@article{fdi:010065390,
  title = {{N}i cycling in mangrove sediments from {N}ew {C}aledonia},
  author = {{N}oel, {V}. and {M}orin, {G}. and {J}uillot, {F}arid and {M}archand, {C}yril and {B}rest, {J}. and {B}argar, {J}. {R}. and {M}unoz, {M}. and {M}arakovic, {G}. and {A}rdo, {S}. and {B}rown, {G}. {E}.},
  editor = {},
  language = {{ENG}},
  abstract = {{C}overing more than 70% of tropical and subtropical coastlines, mangrove intertidal forests are well known to accumulate potentially toxic trace metals in their sediments, and thus are generally considered to play a protective role in marine and lagoon ecosystems. {H}owever, the chemical forms of these trace metals in mangrove sediments are still not well known, even though their molecular-level speciation controls their long-term behavior. {H}ere we report the vertical and lateral changes in the chemical forms of nickel, which accumulates massively in mangrove sediments downstream from lateritized ultramafic deposits from {N}ew {C}aledonia, where one of nature's largest accumulations of nickel occurs. {T}o accomplish this we used {N}i {K}-edge {E}xtended {X}-ray {A}bsorption {F}ine {S}tructure ({EXAFS}) spectroscopy data in combination with microscale chemical analyses using {S}canning {E}lectron {M}icroscopy coupled with {E}nergy-{D}ispersive {X}-ray {S}pectroscopy ({SEM}-{EDXS}). {A}fter {P}rincipal {C}omponent and {T}arget {T}ransform analyses ({PCA}-{TT}), the {EXAFS} data of the mangrove sediments were reliably least-squares fitted by linear combination of 3-components chosen from a large model compound spectral database including synthetic and natural {N}i-bearing sulfides, clay minerals, oxyhydroxides, and organic complexes. {O}ur results show that in the inland salt flat {N}i is hosted in minerals inherited from the eroded lateritic materials, i.e. {N}i-poor serpentine (44-58%), {N}i-rich talc (20-31%), and {N}i-goethite (18-24%). {I}n contrast, in the hydromorphic sediments beneath the vegetated {A}vicennia and {R}hizophora stands, a large fraction of {N}i is partly redistributed into a neoformed smectite pool (20-69% of {N}i-montmorillonite), and {N}i speciation significantly changes with depth in the sediment. {I}ndeed, {N}i-rich talc (25-56%) and {N}i-goethite (15-23%) disappear below similar to 15 cm depth in the sediment and are replaced by {N}i-sorbed pyrite (23-52%) in redox-active intermediate depth layers and by pyrite (34-55%) in the deepest sediment layers. {N}i-incorporation in pyrite is especially observed beneath an inland {A}vicennia stand where anoxic conditions are dominant. {I}n contrast, beneath a {R}hizophora stand closer to the ocean, where the redox cycle is intensified due to the tide cycle, partial re-oxidation of {N}i-bearing pyrites favors nickel mobility, as confirmed by {N}i-mass balance estimates and by higher {N}i concentration in the pore waters. {T}hese findings have important environmental implications for better evaluating the protective role of mangroves against trace metal dispersion into marine ecosystems. {T}hey may also help in predicting the response of mangrove ecosystems to increasing anthropogenic pressure on coastal areas.},
  keywords = {{NOUVELLE} {CALEDONIE}},
  booktitle = {},
  journal = {{G}eochimica et {C}osmochimica {A}cta},
  volume = {169},
  numero = {},
  pages = {82--98},
  ISSN = {0016-7037},
  year = {2015},
  DOI = {10.1016/j.gca.2015.07.024},
  URL = {https://www.documentation.ird.fr/hor/fdi:010065390},
}