CHAPTERS
Biological Utilisation of the Major Nutrients in the Western Coastal
Waters of the North Adriatic Sea
S. Cozzi and G. Catalano
ABSTRACT
The availability and distribution of the dissolved inorganic and organic fractions of nitrogen
(DIN and DON) and phosphorus (DIP and DOP) are extremely variable in the north-western
Adriatic Sea. Freshwater inputs, mainly from the Po River, and biological processes significantly
affect the nutrient behaviour in this region. The purpose of this contribution is to describe these
processes by the comparison of the dissolved nitrogen and phosphorus distributions to computed estimates of their biological production or consumption in the marine environment.
The variations of dissolved nitrogen were mainly due to freshwater inputs of DIN, especially in
winter (up to 18 Jlmol-N-dm- 3 ), while a high marine release of DON was observed in summer (up
to +22 Jlmol-N-dm- 3 compared to the contribution of advection). The DIP concentrations were
generally lower than 0.06 Jlmol-P·dm- 3 , while DOP values ranged from 0.01 to 0.1 Jlmol-P·dm- 3 •
The evident inverse relationship between DIP and DOP behaviours indicated that the phosphorus availability in the coastal zone is mainly regulated by recycling processes rather than by terrestrial inputs.
Introduction
The knowledge of the distribution of inorganic
and organic nutrients and their biological pathways are fundamental to understanding a
marine ecosystem. This is particularly important
in a region like the northern Adriatic Sea, where
nutrient availability is strongly influenced by the
concurrent effects of heavy terrestrial inputs,
transport due to water circulation and biological
processes (Degobbis and Gilmartin 1990;
Zoppini et al. 1995; Artegiani et al. 1997). Their
fate has been related to undesirable phenomena
that have occurred in this area: unusually intense
algal blooms, near anoxia or anoxia in bottom
layers and more frequent mucilage formation
events than in other Adriatic regions
(Vollenweider et al. 1992; Degobbis et al. 1995;
Obernosterer and Herndl 1995; Tommasino
1996; Malone et al. 1999).
The aim of this work is to describe the availability of dissolved nitrogen and phosphorus. and
the effects of biological phenomena of removal
and release on their inorganic and organic fractions, in the western waters of the northern
Adriatic Sea, which are heavily influenced by the
Po River plume. These processes are discussed by
comparing the relevant distributions of concentration to computed estimates of their conservative (driven by mixing processes) and non-conservative (basically attributed to biological
assimilation or regeneration) components in the
marine environment, obtained assuming the
existence of a net nutrient balance during the
dilution of the Po River waters in the basin.
Materials and Methods
The presented data were collected during two
cruises of the PRISMA 2 "Biogeochemical
Cycles" Research Project (June 1996 and
February 1997). In both cruises, we chose transects (EF and EF-A, respectively), which are representative of the mixing between seawater and
the Po River waters (Fig. 1), considered to be the
main allocthonous source of nutrients in the
northern Adriatic Sea.
CNR, Istituto Talassografico di Trieste, Viale Romolo Gessi 2, 34123 11:ieste, Italy
EM. Faranda, L. Guglielmo, G. Spezie (eds)
Mediterranean Ecosystems: Structures and Processes
@ Springer-Verlag Italia 2001
Biological Utilisation of the Major Nutrients in the Western Coastal
Waters of the North Adriatic Sea
S. Cozzi and G. Catalano
ABSTRACT
The availability and distribution of the dissolved inorganic and organic fractions of nitrogen
(DIN and DON) and phosphorus (DIP and DOP) are extremely variable in the north-western
Adriatic Sea. Freshwater inputs, mainly from the Po River, and biological processes significantly
affect the nutrient behaviour in this region. The purpose of this contribution is to describe these
processes by the comparison of the dissolved nitrogen and phosphorus distributions to computed estimates of their biological production or consumption in the marine environment.
The variations of dissolved nitrogen were mainly due to freshwater inputs of DIN, especially in
winter (up to 18 Jlmol-N-dm- 3 ), while a high marine release of DON was observed in summer (up
to +22 Jlmol-N-dm- 3 compared to the contribution of advection). The DIP concentrations were
generally lower than 0.06 Jlmol-P·dm- 3 , while DOP values ranged from 0.01 to 0.1 Jlmol-P·dm- 3 •
The evident inverse relationship between DIP and DOP behaviours indicated that the phosphorus availability in the coastal zone is mainly regulated by recycling processes rather than by terrestrial inputs.
Introduction
The knowledge of the distribution of inorganic
and organic nutrients and their biological pathways are fundamental to understanding a
marine ecosystem. This is particularly important
in a region like the northern Adriatic Sea, where
nutrient availability is strongly influenced by the
concurrent effects of heavy terrestrial inputs,
transport due to water circulation and biological
processes (Degobbis and Gilmartin 1990;
Zoppini et al. 1995; Artegiani et al. 1997). Their
fate has been related to undesirable phenomena
that have occurred in this area: unusually intense
algal blooms, near anoxia or anoxia in bottom
layers and more frequent mucilage formation
events than in other Adriatic regions
(Vollenweider et al. 1992; Degobbis et al. 1995;
Obernosterer and Herndl 1995; Tommasino
1996; Malone et al. 1999).
The aim of this work is to describe the availability of dissolved nitrogen and phosphorus. and
the effects of biological phenomena of removal
and release on their inorganic and organic fractions, in the western waters of the northern
Adriatic Sea, which are heavily influenced by the
Po River plume. These processes are discussed by
comparing the relevant distributions of concentration to computed estimates of their conservative (driven by mixing processes) and non-conservative (basically attributed to biological
assimilation or regeneration) components in the
marine environment, obtained assuming the
existence of a net nutrient balance during the
dilution of the Po River waters in the basin.
Materials and Methods
The presented data were collected during two
cruises of the PRISMA 2 "Biogeochemical
Cycles" Research Project (June 1996 and
February 1997). In both cruises, we chose transects (EF and EF-A, respectively), which are representative of the mixing between seawater and
the Po River waters (Fig. 1), considered to be the
main allocthonous source of nutrients in the
northern Adriatic Sea.
CNR, Istituto Talassografico di Trieste, Viale Romolo Gessi 2, 34123 11:ieste, Italy
EM. Faranda, L. Guglielmo, G. Spezie (eds)
Mediterranean Ecosystems: Structures and Processes
@ Springer-Verlag Italia 2001