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 (r(2) = 0.43-0.81) and related to elevation (r(2) = 0.39) across lakes. Methane concentrations in lakes at elevations <3000 m were strongly related to temperature, nitrite concentrations, and elevation (r(2) = 0.90), whereas at elevations >3000 m, CH4 was related to dissolved inorganic nitrogen to dissolved inorganic phosphorus ratios and elevation (r(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.

Automated summary

The study found that methane concentrations in lakes below 3000m were strongly related to temperature, nitrite concentrations, and elevation, while lakes above 3000m showed a relationship between methane and dissolved inorganic nitrogen to dissolved inorganic phosphorus ratios and elevation.