Changes of organic matter composition in surface sediments from the Pearl River estuary to the coastal South China Sea revealed by rapid molecular screening using FTICR-MS.

Molecular composition of surface sediments reflects a shift in the nature of organic matter along the land-sea transect in the Pearl River estuary and coastal South China Sea. [Display omitted] • Comprehensive molecular screening of organic matter in surface sediment from land to sea. • Freshwater site is characterized by hydrocarbon and sulfur-containing compound classes. • Marine site shows molecular indicators of phototroph sourced biomass. • FTICR-MS rapidly characterized dynamic changes of organic matter along environmental gradients. The Pearl River drains the second largest watershed in China, funnelling large amounts of freshwater and organic matter into the northern part of the South China Sea through an estuary characterized by pronounced biogeochemical gradients. In this study we used a newly developed single injection Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) method to analyze organic extracts of surface sediments transitioning from freshwater to marine settings in the Pearl River estuary and coastal South China Sea. Results show a complex mixture of molecular markers, with distinct fingerprints characterizing the freshwater and saline sites. Notable examples include steroidal and thiophenic species at the freshwater site, indicative of possible anthropogenic organic matter inputs from the continent; on the other hand, samples from the coastal site are uniquely characterized by putative tetrapyrrole species, indicative of phaeopigments sourced from marine phytoplankton. This study demonstrates the potential application of single injection FTICR-MS in rapidly probing the dynamic changes of organic matter sources and fates occurring in estuaries influenced by anthropogenic activities. [ABSTRACT FROM AUTHOR]