Climate change is expected to induce more frequent and intense extreme rainfall events in the Mediterranean region, causing increased runoff of land-derived matter into coastal waters. To understand how this affects plankton communities, an in situ mesocosm experiment was conducted in the Mediterranean Thau lagoon (43°24’53’’N, 3°41’16’’E), south of France, in spring 2021. Soil from a nearby oak forest, the Puéchabon state forest (43°44’29’’N, 3°35’45’’E), mixed with water from the main river tributary, La Vène (43°30'56.4"N 3°41'33.5"E), was used to simulate terrestrial runoff in replicate mesocosms. High-frequency monitoring of dissolved oxygen concentration, chlorophyll-a fluorescence, salinity, photosynthetically available radiation (PAR), and temperature was performed during the entire experiment in every mesocosm enclosure at a depth of 1m. Additionally, manual sampling for the analysis of organic and inorganic nutrients (nitrate, nitrite, ammonium, silicate, orthophosphate, particulate organic carbon, particulate organic nitrogen, dissolved organic carbon, dissolved inorganic carbon), pH, carbonate chemistry, and maximum quantum yield (Fv : Fm) of Photosystem II (PSII) was performed multiple time during the experiment. High-frequency data were used to estimate gross oxygen primary production (GPP), respiration (R), and phytoplankton growth (µ) and loss (L) rates, fllowing two recently published methods (Soulié et al. 2021; 2022).