Structure, fonctionnement, évolution des communautés benthiques ...

tel-00009359, version 1 - 1 Jun 2005
Chapitre 3 - Fonctionnement du réseau trophique benthique de la Grande Vasière
Table 3. Composition and mean daily concentrations of bottom-water suspended particulate matter in
April-May (Sp) and September (Su) 2002.
Station A B C D E F G
Season Sp Su Sp Su Sp Su Sp Su Su Sp Su Sp Su
SPM
(g DW.m -3 )
Load
PTC
(mg C.m -3 )
POC
(mg C.m -3 )
POC:PTC
(%)
PON
(mg N.m -3 )
Chl a
(mg.m -3 )
Phaeopigments
(mg.m -3 )
14.24
(1.68)
0.31
(0.03)
191.26
(29.27)
141.86
(29.43)
9.35
(1.22)
0.28
(0.06)
120.29
(14.82)
87.73
(16.91)
8.01
(0.30)
0.10
(0.02)
106.42
(8.41)
95.89
(15.81)
7.28
(0.33)
0.13
(0.01)
67.96
(4.62)
63.94
(25.12)
11.50
(2.90)
0.26
(0.11)
147.38
(29.84)
97.30
(22.53)
7.65
(0.10)
0.15
(0.02)
72.35
(5.87)
49.41
(3.56)
185
7.24
(0.39)
0.07
(0.04)
88.89
(13.62)
70.17
(6.21)
6.91
(0.35)
0.14
(0.04)
74.92
(7.15)
56.33
(16.17)
4.46
(1.36)
0.07
(0.03)
73.63
(18.42)
50.50
(10.57)
10.58
(1.02)
0.36
(0.11)
217.70
(57.93)
202.10
(81.05)
6.55
(0.07)
0.12
(0.05)
92.49
(6.14)
85.88
(9.38)
8.72
(0.90)
0.32
(0.05)
121.34
(18.94)
77.84
(10.44)
9.95
(1.00)
0.21
(0.01)
155.39
(15.83)
104.77
(7.60)
74.17 72.93 90.11 94.09 66.02 68.29 78.94 75.19 68.59 92.83 92.85 64.15 67.42
21.52
(3.92)
0.04
(0.00)
0.10
(0.01)
12.12
(1.54)
0.11
(0.02)
0.18
(0.02)
15.01
(3.75)
0.04
(0.01)
0.07
(0.01)
6.91
(0.58)
0.10
(0.03)
0.10
(0.02)
15.71
(3.39)
0.04
(0.00)
0.09
(0.02)
7.08
(0.30)
0.07
(0.00)
0.09
(0.01)
11.90
(2.63)
0.04
(0.00)
0.06
(0.01)
7.06
(0.92)
0.18
(0.02)
0.12
(0.02)
6.58
(0.62)
0.05
(0.01)
0.09
(0.01)
26.64
(5.98)
0.98
(0.14)
0.47
(0.04)
15.38
(1.38)
0.60
(0.06)
0.34
(0.08)
12.18
(1.46)
0.08
(0.02)
0.15
(0.02)
δ 13 C (‰) -22.20 -22.20 -23.00 -23.20 -23.15 -22.90 -23.00 -23.50 -23.25 -19.70 -21.55 -22.85 -20.90
δ 15 N (‰) 5.75 5.35 6.10 4.05 5.45 4.00 5.70 3.50 6.90 4.50 5.70 4.60 3.80
POC:PON
(W:W)
Chl a:Pheo
(W:W)
POC:SPM
(W:W%)
5.58
(0.56)
0.41
(0.07)
1.00
(0.17)
6.70
(0.24)
0.62
(0.14)
0.91
(0.25)
6.64
(1.63)
0.57
(0.07)
1.21
(0.22)
6.84
(0.98)
1.03
(0.17)
0.75
(0.22)
7.28
(1.21)
0.46
(0.09)
1.14
(0.27)
6.97
(0.80)
0.79
(0.12)
0.65
(0.05)
6.10
(0.46)
0.65
(0.14)
0.97
(0.05)
7.39
(0.71)
1.51
(0.23)
0.70
(0.08)
7.25
(1.21)
0.55
(0.10)
1.37
(0.47)
7.58
-
2.10
(0.47)
1.93
(1.00)
5.55
(0.16)
1.83
(0.38)
1.35
(0.27)
6.08
(0.30)
0.50
(0.12)
0.94
(0.10)
17.56
(1.17)
0.13
(0.02)
0.19
(0.01)
5.91
(0.46)
0.70
(0.06)
1.01
(0.10)
Low pigment concentrations were measured in bottom waters: the daily means of bottomwater
Chl a concentrations ranged from 0.04 (central ‘Grande Vasière’ stations: A, B, C and D) to
0.98 mg.m -3 (Stn F) in spring, vs. 0.05 (Stn E) to 0.60 mg.m -3 (Stn F) in summer (Table 3). The daily
means of bottom-water phaeopigment concentrations ranged from 0.06 (Stn D) to 0.47 mg.m -3 (Stn F)
in spring, vs. 0.09 (Stn C and E) to 0.34 mg.m -3 (Stn F) in late summer. The Chl a:Phaeo ratios ranged
from 0.41 (Stn A) to 2.10 (Stn F) in spring, vs. 0.55 (Stn E) to 1.83 (Stn F) in September. By
comparison, pigment concentrations in surface water were higher than those in bottom water (e.g.
0.27-1.74 mg.m -3 in spring for Chl a, vs. 0.71-1.25 mg.m -3 in late summer). The low pigment
concentrations in late April-early May and mid-September 2002 can be explained by a late winter