Composition and characterization of colloidal organic matter in the coastal surface waters of Qingdao, China

The composition and characterization of dissolved organic matter (DOM) and colloid organic matter (COM) in the coastal surface waters of Qingdao, China were examined. Water samples were collected in Spring 2008 from the Jiaozhou Bay and its adjacent area and fractionated into total dissolved (< 0.45 μm), colloidal (10 kDa–0.45 μm) and cutoff (< 10 kDa) fractions with the cross-flow ultrafiltration (CFF) system. The excitation–emission-matrix (EEM) spectral properties, the absorbance values at 254 nm (A254) and dissolved organic carbon (DOC) of the DOM were observed having the colloidal ratios of 8.7%, 6.2%, and 2.2%, respectively, and exhibiting a decreasing trend. Total dissolved carbohydrates (TCHO) and total hydrolysable amino acids (THAA) comprised 24% of the bulk DOC. Among them, the free monosaccharides (MCHO) and dissolved combined amino acids (DCAA）were the major fractions, followed by polysaccharides (PCHO) and dissolved free amino acids (DFAA). Colloidal TCHO and THAA concentrations were 3.2 µM C and 0.3 µM, respectively. They comprised ∼ 35% of the colloid organic carbon (COC), among which PCHO and DCAA were the dominating fractions. The dissolved carbohydrates and amino acids are mostly concentrated in the cutoff fraction. The A254 values and DOC concentrations inside the Jiaozhou Bay were apparently higher than those outside, while pH and salinity were slightly lower, which might be due to the influence of terrestrial input and the semi-enclosed bay. The distribution pattern of TCHO was found having basically the same as the distributions of A254 and DOC.