Characterization of Biologically Produced Colored Dissolved Organic Matter in Seawater

摘要

Chromophoric, or colored dissolved organic maller (CDOM), influences the structure of aquatic ecosystems, complicates satellite measurements of ocean productivity, and affects the bioavailability and fate of important trace organic and metal species in seawater. The goals of this project were to chemically characterize biologically produced CDOM components, to characterize CDOM in laboratory algal cultures, and to develop techniques for studying CDOM cycling in seawater. Specifically, we compared the chemical characteristics of freshwater and marine CDOM in the Mississippi River estuary and Gulf of Mexico, characterized CDOM at two open ocean sites (N. Pacific Ocean, Sargasso Sea) and compared CDOM components with CDOM produced by laboratory cultures of marine algae. CDOM was collected by adsorption onto C18 resin from acidified seawater. From this fraction we identified 2,4-dichlorobenzoic acid (2,4-DCBA) and a series of tetrachloro-biphenyl aromatic acids (TCBCAs) that are structurally related to POBs as major components. Structures were determined using proton NMR, gas chromatographylmass spectrometry, and HPLC analyses by co-injection with authentic compounds. High concentrations of chlorinated aromatic acids were found in all seawater samples, but were not found in samples of Mississippi River water. The biological production of 2,4-DCBA and TCBCAs was confirmed by their production in laboratory cultures of the marine algae Emlliana huxleyi and Isochrysis galbana. Spent culture media from these two algae contained up to 500 mug/L 2,4-DCBA and 12 mug/L TCBCAs.