Methane dynamics of high-elevation lakes in the Sierra Nevada California: the role of elevation, temperature, and inorganic nutrients

Freshwater lakes are important but poorly constrained sources of methane (CH₄) to the atmosphere, reflecting high but variable rates of CH₄ production as well as limited and inconsistent measurements worldwide. High-elevation lakes have been particularly overlooked given their high abundance in mountain ranges around the world, and the potential for CH₄ dynamics at high elevations is expected to be disproportionally impacted by increases in temperature due to climate change. We examined variations in surface CH₄ concentrations and diffusive fluxes, temperature, and inorganic nutrients in 5 montane lakes spanning multiple elevations in the Sierra Nevada of California. Over 2 years, we found strong and consistent seasonality in CH₄ concentrations in lakes; higher concentrations were typically observed in the warmest months and lower concentrations right before winter. Changes in CH₄ concentrations were significantly related to temperature in the majority of the individual lakes (<i>r</i>² = 0.43–0.81) and related to elevation (<i>r</i>² = 0.39) across lakes. Methane concentrations in lakes at elevations &lt;3000 m were strongly related to temperature, nitrite concentrations, and elevation (<i>r</i>² = 0.90), whereas at elevations &gt;3000 m, CH₄ was related to dissolved inorganic nitrogen to dissolved inorganic phosphorus ratios and elevation (<i>r</i>² = 0.48). Our results expand our understanding of temporal variations in CH₄ and demonstrate substantial seasonality in CH₄ concentrations and diffusive fluxes in freshwater lakes. We suggest that temporal variation should be considered in large-scale estimates of CH₄ emissions, and these fluxes may be a predictable function of elevation, temperature, and nutrients.