470
M. Pettine . L. Patrolecco . S. Capri
nualloads of organic matter directly discharged into northern Adriatic waters account
for more than 30% of the annual phytoplankton production in its most productive
region along the western side (Pettine et al. 1998).
Responses of plankton biomass and productivity to riverine discharged nutrients
and organic matter have been studied in many coastal ecosystems including
the Hudson River, Narragansett Bay, northern Gulf of Mexico, Chesapeake Bay, Columbia River estuary, and the Baltic Sea (Benner et al. 1992; Maske 1994; Malone 1994;
Cloern 1996; Harding et al. 1999; Kemp et al. 1999; Malone et al. 1999; Klinkhammer
et al. 2000).
River-induced eutrophication is a general observed phenomenon involving a number of negative consequences such as excess phytoplankton growth, increased frequency of blooms, seasonal decline of oxygen in bottom waters, and changes in the
trophic structure (Harding et al.1999). However, the severity of these problems and in
particular the fate of DOM resulting from both autochthonous and allochthonous
sources may be strongly dependent on seasonal variations of freshwater flow, the geomorphology of the receiving systems and the dominant circulation pattern.
This was clearly disclosed by a recent thorough comparison (Malone et al. 1999)
between the Chesapeake Bay (CB) and northern Adriatic (NA). Both of these systems
are dominated by a single river, the Susquehanna in CB and the Po in NA; however,
despite some similarities in terms of freshwater and nutrient loading, they exhibit significantly different trophic status. CB waters appear to be much more efficient in sequestering nutrients and retaining and recycling phytoplankton biomass than NA
waters (Harding et al. 1999); in this latter system the export of nutrients due to water
mass exchanges between the northern and middle basins, favoured by the counterclockwise circulation pattern during most of the year, and the confinement of regenerated nutrients, due to the strong vertical stratification during summer, reduce its
capacity to retain nutrients on time and scale that promote primary and secondary
productivity (Harding et al. 1999).
NA waters exhibit markedly lower average productivity levels than CB waters, although they experience large trophic gradients from coastal eutrophic to off-shore
oligotrophic waters. However, the dynamics of DOM in this basin has resulted in the
formation of a large quantity of sticky mucilaginous masses with serious problems
for tourists and fishery activities; in 1989, the damages amounted to billion of dollars
according to Italian authorities' estimations. This phenomenon is not reported for CB
waters (Malone et al. 1999), while both the CB and NA systems experiment seasonal
oxygen decline; anoxic problems are, however, much more severe in the former compared to the latter system.
There is now wide consensus that mucilaginous aggregates consist of organic and
inorganic material entrapped in a gelatinous polysaccharides matrix (Degobbis et al.
1995), although timing and evolution of mucilaginous aggregates, trigger mechanisms,
and biological species possibly involved in the formation of aggregates are still largely
unknown (Funari et al. 1999). The mean percent values and related standard deviation (±x) of organic carbon, nitrogen, phosphorus, silicon and sulphur in aggregates
collected in the summer of 1991 from surface and deep northern Adriatic waters were
24.0 ±7.2, 2.9 ±1.1, 0.26 ±0.12, 6.4 ±4.5 and 1.1 ±0.5, respectively (Pettine et al. 1995).
M. Pettine . L. Patrolecco . S. Capri
nualloads of organic matter directly discharged into northern Adriatic waters account
for more than 30% of the annual phytoplankton production in its most productive
region along the western side (Pettine et al. 1998).
Responses of plankton biomass and productivity to riverine discharged nutrients
and organic matter have been studied in many coastal ecosystems including
the Hudson River, Narragansett Bay, northern Gulf of Mexico, Chesapeake Bay, Columbia River estuary, and the Baltic Sea (Benner et al. 1992; Maske 1994; Malone 1994;
Cloern 1996; Harding et al. 1999; Kemp et al. 1999; Malone et al. 1999; Klinkhammer
et al. 2000).
River-induced eutrophication is a general observed phenomenon involving a number of negative consequences such as excess phytoplankton growth, increased frequency of blooms, seasonal decline of oxygen in bottom waters, and changes in the
trophic structure (Harding et al.1999). However, the severity of these problems and in
particular the fate of DOM resulting from both autochthonous and allochthonous
sources may be strongly dependent on seasonal variations of freshwater flow, the geomorphology of the receiving systems and the dominant circulation pattern.
This was clearly disclosed by a recent thorough comparison (Malone et al. 1999)
between the Chesapeake Bay (CB) and northern Adriatic (NA). Both of these systems
are dominated by a single river, the Susquehanna in CB and the Po in NA; however,
despite some similarities in terms of freshwater and nutrient loading, they exhibit significantly different trophic status. CB waters appear to be much more efficient in sequestering nutrients and retaining and recycling phytoplankton biomass than NA
waters (Harding et al. 1999); in this latter system the export of nutrients due to water
mass exchanges between the northern and middle basins, favoured by the counterclockwise circulation pattern during most of the year, and the confinement of regenerated nutrients, due to the strong vertical stratification during summer, reduce its
capacity to retain nutrients on time and scale that promote primary and secondary
productivity (Harding et al. 1999).
NA waters exhibit markedly lower average productivity levels than CB waters, although they experience large trophic gradients from coastal eutrophic to off-shore
oligotrophic waters. However, the dynamics of DOM in this basin has resulted in the
formation of a large quantity of sticky mucilaginous masses with serious problems
for tourists and fishery activities; in 1989, the damages amounted to billion of dollars
according to Italian authorities' estimations. This phenomenon is not reported for CB
waters (Malone et al. 1999), while both the CB and NA systems experiment seasonal
oxygen decline; anoxic problems are, however, much more severe in the former compared to the latter system.
There is now wide consensus that mucilaginous aggregates consist of organic and
inorganic material entrapped in a gelatinous polysaccharides matrix (Degobbis et al.
1995), although timing and evolution of mucilaginous aggregates, trigger mechanisms,
and biological species possibly involved in the formation of aggregates are still largely
unknown (Funari et al. 1999). The mean percent values and related standard deviation (±x) of organic carbon, nitrogen, phosphorus, silicon and sulphur in aggregates
collected in the summer of 1991 from surface and deep northern Adriatic waters were
24.0 ±7.2, 2.9 ±1.1, 0.26 ±0.12, 6.4 ±4.5 and 1.1 ±0.5, respectively (Pettine et al. 1995).