Oxygen at nanomolar levels reversibly suppresses process rates and gene expression in anammox and denitrification in the oxygen minimum zone off northern Chile.

Unlabelled: A major percentage (20 to 40%) of global marine fixed-nitrogen loss occurs in oxygen minimum zones (OMZs). Concentrations of O2 and the sensitivity of the anaerobic N2-producing processes of anammox and denitrification determine where this loss occurs. We studied experimentally how O2 at nanomolar levels affects anammox and denitrification rates and the transcription of nitrogen cycle genes in the anoxic OMZ off Chile.

An experiment with forced oxygenation of the deepwater of the anoxic By Fjord, western Sweden.

In a 2.5-year-long environmental engineering experiment in the By Fjord, surface water was pumped into the deepwater where the frequency of deepwater renewals increased by a factor of 10. During the experiment, the deepwater became long-term oxic, and nitrate became the dominating dissolved inorganic nitrogen component.

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.

A critical assessment of the occurrence and extend of oxygen contamination during anaerobic incubations utilizing commercially available vials.

For rate determinations of anaerobic metabolism it is essential to maintain strictly anoxic conditions throughout the experiment. However, even if oxygen contamination can be avoided while preparing the incubation containers, it is still possible that the incubation containers themselves contaminate the samples by oxygen diffusing from or through their plastic or rubber components. In this study, we investigated the sources and extent of oxygen contamination during anoxic incubations, and present solutions to minimize oxygen contamination.

A cryptic sulfur cycle in oxygen-minimum-zone waters off the Chilean coast.

Nitrogen cycling is normally thought to dominate the biogeochemistry and microbial ecology of oxygen-minimum zones in marine environments. Through a combination of molecular techniques and process rate measurements, we showed that both sulfate reduction and sulfide oxidation contribute to energy flux and elemental cycling in oxygen-free waters off the coast of northern Chile. These processes may have been overlooked because in nature, the sulfide produced by sulfate reduction immediately oxidizes back to sulfate.