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Abstract The composition, distribution, indexes and budget of saturated lipid biomarker aliphatic hydrocarbons (AHs) in sediments of the East China Sea (ESC) were analyzed to identify their indications and sources. The resolved n -alkane (R) contents were 0.70–2.89 μg/g, with long-chain n -alkanes as the dominant composition in the ECS. The high R values mainly appeared at south inner shelf and north outer upwelling area, corresponding to the high mud, total organic carbon (TOC) and Chl a contents there. The composition, distribution pattern, combined with indexes of AHs, suggested no petroleum contamination and predominant biogenic sources in the ECS. The biogenic sources mainly were the mixed terrestrial higher plant, marine plankton and bacteria and aquatic macrophyte origins. Biotic source apportionment suggested that terrestrial higher plants were the dominant source of AHs, followed by marine planktons, with the lowest of submerged/floating macrophytes. Quantitative evaluation of R sources suggested that the Changjiang River input was the primary terrestrial contributor, accounting for 67.9% of total terrestrial input. The burial flux of R was 1.11 × 103 t/yr, with inner shelf and estuary as main accumulation areas. Although there was a huge amount of R influx from terrestrial and marine sources, only 9.8% could be preserved in sediments. Highlights • Characteristic parameters and their indications of AHs were discussed. • Biotic source allocation of AHs by primary producers was considered. • Quantitative source, burial and preservation of AHs were evaluated. [ABSTRACT FROM AUTHOR]

Heavy metal contamination is an essential indicator of environmental health. In this work, one sediment core was used for the analysis of the speciation of heavy metals (Cr, Mn, Ni, Cu, Zn, As, Cd, and Pb) in Jiaozhou Bay sediments with different grain sizes. The bioavailability, sources and ecological risk of heavy metals were also assessed on a centennial timescale. Heavy metals were enriched in grain sizes of < 63 µm and were predominantly present in residual phases. Moreover, the mobility sequence based on the sum of the first three phases (for grain sizes of < 63 µm) was Mn > Pb > Cd > Zn > Cu >Ni > Cr > As. Enrichment factors (EF) indicated that heavy metals in Jiaozhou Bay presented from no enrichment to minor enrichment. The potential ecological risk index (RI) indicated that Jiaozhou Bay had been suffering from a low ecological risk and presented an increasing trend since 1940s owing to the increase of anthropogenic activities. The source analysis indicated that natural sources were primary sources of heavy metals in Jiaozhou Bay and anthropogenic sources of heavy metals presented an increasing trend since 1940s. The principal component analysis (PCA) indicated that Cr, Mn, Ni, Cu and Pb were primarily derived from natural sources and that Zn and Cd were influenced by shipbuilding industry. Mn, Cu, Zn and Pb may originate from both natural and anthropogenic sources. As may be influenced by agricultural activities. Moreover, heavy metals in sediments of Jiaozhou Bay were clearly influenced by atmospheric deposition and river input. [ABSTRACT FROM AUTHOR]

Microbial processes during the degradation and transformation of marine organic matter (OM) are thought to play an important role in controlling the strength and efficiency of carbon export and preservation in the ocean. However, the detailed relationship between the diagenetic states of OM and microbial activity and community structures remains poorly understood. In this study, particulate amino acids (PAAs), stable carbon and nitrogen isotopic signatures, heterotrophic bacterial abundance (HBA), bacterial community structure and extracellular hydrolytic enzyme activity (EEA) in particulate OM (POM) were investigated in Jiaozhou Bay (JZB), China, with the aim of investigating bacterial degradation and adaption in response to different sources and reactivity of POM in the coastal environment. The results showed that POM from different sources had distinct PAA compositions, diagenetic states, and bacterial features, such as particle attached HBA, EEA and community structure. High PAA concentrations but low contribution of bacterial carbon to particulate organic carbon (POC) and diagenetic alteration of POM were observed in regions with high in situ marine production, where high Chl-a and autochthonous δ13C and δ15N signatures were observed. In addition, high HBA and D-amino acid (D-AA) concentrations in POM were also found in the same regions, which indicated that fresh POM also induced rapid bacterial growth and reproduction. However, the lowest D-AA proportion to PAA (mol% D-AA) in those regions still indicated a more obvious supply of AAs from marine sources, which was consistent with the low bacterial carbon contribution to POC and fresh states of POM. In contrast, POM in low primary production regions was highly degraded by bacteria, as reflected by an enrichment in D-AAs and high bacterial contribution. However, high EEA probably driven by the priming effect occurred in regions where fresh planktonic POM was mixed with terrigenous POM. High relative abundances of Flavobacteriia, Alphaproteobacteria and Gammaproteobacteria were observed in fresh planktonic, terrestrial and planktonic mixture and highly degraded POM, respectively, indicating a possible bacterial adaptation strategy to their available OM. Our study has important implications for bacteria–POM interactions and provides insight into the role of bacteria in the degradation and transformation of POM of different sources in coastal systems. [Display omitted] • Fresh suspended POM showed not only high PAA concentrations but also high particle-attached HBA and D-AA concentrations. • Highly degraded POM was associated with enrichment in D-AAs and a high bacterial contribution. • POM with mixed planktonic and anthropogenic sources showed the highest bacterial EEA probably driven by the priming effect. • High relative abundances ofcertain bacteria showed adaption shifts to POM with different diagenetic states. [ABSTRACT FROM AUTHOR]

Dissolved Organic Carbon (DOC) is a key organic compound in wet precipitation, but few data are available in China marginal seas. To probe the concentration, deposition flux, seasonality, source and potential ecological environmental effects of precipitation DOC, in this study, one-year precipitation samples were collected at Jiaozhou Bay (JZB), a typical anthropogenic-influenced semi-enclosed bay in the western Yellow Sea for the first time from June 2015 to May 2016. The concentrations of DOC in precipitation were highly variable with a volume-weighted mean (VWM) concentration of 3.63 mg C L−1, which was mostly higher than those in other areas. DOC concentrations were lower in wet season than that in dry season due to the dilution from more amount of rainfall. The wet deposition flux of DOC was calculated to be 3.15 g C m−2 yr−1 with 68.7% of which occurred in wet season mainly owing to the promoting of more rainfall amount. Besides, local emissions together with the long-range transport of pollutants were other factors controlling precipitation DOC. Fossil fuel combustion particularly coal burning was considered to be the leading source of precipitation DOC based on correlation analysis with some generally accepted indicators. Wet deposition dominates the external input of DOC at JZB by comparison with riverine input with a percentage of 54%. Heavy storm may exert enrichment effect on DOC levels in the surface water of JZB, and then promote the secondary productivity. This study emphasizes that wet deposition is an important process that should be seriously considered in the models of global/regional carbon biogeochemical cycling. • Concentration and wet deposition flux of precipitation dissolved organic carbon were high in Jiaozhou Bay. • The factors impacting precipitation dissolved organic carbon were illustrated. • Coal burning is possible the leading source of precipitation dissolved organic carbon. • Wet deposition is the leading external input of dissolved organic carbon in Jiaozhou Bay. • Heavy storm can increase dissolved organic carbon levels of surface waters and promote secondary productivity. [ABSTRACT FROM AUTHOR]

Phosphorus (P) is an important macronutrient that can limit primary productivity in coastal marine ecosystems. In this study, four sediment cores were collected in the Jiaozhou Bay to study the phosphorus forms and their bioavailability, including exchangeable or loosely sorbed P (Ex-P), iron-bound P (Fe-P), authigenic P (Ca-P), detrital P (De-P) and organic P (OP), which were separated and quantified using a sequential extraction method (SEDEX). The results showed that the concentration of total P (TP) in core sediments ranged from 6.23 to 10.46 μmol/g, and inorganic P (IP) was the dominated P form. Fe-P and De-P were the main chemical forms of IP in core sediments. The profile variation of OP presented the most significant among the phosphorus forms. Whereas the concentrations of Ex-P, Fe-P, and Ca-P varied slightly with depth, indicating that the transformation of Ex-P, Fe-P, Ca-P, and OP could occur during sedimentary P burial. Moreover, the distribution of P species was influenced by many factors, including terrigenous input, biological processes, organic matter degradation and increasing human activities. High total organic carbon (TOC)/OP ratio occurred in the Jiaozhou Bay, ranging from 73 to 472 (average, 180 ± 81) in core sediments, which was caused by the increasing terrestrial organic matter. The ratio of TOC/P reactive ranged from 24 to 101 (average 46 ± 15) in core sediments (lower than the Redfield ratio), implying a surplus of sedimentary reactive P compared with TOC. Potential bioavailable P (BAP) accounted for about 28.2–60.8% (average, 47.1 ± 7.4%) of TP in core sediments, and presented an increasing trend since 1980s, which might be responsible for the shift of phytoplankton community composition during these decades. [ABSTRACT FROM AUTHOR]

The acidification of the marginal seawater was a more intricate process than the ocean. Although some studies have been done on seasonal acidification in the bottom water of Chinese marginal seas, research on surface water acidification has still been insufficient. We analyzed the acidification properties and controlling factors in the Bohai Sea (BS) and Yellow Sea (YS) surface water during April 2023. The observation showed that the average surface water pH of the BS, North Yellow Sea (NYS), and South Yellow Sea (SYS) were 8.09 ± 0.06, 8.13 ± 0.05, and 8.15 ± 0.05. Phytoplankton significantly impacted pH and Ω arag , while riverine inputs and biological activity played a vital role in controlling DIC and TA. The Yellow River significantly impacted the BS. The North Yellow Sea Cold Water Mass had a limited impact on acidification, while the South Yellow Sea Cold Water Mass significantly affected the SYS. Regarding seasonal fluctuations, Ω arag was significantly higher in summer than in other seasons. DIC and TA showed different patterns in both the BS and YS, with a minimal fluctuation in pH. Over the last two decades, the pH in the BS showed a slight annual decline, and the rate of change was (−1.45 ± 2.19) × 10−5 yr−1. In contrast, the NYS and SYS have slightly risen, with rates of change of (2.39 ± 1.24) × 10−5 and (1.23 ± 0.76) × 10−5 yr−1. We believed that surface water acidification in the BS and YS did not follow the expected trend of significant acidification observed in open oceanic regions. Instead, the acidification process in these marginal seas was dominated by local factors such as riverine inputs, biological activity, and cold water masses, resulting in minimal pH changes over the last two decades. [Display omitted] • River inputs and phytoplankton influenced BS and YS surface seawater acidification. • Summarizing data of past 20 years on surface water acidification in BS and YS. • The BS and YS surface water may not be acidified. [ABSTRACT FROM AUTHOR]

In an anaerobic sequential batch reactor (SBR), marine anammox bacteria (MAB) were able to enhance microbial activity in nitrogen-rich saline wastewater and it was significantly affected by influent substrate composition and loading strength. This study therefore enhanced nitrogen removal efficiency by adjusting the influent nitrogen loading strength of MAB-inoculated anaerobic SBRs and assessed the correlation with the bacterial community. The results displayed that the system obtained optimal nitrogen removal efficiency (TN = 83.52%, NH 4 –N = 90.14%, and NO 2 –N = 83.57%) as the strength of influent nitrogen loading was increased to 201.35 mg L−1 for NH 4 –N and 266.42 mg L−1 for NO 2 –N. Moreover, the increase in the strength of influent nitrogen loading also enhanced the anammox 16S rRNA abundance (4.09 × 108 copies g−1) and ladderanes content (22.49 ng g−1 dw). Analysis of 15N isotope further illustrated that all systems were dominated by anammox (average ra = 95.22%). In conclusion, these findings provide scientific guidance for the management of eutrophic seawater and contribute to the realization of industrial applications for the treatment of nitrogen-rich saline wastewater. [Display omitted] • Increasing influent nitrogen loading strength enhances anammox nitrogen removal of saline wastewater. • Influent nitrogen load strength significantly affected the abundance of nitrogen transforming microorganisms. • Summed ladderanes increased with the increasing influent nitrogen loading strength. [ABSTRACT FROM AUTHOR]