42
S. Cozzi and G. Catalano
between the inorganic and organic fractions of
phosphorus in the marine environment.
In this case, the A-{DIP) and A-(DOP) distributions (Fig. Sc and d) indicate that the DIP
availability in the inshore zone is determined by
both continental input and assimilationlremineralisation processes. In the upper layer, inorganic phosphorus is partially consumed
[A-(DIP) values up to -0.09 /lmol-P·dm- 3 in Fig.
Sc], while it is regenerated in the bottom layer by
remineralisation [A-(DIP} equal to +0.03
p.mol-P·dm- 3 ]. On the contrary, the offshore
zone shows a depletion of DIP in the entire water
column related to close to zero A-(DIP) values.
Regarding the organic fraction (Fig. Sd), the
main features are the negative A-(DOP) values in
the coastal zone (-0.03 p.mol-P·dm- 3 ) linked to
phosphorus remineralisation and the quasi-conservative behaviour of DOP passing to the offshore zone.
Conclusions
The distributions of concentration and the presented nutrient balance in the northern Adriatic
Sea highlight the roles of the continental inputs
and biological (assimilation and regeneration)
processes as sources or sinks of nitrogen and
phosphorus. In particular, the necessity of the
inclusion of their dissolved organic fractions in
order to assess the total eutrophic state of the
basin and to understand better the seasonal
cycling of these elements is emphasised. In fact,
during some periods. DON and DOP can reach
almost up to 100% of the total dissolved nutrient.
The Po River discharge is an important
source for both DIN and DIP, but, as far as phosphorus is concerned, the river supply is consumed within the coastal zone also in winter,
while this does not occur for DIN. The inverse
relationships between the inorganic and organic
fractions are more evident for phosphorus than
for nitrogen. These results also strongly support
the hypothesis that, in the northern Adriatic Sea)
phosphorus plays a greater role as a limiting element than nitrogen.
With respect to the nutrient balance, the A-{i}
distributions point out the greater importance of
biological cycling jn controlling nitrogen and
phosphorus availability (inorganic and organic)
when compared to advection and mixing processes, also within a few miles from the coast. The
photosynthetic extracellular release by phytoplankton (Fogg 1983; Lancelot 1983; Fogg 1996),
the dissolution of particulate organic matter by
attached bacteria (Azam et aI. 1993), the activity
of grazers (Ducklow and Carlson 1992; Strom et
aI. 1997) and the virus-induced bacteria lysis
(Bratbak et aI. 1990) are all important sources of
dissolved organic matter. Further research is
needed to establish the relative importance of
these mechanisms in the northern Adriatic Sea.
Acknowledgements. The authors wish to thank the ARPA,
Regione Emilia Romagna, Serle Provinciale of Ferrara for the
Po River nutrient data.
References
Artegiani A, Bregant D. Paschini E, Pinardi N, Raicich P, Russo A
(1997) The Adriatic Sea general circulation. I. Air-sea interactions and water mass structure. J Phys Oceanogr 27: 14921514
Azam F. Smith DC, Steward GP, Hangstrom A (1993) Bacteriaorganic matter coupling and its significance for oceanic Calbon cycling. Microb Ecol 28: 167-179
Bratbak G, Hedal M. Norland S, Tbingstad TF (1990) Vlluses as
partners in spring bloom microbial trophodynamics. Appl
Environ Microbiol56: 1400-1405
Degobbis D, Gilmartin M (1990) Nitrogen, phosphorus, and biogenic silicon budgets for the northern Adriatic Sea. Oceanol
Acta 13 1: 31-45
Degobbis D, Fonda Umani S, Franco P, Malej A, Precali R,
Smodlaka N (1995) Changes in the northern Adriatic
ecosystem and the hypertrophic appearance of gelatinous
aggregates. Sci Total Environ 165: 43-58
Ducklow HW, Carlson CA (1992) Oceanic bacterial production.
In: Marshall KC (ed) (Advances in microbial ecology, 12)
Pknum Press, New York, pp 113-181
Fogg GE (1983) The ecological significance of extracellular products of phytoplankton photosynthesis. Bot Mar 24: 3-14
Fogg GE (1996) The extracellular products of algae. Oceanogr
Mar Bioi Annu Rev 4: 195-212
GrasshoffK (1983) Methods of seawater analysis. In: GrasshoffK.
Ehrhardt M, Kremling K (eds). Verlag Chemie, Weinheim, pp
125-215
Lancelot C (1983) Factors affecting phytoplankton extracellular
release in the Southern Bight of the North Sea. Mar Reol
Prog Ser 12: 115-121
Malone Te, Malej A. Harding LW (1999) Ecosystem at the landsea margin. In: Malone TC. Malej A (eds) Coastal Estuarine
Studies 55, AGU, Washington. DC, pp 381
Obernosterer I , Herndl GJ (1995) Phytoplankton extracellular
release and bacterial growth: dependence on the inorganic
N:P ratio. Mar Eeal Prog Ser 116: 247-257
Strom SL, Benner R, Ziegler S, Dagg MJ (1997) Planktonic grazers
are potentially important source of marine dissolved organic carbon. Limnol Oceanogr 42(6): 1364-1374
Tommasino MG {1996} It is feasible to predict "slime blooms" or
"mucilage" in the northern Adriatic Seal Ecol Model 84: 189198
Vollenweider RA, Marchetti R, Viviani R (1992) Marine Coastal
S. Cozzi and G. Catalano
between the inorganic and organic fractions of
phosphorus in the marine environment.
In this case, the A-{DIP) and A-(DOP) distributions (Fig. Sc and d) indicate that the DIP
availability in the inshore zone is determined by
both continental input and assimilationlremineralisation processes. In the upper layer, inorganic phosphorus is partially consumed
[A-(DIP) values up to -0.09 /lmol-P·dm- 3 in Fig.
Sc], while it is regenerated in the bottom layer by
remineralisation [A-(DIP} equal to +0.03
p.mol-P·dm- 3 ]. On the contrary, the offshore
zone shows a depletion of DIP in the entire water
column related to close to zero A-(DIP) values.
Regarding the organic fraction (Fig. Sd), the
main features are the negative A-(DOP) values in
the coastal zone (-0.03 p.mol-P·dm- 3 ) linked to
phosphorus remineralisation and the quasi-conservative behaviour of DOP passing to the offshore zone.
Conclusions
The distributions of concentration and the presented nutrient balance in the northern Adriatic
Sea highlight the roles of the continental inputs
and biological (assimilation and regeneration)
processes as sources or sinks of nitrogen and
phosphorus. In particular, the necessity of the
inclusion of their dissolved organic fractions in
order to assess the total eutrophic state of the
basin and to understand better the seasonal
cycling of these elements is emphasised. In fact,
during some periods. DON and DOP can reach
almost up to 100% of the total dissolved nutrient.
The Po River discharge is an important
source for both DIN and DIP, but, as far as phosphorus is concerned, the river supply is consumed within the coastal zone also in winter,
while this does not occur for DIN. The inverse
relationships between the inorganic and organic
fractions are more evident for phosphorus than
for nitrogen. These results also strongly support
the hypothesis that, in the northern Adriatic Sea)
phosphorus plays a greater role as a limiting element than nitrogen.
With respect to the nutrient balance, the A-{i}
distributions point out the greater importance of
biological cycling jn controlling nitrogen and
phosphorus availability (inorganic and organic)
when compared to advection and mixing processes, also within a few miles from the coast. The
photosynthetic extracellular release by phytoplankton (Fogg 1983; Lancelot 1983; Fogg 1996),
the dissolution of particulate organic matter by
attached bacteria (Azam et aI. 1993), the activity
of grazers (Ducklow and Carlson 1992; Strom et
aI. 1997) and the virus-induced bacteria lysis
(Bratbak et aI. 1990) are all important sources of
dissolved organic matter. Further research is
needed to establish the relative importance of
these mechanisms in the northern Adriatic Sea.
Acknowledgements. The authors wish to thank the ARPA,
Regione Emilia Romagna, Serle Provinciale of Ferrara for the
Po River nutrient data.
References
Artegiani A, Bregant D. Paschini E, Pinardi N, Raicich P, Russo A
(1997) The Adriatic Sea general circulation. I. Air-sea interactions and water mass structure. J Phys Oceanogr 27: 14921514
Azam F. Smith DC, Steward GP, Hangstrom A (1993) Bacteriaorganic matter coupling and its significance for oceanic Calbon cycling. Microb Ecol 28: 167-179
Bratbak G, Hedal M. Norland S, Tbingstad TF (1990) Vlluses as
partners in spring bloom microbial trophodynamics. Appl
Environ Microbiol56: 1400-1405
Degobbis D, Gilmartin M (1990) Nitrogen, phosphorus, and biogenic silicon budgets for the northern Adriatic Sea. Oceanol
Acta 13 1: 31-45
Degobbis D, Fonda Umani S, Franco P, Malej A, Precali R,
Smodlaka N (1995) Changes in the northern Adriatic
ecosystem and the hypertrophic appearance of gelatinous
aggregates. Sci Total Environ 165: 43-58
Ducklow HW, Carlson CA (1992) Oceanic bacterial production.
In: Marshall KC (ed) (Advances in microbial ecology, 12)
Pknum Press, New York, pp 113-181
Fogg GE (1983) The ecological significance of extracellular products of phytoplankton photosynthesis. Bot Mar 24: 3-14
Fogg GE (1996) The extracellular products of algae. Oceanogr
Mar Bioi Annu Rev 4: 195-212
GrasshoffK (1983) Methods of seawater analysis. In: GrasshoffK.
Ehrhardt M, Kremling K (eds). Verlag Chemie, Weinheim, pp
125-215
Lancelot C (1983) Factors affecting phytoplankton extracellular
release in the Southern Bight of the North Sea. Mar Reol
Prog Ser 12: 115-121
Malone Te, Malej A. Harding LW (1999) Ecosystem at the landsea margin. In: Malone TC. Malej A (eds) Coastal Estuarine
Studies 55, AGU, Washington. DC, pp 381
Obernosterer I , Herndl GJ (1995) Phytoplankton extracellular
release and bacterial growth: dependence on the inorganic
N:P ratio. Mar Eeal Prog Ser 116: 247-257
Strom SL, Benner R, Ziegler S, Dagg MJ (1997) Planktonic grazers
are potentially important source of marine dissolved organic carbon. Limnol Oceanogr 42(6): 1364-1374
Tommasino MG {1996} It is feasible to predict "slime blooms" or
"mucilage" in the northern Adriatic Seal Ecol Model 84: 189198
Vollenweider RA, Marchetti R, Viviani R (1992) Marine Coastal