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Title: Oxidation of Ni-Rich Mangrove Sediments after Isolation from the Sea (Dumbea Bay, New Caledonia): Fe and Ni Behavior and Environmental Implications

Formation of Fe-sulfides in anoxic horizons of mangrove sediments makes this ecosystem a potential long-term sink for metal contaminants in the intertropical region. Increasing anthropogenic pressure on coastal areas can alter the physicochemical of mangrove sediments by modifying their redox state, affecting directly the rate of Fe-sulfides that mediate accumulation of metal contaminant. Here, we show that isolation from the sea, due to land use planning, directly modify the redox state of mangrove sediments from reducing condition to oxidizing condition, affecting the stability of Ni-accumulating Fe-sulfides. Unusual suboxic/oxic conditions are indeed observed at intermediate depths in these mangrove sediments and favor the oxidative dissolution of Ni-pyrite (Fe 1–xNi xS 2) that initially formed under anoxic/suboxic conditions. This reaction leads to a significant release of aqueous HS , Fe 2+ and Ni 2+ at the redox boundary. HS and Fe 2+ oxidize into SO 4 2– and Fe 3+ and precipitate as schwertmannite (Fe 8O 8(OH) 6SO 4), leading to acidification of the pore-waters. Meanwhile, aqueous Ni 2+ is mostly leached downward in the underlying anoxic layers of the sediment where it sorbs at the surface of pyrite and/or incorporates in the structure of newly formed pyrites. These results emphasizemore » the potential of Fe-sulfides for mitigating the impact of the oxidation of former Ni-rich mangrove sediments, as long as the anoxic conditions are preserved at depth. Furthermore, this assumption can be expanded to other divalent metals and should be applicable to a larger set of mangrove ecosystems worldwide.« less
Authors:
ORCiD logo [1] ;  [2] ;  [3] ;  [2] ;  [3] ;  [4] ;  [4] ;  [5] ;  [3] ;  [3] ;  [6] ;  [7] ;  [8]
  1. Univ. Pierre et Marie Curie (UPMC), Paris (France); Koniambo Nickel SAS (KNS), Kone (Nouvelle Caledonie)
  2. Univ. Pierre et Marie Curie (UPMC), Paris (France); Institut de Recherche pour le Developpement (IRD), Noumea (Nouvelle-Caledonie)
  3. Univ. Pierre et Marie Curie (UPMC), Paris (France)
  4. Univ. Paris Diderot, Paris cedex (France)
  5. Univ. Pierre et Marie Curie (UPMC), Paris (France); Stanford Univ., Stanford, CA (United States)
  6. Koniambo Nickel SAS (KNS), Kone (Nouvelle Caledonie)
  7. SLAC National Accelerator Lab., Menlo Park, CA (United States)
  8. Stanford Univ., Stanford, CA (United States); SLAC National Accelerator Lab., Menlo Park, CA (United States)
Publication Date:
Grant/Contract Number:
AC02-76SF00515
Type:
Accepted Manuscript
Journal Name:
ACS Earth and Space Chemistry
Additional Journal Information:
Journal Volume: 1; Journal Issue: 8; Journal ID: ISSN 2472-3452
Publisher:
American Chemical Society
Research Org:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 54 ENVIRONMENTAL SCIENCES; 58 GEOSCIENCES; anthropogenic pressure; iron and nickel; Mangrove sediments; oxidation processes; pyrite; X-ray absorption spectroscopy
OSTI Identifier:
1463305