Anammox and denitrification in the oxygen minimum zone of the eastern South Pacific
"We quantified the removal of fixed nitrogen as N2 production by anammox and N2 and N2O production by denitrification over a distance of 1900 km along the coasts of Chile and Peru, using short‐term incubations with 15N‐labeled substrates. The eastern South Pacific contains an oxygen minimum zone (OMZ) characterized by an anoxic, nitrate‐ and nitrite‐rich layer of ∼ 200‐m thickness below 30–90 m of oxic water. [...]"
Source: Limnology and Oceanography
Authors: Tage Dalsgaard et al.
Fixed nitrogen loss from the eastern tropical North Pacific and Arabian Sea oxygen deficient zones determined from measurements of N2:Ar
"Previous work estimating the N2excess above background due to denitrification has suggested that nitrate deficit-type methods may be an underestimate of fixed nitrogen (N) loss in the major oxygen deficient zones of the ocean. The N2excess approach has the advantage over nitrate deficit-type methods in that it does not depend on stoichiometric assumptions of fixed N to phosphate or oxygen utilization and avoids any uncertainly regarding the pathway of N loss. [...]"
Source: Global Geochemical Cycles (2012)
Authors: Bonnie X. Chang, Allan H. Devol and Steven R. Emerson
Vertical partitioning of nitrogen-loss processes across the oxic-anoxic interface of an oceanic oxygen minimum zone
"We investigated anammox, denitrification and dissimilatory reduction of nitrite to ammonium (DNRA) activity in the Eastern Tropical South Pacific oxygen minimum zone (OMZ) off northern Chile, at high‐depth resolution through the oxycline into the anoxic OMZ core. This was accompanied by high‐resolution nutrient and oxygen profiles to link changes in nitrogen transformation rates to physicochemical characteristics of the water column. Denitrification was detected at most depths, but anammox was the most active N2‐producing process, while DNRA was not detectable. [...]"
Source: Environmental Microbiology
Authors: Loreto De Brabandere et al.
Short exposure to oxygen and sulfide alter nitrification, denitrification, and DNRA activity in seasonally hypoxic estuarine sediments
"Increased organic loading to sediments from eutrophication often results in hypoxia, reduced nitrification and increased production of hydrogen sulfide, altering the balance between nitrogen removal and retention. We examined the effect of short-term exposure to various oxygen and sulfide concentrations on sediment nitrification, denitrification and DNRA from a chronically hypoxic basin in Roskilde Fjord, Denmark. Surprisingly, nitrification rates were highest in the hypoxic and anoxic treatments (about 5 μmol cm−3 d−1) and the high sulfide treatment was not significantly different than the oxic treatment. [...]"
Source: FEMS Microbiology Letters
Authors: Jane M. Caffrey, Stefano Bonaglia, Daniel J. Conley
Measuring carbon and nitrogen bioassimilation, burial, and denitrification contributions of oyster reefs in Gulf coast estuaries
"The eastern oyster (Crassostrea virginica) and the reefs they create provide significant ecosystem services. This study measured their possible role in nutrient mitigation through bioassimilation, burial, and oyster-mediated sediment denitrification in near-shore shallow water (< 1 m water depth) and deep-water (> 1 m water depth) oyster reefs in Louisiana. Nitrogen (N) and carbon (C) in shell and tissue differed by oyster reproductive status, size, and habitat type. [...]"
Source: Marine Biology
Authors: Phillip Westbrook, Leanna Heffner, Megan K. La Peyre
A Novel Eukaryotic Denitrification Pathway in Foraminifera
"Benthic foraminifera are unicellular eukaryotes inhabiting sediments of aquatic environments. Several species were shown to store and use nitrate for complete denitrification, a unique energy metabolism among eukaryotes. The population of benthic foraminifera reaches high densities in oxygen-depleted marine habitats, where they play a key role in the marine nitrogen cycle. However, the mechanisms of denitrification in foraminifera are still unknown, and the possibility of a contribution of associated bacteria is debated. Here, we present evidence for a novel eukaryotic denitrification pathway that is encoded in foraminiferal genomes. [...]"
Source: Current Biology
Authors: Christian Woehle et al.
How nutrients are removed in oxygen-depleted regions of the ocean
"In the course of global climate change, scientists are observing the increase of low-oxygen areas in the ocean, also termed oxygen minimum zones (OMZs). Large-scale OMZs exist, for example, in the Pacific off the coast of South America or in the Indian Ocean. Since little to no oxygen is present in these regions - depending on the depth of the water - organisms whose metabolisms is independent of oxygen have a distinct advantage. These organisms include some representatives of the foraminifera: unicellular, shell-forming microorganisms, which have a nucleus and thus belong to the eukaryotes. Their life style involves a particular metabolic pathway termed anaerobic respiration. In the absence of oxygen, they convert nitrate present in the water into molecular nitrogen. [...]"
Source: Kiel University
Physical controls on oxygen distribution and denitrification potential in the north west Arabian Sea
"At suboxic oxygen concentrations, key biogeochemical cycles change and denitrification becomes the dominant remineralization pathway. Earth system models predict oxygen loss across most ocean basins in the next century; oxygen minimum zones near suboxia may become suboxic and therefore denitrifying. Using an ocean glider survey and historical data, we show oxygen loss in the Gulf of Oman (from 6‐12 to < 2 μmol kg‐1) not represented in climatologies. [...]"
Source: Grophysical Research Letters
Authors: B. Y. Queste et al.
Growing 'dead zone' confirmed by underwater robots in the Gulf of Oman
"New research reveals a growing 'dead zone' in the Gulf of Oman. Little data has been collected in the area for almost 50 years because of piracy and geopolitical tensions. The area devoid of oxygen was confirmed by underwater robots. Reasearchers found an area larger than Scotland with almost no oxygen left. The environmental disaster is worse than expected with dire consequences for fish and marine plants, plus humans who rely on the oceans for food and employment. "
Source: Science Daily
Latitudinal variations of δ30Si and δ15N signatures along the Peruvian shelf:
quantifying the effects of nutrient utilization versus denitrification over the past 600 years
"The sedimentary stable nitrogen isotope compositions of bulk organic matter (δ15Nbulk) and silicon isotope composition of diatoms (δ30SiBSi) both mainly reflect the degree of past nutrient utilization by primary producers. However, in ocean areas where anoxic and suboxic conditions prevail, the δ15Nbulk signal ultimately recorded within the sediments is also influenced by water column denitrification causing an increase in the subsurface δ15N signature of dissolved nitrate (δ15NO3−) upwelled to the surface. [...]"
Authors: Kristin Doering et al.