16:00 〜 16:15
[BBG01-02] 17O-rich nitrate as a tracer for constraining nitrogen transformations in coastal sediments
キーワード:nitrogen, isotope, 17O, sediments
Coastal sediments are often replete in organic matter and exhibit sharp gradient in redox conditions. In addition, the oxic-anoxic interfaces are often around a few centimeters if not less below the sediment surface. This make this environment poised to harbor both oxidative and reductive nitrogen transformations. As such, the use of a single or a couple of isotope-labeling tracers to determine the rates of these many processes might suffer from the systems being underconstrained. In this work, we demonstrate how naturally-occurring, 17O-rich nitrate can aid in the studying these complex systems through the ability to follow the transformations of added nitrate (NO3-) into other different pools of N-species and closely investigate the triple isotopic compositions (δ15N, δ18O, and Δ17O). While we followed five different pools of N-species namely NO3-, NO2-, N2O, NH4+, and total reduced N (NH4+ plus DON), we chose to focus this work on the intermediate nitrite, NO2-. For all intact flow-through core incubations done on the sediments collected from Sylt Island, Germany, sediments acted as sources for NO2- in all experimental manipulations including sediment type, dissolved oxygen level, and NO3- loading. Unlike in the environments that are solely driven by reductive processes where the changes in δ15N and δ18O are coupled, the co-occurrence of both oxic and anoxic in the sediments such as ones from this study cause the δ15N and δ18O to decouple primarily because O is often subject to more processes than N. By using three isotope systems along with the change in concentrations, we demonstrate how we can use a natural abundance appraoch and rely on a series of mathematical equations to solve for different N transformation rates.