228
M. Bartoli et aI.
Table. Primary producer biomass, oxygen and DIN concentrations in the water column at
the three sites. At station GiraIda microaIgaI biomass is expressed as mg Chla m- 2 ; at station Smarlacca Ruppia biomass is expressed as g dry weight of roots and leaves. At station
Gorino on 21.08.97 no Ulva thalli were found
Station
Date
Biomass
Oxygen
(11M )
Giralda
03/26/97
39±12
330
(microalgae)
07129/97
48±10
340
11/11197
24±3
290
Gorino
03/4/97
191±5
500
(Ulva)
08/21/97
0
110
11126/97
311±15
400
Smarlacca
03/19/97
Roots 20±2
315
(Ruppia)
Leaves 31±2
07/22/97
Roots 96±15
430
Leaves 318±26
11120/97
Roots 18±3
324
Leaves 75±6
At station Smarlacca, the Ruppia biomass
reached a summer peak of 414±29 gdw m- 2 in July
77% of which was due to the leaves. At this station, the water column was about 100% 02 saturated in March and in November whilst in July 0 2
oversaturation reached 196%. The DIN concentrations were generally very low with a summer
minimum coinciding with the biomass peak. The
NO,- concentrations were almost negligible.
Oxygen and DIN Fluxes
Light and dark oxygen and ammonium fluxes
determined at station Giralda are shown in Fig. 1.
Dark respiration ranged between -3.42±0.18 and
-2.38±0.11 mmol 0 2 m- 2 h- 1 and was not related
to water temperature. A positive net efflux of 02
was determined in July (740±250 !lmol 0 2
m- 2 h- l ) when chlorophyll a attained the highest
concentration in the surficial sediment (Table).
Gross primary productivity values (1.35 to 4.04
mmol m- 2 h- 1 ) demonstrate a high micro algal
photosynthetic activity at the water-sediment
interface (Fig. I). During light incubations a net
ammonium uptake by the benthic micro algal mat
was observed. For example, in July an influx of
197±104!lmol NH/ m- 2 h-1was measured in the
light and an efflux of 515±189!lmol NH/ m- 2 h- 1
was determined in the dark. Nitrate fluxes (values
not shown) were quite variable even if mostly
directed from the water column to the sediment.
A net efflux of nitrates was determined in the
Ammonium
Nitrate
(11 M )
(11M)
32
50
14
16
36
45
18
43
35
11
22
46
15
7
6
5
15
4
light in July (783± 345 llIDol N0 3 - m- 2 h- l ) coinciding with the ammonium uptake. Nevertheless,
nitrate fluxes were not correlated with NO,- concentrations in the water column or ammonium
exchanges between sediment and water.
5000
!i
2500
E
N
0
"0
0
E
::l.
X
:>
-2 500
0::
0
-5000
900
1:
N
600
E
z
"0 300
E
::l.
,(
0
' "
0=
;: -300
Z
-600
3/26/97
alight
_ dar!<
3/26197
o Gross primary production
a Net primary production
_ Dark respiration
7/29/97
11/11/97
7/29/97
11/11/97
Fig.!. Oxygen and ammonium fluxes determined at Station
GiraIda in cores incubated in light and dark conditions
M. Bartoli et aI.
Table. Primary producer biomass, oxygen and DIN concentrations in the water column at
the three sites. At station GiraIda microaIgaI biomass is expressed as mg Chla m- 2 ; at station Smarlacca Ruppia biomass is expressed as g dry weight of roots and leaves. At station
Gorino on 21.08.97 no Ulva thalli were found
Station
Date
Biomass
Oxygen
(11M )
Giralda
03/26/97
39±12
330
(microalgae)
07129/97
48±10
340
11/11197
24±3
290
Gorino
03/4/97
191±5
500
(Ulva)
08/21/97
0
110
11126/97
311±15
400
Smarlacca
03/19/97
Roots 20±2
315
(Ruppia)
Leaves 31±2
07/22/97
Roots 96±15
430
Leaves 318±26
11120/97
Roots 18±3
324
Leaves 75±6
At station Smarlacca, the Ruppia biomass
reached a summer peak of 414±29 gdw m- 2 in July
77% of which was due to the leaves. At this station, the water column was about 100% 02 saturated in March and in November whilst in July 0 2
oversaturation reached 196%. The DIN concentrations were generally very low with a summer
minimum coinciding with the biomass peak. The
NO,- concentrations were almost negligible.
Oxygen and DIN Fluxes
Light and dark oxygen and ammonium fluxes
determined at station Giralda are shown in Fig. 1.
Dark respiration ranged between -3.42±0.18 and
-2.38±0.11 mmol 0 2 m- 2 h- 1 and was not related
to water temperature. A positive net efflux of 02
was determined in July (740±250 !lmol 0 2
m- 2 h- l ) when chlorophyll a attained the highest
concentration in the surficial sediment (Table).
Gross primary productivity values (1.35 to 4.04
mmol m- 2 h- 1 ) demonstrate a high micro algal
photosynthetic activity at the water-sediment
interface (Fig. I). During light incubations a net
ammonium uptake by the benthic micro algal mat
was observed. For example, in July an influx of
197±104!lmol NH/ m- 2 h-1was measured in the
light and an efflux of 515±189!lmol NH/ m- 2 h- 1
was determined in the dark. Nitrate fluxes (values
not shown) were quite variable even if mostly
directed from the water column to the sediment.
A net efflux of nitrates was determined in the
Ammonium
Nitrate
(11 M )
(11M)
32
50
14
16
36
45
18
43
35
11
22
46
15
7
6
5
15
4
light in July (783± 345 llIDol N0 3 - m- 2 h- l ) coinciding with the ammonium uptake. Nevertheless,
nitrate fluxes were not correlated with NO,- concentrations in the water column or ammonium
exchanges between sediment and water.
5000
!i
2500
E
N
0
"0
0
E
::l.
X
:>
-2 500
0::
0
-5000
900
1:
N
600
E
z
"0 300
E
::l.
,(
0
' "
0=
;: -300
Z
-600
3/26/97
alight
_ dar!<
3/26197
o Gross primary production
a Net primary production
_ Dark respiration
7/29/97
11/11/97
7/29/97
11/11/97
Fig.!. Oxygen and ammonium fluxes determined at Station
GiraIda in cores incubated in light and dark conditions