TY - JOUR
T1 - Impact of isostatic land uplift and artificial drainage on oxidation of brackish-water sediments rich in metastable iron sulfide
AU - Boman, Anton
AU - Fröjdö, Sören
AU - Backlund, Krister
AU - Åström, Mats E.
PY - 2010
Y1 - 2010
N2 - This study examines the dynamics of sulfur and trace elements (As, Co, Mo, Ni, Ti and Zn) when brackish-water sediments, unusually rich in metastable iron sulfide (probably a mixture of mackinawite and greigite), are brought into the oxidation zone by postglacial isostatic land uplift and farmland drainage. When subaqueous sediments approach the sea level, metastable iron sulfide is oxidized in the upmost layers and pyrite preserved and even accumulated concomitantly trapping Co, Ni and Zn but not As and Mo. When the land uplift has brought the sediments above sea level and natural drainage thus is initiated, the pyrite is oxidized and Co, Ni and Zn are released and transported down the profile. If this setting remained undisturbed, the slightly oxidized sediment (unripe soil) would become covered by peat and thus protected from further oxidation and metal translocation. Often these sediments are, however, artificially drained resulting in extensive oxidation and fast soil-profile development. The soil is an acid sulfate (AS) soil, characterized by low pH (<4), extensive leaching of metals and an abundance of disseminated brownish Fe(III) precipitates. We suggest that the fast soil development is due to initial oxidation of metastable iron sulfide, followed by pyrite oxidation. Drain bottom sediment, which in terms of chemistry and S-isotopes resembled that of the surfacing sea bottom strata, acted during the sampling period as a sink for metals. The abundant preservation of metastable iron sulfide below the groundwater table, even long periods after uplift above the sea level, is a puzzling feature. We suggest that it is the net result of sulfur starvation, an abundance of Fe(II) and strongly reducing conditions.
AB - This study examines the dynamics of sulfur and trace elements (As, Co, Mo, Ni, Ti and Zn) when brackish-water sediments, unusually rich in metastable iron sulfide (probably a mixture of mackinawite and greigite), are brought into the oxidation zone by postglacial isostatic land uplift and farmland drainage. When subaqueous sediments approach the sea level, metastable iron sulfide is oxidized in the upmost layers and pyrite preserved and even accumulated concomitantly trapping Co, Ni and Zn but not As and Mo. When the land uplift has brought the sediments above sea level and natural drainage thus is initiated, the pyrite is oxidized and Co, Ni and Zn are released and transported down the profile. If this setting remained undisturbed, the slightly oxidized sediment (unripe soil) would become covered by peat and thus protected from further oxidation and metal translocation. Often these sediments are, however, artificially drained resulting in extensive oxidation and fast soil-profile development. The soil is an acid sulfate (AS) soil, characterized by low pH (<4), extensive leaching of metals and an abundance of disseminated brownish Fe(III) precipitates. We suggest that the fast soil development is due to initial oxidation of metastable iron sulfide, followed by pyrite oxidation. Drain bottom sediment, which in terms of chemistry and S-isotopes resembled that of the surfacing sea bottom strata, acted during the sampling period as a sink for metals. The abundant preservation of metastable iron sulfide below the groundwater table, even long periods after uplift above the sea level, is a puzzling feature. We suggest that it is the net result of sulfur starvation, an abundance of Fe(II) and strongly reducing conditions.
KW - Acid sulphate soils
KW - Acid sulphate soils
KW - Acid sulphate soils
U2 - 10.1016/j.gca.2009.11.026
DO - 10.1016/j.gca.2009.11.026
M3 - Artikel
SN - 0016-7037
VL - 74
SP - –
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
IS - 4
ER -