Abiotic Aggregation of Organic Matter in Coastal and Estuarine Waters: Cases in the Eastern Long Island Sound, USA

Organic aggregates, which formed from small particles and dissolved material, were chemically characterized in the Long Island Sound coastal waters. In this study, six aggregation experiments were conducted on low-salinity samples (the Thames River, CT, USA; salinity of 6.3–6.8) and high-salinity samples (the coast of Avery Point, CT, USA; salinity of 21.4–26.7). Water samples were incubated on a roller table for two days under dark conditions to generate laboratory-made aggregates. Particulate organic carbon (POC) concentrations increased 5–39% after two days of rolling. A higher POC increase occurred in low-salinity samples. The concentrations of neutral aldoses and amino acids, as well as their C- and N-yields, decreased during the experiments (except for particulate hydrolysable amino acid in low-salinity samples), while bacterial abundance increased 50–476%, indicating microbial degradation of biologically labile organic matter. Particulate hydrolysable amino acid was preferentially preserved in P-limited systems. An enrichment factor analysis showed the preferential microbial degradation of particulate hydrolysable neutral aldose and glucose appeared as the most labile aldose. The increase in bulk POC and the decrease in the fraction of labile organic carbon (neutral aldose and amino acid) in the particulate phase resulted in an accumulation of uncharacterized (presumably more refractory) particulate organic matter.