Aerobic denitrification in permeable Wadden Sea sediments

Abstract

Permeable or sandy sediments cover the majority of the seafloor on continental shelves worldwide, but little is known about their role in the coastal nitrogen cycle. We investigated the rates and controls of nitrogen loss at a sand flat (Janssand) in the central German Wadden Sea using multiple experimental approaches, including the nitrogen isotope pairing technique in intact core incubations, slurry incubations, a flow-through stirred retention reactor and microsensor measurements. Results indicate that permeable Janssand sediments are characterized by some of the highest potential denitrification rates (X0.19 mmol N m À2 h À1 ) in the marine environment. Moreover, several lines of evidence showed that denitrification occurred under oxic conditions. In intact cores, microsensor measurements showed that the zones of nitrate/nitrite and O 2 consumption overlapped. In slurry incubations conducted with 15 NO 3 À enrichment in gas-impermeable bags, denitrification assays revealed that N 2 production occurred at initial O 2 concentrations of up to B90 lM. Initial denitrification rates were not substantially affected by O 2 in surficial (0-4 cm) sediments, whereas rates increased by twofold with O 2 depletion in the at 4-6 cm depth interval. In a well mixed, flow-through stirred retention reactor (FTSRR), 29 N 2 and 30 N 2 were produced and O 2 was consumed simultaneously, as measured online using membrane inlet mass spectrometry. We hypothesize that the observed high denitrification rates in the presence of O 2 may result from the adaptation of denitrifying bacteria to recurrent tidally induced redox oscillations in permeable sediments at Janssand.

Deep Nitrate Deficit Observed in the Highly Oxygenated East/Japan Sea and Its Possible Cause

“…This gives rise to the implicit possibility wherein aerobic denitrification may occur simultaneously with re-mineralization even in highly oxygenated water. Aerobic denitrification was reported for shallow intertidal waters in the German Wadden Sea (Gao et al 2010). Sufficient supplies of organic matter and nitrate with high oxygen consumption in the UB and EJB near the TtS might stimulate the aerobic denitrification, using nitrate and DO at the same time.…”

Doubling of marine dinitrogen-fixation rates based on direct measurements

“…The 'slapping' lead to a dispersion of the large bubble into numerous small bubbles and thus an increase in the surface area to volume ratio which facilitated gas diffusion. After complete dissolution of the added 15 N 2 gas ( 15 N 2 -enriched seawater), an aliquot of the 15 N 2 enriched water was collected for each preparation of enriched seawater and stored in an Exetainer until return to the laboratory where the isotopic composition was measured by membrane-inlet mass spectrometry 3 .…”

Nitric oxide turnover in permeable river sediment

“…Permeable sediments are widespread in streams and rivers, but so far little is known about the mechanisms of N 2 O production in these systems. In marine systems, permeable sediments have been shown to promote high turnover rates of inorganic nitrogen (Gao et al 2010). Thus, permeable freshwater sediments represent relevant sites to investigate the mechanisms of NO turnover to N 2 O.…”