Spatiotemporal variation of dissolved carbohydrates and amino acids in Jiaozhou Bay, China

Abstract

Surface seawater samples were collected from Jiaozhou Bay, China, during six cruises (March–May 2010, September–November 2010) to study the distribution of dissolved organic matter including dissolved organic carbon (DOC), total dissolved carbohydrates, namely monosaccharides (MCHO) and polysaccharides (PCHO) and total hydrolysable amino acids. These included dissolved free amino acids (DFAA) and combined amino acids (DCAA). The goal was to investigate possible relationships between these dissolved organic compounds and environmental parameters. During spring, the concentrations of MCHO and PCHO were 9.6 (2.8−22.6) and 11.0 (2.9−42.5) μmol C/L, respectively. In autumn, MCHO and PCHO were 9.1 (2.6−27.0) and 10.8 (2.4−25.6) μmol C/L, respectively. The spring concentrations of DFAA and DCAA were 1.7 (1.1−4.1) and 7.6 (1.1−31.0) μmol C/L, respectively, while in autumn, DFAA and DCAA were 2.3 (1.1−8.0) and 3.3 (0.6−7.2) μmol C/L, respectively. Among these compounds, the concentrations of PCHO were the highest, accounting for nearly a quarter of the DOC, followed by MCHO, DCAA and DFAA. The concentrations of the organic compounds exhibited a decreasing trend from the coastal to the central regions of the bay. A negative correlation between concentrations of DOC and salinity in each cruise suggested that riverine inputs around the bay have an important impact on the distribution of DOC in the surface water. A significant positive correlation was found between DOC and total bacteria count in spring and autumn, suggesting bacteria play an important role in the marine carbon cycle.