From storage to release: how depth, temperature and texture shape methane emission in a tropical lake

We tested how depth-linked hydrostatic pressure, sediment temperature, and sediment texture 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, sand-richer sites, whereas porewater methane accumulated at deeper, cooler sites, yielding an inverse spatial pattern of the two phases. Simple regressions identified sand content as the strongest single predictor 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, indicating that the spatial template dominated short-term variability during stratification. These results establish depth, temperature, and texture as first-order controls on methane partitioning and suggest that catchment-driven infilling and sediment coarsening can shift emissions toward the ebullitive pathway, increasing the fraction of methane that bypasses oxidation. Monitoring designs that couple bathymetric change, sediment texture, and meteorological drivers will better constrain tropical lake methane budgets.