Fluocopée® probe deployment in the Seine river (France): Towards high-frequency in situ monitoring of aquatic environments using fluorescence spectrometry

      Over the past two decades, there has been a notable advancement in the development of high-frequency measuring equipment for the monitoring of biophysical and chemical parameters in surface water. Optical probes, especially fluorescence probes, are of particular importance in the integration of high-frequency measurements into environmental monitoring. The joint development of the Fluocopée® probe by LEESU and SIAAP represents a further contribution to this dynamic. This innovative fluorescence probe is capable of monitoring temporal evolution of 25 fluorophores in situ at high frequency (every 15 minutes), thereby enabling the characterization of dissolved organic matter (DOM). The extensive range of fluorophores monitored by the Fluocopée® probe facilitates the monitoring of water quality and the investigation of the biogeochemical processes linked to DOM in aquatic environments. Furthermore, its sensitivity is compatible with the levels of OM concentration observed in continental aquatic environments.

      Since October 2023, several Fluocopée® probes have been implemented on the river Seine and its two main tributaries (the Marne and Oise rivers) at six sites upstream and downstream of the Paris conurbation (see Figure 1). This allows us to assess the spatial variability of organic matter in the river Seine across the Paris conurbation at a high temporal frequency and provides a valuable opportunity to enhance our comprehension of the organic matter biogeochemical dynamics in the river Seine as well as to assess the impact of urban pressures. The installation of Fluocopée® probes at sites already equipped (as part of the MeSeine monitoring system or drinking water treatment plants intakes) with numerous measuring devices has been shown to facilitate the interpretation of fluorescence data by providing supplementary information from the chronicles of other physicochemical parameters (pH, turbidity, dissolved O2, TSS, Abs254nm, fecal indicator bacteria etc.). 

      Furthermore, proxies for determining dissolved organic carbon (DOC) and its biodegradable fraction on the basis of fluorescence measurements have been developed in our laboratory. The development of these models was achieved by identifying the most suitable existing correlation between these physiochemical parameters and fluorescence measurements using various statistical algorithms (e.g., multilinear regressions, partial least squares regressions, machine learning algorithms, etc.). Used in association with Fluocopée®, these proxies provide estimation of these parameters at high frequency in addition to fluorescence measurements.

      The fluorescence, DOC and biodegradable DOC concentration measurements acquired at high frequency over a year using our monitoring system will be presented and discussed. The influence of the hydroclimatic situation and the impact of urban pressures on the organic matter dynamics in the Seine across Paris Conurbation will be assessed. Additionally, it will provide a detailed account of the methodology employed to process these data sets, from the initial acquisition of raw data to its subsequent validation.

Figure 1 : Implantation of Fluocopée® probes