Abstract:

This dataset was a photo-simulation experiment that collected ammonium N-15 isotope measurements from photooxidation experiments on porewater samples. Porewater samples were collected from 2021-10-06 to 2022-05-26 at multiple locations in Baffin Bay, Texas. These samples were used for the photooxidation experiments after all present ammonium ions (NH4+) had been removed. Photooxidation experiments occurred at 24-hour and 72-hour intervals.

Suggested Citation:

Abdulla, Hussain. 2024. Ammonium N-15 isotope data from photooxidation experiments of porewater samples in Baffin Bay, Texas obtained from 2021-10-06 to 2022-05-26. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/dk7wzg8f

Purpose:

To construct an isotope source model based on the 15N isotope.

Data Parameters and Units:

Sampling date (yyyy-mm-dd); latitude (decimal degrees); longitude (decimal degrees); Station; Original porewater NH4+ (µM); Original porewater δ15N-NH4+ (‰).

Methods:

Porewater NH4+ and photo-produced NH4+ was oxidized to NO2- before isotope analysis so it could be measured by the denitrifier bacteria method at the University of California, Davis Stable Isotope Facility. International δ15N-NH4+ standards USGS25 and USGS26 were prepared, oxidized, and analyzed in the same manner as the samples for data normalization and to test the efficiency of the coupled method oxidation and denitrifier method. Additional internationally recognized standards (USGS32, USGS34, USGS35, IAEA-N3) were measured during sample analysis to provide known δ15N-NO3- references for data correction. Average standard deviation for δ15N-NO3- reference materials was 0.2‰. Propagated standard deviation for the NH4+ and NO3- isotope standards was 0.9‰. Nitrate and NO2- were not detected in original pore water samples and due to observations in previous experiments and literature, any photochemical NO3- and NO2- production is assumed to be minimal relative to ammonium production thus not significantly affecting the reported δ15N-NH4+. The NH4+ nitrogen isotopic composition (δ15N-NH4+) was denoted by the following equation and was reported in permil (‰): δsample (‰) = (Rsample/Rstandard - 1) * 1000 (3) where R is the ratio of 15N/14N and the Rstandard is atmospheric nitrogen with an accepted value of 0‰.

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