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Rare earth elements (REEs) can be used to trace source materials and identify their provenances, because of significant conservation and immobility during chemical alteration processes after erosion of materials from the provenance. This study focused on the temporal variation of REEs for columnar sediments from the mouth of Jiaozhou Bay in North China to understand the potential controls for the geochemical variations of sediments. Through extraction experiments, we identified that the residual fraction is the main host for REEs compared with other fractions (i.e., exchangeable and carbonate fraction, easily reducible oxides fraction, reducible oxides fraction, magnetite fraction). REE ratios (e.g., LaN/SmN and LaN/YbN; N: normalized by chondrite) lack correlations with grain size or the chemical index of alteration (CIA), which is correlated with major elements. All these indicate that these REE variations reflect the varying contribution of source materials from different provenances instead of grain size or chemical weathering effects. REE ratios (e.g., LaN/SmN and LaN/YbN) remain relatively constant until the depth of roughly 40 cm (equivalent to the year 1995), and show obvious changes beyond this depth. Compared REE characteristics of Jiaozhou Bay with those of neighboring rivers and bedrocks, the relative contributions of Dagu River-Jiaolai River, and Licun River may have been increased during the sedimentary processes, which could be caused by the construction of reservoir and related change of aquaculture (e.g., rapid accumulation of organic materials). [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]

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]

Sediment geochemical technique was employed to assess how the sediment records reflect the environmental changes of Jiaozhou Bay, a semi-enclosed bay adjacent to Qingdao, China. In the past hundred years, Jiaozhou Bay has been greatly impacted by human interventions. A dated core sediment by 210Pb chronology was analyzed for trace metals including Li, Cd, Cr, Pb, Cu, Ni, Co, Zn together with C, N, P and BSi. Based on the research, the development of Jiaozhou Bay environment in the past hundred years can be divided into three stages: (1) before the 1980s characterized by relatively low sedimentation rate, weak heavy metal pollution and scarce eutrophication; (2) from the 1980s to 2000, accelerating in the 1990s, during which high sedimentation rates, polluted by heavy metals and the frequent occurrence of red tide; (3) after 2000, the period of the improvement of environment, the whole system has been meliorated including the heavy metal pollution and hypernutrification. [Copyright &y& Elsevier]

To probe the deposition velocities ( V d ), fluxes, origins and biogeochemical significance of atmospheric dry deposition (ADD) of nutrients in coastal waters, aerosol and dry deposition samples were collected in Jiaozhou Bay (JZB) from June 2015 to May 2016. We measured water-soluble inorganic nitrogen (WSIN; including ammonium (NH 4 N), nitrate (NO 3 N) and nitrite (NO 2 N)), organic nitrogen (WSON), inorganic phosphorus (WSIP; including reactive phosphate (PO 4 P)) and organic phosphorus (WSOP) for all samples. The concentrations of aerosol N species were comparatively higher than those in other aquatic ecosystems worldwide. Although WSIN and WSIP represented relatively large percentages of species, WSON (~16%) and WSOP (~35%) cannot be ignored in aerosols. The dry deposition fluxes for NH 4 N, NO 3 N, NO 2 N, WSON, PO 4 P and WSOP were 29.4, 29.9, 0.058, 15.4, 0.099 and 0.165 mmol m −2  yr −1 , respectively, with apparent seasonal variations. The average annual V d values of NH 4 N, NO 3 N, NO 2 N, WSON, PO 4 P and WSOP were indirectly calculated as 0.17 ± 0.11, 0.35 ± 0.20, 0.34 ± 0.25, 0.30 ± 0.22, 0.43 ± 0.28 and 0.91 ± 0.60 cm s −1 , respectively. The considerable differences between the percentages of corresponding nutrient concentrations and ADD fluxes were mainly attributed to V d variations. Anthropogenic emissions were the most common source of WSON and WSIN based on a correlation analysis. WSIP was highly correlated with WSOP, suggesting that they may share similar sources. Additionally, the long-range transport of natural and anthropogenic pollutants, especially the air-masses originating from the northwest direction, exerted greater effects than local emissions on aerosol N and P species in JZB based on an air mass backward trajectory analysis. The increasing ADD flux may have non-negligible biogeochemical effects on JZB by increasing primary productivity and altering the nutrient structure due to the high WSIN/WSIP ratio. [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]