Reduction of Nitrate By Fe2+ in Clay Minerals
In the 12 km2 catchment area of Syv creek, Denmark, moderate to high concentrations of nitrate (NO3−) occurred in the upper part of the oxidized zone (oxic-I), but dropped within the lower suboxic part (oxic-II), to below the detection limit in the unoxidized zone. Structural Fe2+ in the clay minerals made up 10 to 12% of the Fe in the oxidized zone and increased to approximately 50% in the unoxidized zone. Concurrent with changes in the distribution of structural Fe2+ the clay mineral constituents changed. Vermiculite was typically found in the oxidized zone whereas chlorite was found in the unoxidized zone only. A conversion of illite and chlorite into vermiculite seems to take place. A significant correlation between NO3− and the amount of reduced Fe2+ in the suboxic (oxic-II) zone, indicates that primary structural Fe2+ in the clay minerals is the reductant in a NO3− reduction process.
Key WordsChlorite Clayey till Exchangeable ferrous iron Illite Mössbauer Nitrate Oxidized Structural ferrous iron Unoxidized Vermiculite Weichselian X-ray
Unable to display preview. Download preview PDF.
- Christensen W. 1970. Nitrate in surface water and ground water. Vandteknik 38:24–29. (in Danish).Google Scholar
- Emstsen V. 1989. Nitrate reduction in clayey till. Report no. 40. Copenhagen: Geological Survey of Denmark. 69 p. (in Danish).Google Scholar
- Emstsen V, Gravesen P, Nielsson B, Briisch W, Fredericia J, Genders S. 1990. Transport and transformation of N and P in the catchment area of Langevad river. Copenhagen: Geological Survey of Denmark. Report no. 44. 63 p. (in Danish).Google Scholar
- Ernstsen V, Lindgreen H. 1985. Inorganic nitrate reduction and reduction capacity of clayey till. Report no.33. Copenhagen: Geological Survey of Denmark. 61 p. (in Danish).Google Scholar
- Houmark-Nielsen M. 1987. Pleistocene stratigraphy and glacial history of the central parts of Denmark. Bull Geolog Soc Denmark 36:3–189.Google Scholar
- Jacobsen OS, editor. 1995. The ground water monitoring programme. Brenderup: Geografforlaget Aps. p 209. (conclusion in English).Google Scholar
- Lind A-M, Pedersen MB. 1976. Nitrate reduction in the subsoil. II. General description of boring profiles, and chemical investigations on the profile cores. Danish J Plant Soil Sci 80:82–99.Google Scholar
- Mehra OP, Jackson ML. 1960. Iron oxide removal from soils and clays by dithionite citrate system buffered with sodium bicarbonate. Clays Clay Miner 5:317–327.Google Scholar
- Melkerud P-A. 1984. Distribution of clay minerals in soil profiles. A tool in chronostratigraphical investigations of till. Striae 20:31–37.Google Scholar
- Munsell Color Company. 1976. Munsell soil color charts. Baltimore.Google Scholar
- Petersen HJS. 1979. Reduction of nitrate by iron(II). Acta Chem Scan A:795–796.Google Scholar
- Zeuthen SB, Vinter FP, Eiland F. 1991. Transport and transformation of and P in the surrounding area of Langvad river. Microbial nitrate reduction in the unsaturated zone. In: Nitrogen and phosphorous in groundwater, B-abstracts. Copenhagen: National Agency of Environmental Protection. p 116–132.Google Scholar