Influence of the hydrodynamic regime on nitrogen transformation processes in lacustrine sediments
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Vertical and temporal distribution of nitrogen transformation rates in two monomictic lake sediments. Rate process measurements were quantified from <sup>15</sup>N-stable isotope addition experiments for Lakes Baldegg and Sarnen located in central Switzerland. Rates were sampled from 0-15 cm depth, and measured on a bi-monthly basis (March 2021-March 2022). Rates were determined from <sup>15</sup>N labeled substrate additions: (Exp1) <sup>15</sup>N-NO<sub>3</sub><sup>-</sup>; (Exp2) <sup>15</sup>N-NH<sub>4</sub><sup>+</sup> + <sup>14</sup>N-NO<sub>2</sub><sup>-</sup>; (Exp3) <sup>13</sup>C/<sup>15</sup>N-lypholized algae biomass (98% <sup>13</sup>C- and <sup>15</sup>N-labelled <em>Spirulina platensis</em>, Sigma-Aldrich). From the headspace, the production of <sup>14</sup>N<sup>15</sup>N and <sup>15</sup>N<sup>15</sup>N (N<sub>2</sub> gas) was determined by gas-chromatography isotope ratio mass spectrometry.
