Download Stable isotope technique for evaluation of organic matter movement

Transactions on Ecology and the Environment vol 23, © 1998 WIT Press, www.witpress.com, ISSN 1743-3541
Stable isotope technique for evaluation of
organic matter movement and coastal
environment status
S. Meksumpun, C. Meksumpun, A. Hoshika,
Y. Mishima & T. Tanimoto
Marine Environment Section, Chugoku National
Industrial Research Institute, 2-2-2, Hiroshima 737-0197,
Japan
Email: [email protected]
Abstract
Stable carbon and nitrogen isotope techniques were used to clarify the movement
of terrestrial organic matter and the status of coastal environment of the Osaka Bay
which was known as one of the most polluted coastal areas in Japan. Sedimental
cores and particulate matter samples from the Yodo River and the Osaka Bay were
collected for examination of 6^C, 6^N, carbon and nitrogen contents. Means
6^C for sediment, large size of participate organic matter (15-149 jum) and small
size of particulate organic matter (<15 //m) in the Yodo River were -25.1 ±0.2 %o,
-25.3±0.6%o and -25.5±0.4%o, respectively, whereas means of those the inner part
of the Osaka Bay were -20.6±0.3 %o, -21.6±1.6%o and -22.3±1.7%o, respectively.
In the outer part of the Osaka Bay, mean 6"C for large size of particulate organic
matter (-20.7±0.9%c) was slightly increased, but for small size of particulate
organic matter (-22.5±1.3%<?) was nearly similar to those in the inner part. Our
results suggest that the sediments in this coastal area were mostly derived from
primary production in the bay. Almost of the large particle of terrestrial organic
matter discharged from the Yodo River into the Osaka Bay had been deposited onto
the bottom sediment at the inner part, within a few kilometers close to the river
mouth, while the small particle of terrestrial organic matter was more transported
through the bay to neighbor sea areas. Nitrogen sources as nutrients for
phytoplankton growth in each area of the bay may be different since the values of
6^N for sediment, large and small size of particulate organic matters significantly
varied. Such nutrients should be great contributed from marine origin.
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1 Introduction
Stable carbon and nitrogen isotope technique are a possible way to
clarify the movement of terrestrial organic matter and get more
understanding of the coastal environment. These techniques have
been used by a number of authors to identify the origins of organic
matters (Freemanfl], Thornton[2], Guo[3]) and to determine the
trophic structure of marine communities (Wada[4], Parson[5], Wu[6]).
Moreover, the values of 6^N lower than 6%o and approaching 0%o for
particulate nitrogen in oligotrophic regions have been interpreted as
indicating a large contribution from nitrogen fixation (Minagawa[7J,
Saino[8], Carpenter[9J). Our present study attempted to use stable
carbon and nitrogen isotope techniques to clarify the movement of
terrestrial organic matter and understand the environmental status of
the Osaka Bay. The Osaka Bay is located at the eastern part of the Seto
Inland Sea, Japan. This bay has been faced problems of organic
matter loading from the land by recent man-made activities and natural
runoff of rivers since several decades. Outbreaks of red tides occurred
throughout the year in the inner part of the bay since large amounts of
industrial and domestic waste water from the Osaka region have entered
the inner part of the bay. Nowadays, organic pollution in the bay
seem to be a serious problem due to natural primary production rather
than the organic materials discharged from the land. Hence,
movements of both terrestrial and marine organic matters in the bay
and related water areas are needed to be clarified for further assessment
of coastal pollution.
Here we report a study of the carbon and nitrogen contents and
the stable carbon and nitrogen isotope ratios of particu late organic
materials in surface sediments and overlying water samples collected
from the Osaka Bay and the Yodo River. The goal of this study is to
evaluate recent marine environmental status, and to extend the available
information on o^Con and 5^N of the Osaka Bay for understanding
the source and subsequent movement of particulate matter in the bay.
2 Materials and methods
Sedimental cores and water samples were collected from each sampling
station in the Yodo River and the Osaka Bay (Fig. 1). Water depth and
salinity were also measured with CTD meter (Alec ASTU-1000M).
The depth and surface salinity contour lines are shown in Figs. 2 and 3,
respectively. Sediment samples were collected by a gravity
Transactions on Ecology and the Environment vol 23, © 1998 WIT Press, www.witpress.com, ISSN 1743-3541
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50'
40'
30'
20'
134' 50'1C
135' 00'
20'
30'
40'
34'10'N
Figure 1. Sampling stations for 6^C and 5^N (#) and additional stations for
depth and salinity contours (o)in the Yodo River and the Osaka Bay.
core sampler during winter period in 1990 and 1993.
The surface
(0-2 cm) of the obtained sediment cores was sectioned and immediately
frozen at -60 °C until further analysis. The sediment samples were
freeze-dried in laboratory. The dried sediment samples were then
ground and packed in silver cups. In order to remove carbonate, the
sediments in silver cups were treated with 1M-HC1 solution. They
were again dried and packed in tin cups prior to analysis.
Water samples were collected from discrete depths with a VanDorn bottle sampler in December 1996 and 1997. These samples
were sieved through 149 jum mesh sieve first, then they were sieved
through 15 jum mesh sieve. Particulate matters remained on 15 /urn
sieve were resuspended in filtered seawater. Large (15-149 jum) and
small (<15//m) sizes of particulate matters in the water were recollected
on Whatman GF/C filters (free of organic matter by ignition at 450 °C
for 2 h) and the filters were stored at -80 °CtiJl analysis. Filters were
Transactions on Ecology and the Environment vol 23, © 1998 WIT Press, www.witpress.com, ISSN 1743-3541
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192
134* 50'K
135* 00'
20'
30'
Figure 2. Depth contour of the Osaka Bay.
freeze-dried below -80 °C. These samples were exposed to the vapor of
concentrate HCI for one night before packed in tin cups for analysis.
The total organic carbon and nitrogen contents, together with
carbon and nitrogen isotopic compositions of the sediments and
filtered samples were determined using an continuous flow analytical
system joining an elemental analyzer (Carlo Erba, NA-1500) with a
stable isotope ratio analyzer (Finnigan MAT252 delta S). Measuring
standards consisted of CO% gas produced from NBS 18 standard and Nz
gas produced from L-alanine. The final results are reported as ft"C
and 6*N (%o) relative to the Peedee belemnite (PDB)
limestone
standard (carbon) and atmospheric Ni (nitrogen), as defined by the
following equation:
R sample
standard
X
1000
R standard
where R = 'W*N
or "C/*C. Data quality control throughout the
analysis was ensured by running a reference standard after every 10
runs. The analytical precision for standard preparation and mass
spectrometric analysis was less than ± 0.1 %o and ± 0.2 %ofor S^Cand
5^N, respectively.
Nutrients in water samples were determined using an autoanalyzer (Bran & Luebbe Traacs 800).
Transactions on Ecology and the Environment vol 23, © 1998 WIT Press, www.witpress.com, ISSN 1743-3541
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10
134" 50'K
193
ZOlun
135" 00'
Figure 3. Salinity contours of the Osaka Bay in December 1996 (upper)
and 1997 (lower).
3 Result
3.1 Variation in 5 C and organic carbon contents
The 8"C values of surface sediment in the Yodo River and the Osaka
Bay are shown in Table 1. The (V'c values of surface sediments in the
Yodo River (-25.3 to -24.9%o), inner (-20.8 to -20.3%o ) and outer
(-20.3 to -20.2 %o) parts of the Osaka Bay show relatively narrow
ranges. Mean of total organic carbon contents of surface sediments in
the inner part of the bay (22.6±1.5 mg/g) was markedly higher than
that in the outer part (15.8±0.1 mg/g ).
Tables 2 and 3 show the fi^C values and total carbon contents of
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194
Table 1. Stable carbon isotope ratios (o^C), total organic carbon (C)
and nitrogen contents (N), and calculated percentages of
terrestrial organic matter (Terr-OM) of sediment samples for
each sampling station.
Station
1
2
3
4
5
6
7
8
9
ft
"C
-25 .2
-24 .9
-25 .3
-20 .8
-20 .5
-20 .3
-20 .3
-20 .2
-20 .2
ft'
'N
(*»)
C
(mg, 'g)
3,.1
5,.5
5,.3
5,,2
6,.2
5.9
6,,3
2. 1
1. 1
27.2
23.4
23.8
22.8
20.4
15.8
15.7
rvf
(mj
0.2
0.1
2,.2
2,.7
2,.8
2,.8
2,.5
2,.0
2,.0
Terr- OM
(%0
80 .0
75 .4
81 .5
12 .3
7.7
4.6
4.6
3. 1
3. 1
large (15-149 >.im) and small (<15 ^m) sizes of particulate organic
matter in December 1996 and 1997, respectively. Means ft C for
large (-25.3±0.6%o) and small (-25.5±0.4%o) sizes of particulate
organic matters in the Yodo River were almost same value as that of the
sediment (-25.1±0.2%^). Means ft^C for the large size of particulate
organic matter in the inner and outer parts of the Osaka Bay were
-21±1.6%0 and -20.7±0.9%0, respectively, whereas means for the small
size of particulate organic matter were -22.3±1.7%« and -22.52±1..3%o,
respectively. The ft^C values for large size of particulate organic
matter in the outer part of the bay (stations 8-11, Table 2) at the water
depth of 10 m were higher than those of surface water. In December
199, highest and lowest values of total carbon content of large size of
particulate organic matter of surface water were found at station 10
(97.0 pg/1) and station 6 (21.6 f.ig/1), respectively. The highest values
of total carbon content of small size of particulate organic matters in
both 1996 and 1997 were found in the surface water of station 4 with
the values of 271.5 ng/1 and 311.5 ug/l, respectively (Tables 2, 3).
3.2 Variation in 5^N and organic nitrogen contents
The ft^N value of surface sediment in the Yodo River (station 3) was
3.1%o (Table 1), whereas those in the inner and the outer parts of the
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195
Table 2. Stable carbon isotope ratios (cY*C), total organic carbon
contents (C), and calculated percentage of terrestrial organic
matter (Terr-OM) of the small (<15 /urn) and large (15-149
jam) sizes of particulate matter samples collected in December
1996.
<15 fim
Station
(%o)
4
Surface
bottom+0.5m
5 Surface
10 m depth
bottom+0.5m
6 Surface
10 m depth
bottom+0.5m
7 Surface
10 m depth
boltom+0.5m
8 Surface
10 m depth
bottom+0.5m
10 Surface
10 m depth
bottom+0.5m
11 Surface
10 m depth
bottom + 0.5m
-27.3
-21.1
-23.5
-22.3
-20.6
-22.7
-21.5
-20.8
-23.5
-22.4
-20.9
-21.1
-20.5
-20.5
-222
-24.8
-23.6
-21.6
-23.7
-24.4
15- 149 /mi
C
Terr- OM
W/I)
271 .5
231 .7
165 .1
133 .7
105 .3
112.8
142.2
138.3
134.7
115 .9
122,.4
151,.1
231. 1
153.9
131. 2
224. 2
92.3
98.8
79.9
100.0
16..9
53 .8
35 .4
9.2
41 .5
23 .1
12.3
53 .8
36.9
13..8
16,.9
7.7
7.'7
33J%
73.;S
55.4
24.6
56.9
67.7
&'"C
(
Terr-OM
(wj5/1)
-25 .1
54 .1
-23 .2
41 .7
-22 .4
72,2
-22.1
-20 .4
-19 .8
21 .6
-20.1
29.0
-19 .8
42.2
-21 .9
42.6
-22.5
72.5
89 1
-7,0 0
-21.,4
84..9
-20. 1
83.6
-21.2 146.16
-21.3
97.0
-20.5
89.8
-19.2 123. 1
-21.8
39.7
-20.4
44.0
-20. 1
69.7
87.7
49.2
36.9
323
6.2
0.0
1.5
0.0
292
38.5
0.0
21.5
1.5
18.5
20.0
7.7
0.0
27.7
6.2
1.5
Osaka Bay ranged from 5.2 to 6.2%o and from 5.9 to 6.3%o,
respectively. Mean of total nitrogen contents in sediment in the inner
part of the bay was 2.7±0.1 mg/g, whereas that in the outer part was
2.0=1=0 mg/g.
In December 1996, the cV^N values for large size of particulate
organic matters in the surface water were 3.9-4.6%o in the inner part of
the bay and were 6.8- 12.8%o in the outer part (Table 4). At the depth
of 10 m, the S^N values for large size of particulate organic matters in
the inner and outer parts of the bay varied in 6.2-7.2%o and 6.5-10.5%o,
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Table 3. Stable carbon isotope ratios (S^C), total organic carbon
contents (C), and calculated percentage of terrestrial organic
matter (Terr-OM) of the small (<15 /on) and large (15-149
jam) sizes of participate matter samples collected in
December 1997.
15-149 jum
<15 /nn
Station
Surface
Surface
Surface
Surface
10 m depth
bottom+0.5m
7 Surface
10 in depth
8 Surface
10 m depth
9 Surface
10 m depth
bottom+0.5m
1
2
3
4
C
8^
Terr-OM
')"
(%6
c%>)
(%g/ 0
-25 .4
-26, .0
-25,,1
-23,.1
-20,.4
-22, .9
-22, .5
-22, .1
-22.,3
-22..9
-22, .9
-22.,3
-22, .6
765,.5
215.,8
311,,5
271.,4
148,.2
174,,4
103, .2
85.,0
90.,3
97,2
89.,8
142,,0
83 .1
92.3
78.5
47.7
6.2
44.6
38.5
32.3
35.4
44.6
44.6
35 .4
40.0
cV-3/y
C
Terr-OM
(%)
-26 .0
-25,.0
-24,.9
-22,.8
-21,.3
-21,.9
-21,.7
-19,.8
-19,,8
-20,,1
107.1
69.4
71.4
64.2
71.9
56.0
64.6
62.0
30.0
41.5
923
76.9
75.4
43.1
20.0
29.2
26.2
0.0
0.0
1.5
-22, .1
65.6
323
respectively. The ft N values for small size of particulate organic
matter in the surface water in the inner part of the bay ranged from 0.3
to 2.8%o and from 5.0 to 9.8%o, respectively. In December 1997, the
6 N of large and small size of particulate organic matters in the Yodo
River ranged from 0 to 5A%o and from 2.8 to 4.7%o, respectively
(Table 5). The ft N values for the large size of particulate organic
matter in the surface water in the inner part of the bay ranged from 8.0
to 8.2%o. The ft N values for small size of particulate organic matter
in the surface water in the inner part and outer parts of the bay ranged
from 4.7 to 9A%o and 7.0 to 8.6%o, respectively. Table 6 showed
concentrations of NH/-N, NCV-N and total inorganic nitrogen (TIN) in
the water samples. The concentration of NH/-N found in the surface
water in the outer part of the Osaka Bay was less than 12% of those of
the Yodo River and the innermost part of the bay (station 4).
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197
Table 4. Stable nitrogen isotope ratios (fi^N)and total organic nitrogen
contents (N) of the small (<15 /mi) and large (15-149 //m)
sizes of particulate matter samples collected in December
1996.
<1 5 jum
Station
4
5
6
7
8
10
11
Surface
bottom+0.5m
Surface
10 m depth
bottom+0.5m
Surface
10 m depth
bottom+0.5m
Surface
10 m depth
bottom+0.5m
Surface
10 m depth
bottom+0.5m
Surface
10 m depth
bottom+0.5m
Surface
10 m depth
bottom+0.5m
ISI
15 - ;149 um
6"N
7/ \
C
f4
Vk)
(A5/1)
0.3
5.8
2.8
9.3
5.9
2.4
2.8
73 .2
59 .4
41 .5
35 .0
4.6
6.6
29 .8
30 .3
3.9
6.0
1 .3
4,,1
6.7
8. 1
10.!•?
9.9
5.0
8.4
9.0
9.8
9.6
)
10. (
39 .0
39 .3
32 1
33,.8
40.,8
55.3
33.5
33.0
54.2
25.0
27.9
23.3
4.0
7.2
7.2
12.8
10.6
8.,7
8.3
6.5
6.0
7.8
18 .7
10 .5
15 .4
97 1
20. 1
17.8
27.3
19.4
19.8
6.8
10.5
9.5
13.6
(/4
14 .5
10 .0
16 .1
4 Discussions
Stable carbon and nitrogen isotope compositions of organic matter in
sediment have been studied to examine the movement of terrestrial
organic matter by several workers (e.g. WadaflO], Thornton|2],
Yamada[ll], Mishima[12j). Goering|13] reported that the ft^Cand
6 N of the particulate matter in water column and sedimental samples
collected simultaneously from off shore areas had no statistical
difference at the a=0.10 level and were thus assumed to be isotopically
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Applied Science* ami the Environment
Table 5. Levels of ammonium nitrogen, nitrate nitrogen, and total
inorganic nitrogen concentrations of the water samples
collected from each station in December 1996 and 1997.
<1J) ium
Station
1
2
3
4
7
8
9
10
11
Surface
Surface
Surface
Surface
10m depth
bottom+0.5m
Surface
10 m depth
Surface
10 m depth
bottom+0.5m
Surface
10 m depth
bottom+0.5m
Surface
10m depth
bottom+0.5m
Surface
10 m depth
bottom+0.5m
6 "N
/\
(9
4.7
3.0
2.8
9.4
7.4
7.2
4.7
9.8
8.6
9.4
9.6
7.1
9.4
14.4
5.0
8.4
9.0
9.8
9.6
10.0
N
4)
us1.9
37.8
64.3
65.7
24.6
29.2
20.3
14.1
16.7
13. 1
17. 1
13.7
20.6
33.5
33.0
54.2
25.0
27.9
23.3
15 - 149^ m
6 "N
(9%>)
N
l%&/I)
5.4
4.6
0.0
8.2
1 .5
8.1
8.0
9.1
8.3
6.9
9.6
18.1
8.1
12.5
9.6
13.1
7.6
8.5
14.2
5.5
8.7
7.7
8.3
6.5
7.0
19.4
19.8
6.8
10..5
9.5
13.6
equivalent.
Our (Y C data also indicated that the o^C values of particulate
organic matter in the Yodo River were almost similar as those of
sediments although the samplings had been conducted in different year.
Yamada|l 1] reported nearly similar values of mean b ^C for organic
matter in surface sediments which collected during February and May
1994 in the Yodo River (-25.2±0.7). These results have revealed that
the terrestrial organic matters which were transported from the Yodo
River watershed to the Osaka Bay during 1993 to 1997 were similar.
The o^C data of this study corresponded with the report of
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199
Gearing! 14] in which the (V'c of Narragansett Bay phytoplankton
ranged from -22.2±0.6%o (nanoplankton; primarily microflagellates
and non-motile ultraplankton) to -20.3±0.6%« (diatoms; primarily
.SW^r^^a cY;^a^/M). Although the 8^C of phytoplankton
populations collected from different locations and/or different dates at
same location had some variations caused by the differences in species
composition (Falkowski[15J, Fry [16]), temperature (Francois) 17],
Dehairs[18]), light (Thompson [19]), and the 8^C of inorganic carbon
fixed during photosynthesis (Rau[20], [21], Laws[22]), the cf Cof the
marine planktonic source was still definitely different from those of
terrestrial organic material sources.
Several authors found that the
8' C for terrestrial organic matters ranged from -28 to -26%o (e.g.
Tan[23],^Thornton[2], MishimaJ 12]).
Therefore, the relatively
narrow 8 C range of sedimentary organic carbon in the outer part of
the Osaka Bay (with a mean value close to -20%%) clearly indicates a
Significance of marine planktonic source.
In order to evaluate the movement of terrestrial organic matter
from the Yodo River into the Osaka Bay, the ratio of terrestrial organic
carbon (/) was calculated by the following equation.
f /., x
./ (%)
= -
marine --
& C marine
: 8* C of marine organic matter
8 C sample
: 8 C of measured sample
8 C ten
: 8 C of terrestrial organic matter
^ sample
• X
100
Based on our 8"Cdata and that reported by WadaflO], we decided
the end members of 8^C mannc and 8^C ,_ to be -20.0 and -26.5%o,
respectively. Our calculated data showed that the percentage of
terrestrial organic matters in the sediment in the outer part of the Osaka
Bay was only 3.1% (Table 1). It can be concluded that the sediments
irUhe Osaka Bay were mostly derived from marine source. Data of
8 Cfor particulate materials from each station in different sampling
occasion were slightly different. These occurrences were considered
to be influenced by variation in water volume loaded from the Yodo
River. The data on salinity distribution (Fig. 3) responded well with
this consideration.
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Table 6. Stable carbon isotope ratios (ft^C), total organic carbon
contents (C), and calculated percentage of terrestrial organic
matter (Terr-OM) of the small (<15/an) and large (15-149
//m) sizes of particulate matter samples collected in
December 1997.
199 7
1996
Station
1
2
3
4
5
6
7
8
9
10
11
Surface
Surface
Surface
Surface
10 m depth
bottom+0.5m
Surface
10 m depth
bottom+0.5m
Surface
10 m depth
bottom+().5m
Surface
10 m depth
bottom + 0.5m
Surface
10 m depth
bottom+0.5m
Surface
10 in depth
bottom+().5m
Surface
10 m depth
bottom+0.5m
Surface
10 m depth
bottom+0.5m
NH/-N
0M)
38.7
13 .0
10.5
2<).8
9.2
10.6
14.5
6.7
6.2
21 .6
9.6
2.9
3.8
1 .4
1 .6
2.0
1 .4
0.6
4.5
4.2
0.9
2..2
0..4
0.5
NCV-N
41.4
18.6
16.7
33.7
15.9
16.0
20.7
14.7
13.1
24.7
17.2
11.4
13.0
11.0
10.7
9.6
10.7
9.2
129
10.8
10.2
9.8
9.2
9.0
Tl N
(jLilVI)
84.6
34.2
29 .7
67.6
27.5
28,.9
38,.1
23,.5
21,.2
49,.5
29,,3
15,,8
18.,5
13.,9
13.,7
13,0
13.6
10.9
19. 1
16.4
12.4
13.3
10.8
10.6
NH
NO
(XM) (MlM)
TIN
(uM)
39,,2
39,,9
39,.0
44,,6
9.,3
6,,3
96.,4
45.,3
46. 1
38.,8
9.1
7.8
138.1
89.4
90.7
88.0
21.1
16.6
4.6
2.6
2.6
2.5
2.6
2.5
4.4
2.5
I.5
6.5
5.8
5.7
5.4
5.2
5.5
7.0
6.0
6. 1
13.4
10.6
10.5
10.1
10.1
10.2
13.8
10.8
9.6
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Applied Sciences and the Environment
201
The movement characteristics of participate organic materials
loaded from the Yodo River was evaluated based on the changes office
and organic carbon content of the material collected in the water
column along a distance from the river mouth to the outer part of the
bay. For the large size of particulate organic matters, a comparison of
organic carbon contents between station 3 and station 8 (1997) was
focused. Our results showed that the high levels of organic carbon of
53.8 ug/1 in station 3 gradually decreased along the distance and
became 0 ug/l in station 8. Base on this result, it can be concluded that
almost of the large size of particulate organic matter discharged from
the Yodo River into the Osaka Bay had been deposited onto the bottom
sediment at the inner part, within a few kilometers closed to the river
mouth. Fort he case of the small size of particulate organic matters,
similar comparison in organic carbon contents had been done.
Although higher levels of the contents were similarly found in station 3
(169.4 Mg/1), the contents only slightly decreased and can still be
observed in a significant level of 44.6 ug/l in station 9 in the outer part
of the bay. Thus, the small size of particulate organic matter may be
more transported through the bay to neighbor sea areas.
The (V*N values of the sediment in the Yodo River were
markedly lower than those in the inner and outer parts of the Osaka Bay.
Moreover, the fi^N value in the sediment of Yodo River was as low as
3.1%o, although the sewage discharged into this area has been estimated
to be about 6%o (Yamada [11]). This characteristic is same as the
Tokyo Bay (Wada [10]) and the observation of Yamadafil] in the
Yodo River (different sampling points). In this study, we have
concentrated on the ft^N values of large size (15-149 urn) of
particulate organic matter because this size was the optimum size for
representative of dominant phytoplankton in the Osaka Bay. As
reported previously by several workers, the 6^N value of
phytoplankton in Pacific Ocean was nearly 6%o (e.g. Minagawa[7],
Goering[13]) which is similar to the mean (6%o) for cV*N of nitrate in
Pacific Ocean surface waters (Cline[24J, Wada[25J). Therefore, the
cV'N value of phytoplankton should be similar to the (V'N of nutrient
source. Our present study showed that the 5^N values in the large size
of particulate organic matter in the bay were varied. These results can
be concluded that nitrogen sources as nutrient for phytoplankton
growth in each area of the bay were different. Surprisingly, the fi^N
values in the sediment between the inner and outer parts of the bay were
not significantly different, but those in the particulate organic matter
were significantly different. If we focused on the data of (V'N values
Transactions on Ecology and the Environment vol 23, © 1998 WIT Press, www.witpress.com, ISSN 1743-3541
202
Applied Sciences ami the Environment
of the large size of participate organic matter which composed of
terrestrial organic matter less than 10%, we can remarkably observe that
the phytoplankton in the outer part of the bay had higher cV*N values
than those in the inner part. Since the 6^N of dissolved ammonium in
the pore water which produced from bacterial degradation of marine
organic matter have been estimated to be 10%o (Robert [26]) and that of
nitrate in rain was ca Woo (Wada [10]), the phytoplankton with higher
value of 8^N in the outer part of the bay should uptake nutrients which
mostly derived from the bottom sediment. More detail study on the
distribution of 8^N values of dissolved nitrogen will be further carried
out in order to find out the actual ratio of marine-derived and landderived nitrogen sources for phytoplankton production in the bay.
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