Controlling Factors of Methane in Tropical Lakes of Different Depths
Milette U. Mendoza‐Pascual, Masayuki Itoh, Jaydan I. Aguilar, Karol Sophia Agape R. Padilla, Rey Donne S. Papa, Noboru Okuda
Abstract
Abstract To understand methane (CH 4 ) dynamics in tropical lakes and describe their importance in overall CH 4 emissions, we observed temporal trends of CH 4 stored in the water columns of Philippine lakes of different depths (shallow, moderately deep, and deep). We detected higher CH 4 stored in profundal anoxic layers of deeper lakes. The average surface and profundal CH 4 concentrations throughout our monthly monitoring were 0.27 ± 0.07 and 421 ± 189 μmol L –1 in the shallow lake, 0.48 ± 0.37 and 1,121 ± 125 μmol L –1 in the moderately deep lake, and 0.34 ± 0.23 and 943 ± 119 μmol L –1 in the deep lake. The fate of CH 4 stored in the water column was related to depth, owing to different stratification and mixing regimes. Analyses of temporal relationships of CH 4 with daily weather and physicochemical parameters revealed their impact on CH 4 dynamics by controlling the frequency and mixing intensity throughout the year. Only shallow lake exhibited increase in CH 4 concentrations with lowering atmospheric pressure. This allows vertical mixing and transport of CH 4 from deeper to shallower layers. In moderately deep, and deep lakes, effects of daily weather parameters were not apparent on CH 4 concentrations in the deepest layers (below 30 m depth). This suggests that lake depth and stratification should be considered for precise estimation of tropical lakes' CH 4 emissions. Comparison with lakes under different climate conditions revealed the importance of tropical lakes for surface CH 4 emission due to higher surface CH 4 concentrations. Changes in water temperature is one of the factors controlling profundal CH 4 production, storage, and its transport to shallower layer.