Nitrogen
fixation in Tikehau atoll : tables
Table 1. Taxonomic characteristics of
the soft bottom communities and limestone surfaces of pinnacles
studied in the lagoon of Tikehau Atoll.
|
The following cyanobacterial
genera were observed: Anabaena, Calothrix, Lyngbya, Oscillatoria,
Pleurocapsa, Spirulina
|
|
Communities
|
Dominant organisms
|
Other organisms
|
|
Sand 0
|
Diatoms, dinoflagellates
|
Undetermined algal species and other
organisms, no apparent cyanobacteria
|
|
Sand 1
|
Spirulina, Oscillatoria
|
Prorocentrum, undetermined algal species
|
|
Sand 2
|
Spirulina, Oscillatoria, Anabaena
|
Dinoflagellates, undetermined organisms
|
|
Sand 3
|
Lyngbya associations
|
Some undetermined organisms
|
|
Limestone surfaces
|
Calothrix, Oscillatoria, Pleurocapsa
|
Some undetermined organisms
|
Table 2.
Acetylene reduction rates (mean±SE; nmol cm-2 h-1)
measured in lagoonal communities during day time and during the night.
|
D/N
daylight/night;
%
Surf Percent of reduction rate measured at 25m compared to
the surface where the most of the incubations were done; DARR25m
daily acetylene
reduction rate at 25 m depth (µmol m-2 day-1).
Only sand 3 showed a difference with the surface (49%).
|
|
Communities
|
Acetylene
reduction rate
|
D/N
|
% Surf
|
DARR25m
|
|
|
Day
|
Night
|
|
|
|
|
Sand
0
|
0.33±0.03
|
0.03±0.01
|
11
|
100
|
43
|
|
Sand
1
|
0.52±0.23
|
0.32±0.06
|
1.6
|
100
|
101
|
|
Sand
2
|
1.30±0.97
|
0.74±0.14
|
1.7
|
100
|
245
|
|
Sand
3
|
0.99±0.36
|
0.16±0.02
|
6.2
|
49
|
68
|
|
Pinnacles
|
1.83±0.26
|
0.26±0.08
|
7
|
100
|
251
|
Table 3.
Budget for benthic dinitrogen fixation in Tikehau Lagoon.
|
[DARR25m
acetylene reduction rate at 25 m depth (µmol C2H2
m-2 day-1) (day=24h);
C2H2/N2 ratio of C2H2
reduction to N2
fixation;
(N2Fix)S
specific N2 fixation (mg N m-2 day-1)
= DARR25m
x 14 x 2 / C2H2/N2
/ 1000;
TA percentage of total area occupied by each soft
bottom community =
soft bottom (392.2 km2) + pinnacle (8 km2);
(N2Fix)M daily fixation per
projected square metre of lagoon (mg N m-2
day-1) =
(N2Fix)S * TA / 100;
(N2Fix)T
total benthic N2 fixation (kg N day-1)
for each community and for the whole of the lagoon = (N2Fix)M
x
la surface totale du lagon (400.2 km2)
|
| Communities
|
DARR25m
|
C2H2/N2
|
(N2Fix)S |
TA (%) |
(N2Fix)M
|
(N2Fix)T
|
| Sand 0
|
43.2
|
3.0
|
0.40
|
46.2 |
0.18
|
72 |
| Sand 1
|
100.8 |
2.2 |
1.26 |
42.4 |
0.53
|
212
|
| Sand 2 |
244.8
|
1.8
|
3.90
|
2.8 |
0.11
|
44 |
| Sand 3
|
67.6
|
4.8 |
0.39 |
6.7 |
0.26 |
104
|
| Total soft bottom |
|
|
|
98.1 |
1.08
|
432
|
| Total limestone surface |
251.0 |
3.3 |
2.12 |
2 x 3* |
0.13 |
51 |
| Total
benthic lagoonal N2 fixation
|
|
|
|
|
|
483 |
* =
pinnacle projected area x 3 = pinnacle limestone area
Table 4.
Summary
of dinitrogen fixation by the four soft bottom communities of
Tikehau Lagoon (order of importance).
|
[(N2Fix)S
and (N2Fix)T as in Table 3]
|
| |
Sand
0 |
Sand
1 |
Sand
2 |
Sand
3 |
| Acetylene
reduction rate
|
4th |
2nd
|
1st
|
3rd |
| (N2Fix)S |
3rd |
2nd
|
1st |
4th |
| %Highest
rate
|
10.3% |
32.3% |
100%
|
10%
|
| (N2Fix)T
|
3rd |
1st
|
4th
|
2nd
|
| %Total
|
16% |
49% |
10%
|
25% |
|
Atoll_site_