Redox Changes of Iron Caused by Erosion,Resuspension and Sedimentation in Littoral Sediment of a Freshwater Lake |
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Authors: | Simone?Gerhardt Email author" target="_blank">Bernhard?SchinkEmail author |
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Institution: | 1.Fachbereich Biologie, LS Mikrobielle ?kologie,Universit?t Konstanz,Konstanz,Germany |
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Abstract: | Depth profiles of oxygen concentration and the redox status of acid-extractable iron were measured in littoral sediment cores
of Lake Constance after mechanical removal of surface sediment, mixing, and re-deposition. In undisturbed sediment cores,
oxygen penetrated down to 2.9±0.4 mm or 4.6±0.4 mm depth, respectively, after 12 h of incubation in the dark or light; causing
a net diffusive flux of 108±20 nmol cm−2 h−1 oxygen into or 152±35 nmol cm−2 h−1 out of the sediment. The uppermost 20 mm layer of the undisturbed sediment cores contained 10.2± 0.7 μmol cm−3 ferrous and 3.8±1.1 μmol cm−3 ferric iron. After erosion, the oxic–anoxic interface in the newly exposed sediment was shifted to about 2 mm depth within
30 min, causing an oxygen flow into the sediment. During the following 12 h, oxygen penetrated deeper into the sediment, and
in the light oxygen was produced photosynthetically. Ferrous iron was largely oxidized within two days after erosion. The
oxidation rates were higher in oxic than in anoxic sediment layers, and decreased with time. This oxidation process took the
longer and was confined closer to the surface the more reduced the exposed sediment had been before. Resuspension of eroded
sediment in aerated lake water did not cause a significant oxidation or reduction of iron. After re-deposition, the oxic–anoxic
interface in the re-sedimented material shifted to about 2 mm depth within 30 min, causing an oxygen flow into the sediment.
During the following 12 h, the oxygen penetration depth and the oxygen flow rate into the re-deposited sediment did not change
any further, and no oxygen was produced in the light. Ferric iron was reduced during the first day after re-deposition, and
partly re-oxidized during the second day. The extent of reduction was stronger and the extent of oxidation weaker the more
reduced the resuspended sediment was before. Oxic conditions in the sediment surface were established faster and ferrous iron
was oxidized to a larger extent after erosion of sediment than after resuspension and sedimentation. |
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Keywords: | Erosion Freshwater sediment Iron cycle Oxygen Resuspension Sedimentation |
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