Utilization of a Submersible Ultra-Violet Fluorometer for Monitoring Anthropogenic Inputs in the Mediterranean Coasts

Abstract

The Mediterranean Sea coasts are subject to a strong anthropogenic pressure because of an intensification of urban, industrial, agricultural, and tourist activities. This anthropogenic pressure is reflected in the direct (from coastal sources) and indirect (via rivers) discharge of terrigenous materials and pollutants. These contributions promote transformations of ecosystems and associated biogeochemical cycles. In order to assess environmental changes, discrete measurements at fixed observation sites are useful, but remain insufficient to describe the synoptic extension and the impact of these released terrigenous inputs. An objective of the laboratory is to develop and use in situ UV fluorometers for the quantification at high spatial and temporal frequency of terrigenous and anthropogenic tracers such as polycyclic aromatic hydrocarbons (PAHs, index of chemical contaminations) and "tryptophan-like" material (rough index of bacterial contaminations). An in situ UV fluorometer (EnviroFlu-HC, TriOS Optical Sensors) was deployed in the coastal area of Marseilles from January to July 2008. The fluorescence signal of this probe (Ex/Em: 254 +/- 12.5/360 +/- 25 nm) was compared to the spectrofluorimetric excitation emission matrices (EEMs) of discrete samples taken from the same area. The probe signal, due to its relative large excitation and emission bands, covers the EEM signature of several groups of compounds: PAHs, tryptophan-like material, and humic substances. Based on our in situ observations, and in collaboration with a French company specialized in optical sensors, we propose solutions for improving the optical properties of the EnviroFlu-HC fluorometer to better target compounds of interest and miniaturize the probe. Ultimately, these miniaturized UV fluorometers will be integrated to autonomous mobile platforms (gliders). This study is part of a laboratory program that aims to develop observation tools for operational oceanography and urban marine zone management: The project SEA EXPLORER (leader ACSA underwater GPS, partnerships: ACRI-IN, ACRI-ST, IFREMER, LMGEM-COM, LOV) funded by the Ministry of Industry (Fond de Competitivite des Entreprises, FCE). This work also received the financial support of the Conseil General des Bouches-du-Rhone (CG 13) and Agence de l'Eau Rhone-Mediterranee.