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Dissimilatory reduction of nitrate to ammonium, not denitrification or anammox, dominates benthic nitrate reduction in tropical estuaries
Author(s) -
Dong Liang F.,
Sobey Milika Naqasima,
Smith Cindy J.,
Rusmana Iman,
Phillips Wayne,
Stott Andrew,
Osborn A. Mark,
Nedwell David B.
Publication year - 2011
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.2011.56.1.0279
Subject(s) - nitrate , denitrification , benthic zone , estuary , anammox , environmental chemistry , chemistry , ammonium , anoxic waters , environmental science , ecology , denitrifying bacteria , nitrogen , biology , organic chemistry
We measured benthic denitrification (DN) and dissimilatory reduction of nitrate to ammonium (DNRA) using the isotope‐pairing technique in three tropical estuaries in Thailand (Mae Klong), Indonesia (Cisadane), and Fiji (Vunidawa‐Rewa) during rainy, dry, and intermediate seasons along the salinity gradient of each estuary. DNRA dominated. Anammox (AN) was measured initially but neither AN activity nor AN bacteria‐related 16S ribosomal RNA genes were detected in any of the estuaries. DN was either zero or extremely low, driven by water column nitrate and not from benthic nitrification‐DN. N2O was not formed during DN. N 2 O saturations in estuary water were low, except in the nutrified Indonesian estuary, and tropical estuaries are therefore likely to be only small sources of N 2 O. Benthic nitrate reduction was nitrate limited; when nitrate was enhanced experimentally, DN increased slightly, but DNRA increased proportionately much more. Predominance of DNRA over DN in tropical estuaries may be due both to an energetic advantage (greater standard free energy change, ΔG°) of nitrate ammonifiers over denitrifiers when competing for limited nitrate, and also to higher affinity for nitrate by the nitrate ammonifiers. At tropical temperatures the three processes occur in the order DNRA > DN > AN. In contrast, temperate estuaries, at lower temperature and higher nitrate concentrations, exhibit proportionately greater levels of AN and DN. The Cisadane estuary became anoxic during the dry season, with high ammonium and sulfide, but no nitrate reduction because of lack of nitrate. Addition of nitrate stimulated high rates of autotrophic DN driven by sulfide, but not DNRA.