碩士 / 國立臺灣大學 / 海洋研究所 / 85 / AbstractThere are two major parts in the thesis: (1)
determination of nitrate (including nitrite) in the upper water
column, and (2) analysis of the nitrogen isotopic composition of
nitrate (including nitrite) also with empahsis in the upper
water column.Due to its low concentration, precise measurement
of nitrate in the oligotrophic upper water column by the
colorimetric method is difficult. In this study, a
chemiluminescent method was employed to determine nitrate in the
upper water column in the West Philippine Sea. A good linear
correlation between the peak height of the chemiluminescent
signal and nitrate concentration was found in the concentration
range of 40 to 1000 nM. The detection limit was estimated to be
3 nM. The precision for this method was±10％when the nitrate
concentrations were about 60 nM. The highest nitrate
concentrates observed in the West Philippine Sea surface water
were 8 nM. The concentration, however, decreased to non-
detectable level in the subsurface water, but increased
exponentially below the depth of 50 m, reaching concentrations
around 1000 nM at 200m. The nitrate concentrations were mostly
within 10 nM in the euphotic zone (100m). In the determination
of new production, the spiked 15NO3-concentration should not
exceed 1nM. Because of such a low concentration, determination
of new production in the West Philippine Sea euphotic zone would
be very difficult.Analysis of nitrogen isotopic composition of
nitrate in the water column has been hindered by the rather high
background of the analytical procedure. In this study, Devarda''s
alloy was replaced by high purity aluminum as the nitrate
reducing agent in order to lower the background level. In the
distilled water system, the lowest blank ever obtained was 0.5
nmol N and the highest reduction efficiency obtained was about
100％. However, significant blank value was attributable to the
other reagents and, probably, airborne ammonia. For the set of
reagents used for the sample processing, the reagent blank was
1.5 mmol N and the reduction efficiency was 85% with a d15N
shift of -0.8 * due to isotope fractionation. Interference from
the dissolved organic nitrogen was found to be 1.25 mmol..The
nitrogen isotopic analyses revealed that 15N was enriched in the
nitrate in the euphotic zone in the South China Sea with the
d15N maximum value at 16.2+/-1.6*. The minimum value of
4.4+/-0.4 * was found at 100m. The d15N variation was negatively
correlated with the variation of N/P ratio. The sample with low
d15N and high N/P ratio was probably affected by
remineralization of nitrogen fixing organisms, such as
Trchodesmium.
| Identifer | oai:union.ndltd.org:TW/085NTU00274007 |
| Date | January 1997 |
| Creators | Chiang, Dong-Shan, 江東山 |
| Contributors | Kon-Kee Liu, 劉康克 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 85 |
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