Distribution Characteristics of Chromophoric Dissolved Organic Matter and Nutrients from the Yellow Sea and Bohai Sea in Autumn

Abstract

Water samples were collected from the Yellow and Bohai seas during November 2013 and the chromophoric dissolved organic matter (CDOM) and nutrients concentrations were investigated, including their composition, source and distribution characteristics. CDOM was analyzed by excitation-emission matrix spectroscopy (EEMS) in combination with a parallel factor analysis (PARAFAC). Three terrestrial humic-like substances (C1, C2, and C3) and one protein-like (C4) substances were identified. The three terrestrial humic-like components had a similar horizontal distribution, decreasing from inshore to offshore. The protein-like component, showed higher values for both inshore and offshore areas in the Yellow Sea at the surface layer and the middle layer of the Bohai Sea, while in other layers it had a similar distribution pattern as the terrestrial humic-like components. In the Bohai Sea, the dissolved inorganic nitrogen (DIN) concentration showed a decreasing trend from inshore to offshore areas and the concentration of dissolved inorganic phosphorus (DIP) gradually decreased from the Caofeidian coastal and central areas to other adjacent areas. The dissolved organic nitrogen (DON) showed an increasing from inshore to the central area of the Bohai Sea. DIN and DON were higher in surface layer than in the bottom layer and for DIP this was the opposite in the Bohai Sea. In the Yellow Sea, DON concentrations showed a decreasing trend from inshore to offshore areas. DIN and DIP had higher concentrations at inshore areas in the surface and middle layers, while in the bottom layer they had higher concentrations in offshore areas. The vertical distribution of the DIN and DIP showed higher values in the bottom layer than surface layers and for DON this was the opposite. These results also showed that the concentrations of DIN, DON, and DIP in the Bohai sea were overall higher than the Yellow Sea. A discriminant analysis was performed through redundancy analysis (RAD) of these water quality parameters, including the four fluorescent components, an absorption coefficient (a355), chlorophyll a concentration, conductivity, dissolved oxygen (DO), dissolved organic carbon (DOC), DIN, DON, and DIP. The RDA indicated that the four fluorescent components are mainly affected by terrestrial inputs. DOC was affected by both terrestrial and marine sources but terrestrial inputs were the major contributor. It was also indicated that the DIN concentration was affected by terrestrial inputs in the Bohai Sea area and by both terrestrial and marine sources in the Yellow Sea. DON concentrations were mainly affected by marine sources in the Bohai Sea and terrestrial inputs in the Yellow Sea. DIP concentrations were affected by both terrestrial and marine sources in the studied areas.