Exchange of ¹⁵NO₃⁻ and ¹⁴NO₃⁻ over time in summer incubations.

<p>The dashed line indicates the initial amount of ¹⁵NO₃⁻ added to the incubation</p

Seasonal patterns in DNRA rates mediated by the prokaryotic and eukaryotic community.

<p>A) Eukaryotic DNRA rates B) Prokaryotic DNRA rates C) Overall DNRA rates. Total rates were determined from the incubation amended with ¹⁵NO₃⁻. Prokaryotic rates were determined after addition of the eukaryote inhibitor cycloheximide. Eukaryotic rates were calculated by subtracting prokaryotic rates from total rates. Error bars are SD (n = 3)</p

Respiration of stored intracellular nitrate by eukaryotes and prokaryotes.

<p>A) Example of the appearance of ¹⁵N labeled compounds stored in the sediment during the secondary incubation to which no label was added (example from spring incubations) B) Comparison of the overall fraction of ¹⁵N recovered as either N₂ or NH₄⁺ in both the ¹⁵NO₃⁻ incubation and the subsequent incubation with no additional ¹⁵NO₃⁻ and the partitioning between eukaryotes and prokaryotes C) Eukaryotic denitrification rates E) prokaryotic denitrification rates D) eukaryotic DNRA rates F) prokaryotic DNRA rates. Error bars are SD (n = 3).</p

Rates of nitrogen cycling processes determined over 3 seasons.

<p>Anaerobic dissimilatory nitrate reduction to ammonium (DNRA) and denitrification (Denit.) rates from the incubation amended with ¹⁵NO₃⁻. Rates were determined from linear production slopes after oxygen had been consumed. Error bars are SD (n = 3)</p

Comparison of incubation methods.

<p>Incubations were carried out using either membrane inlet mass spectrometry (MIMS) which allowed for continuous online measurements or by discrete porewater sampling into exetainers and subsequent measurement on a GC-IRMS. The example shown is taken from a replicate during the spring incubations directly after the addition of ¹⁵NO₃⁻.</p

Average percentage of ¹⁵N recovered in various pools.

<p>Denitrification denotes ¹⁵N that was present as ²⁹⁺³⁰N₂, DNRA denotes ¹⁵N that was present as ¹⁵NH₄⁺ and intracellular storage represents ¹⁵N which was present as either ²⁹⁺³⁰N₂ or ¹⁵NH₄ at the termination of the secondary incubation to which no additional ¹⁵NO₃ was added. The ‘missing label’ fraction refers to the discrepancy between added ¹⁵NO₃⁻, measured ¹⁵NO₃⁻ and ¹⁵N₂ production (shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0104517#pone-0104517-g004" target="_blank">Fig. 4</a>). Error bars are overall SD (n = 3)</p

Summary of measured O₂ consumption rates, method settings and statistics.

<p>The O₂ consumption rates (O₂ Rate) measured at different O₂ concentrations (O₂ Conc.) and with different sensors and sampling frequencies (F) are summarized. For each rate measurement, standard errors (SE) and root mean square of the residuals (RMS_RES) were calculated from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0089369#pone.0089369.e001" target="_blank">equations 1</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0089369#pone.0089369.e003" target="_blank">2</a>. The potential rate detection limit of an assumed 24 hour incubation (Pot.Det.Lim.) was calculated from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0089369#pone.0089369.e004" target="_blank">equation 3</a>. Please note, a low RMS_RES denotes a high precision, and potential rate detection limits are only based on precision and measuring frequency, but do not consider possible limitation from sensor drift or O₂ contamination.</p

O₂ consumption rates versus O₂ concentrations.

<p>The O₂ consumption rates of Experiment 1, 2 and 3 are summarized and plotted over the initial O₂ concentrations of the respective incubation. Experiment 3: The dashed line represents diffusion limited rates estimated from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0089369#pone.0089369.e005" target="_blank">equation 4</a> assuming aggregate diameters (r₀) of 0.14 mm. Please note: rates in Experiment 1 also increase with incubation time and could as well reflect bacterial growth over time.</p

Experiment 1: Comparison of O₂ decrease over time.

<p>The O₂ consumption measured by optodes and STOX sensor after the adjustment to O₂ concentrations of 1.2 µmol L⁻¹ (A), 5.5 µmol L⁻¹ (B) and 14.3 µmol L⁻¹ (C), and after the addition of 20 ml ZnCl₂ (D). Linear fits are indicated by the straight lines. Please note, the aspect ratio of time and concentration axis (µmol L⁻¹ to hour) is the same for all figures to allow comparison of slopes.</p

Experiment 3: Time series of ^18-18O₂ concentrations in Exetainers.

<p>The O₂ consumption in 5 incubations with different initial ^18-18O₂ concentrations was measured. For each Exetainer, individual MIMS measurements are averaged (black dots) and presented with the respective standard deviation.</p