CHAPTER 22 • Organic Matter Sources and Dynamics in Adriatic Coastal Waters
471
The scarce information available on the distribution and variability of dissolved
organic matter and its important components in the northern Adriatic is one of the
restrictions on the understanding of the mucilage occurrences.
In an attempt to improve our knowledge on sources, concentrations and variability of organic matter in coastal waters, we have determined organic matter loads discharged by the Po River in the dissolved and particulate phases, and the concentrations of dissolved (DOC) and colloidal (COC) organic carbon, together with those of
total dissolved carbohydrates (TDCHO), free (DFAA) and total dissolved (TDAA) amino
acids in two frontal regions of the northern Adriatic system (see Fig. 22.2). Polymeric
organic compounds that are included in the colloidal fraction and in the TDCHO and
TDAA variables are of particular interest in northern Adriatic waters for their involvement in the formation of micro- and macro aggregates.
This paper summarizes the results obtained in previous investigations (Pettine et al.
1998, 1999, 2001) highlighting an interannual variability in seasonal changes of DOC
concentrations, which is strongly dependent on the hydrological regime of the Po River.
Experimental findings also point out contrasting behaviours of mucilage and seasonal
changes in DOC, COC and TDCHO concentrations, which strengthen the importance
of the qualitative character of DOM, rather than its quantitative concentrations in triggering the formation of large mucilaginous aggregates.
22.2
Analytical Methodologies
Dissolved Organic Carbon. Samples were filtered through precombusted (4 hours at
480°C) and preweighed Whatman GF/F glass fibre filters (0.7Ilm nominal pore size).
For freshwater samples, filtration was performed in a laboratory within a few hours
from collection: in this case about 1 I samples were filtered under negative pressure
and the filters, washed with 20 ml milli Q water, were stored at -20°C for the analysis
of Poe. Filtered freshwater samples for DOC analysis were stored in high density polyethylene (HDPE) bottles as in the case of filtered sea water samples (see after) while
the filtration procedure was different. For sea water samples, the filtration was performed aboard, and we were not interested in the analysis of POC: about 100 ml were
filtered in this case by using a disposable polycarbonate syringe and a polypropylene
filter holder (Nucleopore). Filtered samples were stored in duplicate into 25 ml HDPEbottles (previously treated with HN0 3 1.2 M at 50°C for 1 h), which were quickly frozen in an aluminum block at -20°C. The suitability of HDPE containers for the storage of DOC samples was proved by recent findings (Norrman 1993; Tupas et al. 1994;
Yoro et al. 1999), and confirmed by our preliminary tests. For DOC analysis, filtered
samples were thawed in the laboratory, acidified to pH 2 with ultrapure HCI and purged
with Nz for about 10 minutes to remove inorganic carbon. Dissolved organic carbon
(DOC) was assayed by high temperature catalytic oxidation (HTCO) and infrared detection using a Shimadzu TOC-5000 A analyser. Carbon concentrations were determined against potassium hydrogen phthalate standards after correction for total blank.
This value, which is the analytical system blank plus a Milli Q water blank, was approximately 10-15 IlM C under our experimental conditions and was mostly due to the
471
The scarce information available on the distribution and variability of dissolved
organic matter and its important components in the northern Adriatic is one of the
restrictions on the understanding of the mucilage occurrences.
In an attempt to improve our knowledge on sources, concentrations and variability of organic matter in coastal waters, we have determined organic matter loads discharged by the Po River in the dissolved and particulate phases, and the concentrations of dissolved (DOC) and colloidal (COC) organic carbon, together with those of
total dissolved carbohydrates (TDCHO), free (DFAA) and total dissolved (TDAA) amino
acids in two frontal regions of the northern Adriatic system (see Fig. 22.2). Polymeric
organic compounds that are included in the colloidal fraction and in the TDCHO and
TDAA variables are of particular interest in northern Adriatic waters for their involvement in the formation of micro- and macro aggregates.
This paper summarizes the results obtained in previous investigations (Pettine et al.
1998, 1999, 2001) highlighting an interannual variability in seasonal changes of DOC
concentrations, which is strongly dependent on the hydrological regime of the Po River.
Experimental findings also point out contrasting behaviours of mucilage and seasonal
changes in DOC, COC and TDCHO concentrations, which strengthen the importance
of the qualitative character of DOM, rather than its quantitative concentrations in triggering the formation of large mucilaginous aggregates.
22.2
Analytical Methodologies
Dissolved Organic Carbon. Samples were filtered through precombusted (4 hours at
480°C) and preweighed Whatman GF/F glass fibre filters (0.7Ilm nominal pore size).
For freshwater samples, filtration was performed in a laboratory within a few hours
from collection: in this case about 1 I samples were filtered under negative pressure
and the filters, washed with 20 ml milli Q water, were stored at -20°C for the analysis
of Poe. Filtered freshwater samples for DOC analysis were stored in high density polyethylene (HDPE) bottles as in the case of filtered sea water samples (see after) while
the filtration procedure was different. For sea water samples, the filtration was performed aboard, and we were not interested in the analysis of POC: about 100 ml were
filtered in this case by using a disposable polycarbonate syringe and a polypropylene
filter holder (Nucleopore). Filtered samples were stored in duplicate into 25 ml HDPEbottles (previously treated with HN0 3 1.2 M at 50°C for 1 h), which were quickly frozen in an aluminum block at -20°C. The suitability of HDPE containers for the storage of DOC samples was proved by recent findings (Norrman 1993; Tupas et al. 1994;
Yoro et al. 1999), and confirmed by our preliminary tests. For DOC analysis, filtered
samples were thawed in the laboratory, acidified to pH 2 with ultrapure HCI and purged
with Nz for about 10 minutes to remove inorganic carbon. Dissolved organic carbon
(DOC) was assayed by high temperature catalytic oxidation (HTCO) and infrared detection using a Shimadzu TOC-5000 A analyser. Carbon concentrations were determined against potassium hydrogen phthalate standards after correction for total blank.
This value, which is the analytical system blank plus a Milli Q water blank, was approximately 10-15 IlM C under our experimental conditions and was mostly due to the