Denitrification prevails over anammox in tropical mangrove sediments (Goa, India)

Denitrification, anammox (Anx) and di-nitrogen fixation were examined in two mangrove ecosystemsthe anthropogenically influenced Divar and the relatively pristine Tuvem. Stratified sampling at 2 cm increments from 0 to 10 cm depth revealed denitrification as the main process of N-2 production in mangrove sediments. At Divar, denitrification was similar to 3 times higher than at Tuvem with maximum activity of 224.51 +/- 6.63 nmol N-2 g(-1) h(-1) at 0-2 cm. Denitrifying genes (nosZ) numbered up to 2 x 10(7) copies g(-1) sediment and belonged to uncultured microorganisms clustering within Proteobacteria. Anammox was more prominent at deeper depths (8-10 cm) mainly in Divar with highest activity of 101.15 +/- 87.73 nmol N-2 g(-1) h(-1) which was 5 times higher than at Tuvem. Di-nitrogen fixation was detected only at Tuvem with a maximum of 12.47 +/- 8.36 nmol N-2 g(-1) h(-1). Thus, in these estuarine habitats prone to high nutrient input, N-2-fixation is minimal and denitrification rather than Anx serves as an important mechanism for counteracting N loading. (C) 2011 Elsevier Ltd. All rights reserved.