Redox potential of bulk soil and soil solution concentration of nitrate,manganese, iron,and sulfate in two Gleysols |
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Authors: | Tim Mansfeldt |
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Abstract: | While the reduction of nitrate‐N, Mn(III,IV), Fe(III), and sulfate‐S in soil has been studied intensively in the laboratory, field research has received only limited attention. This study investigated the relationship between redox potential (EH) measured in bulk soil and concentrations of nitrate, Mn2+, Fe2+, and sulfate in the soil solution of two Gleysols differing in drainage status from the Marsh area of Schleswig‐Holstein, Northern Germany. The soils are silty‐sandy and developed from calcareous marine sediments. Redox potentials were monitored weekly with permanently installed Pt electrodes, and soil solution was obtained biweekly by ceramic suction cups from 10, 30, 60, and 150 cm depth over one year. Median EH at 10, 30, 60, and 150 cm depths was 470, 410, 410, and 20 mV in the drained soil and 500, 480, 30, and –170 mV in the undrained soil, respectively. A decrease in EH below critical values was accompanied in the soil solutions (pH 7.4 to 7.8) by disappearance of nitrate below 0 to 200 mV, appearance of Mn2+ below 350 mV, and Fe2+ below 0 to 50 mV. Both metals disappeared from soil solution after aeration. In the sulfide‐bearing environment of the 150 cm depth of the undrained soil, however, the sulfate concentrations were highest at such EH values at which sulfate should be unstable. This discrepancy was reflected in the fact that at this depth bulk soil EH was about 400 mV lower than soil solution EH (250 mV). When investigating the dynamics of nitrate, Mn, and Fe in soils, bulk soil EH provides semi‐quantitative information in terms of critical EH ranges. However, in sulfidic soil environments the interpretation of EH measured in bulk soil is uncertain. |
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Keywords: | redox potential EH bulk soil soil solution nitrate sulfate manganese iron |
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