Thesis (M.S.) University of Alaska Fairbanks, 2010"Large uncertainties in first-order estimates of the magnitude of CH₄ emissions from lakes (global lakes: 8-48 Tg CH₄ yr⁻¹ Bastviken et al. 2004) result from variation in ebullition (bubbling) rates between and within lakes. Based on a comparison of two interior Alaska thermokarst lakes, I suggest that variation in CH₄ ebullition observed within and between lakes can be explained by a few key differences in substrate quality and sediment density. Killarney Lake, which has a 130 cm-thick modern sediment package, emitted 120 mg CH₄ M⁻² day⁻¹ produced from a mixture of modern C and permafrost C sources, while Goldstream Lake, a younger lake with only 2-5 cm of modern lake sediment, emitted more CH₄ (183 mg CH₄ M⁻² day⁻¹) produced mostly from thawed permafrost. Incubated thawed permafrost supported production of substantially more CH₄ (0.25 ± 0.04 mg CH₄ g TC⁻¹ d⁻¹) than did taberal lake sediments (0.08 ± 0.02 mg CH₄ g TC⁻¹ d⁻¹). Together, these lines of evidence support the importance of permafrost C availability as control on CH₄ production and bubbling in thermokarst lakes. Stable isotope and radiocarbon values of contemporary interior Alaska thermokarst lake CH₄ emissions reported in this study could help constrain contributions of thermokarst lakes to the global atmospheric CH₄ budget. I show here that methanogens in close proximity to thermokarst utilized pore water derived from melted permafrost ice as a hydrogen source, and that [delta]DCH₄ values reflected ancient [delta]D of precipitation. [Delta]DCH₄ values from Alaskan thermokarst lakes were less-depleted than [delta]DCH₄ values from Siberian lakes. Thus, thermokarst lake contributions to early Holocene atmospheric CH₄ concentrations were likely higher than originally thought"--Leaf iiiAlaska ESPSoR, Center for Global Change Global Change Grants, Institute of Northern Engineering, Institute of Arctic Biology, IARC, DOE #DE- NT0005665, and NSF grants IPY #0732735 and OPP #06322641. Introduction and overview -- 1.1. Introduction -- 1.2. The interior environment -- Permafrost -- Organic matter inputs to Alaskan lake sediments -- Vegetation -- Study sites -- 1.3. Methanogenesis -- Physical and biological controls -- Pathway controls -- Methane oxidation -- 1.4. Stable isotopes -- Carbon isotopes -- Hydrogen isotopes -- 1.5. CH₄ bubbling in northern lakes -- 1.6. Conclusion -- References -- Tables -- 2. A comparison of CH₄ production and bubbling from two interior Alaskan thermokarst lakes -- Abstract -- 2.1. Introduction -- 2.2. Methods -- Physiography of study area -- Study lakes -- Sample collection and analysis -- Geophysics -- Anaerobic laboratory incubation -- Calculations -- 2.3. Results -- Whole-lake CH₄ production -- Bubble fluxes and composition -- Production pathway -- Anaerobic incubation results -- Permafrost and sediment characteristics -- Geophysics -- Limnology -- 2.4. Discussion -- Temperature and production pathway -- Bubble gas composition variation -- Whole-lake CH₄ production -- 2.5. Conclusion -- Acknowledgements -- References -- Figures -- Tables -- 3. Implications of [delta]DCH₄ from Alaskan thermokarst lakes for past and present atmospheric CH₄ budgets -- Abstract -- 3.1. Introduction -- 3.2. Methods -- Study site -- Sample collection and analysis -- Calculations -- 3.3. Results -- Bubble isotopic and elemental composition -- Water isotopes and H mixing model -- 3.4. Discussion -- 3.5. Conclusion -- Acknowledgements -- References -- Figures -- Tables -- Appendix
