Substantial Contribution of nocturnal oxic methane production in eutrophic freshwaters. Data

Sampling activities and field experiments were organized into the following three sections:<br>1) Diel sampling was conducted from 12:00 a.m. on August 31 to 12:00 a.m. on September 1 on a deck floating in the center of the bay. During the Diel cycle, collections were made every three hours for chemical analyses and air-water gas fluxes (CO2 and CH4. Sampling depths were 0.5 m, 3.0 m, 6.0 m, 12 m, 18 m, and 21 m below the water surface, respectively.A multiparameter water quality probe (YSI® EXO2, USA) was deployed in the field to continuously obtain water temperature, dissolved oxygen (DO), pH, and other water quality parameters along the vertical profiles. Physical and chemical parameters were continuously obtained along the vertical profile.<br>2) Quantitative evaluation of oxygenated CH4. The field experiment consisted of the following three additional pathways: a) Funnel-collected sediment-water and air-water boiling fluxes of CH 4 in the coastal region of the bay.4 Sediment-water diffusion of CH4 was estimated by sampling and analyzing the transport of sediment pore water within the bay.4 The mass of the water column was estimated by acoustic Doppler velocimetry (Flow Quest, US) on both sides of the floating deck in the Two sampling transects were sampled and flow measurements were made along vertical profiles, i.e., inside (InCx) and outside (OutCx Supplementary Figure S1<br>3)4 In-situ incubation experiments were conducted for 4 days at depths of 0.5 m, 6 m and 20 m below the water surface to track microbial metabolism-driven CH 4 kinetics. Water samples were collected in situ and sealed in 624 mL brown glass vials wrapped in black plastic bags to prevent photosynthesis during incubation. Four identical incubation bottles were deployed in the field at each depth to facilitate daily sampling over a 24-hour period.4 concentration changes and their stable isotope signatures I isotope analyzer (Picarro®, CA, USA.). Triplicate copies were performed for quality control.<br>