Search

Distribution of total organic carbon (TOC), total nitrogen (TN), stable isotope ratio of organic carbon and nitrogen (δ13C and δ15N) in 31 surface sediments were examined to quantitatively discriminate the source and burial of sedimentary organic matter (SOM) in the East China Sea (ECS). Results show that high content of TOC and TN occurred in the southern inner shelf and the northeast area due to the transport of organic matter (OM) from the Changjiang (Yangtze) River southwards by the Zhejiang Fujian Coastal Current (ZFCC) and the delivery from the old Huanghe (Yellow) River estuary by the Subei Coastal Current (SbCC), respectively. The significant relationship of TOC to clay provided evidence that the fine-grained sediment was the primary carrier for SOM from the inner shelf to open sea. The TN varied proportionally to the TOC with the neglected intercept, suggesting that most of nitrogen measured was related to the SOM and the influence of the sorption of inorganic nitrogen was insignificant. The seaward enrichment of δ13C and seaward depletion of C/N and δ15N illustrated the decrease of terrestrial OM (TOM) and the increase of marine OM (MOM). The close of average C/N ratio to the Redfield ratio indicated the minor role of terrestrial plant debris in the SOM. Distribution of bulk OM properties was ascribed to the terrestrial and marine input by the shelf circulation and phytoplankton with the contributions of 76.1% MOM and 23.9% TOM to SOM, respectively. The burial flux of OC ranged within 0.34–7.56 mg/(cm2·a) (averaged 2.80 mg/(cm2·a)) and enriched along the shore and in the fine-grained area, manifesting the significant input of the land-based sources and the effect of shelf mud depositional process on the fate of SOM. The sharp seaward decrease of burial fluxes of terrestrial and marine OC gave evidences that the majority of organic carbon were settled in the inner shelf with the small fraction of them further transported eastwards. [ABSTRACT FROM AUTHOR]

With sulfide increasingly recognized as an important parameter to assess the oxidation-reduction level in aqueous environment, research on its geochemical behavior is becoming important. Water samples collected in Bohai Sea (1-19 August, 2010), Yellow Sea (20-30 November, 2010) and East China Sea (3-17 June, 2010 and 1-10 November, 2010) were used to determine the occurrence and distribution of dissolved sulfide by methylene blue spectrophotometric method. Results show that: (1) horizontally, concentration of dissolved sulfide significantly varied from the coastal region to the open sea and profoundly influenced by physical processes. High values occurred in the river-sea boundary zone 'marginal filter' due to rich riverine input, frequent upwelling and active exchange in shelf edge. Terrestrial input from adjacent rivers and the current cycling contributed to the high sulfide appeared in western Bohai Sea, eastern Shandong Peninsula, and northeast of Changjiang (Yangtze) River estuary. Especially, relative higher sulfide values occurred in Yellow Sea, which is consistent with the variation of salinity largely due to the hydrodynamic feature; (2) vertically, measurement of dissolved sulfide in bottom water was higher and more variable than that in surface water caused by the wind-induced resuspension and dissimilatory sulfate reduction. Moreover, nutrient-type profile clearly identified that oxidation plays a major role in the biogeochemistry cycle of sulfide in water; (3) seasonally, investigation for East China Sea in June and November reflected seasonal variation of Changjiang River Diluted Water, Kuroshio Current, and Taiwan Warm Current. Concentration in June was much higher than that sampled in November at most stations. Mean concentration of dissolved sulfide varied seasonally from 2.26 μg/L (June) to 1.16 μg/L (November) in surface and 3.00 μg/L (June) to 1.56 μg/L (November) in bottom. Progress in the field is slow and more effort is needed to ensure the accuracy and reliability of determination and estimate the natural or anthropogenic contribution of dissolved sulfide in ecosystems. [ABSTRACT FROM AUTHOR]