日本地球惑星科学連合2019年大会

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[E] 口頭発表

セッション記号 B (地球生命科学) » B-BG 地球生命科学・地圏生物圏相互作用

[B-BG01] Elemental cycling in terrestrial and coastal ecosystems- Carbon and Nitrogen perspectives

2019年5月27日(月) 15:30 〜 17:00 201A (2F)

コンビーナ:Punyasloke Bhadury(Indian Institute of Science Education and Research Kolkata)、座長:Punyasloke Bhadury(Indian Institute of Science Education and Research Kolkata)

16:00 〜 16:15

[BBG01-02] 17O-rich nitrate as a tracer for constraining nitrogen transformations in coastal sediments

*Chawalit Charoenpong1,2Scott D Wankel2Carolyn Buchwald3,2Wiebke Ziebis4 (1.Chulalongkorn University、2.Woods Hole Oceanographic Institution、3.Dalhousie University、4.University of Southern California)

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.