Exploration on the role of the Fe(II)-Fe(III) cycle on nitrate reduction in a tile-drained moraine subcatchment (Fensholt, Denmark)

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The highly dynamic water table in the unsaturated zone of the tile drainage depth is commonly characterized by the presence of red/orange mottles on a gray matrix. These redoximorphic features are due to the accumulation of Fe(III) oxides during oxidizing conditions and the formation of Fe(II) during reduced conditions. This study aimed to explore possible interactions between the Fe(III)-Fe(II) redox pair and nitrate transformations in a tile drained area. It is hypothesized that the cycle between Fe(III) and Fe(II) has two effects: 1) the reduction of Fe(III) to Fe(II) disintegrates the soil matrix and illuviates clay to the deeper/ least elevated areas which creates a perched water table and/or anoxic microsites supporting denitrification; and 2) the immobilization of inorganic nitrogen by its possible conversion into organic nitrogen. Other possible interactions between Fe and nitrate are being studied under controlled laboratory conditions. A total of 150 piezometers and redox probes were installed at 51 points, generally at three depths, throughout the different parts of the subcatchment. Piezometers were installed at several transects according to the assumed groundwater flow direction and at areas of different conductivities as measured by DUALEM1. Water level depths, physico-chemical measurements, and water samples were obtained approximately every three weeks from January to August 2017. Piezometers installed at the deeper portions, at depths from 125 to 165 cm, were most likely to be saturated. Statistical analysis showed a significant difference in the total nitrogen (TN) concentration (TN = total inorganic N + total organic N) between high and low conductivity areas. High conductivity areas showed lower TN, but higher total organic nitrogen (TON) proportions. Nitrate reduction may have been enhanced in high conductivity areas due to the greater interaction between the mobile and immobile phases. The significant difference in the TON proportions between high and low conductivity areas may be evidence for possible immobilization of inorganic nitrogen.
Udgivelsesårjan. 2019
StatusUdgivet - jan. 2019
BegivenhedSoil Science Society of America International Soils Meeting 2019 - Sheraton San Diego Hotel & Marina, San Diego, USA
Varighed: 6 jan. 20199 jan. 2019


KonferenceSoil Science Society of America International Soils Meeting 2019
LokationSheraton San Diego Hotel & Marina
BySan Diego

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