DENITRIFICATION IN AN OXBOW LAKE IN TROPICAL FLOODPLAIN RIVER

Abstract

The qualitative and quantitative importance of the denitrification process in sediment and aquatic macrophyte in an oxbow lake in tropical floodplain river have been assessed. The decnitrification rate was estimated using acctylene to block reduction of N 2 O to N 2 , and denitrifying bacteria numbers were estimated by the Most Probable Number technique, The denitrification rates at "real condition", taking into account endogenous nitrogen, ranged from 5.45.10 -10 to 2.66.10 -9 moles N 2 O/g/h for sediment (sampling station 1) and 4.35.10 -10 to 1.96.10 -9 moles N 2 O/g/h for sampling station 2. The "potential" denitrification rate, with supplementary nitrate, ranged from 3.77.10 -10 to 1.35.10 -7 moles N 2 O/g/h and 1.06.10 -9 to 5.39.10 -8 moles N 2 O/g/h for sediment at sampling station I and 2, respectively; and 1.73.10 -7 to 1.08.10 -6 moles N 2 O/g/h for macrophyte roots. The highest denitrification rates and bacteria numbers were observed in the rainy season, which was correlated to an increase of organic matter and nutrient input as a result of the hydrological period in Mogi-Guaçu floodplain river.