Nitrogen isotopic discrimination by water column nitrification in a shallow coastal environment
- 189 Downloads
Temporal changes in nitrogen isotopic composition (δ15N) of the NO3 − pool in the water column below the pycnocline in Ise Bay, Japan were investigated to evaluate the effect of nitrification on the change in the δ15N in the water column. The δ15N of NO3 − in the lower layers varied from −8.5‰ in May to +8.4‰ in July in response to the development of seasonal hypoxia and conversion from NH4 + to NO3 −. The significantly 15N-depleted NO3 − in May most likely arose from nitrification in the water column. The calculated apparent isotopic discrimination for water column nitrification (ɛnit = δ15Nsubstrate − δ15Nproduct) was 24.5‰, which lies within the range of previous laboratory-based estimates. Though prominent deficits of NO3 − from hypoxic bottom waters due to denitrification were revealed in July, the isotopic discrimination of denitrification in the sediments was low (ɛdenit = ∼1‰). δ15NNO3 in the hypoxic lower layer mainly reflects the isotopic effect of water column nitrification, given that water column nitrification is not directly linked with sedimentary denitrification and the effect of sedimentary denitrification on the change in δ15NNO3 is relatively small.
KeywordsIsotopic discrimination nitrification denitrification hypoxic waters
Unable to display preview. Download preview PDF.
- Altabet, M. A., C. Pilskaln, R. Thunell, C. Pride, D. Sigman, F. Chavez and R. Francois (1999): The nitrogen isotope biogeochemistry of sinking particles from the margin of the Eastern North Pacific. Deep-Sea Res. I, 46, 655–679.Google Scholar
- Barford, C. C., J. P. Montoya, M. A. Altabet and R. Mitchell (1999): Steady-state nitrogen isotope effects of N2 and N2O production in Paracoccus denitrificans. Applied and Environmental Microbiology, 65, 989–994.Google Scholar
- Berounsky, V. M. and S. W. Nixon (1990): Temperature and the annual cycle of nitrification in waters of Narragansett Bay. Limnol. Oceanogr., 35, 1610–1617.Google Scholar
- Kasai, A., T. Fujiwara, T. Kimura and H. Yamada (2004): Fort-nightly shifts of intrusion depth of oceanic water into Ise Bay. J. Oceanogr., 60, 817–824.Google Scholar
- Mariotti, A., J. G. Germon, P. Hubert, P. Kaiser, R. Letolle, A. Tardieux and P. Tardieux (1981): Experimental determination of nitrogen kinetic isotope fractionation: some principles; illustration for the denitrification and nitrification processes. Plant and Soil, 62, 413–430.CrossRefGoogle Scholar
- Naqvi, S. W. A., H. Naik, A. Prathihary, D. Souza, P. V. Narvekar, D. A. Jayakumar, A. H. Devol, T. Yoshinari and T. Saino (2006): Coastal versus open-ocean denitrification in the Arabian Sea. Biogeosciences, 3, 621–633.Google Scholar
- Redfield, A. C., B. H. Ketchum and F. A. Richard (1963): Chapter 2, The influence of organisms on the composition on sea-water. p. 26–77. In The Sea, Vol. 2, ed. by M. N. Hill, Inter Sci. Pub., New York and London.Google Scholar
- Sigman, D. M., R. Robinson, A. N. Knapp, A. van Geen, D. C. McCorkle, J. A. Brandes and R. C. Thunell (2003): Distinguishing between water column and sedimentary denitrification in the Santa Barbara Basin using the stable isotopes of nitrate. Geochemistry, Geophysics, Geosystems, 4, 1040, doi:10.1029/2002GC000384.CrossRefGoogle Scholar
- Takahashi, T., T. Fujiwara, M. Kuno and Y. Sugiyama (2000): Seasonal variation in intrusion depth of oceanic water and the hypoxia in Ise Bay. Umi no Kenkyu, 9, 265–271 (in Japanese with English abstract).Google Scholar
- Yoshioka, T. and Y. Saijyo (1984): Photoinhibition and recovery of NH4 +-oxidizing bacteria and NO2 −-oxidizing bacteria. J. Gen. Appl. Microbiol., 30, 151–166.Google Scholar
- Yoshioka, T. and Y. Saijyo (1985): Active nitrification in the hypolimnion on Lake Kizaki in early summer. 2. Effects of light on nitrification in water. Arch. Hydrobiol., 105, 1–9.Google Scholar