ABSTRACT
The fluorescence characteristics of dissolved organic matter (DOM) were determined in the seagrass ecosystem collected in Xincun Bay of Hainan Island in late January, 2013, using fluorescence excitation-emission matrix spectroscopy (EEMs). EEMs spectra showed 2 types of fluorescence signals in DOM samples, three hurnic-like fluorescence peaks and two protein-like fluorescence peaks, respectively. The former included UVC peak A (Ex/Em: 230/430 nm), UVA peak C (Ex/Em: 350/440 nm), and UVA peak M (Ex/Em: 300/380-400 nm), while the latter included tryptophan-like peaks R (Ex/Em: 230/355 - 375 nm) and N (Ex/Em: 280-300/365-380 nm). Peak N was more like a combination of Peak M and Peak R. Moreover, free tyrosine-like molecules in DOM from the seagrass-beds ecosystem did not exist because the tyrosine-like fluorescence was not found. There were significant positive correlations of peak N with M and R (0. 97 and 0. 54 for R2, respectively), and peak A with C (0. 86 for R2), showing their same sources and biogeochemical behaviors. The change law of mean fluorescence intensities of those fluorescence signals was R (0. 304 RU) >A (0. 194 RU) >M (0. 147 RU) >N (0. 125 RU) >C (0. 051 RU). And, higher . L-1 concentrations of all the fluorescence occurred in the coastal waters inshore, with low values in two small regions located in the southwest and southeast of the bay where the seagrasses flourished. The distributions of those fluorescence signals in Xincun Bay suggested that the dynamics responsible for the humic-like fluorescence might be the same as that responsible for the protein-like fluorescence. The high fluorescence index (FI: 1. 81), high biological index (BIX: 1. 44) and low humification index (HIXa: 4. 2 and HIXb: 0. 81) showed that the DOM from the seagrass-dominant ecosystem has a strong autochthonous contribution and poor humification degree. The results clearly suggested that the DOM in this region has a rather unique fluorescence characteristic and is quite different from other aquatic environments.
