Chapter 22
Organic Matter Sources and Dynamics in northern
Adriatic Coastal Waters
M. Pettine . L. Patrolecco . S. Capri
22.1
Introduction
Organic matter in marine environments results from both autochthonous and
allochthonous sources. Phytoplanktonic production is responsible for the internal
production of organic matter, which according to dominant biological processes, distributes between the particulate and dissolved phases. Photosynthetic activity transforms, in the presence of inorganic nutrients and light, inorganic carbon into particulate organic matter (POM), of which more than 30% consists of carbon (POC) according to the Redfield stoichiometry and its revisitation by Morel and Hudson (1985).
During photosynthetic processes, a variable percentage of photosynthates is released
in the surrounding water as dissolved substances (DOM), consisting of monomeric
and low molecular weight polymeric compounds. Other than being directly released
by phytoplankton, DOM may be indirectly produced through sloppy feeding (i.e. the
release of dissolved compounds following the breaking of large preyed cells that cannot be ingested whole by the zooplankton), dissolution of faecal pellets and marine
snow, and virus-induced bacteria cell lysis.
Dissolved organic carbon (DOC) is by far the major carbon pool in oceans, outweighing any other marine source of organic carbon by at least a factor of 10 (Kepkay
1994). Furthermore, although algal biomass in oceans is only 0.2% of that of terrestrial plants, annual phytoplankton photosynthesis is roughly equivalent to that of
plants, since algae have duplication rates on the order of days compared to month to
years for plants (Chisholm 1992). Therefore, the fate of carbon in oceans not only influences the trophic food chain but also affects the exchange of carbon at the sea water-atmosphere interface.
In addition to the autochthonous sources, external inputs may further supply organic matter for marine ecosystems. On a world scale, terrestrial sources contribute
about 10% to the total sea water DOM, while on a local scale their contribution may be
much more important. Riverine inputs either directly discharge organic matter into
sea water or indirectly provide new organic matter through the discharge of nutrients
that feed primary production.
External inputs have markedly increased the productivity of the shallow and small
northern Adriatic over the oligotrophic features of the Mediterranean. External annual contributions of nutrients in this basin have been estimated to be of the same
order of magnitude as the regeneration rate, thus giving similar contributions to primary production from new and regenerated material (Degobbis and Gilmartin 1990).
This evaluation strengthens the vulnerability of the northern Adriatic to external inputs and therefore to water management of rivers that discharge into this basin. An-
Organic Matter Sources and Dynamics in northern
Adriatic Coastal Waters
M. Pettine . L. Patrolecco . S. Capri
22.1
Introduction
Organic matter in marine environments results from both autochthonous and
allochthonous sources. Phytoplanktonic production is responsible for the internal
production of organic matter, which according to dominant biological processes, distributes between the particulate and dissolved phases. Photosynthetic activity transforms, in the presence of inorganic nutrients and light, inorganic carbon into particulate organic matter (POM), of which more than 30% consists of carbon (POC) according to the Redfield stoichiometry and its revisitation by Morel and Hudson (1985).
During photosynthetic processes, a variable percentage of photosynthates is released
in the surrounding water as dissolved substances (DOM), consisting of monomeric
and low molecular weight polymeric compounds. Other than being directly released
by phytoplankton, DOM may be indirectly produced through sloppy feeding (i.e. the
release of dissolved compounds following the breaking of large preyed cells that cannot be ingested whole by the zooplankton), dissolution of faecal pellets and marine
snow, and virus-induced bacteria cell lysis.
Dissolved organic carbon (DOC) is by far the major carbon pool in oceans, outweighing any other marine source of organic carbon by at least a factor of 10 (Kepkay
1994). Furthermore, although algal biomass in oceans is only 0.2% of that of terrestrial plants, annual phytoplankton photosynthesis is roughly equivalent to that of
plants, since algae have duplication rates on the order of days compared to month to
years for plants (Chisholm 1992). Therefore, the fate of carbon in oceans not only influences the trophic food chain but also affects the exchange of carbon at the sea water-atmosphere interface.
In addition to the autochthonous sources, external inputs may further supply organic matter for marine ecosystems. On a world scale, terrestrial sources contribute
about 10% to the total sea water DOM, while on a local scale their contribution may be
much more important. Riverine inputs either directly discharge organic matter into
sea water or indirectly provide new organic matter through the discharge of nutrients
that feed primary production.
External inputs have markedly increased the productivity of the shallow and small
northern Adriatic over the oligotrophic features of the Mediterranean. External annual contributions of nutrients in this basin have been estimated to be of the same
order of magnitude as the regeneration rate, thus giving similar contributions to primary production from new and regenerated material (Degobbis and Gilmartin 1990).
This evaluation strengthens the vulnerability of the northern Adriatic to external inputs and therefore to water management of rivers that discharge into this basin. An-