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