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Title: Key nitrogen biogeochemical processes revealed by the nitrogen isotopic composition of dissolved nitrate in the Changjiang River estuary, China
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Abstract: Seasonal variations in the nitrogen isotopic composition of dissolved nitrate (delta(NO3)-N-15) were investigated in the surface waters of the Changjiang River estuary in 2009 and 2010. delta(NO3)-N-15 varied between -4.6aEuro degrees and 8.9aEuro degrees with changes in temperature, salinity, dissolved oxygen concentrations, and the composition of the dissolved inorganic nitrogen pool. In February, biological processes decreased because of low temperature, and the mean delta(NO3)-N-15 near the river mouth was 2.4aEuro degrees. In May, delta(NO3)-N-15 was the highest in the surface waters among all seasons. Analysis on the conservative mixing revealed assimilation, and this finding is supported by positive relationship between Chl a and delta(NO3)-N-15. The fractionation factor of assimilation was estimated to be 2.0aEuro degrees by the Rayleigh equation. Nitrification was supported based on the mixing behaviors in November 2010 and the low delta(NO3)-N-15 values in May and November 2009. The high ammonium concentrations in the adjacent marine area and positive relationships between total organic nitrogen and delta(NO3)-N-15 in November 2010 indicated that mineralization was taking place.
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PubYear: 2014
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Unit code: 133137
Publication name: CHINESE JOURNAL OF OCEANOLOGY AND LIMNOLOGY
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