CHAPTER 22 • Organic Matter Sources and Dynamics in Adriatic Coastal Waters
475
nomenon consisting of massive occurrences of mucilaginous aggregates. In 1989, these
aggregates covered a large part of the entire surface of the NA basin (Stachowitsch
et al. 1990) and drew the attention of public and scientific opinion. Large quantities of
sticky mucilaginous masses affected biological, chemical and physical characteristics
of the ecosystem (Degobbis et al.1999). Part of the material floating on the sea surface
was deported on beaches by wind and currents, reducing their suitability for bathing
and threatening tourism. Suspended and sinking mucilaginous aggregates created
serious problems for fisheries and biota. Benthic organisms suffered in many areas
from suffocation due to their covering by aggregates.
The impressive mucilage events of 1989-91 stimulated many studies aimed at understanding the possible causes responsible for this phenomenon and its triggering
mechanisms; however, in spite of these efforts, this phenomenon remains substantially
unknown (Funari et al. 1999). Although it was reported that episodes of massive mucilage formation have been recorded for over a century (Fonda-Umani et al.1988), the
similarities between past and recent phenomena in terms of triggering factors and
spatial extensions remain in doubt.
We speculated on the strict temporal parallelism between massive aggregate occurrences and changes in the formulation of detergents (Pettine et al. 1995). In 1988,
in fact, phosphorus was banned from domestic detergents and substituted by zeolite
A particles and about doubled polycarboxylate concentrations. These changes have
further increased the NIP ratio in coastal waters, which was already unbalanced, and
probably they were responsible for the shift in the phytoplankton population from
dinoflagellate to diatom blooms recently reported (Degobbis et al. 1999).
Therefore, P-substitutes, while contributing to diminish the frequency and extension of anoxia in NA coastal waters, apparently cause an external forcing on biological and chemical processes, which could favour an intensification of macroaggregate
occurrences. Possible effects may be on a large scale (changes in algal succession from
dinoflagellate to diatoms and on their released chemical compounds; limitation of the
bacterial activity due to further increase in NIP ratio and consequently increased residence time for DOM) as well as on a micro scale (changes in sorption, partitioning
and gelling of polymers, due to the inclusion in colloidal matter of zeolite A particles
and polycarboxylates).
22.4
Organic Matter Discharged by the Po River
Concentrations of dissolved and particulate organic carbon (DOC, POC) were measured in samples taken monthly for a year at two stations in the lower Po River
(Figs. 22.2 and 22.3). Samples were collected at each station at two depths (about 0.5 m
from surface and 2 m above the bottom) to evaluate possible variations in the water
column that may affect the transport. Two major interrelated variables, solid transport and flow conditions, influenced the variability of organic matter concentrations
in the water and solid phases, while the water column was reasonably homogeneous
(Pettine et al. 1998).
Mass fluxes of DOC and POC to the northern Adriatic basin were calculated by four
different methods. They were based on: (a) the mean of products of the instantaneous
concentrations and the mean daily discharge of the sampling day; (b) the product of
475
nomenon consisting of massive occurrences of mucilaginous aggregates. In 1989, these
aggregates covered a large part of the entire surface of the NA basin (Stachowitsch
et al. 1990) and drew the attention of public and scientific opinion. Large quantities of
sticky mucilaginous masses affected biological, chemical and physical characteristics
of the ecosystem (Degobbis et al.1999). Part of the material floating on the sea surface
was deported on beaches by wind and currents, reducing their suitability for bathing
and threatening tourism. Suspended and sinking mucilaginous aggregates created
serious problems for fisheries and biota. Benthic organisms suffered in many areas
from suffocation due to their covering by aggregates.
The impressive mucilage events of 1989-91 stimulated many studies aimed at understanding the possible causes responsible for this phenomenon and its triggering
mechanisms; however, in spite of these efforts, this phenomenon remains substantially
unknown (Funari et al. 1999). Although it was reported that episodes of massive mucilage formation have been recorded for over a century (Fonda-Umani et al.1988), the
similarities between past and recent phenomena in terms of triggering factors and
spatial extensions remain in doubt.
We speculated on the strict temporal parallelism between massive aggregate occurrences and changes in the formulation of detergents (Pettine et al. 1995). In 1988,
in fact, phosphorus was banned from domestic detergents and substituted by zeolite
A particles and about doubled polycarboxylate concentrations. These changes have
further increased the NIP ratio in coastal waters, which was already unbalanced, and
probably they were responsible for the shift in the phytoplankton population from
dinoflagellate to diatom blooms recently reported (Degobbis et al. 1999).
Therefore, P-substitutes, while contributing to diminish the frequency and extension of anoxia in NA coastal waters, apparently cause an external forcing on biological and chemical processes, which could favour an intensification of macroaggregate
occurrences. Possible effects may be on a large scale (changes in algal succession from
dinoflagellate to diatoms and on their released chemical compounds; limitation of the
bacterial activity due to further increase in NIP ratio and consequently increased residence time for DOM) as well as on a micro scale (changes in sorption, partitioning
and gelling of polymers, due to the inclusion in colloidal matter of zeolite A particles
and polycarboxylates).
22.4
Organic Matter Discharged by the Po River
Concentrations of dissolved and particulate organic carbon (DOC, POC) were measured in samples taken monthly for a year at two stations in the lower Po River
(Figs. 22.2 and 22.3). Samples were collected at each station at two depths (about 0.5 m
from surface and 2 m above the bottom) to evaluate possible variations in the water
column that may affect the transport. Two major interrelated variables, solid transport and flow conditions, influenced the variability of organic matter concentrations
in the water and solid phases, while the water column was reasonably homogeneous
(Pettine et al. 1998).
Mass fluxes of DOC and POC to the northern Adriatic basin were calculated by four
different methods. They were based on: (a) the mean of products of the instantaneous
concentrations and the mean daily discharge of the sampling day; (b) the product of