Assessing the dynamics of dissolved organic matter (DOM) in coastal environments by excitation emission matrix fluorescence and parallel factor analysis (EEM-PARAFAC)

The distributions of fluorescent components in dissolved organic matter (DOM) from Ise Bay, Japan, were determined by excitation emission matrix (EEM) fluorescence spectroscopy combined with parallel factor analysis (PARAFAC). Three terrestrial humic-like, one marine humic-like, and three non–humic-like fluorescent components were identified by PARAFAC, and the environmental dynamics of individual fluorescent components in the bay area were evaluated. The observed linear relationships between salinity and abundance of two of the three humic-like components in the bay area indicate a terrestrial origin and conservative mixing behavior of these components. On the other hand, nonconservative mixing for the other terrestrial and the marine humic-like components was observed, indicating that the sources of these were other than solely riverine inputs. Thus, in addition to riverine sources, this terrestrial humic-like component may receive inputs from biogeochemical reworking of terrestrial DOM and/or particulate organic matter, while the most likely sources for the marine humic-like component are estuarine biological activity and/or microbial reworking of plankton-derived DOM. From the spatial distributions in the bay area as well as their relationships with salinity, two of the non–humic-like components were suggested to be of autochthonous estuarine origin and likely represent biologically labile components. Microbial degradation processes were suggested to be important factors driving the dynamics of another non–humic-like component. This study exemplifies the potential applicability of EEM-PARAFAC in studies of fluorescent DOM dynamics in estuaries. Dissolved organic matter (DOM) is a major form of organic matter in aquatic environments and plays an important role in the global carbon cycle. In coastal environments, substantial terrestrial DOM inputs through river discharges are estimated to contribute 0.25 3 1015 g carbon (C) yr21 to the ocean carbon pool (Hedges et al. 1997). Together with the terrestrial DOM, rivers convey inorganic nutrients, which can result in intense primary productivity, and 30% of primary production in the world oceans is evident in coastal environments (Lalli and Parsons 1997). Such primary production leads to the production of autochthonous DOM. Thus, the dynamics of DOM in coastal environments can be complex, and the fate of terrestrial DOM and the production and degradation of autochthonous DOM need to be assessed separately 1 Corresponding author ([email protected]).