VERTICAL PATTERNS OF NITROGEN TRANSFORMATIONS DURING INFILTRATION IN 2 WETLAND SOILS

The N-15 isotope dilution and pairing methods were applied to investig ate the vertical distribution of nitrogen transformations during infil tration in one peaty soil and one sandy sail. Water containing N-15-ni trate (99.9%; 200 mu M) as the only nitrogen fraction was infiltrated through cores containing homogenized soil, with lengths varying from 5 .5 to 38 cm. Oxygen and nitrogen dynamics were investigated by measuri ng inflowing and outflowing water. The experimental design allowed det erminations of vertical profiles of aerobic respiration. nitrification , and coupled and uncoupled denitrification and ammonification. In the sandy soil, all oxygen was consumed in the upper 14 cm and nitrate wa s subsequently consumed and removed, up to a maximum of 70% in the lon gest core (28 cm). In the peaty soil, oxygen was consumed in the upper 7.5 cm and all nitrate was denitrified in the top 20 cm. In both soil s, nitrogen removal by denitrification was counteracted by the release of ammonium and dissolved organic nitrogen. In the sandy soil, net ni trogen removal occurred in cares of 14 cm and longer; in the longest c ore. 40% was removed. In the pest soil, release was equal to removal i n the top 14 cm but release exceeded removal in the deeper layers, lea ding to a 100% increase of total nitrogen in the effluent water from t he longest core (38 cm).