SEASONAL DYNAMICS OF DENITRIFICATION ACTIVITY IN 2 WATER MEADOWS

Seasonal variation in denitrification activity was measured in two flo oded water meadows, one on peaty and one on sandy soil, over a three-y ear period. Measurements were taken during flooded and drained periods , using the acetylene-blockage technique, and the rates were compared to mass balance estimates of nitrate removal in the percolating water. Denitrification activity was higher in sandy soil than in peaty soil. Higher water infiltration rate and thereby higher nitrate load was co nsidered to be the cause of the higher denitrification in the sandy so il. Flooding significantly increased denitrification, and the rates we re higher in autumn and winter than in spring. This was considered to be a result of higher nitrogen concentration in. inflowing stream wate r during winter. Annual denitrification was estimated to 430-60 kg N h a(-1) yr(-1) in the sandy soil meadow, and 220 kg N ha(-1) yr(-1) in t he peaty soil meadow. In the sandy soil there was a large discrepancy between nitrate removal rates and denitrification rates, which can be explained by nitrification of ammonium released from the soil. In the peaty soil nitrate disappearance and denitrification corresponded fair ly well.