The dynamics of fluorescent dissolved organic matter in the Paranaguá estuarine system, Southern Brazil

Abstract

The aim of this study was to investigate the dynamics of the fluorescent dissolved organic matter (FDOM) in Paranaguá Estuarine System (PES) as to infer about the contribution of allochthonous FDOM to the estuarine waters in relation to tidal condition and seasons. Fluorescence spectroscopy was used for such purpose and DOM characterization through fluorescence emission was performed using excitation wavelengths of λex 350 nm and λex 450 nm, the two main fluorescence groups known to be present in natural DOM. Relations between emission wavelength (λem) and environmental variables, and the relevance of these variables to the different tides and seasons were identified by principal component analysis. The results showed that the first class of fluorophores (λex 350 nm) changed from the river (freshwater) towards the estuary, whilst the second class (λex 450 nm) has a more conservative nature and does not change as significantly as the first. Allochthonous DOM contribution to the estuarine system is intensified during the rainy season, especially in spring tides, whereas in the dry season the ratio of autochthonous DOM to total DOM in PES waters increased. We concluded that the variation of maximum λem of the first class of fluorophores (λex 350 nm) is mainly related to allochthonous contribution, whilst the maximum of emission for the second class of fluorophores (λex 450 nm) is dependent on the contribution of the different sources of organic matter (freshwater and marine water DOM contribution).