From Storage to Release: How Depth, Temperature and Sediment Texture Structure Methane Partitioning in a Tropical Lake

We tested how depth-linked hydrostatic pressure, sediment temperature, and sediment texture, represented here by grain-size distribution, partition methane (CH4) between dissolved storage in sediment porewater and ebullitive release in a tropical monomictic lake. Along a shoreline-to-center transect spanning 1.5–7 m depth, we measured 24-h ebullition with replicated inverted funnels over three consecutive days and quantified porewater methane from short cores while recording depth, sediment temperature, grain size, wind, and barometric pressure. Ebullition was greatest at shallow, warmer, sandier sites, whereas porewater methane accumulated at deeper, cooler sites, yielding an inverse spatial pattern of the two phases. Site-level regressions identified sand content as the strongest spatial correlate of bubbling, while porewater methane increased with depth and declined with sediment temperature. Under weak winds and near-constant barometric pressure, ebullition showed no detectable day-to-day variation over the sampled 72-h interval, indicating that between-site differences exceeded short-term temporal variability. Together, these results describe a spatially resolved storage–release pattern consistent with depth-, temperature-, and texture-related controls on methane retention and bubbling in Lake Carioca.