The tolerance/sensitivity of taxa was inconsistent with the studies of oil impacts in other locations. We suggest revision of the ecological group classification of Sabellidae, Lumbrineridae, Terebellidae, Sternaspidae, and Spionidae. The variation in the frequency of coexistence indicates the potential impact of oil spill pollution on resource occupation. The interaction network involving macrobenthic families and stressors associated with the oil spill highlights how different macrobenthic families respond to different combinations of stressors.

Chemical control of overwintering green algae to mitigate green tide in the Yellow Sea.

It has been 14 years since the world's largest Ulva bloom appeared in the Yellow Sea, China in 2007. Although it is clear that the Ulva bloom originates from the culture system of Porphyra yezoensis (Nori) in the southern Yellow Sea, how to control it is still little understood. Since overwintering banks played a crucial role in the development of spring population of green algae on the cultivation ropes, here, a promising method was presented to prevent the development of Ulva bloom by the inactivation of the overwintering banks of green algae on the P. yezoensis cultivation ropes during February and early March. Chlorine dioxide, an environment-friendly disinfectant was used as algaecide with dosage of no lower than 40 mg/L at the contact time of 1 min. The overwintering green algae gradually disappeared within two weeks after the treatment. Furthermore, the growth of spring population of green algae on the cultivation ropes was effectively inhibited for at least eight weeks, which contribute to prevent the formation of floating populations during cultivation facilities collection. It was expected that the present method, if to be applied in the P. yezoensis cultivation areas in southern Yellow Sea, may mitigate the magnitude of the Ulva blooms in the Yellow Sea at a lower cost.

Baseline survey of sediments and marine organisms in Liaohe Estuary: Heavy metals, polychlorinated biphenyls and organochlorine pesticides.

A geographically extensive investigation was carried out to analyze the concentrations of heavy metals, PCBs and OCPs in the sediments and marine organisms collected from the Liaohe Estuary. In order to determine the spatial distribution and potential ecological risk of heavy metals, the surface sediments were collected from 44 sites in the Liaohe Estuary. The results showed that the heavy metal contents in the sediments were observed in the following order: Cr (11.2-84.8mg/kg)>Cu (1.7-47.9mg/kg)>Pb (4.3-28.3mg/kg)>As (1.61-12.77mg/kg)>Cd (0.06-0.47mg/kg)>Hg (0.005-0.113mg/kg). In comparison with the concentrations of heavy metals and POPs in other regions, the concentrations of As, Pb and DDTs in the Liaohe Estuary were generally low, and other pollutant concentrations were inconsistent with those reported in other regions. The contamination factor (CF), the pollution load index (PLI), the geoaccumulation index and the potential ecological risk index were used to analyze the pollution situation, which showed that the heavy metal pollution in Liaohe Estuary is mainly dominated by Cd and Hg. The concentrations of the four heavy metals varied significantly in the three kinds of tested organisms (fish, mollusk and crustacean), indicating the different accumulative abilities of the species. The results obtained in this study provide useful information background information for further ecology investigation and management in this region.