| Dissolved organic matter (DOM) exists widely in the ocean with considerableamount. It is known that a variety of sources may contribute to the DOM pool, butonly a small part can be identified. Fluorescent dissolved organic matter (FDOM),which is the fraction of DOM that release fluorescence after absorbing light atspecific wavelengths, has been widely studied in the past20years owing toexcitation-emission property. Different fluorescent components of FDOM correspondto different protein-like and humic-like substances. Thus, the EEMs-PARAFACmethod was established to provide specific details of fluorescent components withoutdestroying the structure and concentration of DOM. Due to its simplicity and highsensitivity, this method is now frequently adopted in studies on marine DOM.Using EEMs-PARAFAC, the fluorescent characteristics of DOM in the JiaozhouBay and during the degradation of jellyfish were studied. The short-term variation offluorescent characteristics of DOM was studied through high-frequency fieldsampling in summer of2011whereas the annual pattern was demonstrated by monthlyinvestigation during October2011and September2012. Fluorescent characteristics ofDOM released during decomposing process of three common jellyfish (Aurelia aurita,Cyanea nozakii and Nemopilema nomurai) were studied by laboratory incubation.Three main findings are listed as follow:(1) In summer of2011, four fluorescent components of DOM were identified byEEMs-PARAFAC, including protein-like component C1, terrestrial humic-likecomponent C2and C4, and marine humic-like component C3. The fluorescentintensity of four components was higher in late August and early September than in late September. The intensity of fluorescent components correlated significantly andpositively with chlorophyll a concentration, but negatively with salinity. It wasindicated that the concentration of FDOM in Jiaozhou Bay was determined mainly byincreased biological activities induced by rainfall.(2) Similar fluorescent components were recognized on annual scale, i.e. C1(280,235/330), C2(310,245/410), C3(265,360/455) and C4(305/495). Thefluorescent intensity of both protein-like and humic-like components weresignificantly higher in autumn and summer than in winter and spring, and in eachseason they decreased from the north to the south of Bay.(3) During the decomposing process of three giant jellyfish species, DOconcentration and pH decreased significantly with incubation duration. No significantdifference was observed on DO concentration and pH among various jellyfish species,but significant difference was documented among incubations with different jellyfishbiomass. During the incubation, the intensity of protein-like fluorescent componentincreased in2-8days, and decreased thereafter. The intensity of humic-likefluorescent components increased slowly at the start, but it kept increasing throughoutthe incubation. It shows that more protein-like substances were released during theearly stage of decomposing process, and decomposition of jellyfish may alsocontribute to humic-like fluorescence DOM, most possibly through bio-degradation.By EEMs-PARAFAC, both short-term and annual variation of fluorescentcharacteristics of DOM in Jiaozhou Bay was demonstrated in this study. HigherFDOM concentration was expected in the rainy season in associated with terrestrialinputs. Protein-like and humic-like substances were released in turn during thedecomposing process of jellyfish. However, their contribution to the in situ FDOM... |
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