38
s. Cozzi and G. Catalano
z
c»
"0
::I
45.
45.2
; 44.8
.!!!
44.4
t
N
-----, • Seawater
,
xxx
.... _ - . Sal=37.8
, ••• ···.x.,cx , %02=100
,-- ---- -e= June 1996
x= February 1997
Fig.I. Sampling stations of the PRISMA 2 "Biogeochemical
Cycles" Research Project: June 1996 transect EF (e) and
February 1997 transect EF-A (x)
44.nL--r"-~~--r--'=::::;:::====;:=====-I
12.2
12.6
13.0
13.4
13.8
longitude E
Both transects cut across the frontal system
delimiting the zone directly influenced by the
river plume, and the offshore zone influenced by
the diluted river inputs. This has permitted the
estimate of inorganic and organic nutrient balances in both these environments, in late winter
and early summer, during different phases of the
evolution of the coastal front.
At every station, salinity data were computed
from the downcast, and samples for the determination of the inorganic nutrients and dissolved
organic nitrogen (DON) and phosphorus (DOP)
were filtered through Whatman GF/F glass
microfibre filters. Analyses of dissolved inorganic nitrogen (DIN = nitrates + nitrites + ammonium) and dissolved inorganic phosphorus (DIP =
phosphates) were performed by standard spectrophotometric methods (Grasshoff 1983). The
DON and DOP concentrations were determined
by the photo-oxidation (UV + hydrogen peroxide) method of Walsh (1989).
The DIN, DIP, DON and DOP concentrations
biologically consumed or produced [~-(l)] were
estimated by subtracting the values ascribed to
freshwater dilution from the measured concentrations:
8-(i) = C(i) - (C(riv)i . W(riv» -
(C(sea)i· W(sea»
where C(i) is the concentration (p.mol·dm- 3 ) of
14.2
the nutrient (i) measured in the sample and
C(riv)i and C(sea)i are, respectively, the nutrient
(i) concentrations in Po River waters (monthly
average, n=4, at Po Pontelagoscuro and Po
Serravalle stations, ARPA Regione Emilia
Romagna, Sede Provinciale of Ferrara, personal
communication) and in the sea. The freshwater
and seawater fractions in the sample [W(riv) and
W(sea) respectively] were calculated by assigning a salinity zero to the Po River waters and 37.8
for seawater. This value of salinity and every
C(sea)i concentration are an average of the relevant data from the stations farthest from the
Italian Coast, at depths not significantly influenced by terrestrial inputs, where nutrient
assimilation and regeneration rates were
assumed approximately to be balanced (oxygen
saturation =100%).
By assuming that physico-chemical processes of sedimentation have a negligible influence
on the considered parameters, ~-(i)
was further reduced by phytoplankton assimilation. Thus 8-(i»O indicates that the regeneration prevails over assimilation processes with a
consequent increase in nutrient concentrations.
If 8-(i) is close to zero, assimilation and regeneration should be nearly balanced so that a conservative behaviour of nutrient concentrations
would be expected.
s. Cozzi and G. Catalano
z
c»
"0
::I
45.
45.2
; 44.8
.!!!
44.4
t
N
-----, • Seawater
,
xxx
.... _ - . Sal=37.8
, ••• ···.x.,cx , %02=100
,-- ---- -e= June 1996
x= February 1997
Fig.I. Sampling stations of the PRISMA 2 "Biogeochemical
Cycles" Research Project: June 1996 transect EF (e) and
February 1997 transect EF-A (x)
44.nL--r"-~~--r--'=::::;:::====;:=====-I
12.2
12.6
13.0
13.4
13.8
longitude E
Both transects cut across the frontal system
delimiting the zone directly influenced by the
river plume, and the offshore zone influenced by
the diluted river inputs. This has permitted the
estimate of inorganic and organic nutrient balances in both these environments, in late winter
and early summer, during different phases of the
evolution of the coastal front.
At every station, salinity data were computed
from the downcast, and samples for the determination of the inorganic nutrients and dissolved
organic nitrogen (DON) and phosphorus (DOP)
were filtered through Whatman GF/F glass
microfibre filters. Analyses of dissolved inorganic nitrogen (DIN = nitrates + nitrites + ammonium) and dissolved inorganic phosphorus (DIP =
phosphates) were performed by standard spectrophotometric methods (Grasshoff 1983). The
DON and DOP concentrations were determined
by the photo-oxidation (UV + hydrogen peroxide) method of Walsh (1989).
The DIN, DIP, DON and DOP concentrations
biologically consumed or produced [~-(l)] were
estimated by subtracting the values ascribed to
freshwater dilution from the measured concentrations:
8-(i) = C(i) - (C(riv)i . W(riv» -
(C(sea)i· W(sea»
where C(i) is the concentration (p.mol·dm- 3 ) of
14.2
the nutrient (i) measured in the sample and
C(riv)i and C(sea)i are, respectively, the nutrient
(i) concentrations in Po River waters (monthly
average, n=4, at Po Pontelagoscuro and Po
Serravalle stations, ARPA Regione Emilia
Romagna, Sede Provinciale of Ferrara, personal
communication) and in the sea. The freshwater
and seawater fractions in the sample [W(riv) and
W(sea) respectively] were calculated by assigning a salinity zero to the Po River waters and 37.8
for seawater. This value of salinity and every
C(sea)i concentration are an average of the relevant data from the stations farthest from the
Italian Coast, at depths not significantly influenced by terrestrial inputs, where nutrient
assimilation and regeneration rates were
assumed approximately to be balanced (oxygen
saturation =100%).
By assuming that physico-chemical processes of sedimentation have a negligible influence
on the considered parameters, ~-(i)
was further reduced by phytoplankton assimilation. Thus 8-(i»O indicates that the regeneration prevails over assimilation processes with a
consequent increase in nutrient concentrations.
If 8-(i) is close to zero, assimilation and regeneration should be nearly balanced so that a conservative behaviour of nutrient concentrations
would be expected.