SEDIMENT DENITRIFICATION, DNRA AND ANAMMOX RATES IN TROPICAL FLOODPLAIN LAKE (PANTANAL, BRAZIL)

Abstract

The rates of denitrification, dissimilatory nitrate reduction to ammonia (DNRA) and anammox were evaluated on a typical lake of Pantanal wetlands using the isotope pairing method. Denitrification rates were low at all studied sites, ranging from 3,4 to 34,5µMN₂m^-2h^-1. The rates of O₂ consumption in the sediment were two to three orders of magnitude higher, ranging from 2630 to 3880µMO₂m^-2h^-1. A parallel incubation showed that as 50% of added nitrate was reduced to N₂ through denitrification and that anammox activity was negligible. From this result we estimated that the anaerobic reduction of nitrate is equal between denitrification and DNRA processes. Although microorganisms that carry out denitrification and DNRA were present in the lake, rates were very low. Both denitrification and DNRA in this lake are regulated by very low nitrate concentrations (<5µM).