Earth Science Frontiers ›› 2022, Vol. 29 ›› Issue (4): 144-155.DOI: 10.13745/j.esf.sf.2022.1.9

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Arsenic migration and transformation mechanism and microbial regulation at the sediment-water interface of the Changjiang estuary

ZHANG Yuting1,2,3,4(), DUAN Liqin1,2,3,4,*(), SONG Jinming1,2,3,4, ZHANG Naixing5, YIN Meiling1,2,3,4, LI Xuegang1,2,3,4, YUAN Huamao1,2,3,4   

  1. 1. CAS Key Laboratory of Marine Ecology and Environmental Sciences, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China
    2. University of Chinese Academy of Sciences, Beijing 100049, China
    3. Laboratory for Marine Ecology and Environmental Science, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266237, China
    4. Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao 266071, China
    5. North China Sea Marine Forecasting Center of State Oceanic Administration, Qingdao 266033, China
  • Received:2021-09-15 Revised:2021-11-22 Online:2022-07-25 Published:2022-07-28
  • Contact: DUAN Liqin

Abstract:

In order to understand the arsenic (As) migration and transformation processes at the sediment-water interface (SWI) of the Changjiang estuary, the vertical profiles of the total As concentrations and speciation and redox-sensitive element (Fe, Mn and S) concentrations in the overlaying water and porewater at four sampling sites in the Changjiang estuary in summer 2019 were analyzed. The Fe-Mn-S controlling mechanism was investigated. Combined with As-related functional genes, the microbial regulation process of As cycling at the SWI was discussed. The diffusion fluxes of total As at the SWI were also estimated. It was found that As3+ was the main species of dissolved arsenic at three sites except site A7-4. At all sites, the overlying water had the lowest As concentrations (0.748-1.57 μg·L-1); whilst As concentrations in porewater increased gradually with depth and peaked (7.14-26.9 μg·L-1) at 6-9 cm depths. The vertical profiles of total As and As3+ concentrations in porewater were similar to that of dissolved Fe2+ and Mn2+, with high concentrations in the middle layers due likely to the release of solid-phase As by Fe(Ⅲ) and Mn(Ⅳ) reduction in the Fe/Mn reduction zone. The coupling relationships between porewater As concentration and abundances of arrA and arsC genes at the transition zone between oxic layer and Fe/Mn reduction layer (except for site A1-3) suggested that the reduction of dissolved As5+ or solid As5+ to dissolved As3+, by arsenic dissimilatory reducing bacteria was another important process of As migration and transformation. The combination of decreasing total As and As3+ concentrations and low S2- concentrations in porewater in the sulfate reduction zone indicated that the removal of porewater As was probably due to As complexation with iron sulfide minerals rather than formation of As sulfides. The ambient redox potential in the bottom layer of the estuary was an important factor affecting As migration and transformation at the SWI, as, with decreasing DO concentrations, the processes were more incline to microbial reduction control. The diffusion fluxes of total As at the SWI of the Changjiang estuary were (1.18-2.07)×10-7 μmol·cm-2·s-1, all attributable apparently to As release from porewater into the overlying water, suggesting sediment might be one of the sources of total As in the Changjiang estuary study area.

Key words: arsenic, migration and transformation, arsenic functional genes, diffusive flux, the sediment-water interface, the Changjiang estuary

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