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| Titel |
Authigenic apatite and octacalcium phosphate formation due to adsorption–precipitation switching across estuarine salinity gradients |
| VerfasserIn |
J. F. Oxmann, L. Schwendenmann |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 12, no. 3 ; Nr. 12, no. 3 (2015-02-06), S.723-738 |
| Datensatznummer |
250117800
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| Publikation (Nr.) |
 copernicus.org/bg-12-723-2015.pdf |
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| Zusammenfassung |
| Mechanisms governing phosphorus (P) speciation in coastal sediments remain
largely unknown due to the diversity of coastal environments and poor
analytical specificity for P phases. We investigated P speciation across
salinity gradients comprising diverse ecosystems in a P-enriched estuary. To
determine P load effects on P speciation we compared the high P site with a
low P site. Octacalcium phosphate (OCP), authigenic apatite (carbonate
fluorapatite, CFAP) and detrital apatite (fluorapatite) were quantitated in
addition to Al/Fe-bound P (Al/Fe-P) and Ca-bound P (Ca-P).
Gradients in sediment pH strongly affected P fractions across ecosystems and
independent of the site-specific total P status. We found a pronounced switch
from adsorbed Al/Fe-P to mineral Ca-P with decreasing acidity from land
to sea. This switch occurred at near-neutral sediment pH and has possibly
been enhanced by redox-driven phosphate desorption from iron oxyhydroxides.
The seaward decline in Al/Fe-P was counterbalanced by the precipitation
of Ca-P. Correspondingly, two location-dependent accumulation mechanisms
occurred at the high P site due to the switch, leading to elevated
Al/Fe-P at pH < 6.6 (landward; adsorption) and elevated Ca-P at
pH > 6.6 (seaward; precipitation). Enhanced Ca-P precipitation by
increased P loads was also evident from disproportional accumulation of
metastable Ca-P (Ca-Pmeta) at the high P site. Here, sediments
contained on average 6-fold higher Ca-Pmeta levels compared with
the low P site, although these sediments contained only 2-fold more total
Ca-P than the low P sediments. Phosphorus species distributions indicated
that these elevated Ca-Pmeta levels resulted from transformation
of fertilizer-derived Al/Fe-P to OCP and CFAP in nearshore areas.
Formation of CFAP as well as its precursor, OCP, results in P retention in coastal zones and can
thus lead to substantial inorganic P accumulation in response to
anthropogenic P input. |
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