The work developed during this fellowship was developed under four working packages, each related to one Specific Objective (SO). The fellow conducted her research activities at the “Centre de Recherche sur la Biodiversité et l'Environnement”, Université de Toulouse under the supervision of Dr. Julien Cucherousset (CRBE, Research Director at CNRS) and co-supervision of Dr. Stéphanie Boulêtreau (CRBE), and Dr. Fanny Colas (LEHNA, Université de Lyon 1). The working package (WP) 1 concerned the in-situ monitoring of lakes with and without FPV before and after the FPV installation, providing the monitoring of FPV ecological effects under a BACI (Before-After Control-Impact) framework. Monitoring of the lakes started on September 2022 and by summer 2022 3 lakes were equipped with FPVs (average 49 ±% coverage), generating a database with one year of “before” data for the impacted lakes and 2 years of “after” data by the end of this fellowship. During the fellowship, the fellow participated in seasonal and annual monitoring campaigns to sample abiotic (temperature, light intensity, nutrients), biotic (phytoplankton, periphyton, zooplankton, fish) and ecosystem functioning (decomposition, GHGs, ecosystel metabolism) data in each of the monitored lakes. The results of this monitoring, so far unique in the monitoring of FPV ecological effects, have been statistically analyzed using linear mixed effect models (LMMs) to test interactions between the before-after periods and the control-impact treatments (BACI contrast). They have been presented at a stakeholder final restitution meeting conducted on June 19th, 2025. All tasks related to WP1 were completed. The WP2 involved a mesocosm experiment which was conducted from May to September 2023 at the Aquatic Metatron, an experimental platform located in Moulis, France (42°57'N 1°05'E, Richard et al., 2025). The experimental design combined four levels of FPV coverage (0%, 25%, 45%, 65%), reflecting the global range observed in FPV installations (mean 34.2% ± 22 SD Nobre et al., 2024), across two ecological contexts representing different ecosystem maturities, simulated via nutrient enrichment. Each combination was replicated four times, resulting in 32 mesocosms. Samples were processed and statistical analyses were conducted. All tasks of WP2 were achieved. Currently a manuscript presenting the results of this experiment is under revision by co-authors.WP3 was developed in partnership with Lancaster University. We successfully developed a 3d model (Delft-3D) to simulate the effects of floating photovoltaic (FPV) systems on water thermal properties, including temperature dynamics and stratification. The study was conducted using as a model site, a gravel pit lake (Figure 10) in the south of France (latitude: 43.22º N, longitude: 1.61º E). Although we have simulated climate change scenarios as predicted in WP3, during the meetings between the fellow, the co-advisors and the collaborators from Lancaster University new questions regarding the implications of FPV structural design to its ecological effects raisedand were considered timelier and more relevant. As a result, we expanded the scope and focus of the modelling effort to investigate the ecological implications of different FPV array layouts. Specifically, we introduced the concept of “light islands”, open spaces within the FPV arrays, recognizing that light availability and wind exposure are likely key drivers of FPV-induced changes in water physics and cascading biological responses. The model was developed, calibrated and validated. Scenarios for light islands were developed and tested. The model has been fully developed, calibrated, and validated. We generated and tested multiple scenarios incorporating light island configurations. Currently, in collaboration with Lancaster University, we are conducting statistical analyses to evaluate the ecological effects of these different layouts. A manuscript detailing model development and calibration and one manuscript with the results of the light islands effects are currently in preparation. As far as we know, this is the first time this concept (“light islands”) is introduced and may help guide technical choices related to FPV design.
