Nature and sedimentation of suspended particulate matter during density stratification in shallow coastal waters (Gulf of Trieste, northern Adriatic)

Suspended particulate matter in the Gulf of Trieste (northern Adriatic) during seawater density stratification in summertime consists of about 500 total hydrolyzable carbohydrates, 2 % proteins and 1.0 "10 lipids. The bulk of particulate organic matter (POh4) remains uncharacterized and is probably composed mainly of terrigenous refractory material, evidenced by more negative total POM b13C values (ca -24.5%.) and a somewhat higher C/N atomic ratio (6.5). The composition of diatomaceous macroaggregations observed in the whole northern Adriatic in the summers of 1988 and 1989 (containing 12 to 34 '10 total hydrolyzable carbohydrates, 0.3 to 1.4 proteins, ca 0.08''tt lipids, and a high C/N ratio) differed from that of summer POh4. The predominance of glucose (ca 60 "C, of total hydrolyzable carbohydrates), and bI3C values typical of cultured diatoms (-17 to -19:';rm), suggested that the bulk of macroaggregate organic matter was composed of algal structurdl products, possibly glucans Amino acid composition was dominated by glycine, aspartic acid, alanine and gluta~nic acid and was similar to common summer POM. Sedimented POM, measured by moored sediment tldps, was depleted of proteins and water-soluble carbohydrates by 80 to 85 'L and of lipids by 74 O/O with respect to summer POM composition. Rapid sedimentation of macroaggregates in mid-August 1989 scavenged the POM from the water column during disruption of density stratification. Sedimentation was reflected in higher total sedimented organic matter (ca 25 ":#) but lower protein, water-soluble carbohydrate and l i p ~d contents.