| Estuarine systems, with their high rates of primary production and their potential for significant transformation and transport of carbon, are critical regions which must be understood in order to complete large-scale studies of global carbon cycling. Estuarine high molecular weight dissolved organic matter (HMWDOM), with its high reactivity and chemical complexity, plays a key role in carbon cycling within these dynamic systems. The characterization of this class of material, from estuary-wide scale to molecular scale, is the central focus of this study. An estuary-wide characterization of dissolved organic carbon (DOC) and chromophoric dissolved organic matter (CDOM) fluorescence in the Pearl River Estuary, China, highlights the importance of terrestrial source characterization in estuarine studies. Molecular level analysis of high molecular weight dissolved organic matter (HMWDOM) collected in five US estuaries combines the analyses of CDOM fluorescence of humic substances (H) with protein fluorescence (P) to yield a potentially useful parameter for characterizing anthropogenic impact within estuaries. This parameter, termed H/P, is used in this study for the first time, and shows promise as a useful tool for DOM characterization in a wide variety of estuarine systems. Fluorescence data is further analyzed with other measures of terrestrial influence, including C/N ratios and carbon isotope analyses, in order to compare samples within and among estuaries. Molecular level characterization of total HMWDOM and the corresponding acid insoluble fractions of HMWDOM, using pyrolysis-mass spectroscopy, provides a more detailed view of the differences between organic compound classes. This technique allows for the study of formation pathways of not only total HMWDOM but also its individual constituents. Isotopic composition data in conjunction with pyrolysis-mass spectrometry results provides evidence for a bacterial formation pathway of key refractory constituents of HMWDOM. |
