Japan Geoscience Union Meeting 2015

Presentation information


Symbol M (Multidisciplinary and Interdisciplinary) » M-IS Intersection

[M-IS26] Biogeochemistry

Thu. May 28, 2015 2:15 PM - 4:00 PM 104 (1F)

Convener:*Muneoki Yoh(Tokyo University of Agriculture and Technology), Shibata, Hideaki(Field Science Center fot Northern Biosphere, Hokkaido University), Naohiko Ohkouchi(Japan Agency for Marine-Earth Science and Technology), Youhei Yamashita(Faculty of Environmental Earth Science, Hokkaido University), Chair:Izumi Watanabe(Graduate School of Agriculture, Tokyo University of Agriculture and Technology), Yoriko Yokoo(Faculty of Science and Engineering, Doshisha University), Tomoya Iwata(Faculty of Life and Environmental Sciences, University of Yamanashi), Urumu Tsunogai(名古屋大学大学院環境学研究科)

3:30 PM - 3:45 PM

[MIS26-20] Effects of environmental factors on production of dissolved N2-a product of denitrification. A case study in Tama River

*CONG, Thuan NGUYEN1, Keisuke KOBA1, Midori YANO1, Akiko MAKABE1 (1.Tokyo University of Agriculture and Technology, Japan)

In aquatic ecosystems, denitrification, the nitrate (NO3-) reduction to dinitrogen gas (N2), is considered as the important process to remove nitrogen to improve water quality. However, the denitrification also contributes to the emission of N2O – a greenhouse gas. Many studies of N2 production in river were conducted to estimate the removal of nitrogen under natural condition via the denitrification. To gain more information of key factors for the N2 production, we explore the relationships between dissolved N2 and environmental factors in Tama River.
Water samples in Tama River from eight stations (from stn 1 near the mouth of the Tama River (in Kawasaki City) to stn 8 – Mid-Tama River (in Ohme City)) were collected on 13th November, 2014. Environmental parameters as temperature, pH, EC, concentrations of DO, NH4+, NO2-, NO3-, DIN, DON, TDN, TOC were analyzed. Dissolved nitrogen gases through N2/Ar ratios were analyzed by Membrane Inlet Mass Spectrometer (MIMS) system.
Types of the river water were divided two groups. Upstream stations (stn 6 to 8) located in Mid-Tama River showed low concentrations (TDN: 51.36 – 78.09 μM/L, NH4+: 0.26 – 1.78 μM/L, NO2-: 0.24 – 0.47 μM/L, NO3-: 45.33 – 67.84 μM/L, DON: 3.94 – 11.35 μM/L). Downstream stations (stn 1 to 5) showed high concentrations (TDN: 261.63 – 590.75 μM/L, NH4+: 5.23 – 155.87 μM/L, NO2-: 5.53 – 22.08 μM/L, NO3-: 185.93 – 403.00 μM/L, DON: 14.56 – 64.09 μM/L). Nitrate dominated and accounted for 90.8 ± 11.7% of DIN, 82.4 ± 11.8% of TDN. Station 2 had the highest concentrations of nitrogen compounds expect NO3- concentrations. Water quality of this site was affected by sewage of plants which were in upper near this site. TOC values were also divided two groups as groups of nitrogen compounds (0.41 – 0.50 mg/L for upstream stations, while 1.71 – 2.21 mg/L for downstream stations).
Measured average N2/Ar ratio (37.36 ± 0.45) was lower than the theoretical average N2/Ar ratio (38.05 ± 0.25). Unfortunately remarkable excess in N2/Ar was not observed in our samples. We will present our preliminary isotopic results on NO3-, NO2-, NH4+ and TDN in the presentation to discuss the occurrence of denitrification in the presentation.