Tracking the Impact of Anthropogenic Inputs on Fluorescent Dissolved Organic Matter in the Gapeau River Using 3D Fluorescence Spectroscopy

Abstract

Ibrahim EL-Nahhal, Yasser EL-Nahhal and Stephane Mounier

The spatial and geographical variation of dissolved organic matter fluorescence signal is influenced by various factors, including biodegradation, photochemical degradation, and anthropogenic inputs. Understanding this variation is crucial for environmental studies such as pollution tracking and remote sensing of coastal waters. In this study, we used 3D fluorescence spectroscopy of excitation emission matrices (EEMs) coupled with parallel factor analysis (PARAFAC) to track the geographical variation of fluorescence signal along the urban Gapeau river in the PACA region of France. Two geographical sampling campaigns were conducted in August 2016 at 14 sampling points, resulting in 56 EEMs from nonfiltered and filtered samples. PARAFAC analysis revealed two components (C1 and C2), with C1 showing humic-like fluorescence and C2 showing protein "tyrosine"-like fluorescence. Both C1 and C2 increased at the wastewater treatment plant discharge point of La Crau city before decreasing with distance, indicating the impact of photochemical and biological degradation of dissolved organic matter. There were no significant differences between filtered and nonfiltered samples, indicating a negligible impact of particulate organic matter. The fluorescence signal at each sampling point can be used to determine mixing composition using a model developed elsewhere [1,2]. Future improvements to this work could include boat-based sampling campaigns and depth-profiling of the fluorescence signal to check for variability with depth.

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