*Minagawa M, Usui T, Miura Y, Nagao S, Irino T, Kudo I, and Suzuki K,Graduate School of Environmental Science,
Hokkaido University, Sapporo 060-0810, Japan *also Faculty of Environmental Earth Science,
Hokkaido University, Sapporo 060-0810, Japan ([email protected])
Spatial and temporal variability of nutrient impacts to a coastal biogeochemical systems driven by river water from cultivated land areas
Sampling location
●Sapporo
Tokachi River
Observation and Samples ● Stations off Tokachi (Hydrographic, Nutrients, POM, traps & sediments ) May, August and Nov. 2003 / April, May, July, Nov. and Dec. 2004 / March 2005 ▲ River stations (Hydrographic, nutrients, POM, Sediments) from May 2003 to Sept. 2005
Analyses: temperature, salinity, NO3, NO2, NH4, Si, P, chlorophyll a, POC, PON δ13C of POC and δ15N of PN in river water and seawater
North Pacific
42.8°N
42.2°N200 m
1000 m
100 m500 m
143.6°E 144°E 144.4°E
42.6°N
42.4°N
▲
▲
North Pacific
Tokachi River
Objectives
To estimate nutrients impact from Tokachi river water to the coastal system
To evaluate origin of carbon and nitrogen of POM off Tokachi coast
To elucidate loading pattern of riverine materials from cultivated land
To estimate influence of nutrient impact to coastal production
Vertical profile of Salinity
May 2003
0
10
20
30
40
50
28 30 32 34
Salinity
Dep
th (
m)
May 2003
0
10
20
30
40
50
28 30 32 34
Salinity
Dep
th (
m)
0
10
20
30
40
50
28 30 32 34
Salinity
Dep
th (
m)
August2003
Nov. 2003
◆St.T31: river mouth
■St.T33: in plume
▲St.T35: Outside of the plume▲
◆
28
29
30
31
32
33
3442.8°N
42.2°N200 m
1000 m
100 m500 m
143.6°E 144°E 144.4°E
42.6°N
42.4°N
Tokachi River
■
St.T31
St.T33St.T35
Conclusions
28
29
30
31
32
33
3442.8°N
42.2°N200 m
1000 m
100 m500 m
143.6°E 144°E 144.4°E
42.6°N
42.4°N
Tokachi River August 2003
28
29
30
31
32
33
34
42.8°N
42.2°N200 m
1000 m
100 m500 m
143.6°E 144°E 144.4°E
42.6°N
42.4°N
Tokachi River
42.8°N
42.2°N200 m
1000 m
100 m500 m
143.6°E 144°E 144.4°E
42.6°N
42.4°N
Tokachi River
Sea surface salinity off Tokachi
May 2003
Nov. 2003
B13A-1053
Tokachi riverFlood discharge: 15200 m3/secCatchment area: 9010 Km2
Population: 358000 (density= 33 /Km2)
-19
-20
-21
-22
-23
-24
-25
-26
-27145°E -25
-24
-23
-22
-21
-2043°N
42°N
144°E
200m 1000m2000m
0 500 1000 1500 2000
Water depth (m)
13C of surface sediments and POC
Tokachi River
13C δ13C (‰)
×St.T35
×St.T33St.T31 ×
St.T31(0-5m) POC(May)
St.T33 POC(May)
St.T35 POC(May)
urface Sediments
Surface sediments record 13C pattern indicating terrestrial organic carbon that is rapidly diluted by marine organic carbon on the shelf and most parts of organic carbon are replaced by marine origin toward pelagic (> 200m depth).
0
200
400
600
0
200
400
600
0
200
400
600
J F M A M J J A S O N D Month
Riv
er d
isch
arg
e (m
3/s
) 2003
J F M A M J J A S O N D Month
Riv
er d
isch
arg
e (m
3/s
)
Riv
er d
isch
arg
e (m
3/s
)
J F M A M J J A S O N D Month
Tokachi River (Discharge)
August 10 : 4634 m3/s
20052004Sept. 8 : 2072 m3/s
●River water sampling■Seawater sampling
Main water sources:
Spring-Summer: Snow-melt water
Summer-Autumn: Rainfall
-12
-8
-4
0
4
8
-32
-28
-24
-20
-16
0
100
200
300
400
500
0
50
100
150
200
250
NO
3- +
NO
2- (
μM
)
J F M A M J J A S O N D Month
NO3- + NO2
- (μM)
Surface seawater
Water quality of the Tokachi River
J F M A M J J A S O N D Month
POC (μM)
PO
C (
μM
)
Surface seawater
J F M A M J J A S O N D Month
δ13
C (
‰)
δ13C of POC (‰)
J F M A M J J A S O N D Month
δ15N of PN (‰)
δ15
N (
‰)
Surface seawater
Surface seawater
■ 2003● 2004 ▲ 2005
■ 2003● 2004 ▲ 2005
Sept. 8, 2005 : 2430 μM▲
0
20
40
60
0
5
10
15
J F M A M J J A S O N D
Chl.a
(μg/
l)
Month
Chl.a at 0 m depth POC at 0 m depth
PO
C (
μM
)
J F M A M J J A S O N D
Month
0
5
10
15
■ 2003● 2004 ▲ 2005
NO
3- +
NO
2- (μ
M)
Nitrate + nitrite at 0 m depth
J F M A M J J A S O N DMonth
Seasonal changes at Stn.T35, (outside of the river plume)
0
0.5
1
1.5
J F M A M J J A S O N DMonth
Phosphate at 0 m depth
PO
43- (μ
M)
-15
-20
-25
-3028 30 32 34
0
2
4
6
8
28 30 32 34
0
20
40
60
28 30 32 340
5
10
15
28 30 32 34
Chl.a
(μg/
l)
POC
(μM
)
SalinitySalinity
Salinity
δ15N
-PN
(‰
)
Salinity
Chl.a POC
δ13C
-PO
C (
‰)
Salinity
Chl.a, POC and isotope ratios vs. Sal May, August, November, 2003
δ15N of PNδ13C of POC
River POC
River PN
-20
0
20
40
60
80
28 30 32 34
Riv
er
PO
C f
racti
on
(%
)
Fraction of riverine POC estimated by
δ13C
◆ May◆ August◆ November
13C and 15N of soil, POM and sediments
River POM (sinking POM) might supply more than 40 % organic CN sources of coastal sediments in the Tokachi shelf (<200m)
Peat soil in bankRiver sedimentSinking river particleCoastal surface sediment
POM in river (Kako brg.)Weighted average POMEndmember of marine OM
-1
0
1
2
3
4
5
6
7
-34 -32 -30 -28 -26 -24 -22 -20
13C
・ River water plays an important role for supplying significant amount of nutrients and POM on the shelf off Tokachi (water depth<200 m)
・ Discharge by snow-melting (in early summer) and heavy rain (in summer and autumn) conveys nutrients to support major production at the coastal area in summer
・ Blooming in spring and autumn are supported by nutrients in the pelagic subsurface seawater (Oyashio current)
・ Annual load of DIN, PO43-, Si(OH)4 and POC from the To
kachi River to the coastal waters is corresponding to 37, 3.3, 145 and 7.3% of primary production reported in th
e Oyashio Water, respectively.
References: Usui T. et al. (2006) Distribution and sources of organic matter in surficial sediments on the shelf and slope off Tokachi, western North Pacific, inferred from C and N stable isotopes and C/N ratios, Marine Chemistry 98, 241–259
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