230
M. Bartoli et al.
within the sediment (Dn) are shown in Fig. 4. At
station Giralda the highest total denitrification
rates (Dn+ Dw) were determined in March (256 ±
15 and 267 ± 22 Jlmol N m- 2 h- 1 respectively in
the light and in the dark). The Dn represented 67
and 78% of the total light and dark denitrification, respectively indicating that nitrification is
an important N-process in the microphytobenthic system. Total denitrification was lower in July
and in November (about 100 Jlmol N m- 2 h- 1 )
due to a combination of lower nitrate concentraStation Giralda
'7 100
o light
IiE 75
.dark
z
0 50
E
:::L 25
~ 0
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Station Gorino
... 200
.c:
o light
N
E 150
~ 100
• dark
0
§.50
~ 0
314/97
8121197
11/26197
Station Smarlacca
-
25
.l=
"!
20
o light
E
Z
15
• dark
(5
10
E
:::L
5
~ 0
3119/97
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tions in the water column and lower populations
of benthic infauna.
At station Gorino total denitrification rates
ranged between 63 and 119 Jlmol m- 2 h- 1 • The
Dw was low in March in both light and dark
incubations probably due to the high nitrate
uptake by Ulva (-1197 ± 460 and -454 ± 280
}lmo! N0 3 - m- 2 h- 1 ). The Dn was generally low
with a peak of 49 ± 8 Jlmol N m- 2 h- 1 determined
in the light incubation of August when Ulva was
not present and it was not detectable in the dark
1: 250
o light
1200
• dark
z 150
(5
E 100
:::L
c;:- 50
Q
a
3126/97
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'7 80
o light
.s::.
N
E 60
• dark
~40 0
§..20
c
Q
a
314197
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11/26/97
10
1:
o light
1
8
• dark
z 6
(5
4
E ::L 2
8 0
3119/97
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Fig.4. Uncoupled (Dw, left) and coupled (Dn, right) denitrification rates determined at the three sites during light and dark
incubations. Note different scales of ordinate axes