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The process of atmospheric organic carbon (OC) entering the ocean through wet deposition plays a crucial role in the global carbon cycle. To gain insights into the biogeochemical dynamics of OC at the land-sea margin, we conducted an extensive four-year investigation on precipitation OC in Jiaozhou Bay (JZB). The results showed that the volume-weighted mean concentration of particulate OC (POC) and dissolved OC (DOC) in precipitation were 0.38 and 2.06 mg C L−1 with an average wet deposition flux of OC for 2666.5 mg C m−2 yr−1. The source of POC in precipitation is predominantly by the C3 plant emission and burning and fossil fuel combustion. Wet deposition contributed 986.6 t yr−1 of OC of which 506.3 t yr−1 of bioavailable DOC, which could have significant implications for carbon cycle in the JZB. This study could enhance the understanding of the marine atmospheric OC in coastal areas. [Display omitted] • Long-term observation of DOC and POC in wet deposition in an urbanized coastal bay • Source apportionment of OC in precipitation in Jiaozhou Bay (JZB) • The atmospheric environment of JZB has showed a gradual improvement in terms of OC. • Wet deposition contributed JZB with sizeable amounts of bioavailable and inert OC. [ABSTRACT FROM AUTHOR]

Sediment resuspension in coastal environments is associated with both nutrient repartitioning and with the biological carbon pump, which are further linked to climate change, eutrophication, and marine pollution. To explore these relationships, a resuspension framework, including surficial/core sediments and settling trap-collected particles (TCPs), was assessed in the Jiaozhou Bay (JZB) to examine the behavior and fate of particulate biogenic elements (C, N, P and Si). Resuspension-mediated differences in the concentrations of numerous biogenic proxies were significant and mainly corresponded to selective upwelling of fine-sized, nutrient-enriched particles, to autochthonous organic matter degradation below the trap-deployed level comprising water column transportation and long-term retention at the sediment-water interface. This is further reinforced by smaller inorganic carbon concentrations in sediments and origin-indicating stoichiometric ratio records (OC:ON, OC:OP). Nevertheless, biogenic silica (BSi) exhibited a near homologous concentration and had the largest preservation efficiency. Three principal components, representing production and preservation, remineralisation, and a particle-size effect, accounted for 55.5%, 14.0%, and 9.1% of the total variance, respectively. After calibration, the primary sinking flux was two orders of magnitude smaller than the measured absolute sedimenting flux. Also, the limited bottom achieving contribution with a maximum of 28.3% for freshly biogenic particles produced in autumn/winter circumstances with low primary productivity was inferred. The recurrent resuspension processes in JZB demonstrated that 5–12 cycles of similar or higher intensity resuspension was required before freshly-formed biogenic particles could ultimately be integrated into the sediments. Regarding the internal P sink-switching mechanism, the previously transformed Fe-bound fraction across the estuarine salinity gradient has limited application under offshore redox oscillations, whereas near-quantitative transfer of dissolved P from remineralized organic matter to authigenic carbonate fluorapatite could substantially reduce its bio-availability in resuspended particulate P. • Biogenic element concentration in sinking particles is greater than sediments. • Resuspension correction downgraded sinking flux by two orders of magnitude. • Interior P sink-switching can reduce bio-availability of resuspended particles. [ABSTRACT FROM AUTHOR]

To exploit the resolving ability of rare earth element and yttrium (REY) in resuspension binary mixing model, and discover potential new REY-related resuspension proxy, this preliminary research studied the geochemical signature of REY in different Jiaozhou Bay samples including surficial/core sediments and settling trap-collected particles. Close quantitative relation for bulk concentration in particles, sediments and fine-grained fraction of major river sediments around the Yellow Sea, approved the priority contribution of catchment detrital materials. Moreover, common characteristics occurred for compartment-specific partitioning REY signatures in six operated-defined fractions, and multiple REY normalization pattern indexes (i.e. Y/Ho divergence, and Ce/Eu anomalies). All constrain the application of REY in resuspension discrimination of marginal shallow seas. However, linearity with different slopes and intercepts were plotted for the MREE bulge index versus HREE/LREE figure in reducible amorphous Fe-oxides fraction, which could provide new discrimination perceptions. • The geochemistry of rare earth element and yttrium were evaluated. • Catchment detrital material is responsible for sinking particle and sediment. • Common features occur for specific partitioning REY signatures and indices. • New separated distribution of MREE bulge versus HREE/LREE was discovered. [ABSTRACT FROM AUTHOR]

Abstract The spatial and temporal dynamics of both dissolved and particulate nutrients were studied during 2015–2016 in the Jiaozhou Bay (JZB), a deeply anthropogenic impact ecosystem in China. The dissolved inorganic nutrients was mainly from the wastewater and riverine inputs which is demonstrated from the negative correlation between nutrients with salinity and their higher levels distribution observed in the northeastern and/or northwestern JZB, where mainly received industrial and agricultural source run-off, respectively. The high levels of dissolved and particulate organic pools were also observed in the same area but have autochthonous sources besides terrestrial input, which lead to their higher concentrations in autumn during phytoplankton bloom. The composition of DIN has been changed with the major component from NH 4 + to NO 3 -, which probably due to the controlling load of NH 4 + but no limitation of NO 3 - by human intervention. The average annual DIN/DIP ratio increased by one time but SiO 3 2-/DIN ratio has no obvious variation over the past decade, which indicated that the potential limiting nutrient for phytoplankton growth has been converted from silicon to phosphorus in JZB. Additional, more prone to partition into POC but not DOC pools of organic carbon were found during the phytoplankton bloom in autumn due to the nutrient-rich, diatom dominated condition and both DOP and POP may be the potential P source and can relieve P limitation to some extent during the same time. Nutrient budgets calculation also demonstrated that riverine input and wastewater discharge are major sources of dissolved nitrogen and phosphorus, while silicate were mainly came from submarine fresh groundwater discharge. The mixing flow transported large amounts of nutrients from JZB to the Yellow Sea. Meanwhile, the net ecosystem metabolism and nitrogen metabolism calculation showed the whole ecosystem was heterotrophic and a net nitrogen fixation in JZB. Highlights • The composition of DIN in JZB has been changed with the major component from NH 4 + to NO 3 -. • The proportions of DON and DOP to TDN and TDP has increased obviously over the past decade. • The potential limiting nutrient for phytoplankton growth has been converted from silicon to phosphorus in JZB. • An annual nutrients budget including submarine fresh groundwater discharge is proposed. • JZB is net heterotrophic (57 ×107 mol C/yr) and net nitrogen fixation (74 ×106 mol/yr) on annual basis. [ABSTRACT FROM AUTHOR]

Abstract Reconstructing heavy metal historical trends are essential for better understanding anthropogenic impact on marine ecosystems. In this work, the ecological risk and sources of Cr, Mn, Ni, Cu, Zn, As, Cd, and Pb in Jiaozhou Bay were studied and the anthropogenic metal emissions was also quantified. The ecological risk was mainly caused by Cd, As and Cu, which presented an increasing trend with increased anthropogenic activities since the 1950s. The statistical analysis show that Cr, Mn, Ni, Cu and Zn were primarily from natural sources. Cadmium and Mn might originate from both natural and anthropogenic sources. Arsenic and Pb were sourced from agricultural activities and atmospheric precipitation, respectively. The anthropogenic flux of Cr, Mn, Ni, Cu, Zn, As, Cd and Pb were 138, 586, 63, 66, 161, 35, 0.31 and 44 mg/m2/a since the 1950s. Over 40.0% of Cu and As were quantified from anthropogenic emissions since the 1950s. Highlights • Jiaozhou Bay sediments reflected regional anthropogenic metal emissions. • Anthropogenic source heavy metals present an increasing trend since 1950s. • Risk contribution ratios of Cd, As and Cu were 48.8%, 20.8% and 9.3%, respectively. • Over 40% of Cu and As were quantified from anthropogenic source since the 1950s. [ABSTRACT FROM AUTHOR]

To identify sources and evaluate ecological risks of heavy metals in sediments of Jiaozhou Bay, contents and chemical fractions of Cd, Cr, Cu, Pb, Zn, Ni, Sb and Sn were studied. Results suggested that higher metal contents appeared at inner bay and near marine dumping area. Labile fractions of heavy metals accounted for 0.5–77% (~36%) of total contents indicating their significant anthropogenic sources. The enrichment levels of Cd and Sb were relatively higher. Cu, Ni, Cd and Zn were at low to medium risks. Cr, Pb, Sn and Sb were at no or low risks. Total contents of heavy metals were mainly controlled by natural sources, while anthropogenic inputs were important sources of labile fractions of heavy metals in sediments of Jiaozhou Bay with industrial and domestic activities as main contributors for Cu, Pb, Zn, Cr, Ni and Sn, and agricultural activities for Cd and regional coal combustion for Sb. [ABSTRACT FROM AUTHOR]

Total contents and chemical speciation of Co, Ni, Cu, Ga, Mo, Cd, In, Sn, Sb, V, W, Tl, Bi and U in size-fractionated (< 32, 32–63 and > 63 μm) core sediments from Jiaozhou Bay were investigated to reveal their responses to anthropogenic activities. Metal contents showed a decreasing trend with increasing grain sizes. However, the loadings of metal fraction on < 32, 32–63 and > 63 μm grain sizes were 16%, 47% and 37%, respectively. Anthropogenic fluxes and enrichment factors of metals in > 63 μm fraction were closely linked to anthropogenic activities, with an obvious increase in upper 27 cm (1998–2015) and a slight decrease in 2009 year. Metals (especially for Cd, Co, Cu and Ni) in > 63 μm fraction were more easily released, with the highest percentage of acid soluble form and lowest residual form. Thus, the size fraction of > 63 μm cannot be ignored. [ABSTRACT FROM AUTHOR]

The Jiaozhou Bay is characterized by heavy eutrophication that is associated with intensive anthropogenic activities. Four core sediments from the Jiaozhou Bay are analyzed using bulk technologies, including sedimentary total organic carbon (TOC), total nitrogen (TN), the stable carbon ( δ C) and nitrogen ( δ N) isotopic composition to obtain the comprehensive understanding of the source and composition of sedimentary organic matter and further shed light on the environmental changes of the Jiaozhou Bay on a centennial time scale. Results suggest that the TOC and TN concentrations increase in the upper core, having indicated a probable eutrophication process since the 1920s in the inner bay and the 2000s in the bay mouth. The TOC and TN concentrations outside the bay have also changed since 1916 owing to the variation of terrigenous input. Considering TOC/TN ratio, δ C and δ N, it can be concluded there is a mixture of terrigenous and marine organic matter sources in the study area. A simple two end-member (terrigenous and marine) mixing model using δ C indicats that 45%-79% of TOC in the Jiaozhou Bay is from the marine source. The environmental changes of the Jiaozhou Bay are recorded by geochemical proxies, which are influenced by the intensive anthropogenic activities (e.g., extensive use of fertilizers, and discharge of sewage) and climate changes (e.g., rainfall). [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]

To analyze the fluxes, seasonal variations, sources and potential ecological effects of dissolved trace elements (TEs) in atmospheric wet deposition (AWD), one-year wet precipitation samples were collected and determined for nine TEs in Jiaozhou Bay (JZB) between June 2015 and May 2016. Both the volume-weighted mean (VWM) concentration and flux sequence for the measured TEs was Al > Mn > Zn > Fe > Pb > Se > Cr > Cd > Co. Al was the most abundant TE with a VWM concentration and wet flux of 33.8 μg L −1 and 29.2 mg m −2 yr −1 , which were 2 and 3 orders of magnitude higher than those of Co, respectively. The emission intensities of pollutants, rainfall amount and wind speed were the dominating factors influencing seasonal variations of TEs in AWD. Based on enrichment factors, correlation analysis and principal component analysis, most of the TEs in AWD were primarily originated from anthropogenic activities except for Al and Fe, which are typically derived from re-suspended soil dusts. Although the TE inputs by AWD were significantly lower than those by rivers, the TE inputs via short-term heavy rains would distinctly increase surface seawater TE concentrations and then pollute the marine environment of JZB. AWD would have both profound impacts on the biogeochemical cycles of TEs and dual ecological effects (nutrient and toxicity) on aquatic organisms. [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]

Atmospheric wet deposition (AWD) is an important pathway for anthropogenic and natural pollutants entering aquatic ecosystems. However, the study on the magnitudes and ecological effects of AWD of various nutrient species (nitrogen, phosphorus and silicon) on Jiaozhou Bay is scarce. To address these issues, in this study, wet deposition samples were collected at a coastline site along Jiaozhou Bay from June 2015 to May 2016. Dissolved inorganic nitrogen (DIN, including NH 4 –N, NO 3 –N and NO 2 –N), dissolved organic nitrogen (DON), dissolved inorganic phosphorus (DIP, i.e. PO 4 –P), dissolved organic phosphorus (DOP) and reactive silicate (SiO 3 –Si) were analyzed. The volume-weighted mean (VWM) concentrations of NH 4 –N, NO 3 –N and DON in AWD were higher compared with those of NO 2 –N, PO 4 –P, DOP and SiO 3 –Si. The annual influxes of NH 4 –N, NO 3 –N, NO 2 –N, DON, DIP, DOP, and SiO 3 –Si via AWD were 92.8, 54.5, 0.427, 47.5, 0.274, 0.448 and 1.73 mmol·m − 2 ·yr − 1 respectively; NH 4 –N and DOP were the dominant species for N and P, and the roles of DON and DOP in AWD could not be neglected. Significant seasonal variations were observed in concentrations and fluxes of all nutrient species owing to the effects of rainfall, the intensities of local emission sources and the long-distance transports of natural and anthropogenic pollutants. The major sources of N, Si and P in AWD were agricultural activities, soil dust and a mixing one involving both anthropogenic and natural sources, respectively. Though AWD represents relatively low percentages of external inputs for nutrients and low contribution to primary productivity (PP) of Jiaozhou Bay, large amounts of nutrient inputs originating from sudden heavy rains may enhance PP prominently, as well as aggravate P-limitation and Si-limitation and further affect phytoplankton community structures and size-fractioned structures with the quite high DIN:DIP ratios and extremely low Si:DIN ratios in AWD. [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]