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The Krka River is located in the karstic region without significant anthropogenic influence, thus showing low input of nutrients and terrigenous material in the estuary (Legović et al., 1994). The 23 km long estuary is permanently vertically stratified. These features makes it an interesting and unconventional system for DOM dynamics study. In this work we present first DOM study in the Krka river estuary using UV/Vis and fluorescence spectrometry. Samples were collected at 16 locations during two contrasting periods of the year (summer and winter). Dissolved organic carbon (DOC) is exceptionally low for both seasons (35-145 µM), particulary in winter when it is lower in the river than at the open coastal location. DOC and absorbance (a254) showed nonconservative behaviour in the salinity gradient (increase in the mixing area) for both sampling periods. Regarding this and overall results DOM in the estuary can be divided into three sections with different optical characteristics ; (1) riverine DOM (2) DOM in the mixing area and (3) DOM introduced by seawater. Results also showed evident differences in DOM composition between contrasting seasons. Lower SUVA (chromophoric content) and higher spectral slope S275 (lower molecular weight and aromaticity) in summer point to the higher degree of photodegradation or/and in-situ production. PARAFAC analysis of EEMs of winter samples provided three distinct components. Microbial (C1) and terrestrial (C2) humic-like components showed conservative behaviour indicating terrestrial origin. Conversely, protein-like component (C3) showed increased intensities in the mixing area and at the halocline, clearly indicating in- situ production. References: Legović, T., Žutić, V., Gržetić, Z., Cauwet, G., Precali, R. and Viličić, D. (1994) Eutrophication in the Krka estuary. Marine chemistry, 46 (1-2), 203-215. |
