Integrating isotopic, microbial, and modeling approaches to understand methane dynamics in a frequently disturbed deep reservoir in Taiwan

Abstract

It has been estimated that more than 48% of global methane emissions from lakes and reservoirs occur at low latitudes (<24°). To improve this estimate, knowledge regarding underexplored ecosystems, particularly deep lakes and reservoirs in Asian monsoon regions, is needed because the magnitude of methane emissions is influenced by lake bathymetry and climatic conditions. We conducted long‐term studies beginning in 2004 at Feitsui Reservoir (FTR) in Taiwan, a subtropical monomictic system with a maximum depth of 120 m to monitor seasonal and interannual variations of three key characteristics and to understand the mechanisms underlying these variations. Key characteristics investigated were as follows: (1) the balance of primary production and heterotrophic respiration as a determinant of vertical oxygen distribution, (2) methane production at the bottom of the reservoir, oxidation in the water column, and emissions from the lake surface, and (3) the contribution of methane‐originated carbon to the pelagic food web through methane‐oxidizing bacteria (MOB). This review highlights major achievements from FTR studies integrating isotopic, microbial, and modeling approaches. Based on our findings, we proposed two conceptual models: (1) a model of methane dynamics, which addresses the differences in methane emission mechanisms between deep and shallow lakes, and (2) a spatially explicit model linking benthic methane production to the pelagic food web, which addresses the diversity of MOB metabolisms and their dependence on oxygen availability. Finally, we address why long‐term studies of subtropical lakes and reservoirs are important for better understanding the effects of climate on low‐ to mid‐latitude ecosystems.

Environmental Controls of Diffusive and Ebullitive Methane Emissions at a Subdaily Time Scale in the Littoral Zone of a Midlatitude Shallow Lake

“…Note that the CH 4 flux observed in our lake represents emission from the littoral zone, where ebullition is more frequent than in the pelagic deep zone due to higher CH 4 production and lower hydrostatic pressure (DelSontro et al, 2016; Itoh et al, 2017). Thus, the contribution of ebullition may be lower when CH 4 flux in the pelagic zone of this lake is considered.…”

Controlling Factors of Methane in Tropical Lakes of Different Depths

“…Fluctuations in weather conditions can alter the lake environment, physicochemical, and CH 4 dynamics (Mitsch et al., 2010). To attain a more realistic global CH 4 estimation, it is necessary to look at tropical lakes located in monsoon Asia (Itoh, Kojima, et al., 2017). One of the reasons for this is the area's higher potential for contributing CH 4 into the atmosphere, because emissions are thought to be driven by typhoons and seasonal winds, such as the northeast (NE) and southwest (SW) monsoons, which are common drivers of lake mixing in this region (Tsai et al., 2008).…”

Establishment of an ecological research network involving Taiwan and Japan: developing a better understanding of ecological phenomena unique to East Asia

“…Itoh et al (2017) summarized the achievements of long-term observation study since 2004 at Feitsui Reservoir in Taiwan, focusing on seasonal and interannual variation of methane dynamics and their contributions to the pelagic food web. They addressed the specificity of methane dynamics in a subtropical deep lake and the importance of metabolic diversity of methane-oxidizing bacteria.…”