Anammox, denitrification and fixed-nitrogen removal in sediments from the Lower St. Lawrence Estuary

[摘要] Incubations of intact sediment cores and sediment slurries reveal thatanammox is an important sink for fixed nitrogen in sediments from the LowerSt. Lawrence Estuary (LSLE), where it occurs at a rate of 5.5 ±1.7 µmol N m⁻² h⁻¹. Canonical denitrification occurs at arate of 11.3 ± 1.1 µmol N m⁻² h⁻¹, and anammox isthus responsible for up to 33% of the total N₂ production. Bothanammox and denitrification are mostly (> 95%) fueled by nitrate andnitrite produced in situ through benthic nitrification. Nitrification accounts for> 15% of the benthic oxygen demand and may, therefore, contributesignificantly to the development and maintenance of hypoxic conditions inthe LSLE. The rate of dissimilatory nitrate reduction to ammonium is threeorders of magnitude lower than denitrification and anammox, and it isinsignificant to N-cycling. NH₄⁺ oxidation by sedimentary Fe(III)and Mn(III/IV) in slurry incubations with N isotope labels did not occur atmeasurable rates; moreover, we found no evidence for NH₄⁺ oxidation byadded Mn(III)-pyrophosphate.

[学科分类] 地球化学与岩石