Characterization of dissolved organic matter in a coral reef ecosystem subjected to anthropogenic pressures (La Réunion Island, Indian Ocean) using multi-dimensional fluorescence spectroscopy Marc Tedetti a, ⁎, Pascale Cuet b , Catherine Guigue a , Madeleine Goutx a a Laboratoire de Microbiologie Géochimie et Ecologie Marines (LMGEM), Centre d'Océanologie de Marseille, Université de la Méditerranée, CNRS, INSU; Case 901, 13288 Marseille Cedex 9, France b Laboratoire d'Ecologie Marine (ECOMAR), BP 7151, Université de La Réunion, 15, avenue René-Cassin, 97715 Saint-Denis Messag Cedex 9, La Réunion, France abstract article info Article history: Received 14 October 2010 Received in revised form 24 January 2011 Accepted 30 January 2011 Keywords: Fluorescent dissolved organic matter EEM spectrofluorometry Coral reef ecosystem La Réunion Island Groundwater Anthropogenic pressure La Saline fringing reef is the most important coral reef complex of La Réunion Island (southwestern Indian Ocean; 21°07′S, 55°32′E). This ecosystem is subjected to anthropogenic pressures through river inputs and submarine groundwater discharge (SGD). The goal of this study was to characterize the pool of fluorescent dissolved organic matter (FDOM) in different water bodies of La Saline fringing reef ecosystem using excitation–emission matrix (EEM) spectrofluorometry. From EEMs, we identified the different fluorophores by the peak picking technique and determined two fluorescence indices issued from the literature: the humification index (HIX) and the biological index (BIX). The main known fluorophores were present within the sample set: humic-like A, humic- like C, marine humic-like M, tryptophan-like T1 and T2, and tyrosine-like B1 and B2. In some samples, unknown fluorophores (“U”) were also detected. The surface oceanic waters located beyond the reef front displayed a typical oligotrophic marine signature, with a dominance of autochthonous/biological material (presence of peaks: T1 N B1 N A N T2 N MN C; HIX: 0.9±0.4; BIX: 2.3±1.1). In the reef waters, the autochthonous/biological fingerprint also dominated even though the content in humic substances was higher (same relative distribution of peaks; HIX: 1.6±0.6; BIX: 1.0±0.1). Sedimentary and volcanic SGD showed very different patterns with a strong terrestrial source for the former (A N T1 N C N B1 and A N C N B1; HIX: 9.8±2.0; BIX: 0.8±0.0) and a weak terrestrial source for the latter (A N B1 N U3 N B2 N C and A N U4 N C; HIX: 2.4 ± 0.3; BIX: 0.9 ± 0.0). In the Hermitage River, both humic substances and protein-like material were abundant (T1 N A N U5 N B1 N C N B2; HIX: 2.3; BIX: 1.4). We provide evidences for the presence of anthropogenic DOM in some of these water bodies. Some oceanic samples (presence of peaks U1 and U2) were likely contaminated by oil-derived PAHs from ships navigating around the reef front, whereas the Hermitage River was highly impacted by sewage effluents, numerous in this coastal area of La Réunion Island. We conclude that multi-dimensional fluorescence spectroscopy (EEM) coupled to the determination of HIX and BIX is a good tool for assessing the origin and distribution of DOM in the coral reef ecosystems submitted to anthropogenic impacts. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Dissolved organic matter (DOM), which represents one of the largest reservoirs of organic carbon on Earth (~700 Gt C), plays a key biogeochemical role in the aquatic environment (Hedges, 1992). It is the main source of energy (carbon) for heterotrophic bacteria (Carlson, 2002) and strongly interacts with various anthropogenic contaminants such as polycyclic aromatic hydrocarbons (PAHs), metals and pesticides, thus influencing their bioavailability, transport and fate (Hirose, 2007). DOM consists of a heterogeneous mixture of organic compounds originating from a wide variety of sources including the dissolution of soil/terrestrial organic matter, excretion by primary producers, grazing by zooplankton, cellular lysis, degradation/exudation of macrophytes and release from sediments (Nagata, 2000). Due to its complexity, only 25% of DOM has been identified at the molecular level so far (Benner, 2002). In recent years, the optical properties of DOM (i.e. absorbance and fluorescence) have been fruitfully employed to study its origin, composition and dynamics in the natural waters (Blough and Del Vecchio, 2002). In the past 15 years, fluorescent DOM (FDOM) has been extensively investigated owing to recent advances in fluorescence spectroscopy techniques, in particular the development of excitation– emission matrices (EEMs) (Coble, 1996). EEMs involve the collection of sequential fluorescence emission (Em) spectra at successively increas- ing excitation (Ex) wavelengths. The Em spectra obtained are concatenated to produce a plot in which the fluorescence intensity is displayed as a function of Ex and Em wavelengths. EEMs, which usually encompass a range of Ex and Em wavelengths from ~230–300 nm (UV wavelengths) to ~500–600 nm (green–red visible light), allow the Science of the Total Environment 409 (2011) 2198–2210 ⁎ Corresponding author. Tel.: +33 4 91 82 90 62; fax: +33 4 91 82 90 51. E-mail address: marc.tedetti@univmed.fr (M. Tedetti). 0048-9697/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.scitotenv.2011.01.058 Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv