REDUCTION OF NITRATE BY FE2+ IN CLAY-MINERALS

In the 12 km(2) catchment area of Syv creek, Denmark, moderate to high concentrations of nitrate (NO3-) occurred in the upper part of the ox idized zone (oxic-I), but dropped within the lower suboxic part (oxic- II), to below the detection limit in the unoxidized zone. Structural F e2+ in the clay minerals made up 10 to 12% of the Fe in the oxidized z one and increased to approximately 50% in the unoxidized zone. Concurr ent with changes in the distribution of structural Fe2+ the clay miner al constituents changed. Vermiculite was typically found in the oxidiz ed zone whereas chlorite was found in the unoxidized zone only. A conv ersion 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.