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| Titel |
Iron oxidation kinetics and phosphate immobilization along the flow-path from groundwater into surface water |
| VerfasserIn |
B. Van der Grift, J. C. Rozemeijer, J. Griffioen, Y. van der Velde |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 18, no. 11 ; Nr. 18, no. 11 (2014-11-27), S.4687-4702 |
| Datensatznummer |
250120535
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| Publikation (Nr.) |
 copernicus.org/hess-18-4687-2014.pdf |
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| Zusammenfassung |
| The retention of phosphorus in surface waters through co-precipitation of
phosphate with Fe-oxyhydroxides during exfiltration of anaerobic Fe(II) rich
groundwater is not well understood. We developed an experimental field
set-up to study Fe(II) oxidation and P immobilization along the flow-path
from groundwater into surface water in an agricultural experimental
catchment of a small lowland river. We physically separated tube drain
effluent from groundwater discharge before it entered a ditch in an
agricultural field. Through continuous discharge measurements and weekly
water quality sampling of groundwater, tube drain water, exfiltrated
groundwater, and surface water, we investigated Fe(II) oxidation kinetics
and P immobilization processes. The oxidation rate inferred from our field
measurements closely agreed with the general rate law for abiotic oxidation
of Fe(II) by O2. Seasonal changes in climatic conditions affected the
Fe(II) oxidation process. Lower pH and lower temperatures in winter
(compared to summer) resulted in low Fe oxidation rates. After exfiltration
to the surface water, it took a couple of days to more than a week before
complete oxidation of Fe(II) is reached. In summer time, Fe oxidation rates
were much higher. The Fe concentrations in the exfiltrated groundwater were
low, indicating that dissolved Fe(II) is completely oxidized prior to inflow
into a ditch. While the Fe oxidation rates reduce drastically from summer to
winter, P concentrations remained high in the groundwater and an order of
magnitude lower in the surface water throughout the year. This study shows
very fast immobilization of dissolved P during the initial stage of the
Fe(II) oxidation process which results in P-depleted water before Fe(II) is
completely depleted. This cannot be explained by surface complexation of
phosphate to freshly formed Fe-oxyhydroxides but indicates the formation of
Fe(III)-phosphate precipitates. The formation of Fe(III)-phosphates at redox
gradients seems an important geochemical mechanism in the transformation of
dissolved phosphate to structural phosphate and, therefore, a major control
on the P retention in natural waters that drain anaerobic aquifers. |
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