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 N₂O to N₂, 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 N₂O/g/h for sediment (sampling station 1) and 4.35.10^-10 to 1.96.10^-9 moles N₂O/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 N₂O/g/h and 1.06.10^-9 to 5.39.10^-8 moles N₂O/g/h for sediment at sampling station I and 2, respectively; and 1.73.10^-7 to 1.08.10^-6 moles N₂O/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.