Fluorescence characterization of daily and intertidal changes in estuarine water DOM related to the presence of Sarcocornia perennis (L.) A.J. Scott

The influence of the colonization of salt marsh sediments with Sarcocornia perennis on the DOM quantity and its nature in the water column was evaluated by way of UV–visible and molecular fluorescence spectroscopy. Different light conditions occur along the night and the day periods, while, in parallel, flooding conditions vary along consecutive tidal cycles. Thus, a 24 hour field assessment was carried out in order to encompass the daily (day/night) and intertidal (high/low tide) variations. The E2:E3 ratio and spectral slope (S) from UV–visible spectra pointed to an export of compounds of high molecular weight (MW) to surface waters during the tidal ebbing at the colonized site. Furthermore, three main types of fluorescent compounds were found in the water synchronous fluorescence spectra: one corresponding to protein-like compounds and two to humic-like compounds. Fluorescence intensity increased during tidal ebbing, both during the day and during the night and especially for water from the colonized site. However, major increases occurred for the protein-like fluorescence band at the S. perennis colonized site during the nocturnal tide ebbing, which may be related to the activity of plants at the rhizosphere.