Investigating controls over methane production and bubbling from Interior Alaskan lakes using stable isotopes and radiocarbon ages

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

The role of wetland expansion and successional processes in methane emissions from northern wetlands during the Holocene

The contribution from northern high latitude wetlands are a major uncertainty in the atmospheric methane (CH4) budget throughout the Holocene. We reconstructed CH4 emissions from northern peatlands from 13,000 BP to present using an empirical model based on observations of peat initiation (>3600 dates), peatland type (>250 peat cores), and observed CH4 emissions in order to explore the effects of changes in wetland type on CH4 emissions over the end of the late glacial and the Holocene. Fen area increased steadily before 8000 BP as fens formed in major wetland complexes. After 8000 BP, new fen formation continued but widespread peatland succession (to bogs) and permafrost aggradation occurred. Reconstructed CH4 emissions from peatlands increased rapidly between 10,600 BP and 6900 BP due to fen formation and expansion. Emissions stabilized after 5000 BP at 42 ± 25 Tg CH4 y-1 as high-emitting fens transitioned to lower-emitting bogs and permafrost peatlands. Widespread permafrost formation in northern peatlands after 1000 BP decreased CH4 emissions by 20% to 34 ± 21 Tg y-1 by the present day and suggests peatland CH4 emissions will increase with permafrost thaw

Methane emissions from high-latitude peatlands during the Holocene from a synthesis of peatland records

The sources of atmospheric methane (CH4) during the Holocene remain widely debated, including the role of high latitude wetland and peatland expansion and fen-to-bog transitions. We reconstructed CH4 emissions from northern peatlands from 13,000 before present (BP) to present using an empirical model based on observations of peat initiation (>3600 14C dates), peatland type (>250 peat cores), and contemporary CH4 emissions in order to explore the effects of changes in wetland type and peatland expansion on CH4 emissions over the end of the late glacial and the Holocene. We find that fen area increased steadily before 8000 BP as fens formed in major wetland complexes. After 8000 BP, new fen formation continued but widespread peatland succession (to bogs) and permafrost aggradation occurred. Reconstructed CH4 emissions from peatlands increased rapidly between 10,600 BP and 6900 BP due to fen formation and expansion. Emissions stabilized after 5000 BP at 42 ± 25 Tg CH4 y-1 as high-emitting fens transitioned to lower-emitting bogs and permafrost peatlands. Widespread permafrost formation in northern peatlands after 1000 BP led to drier and colder soils which decreased CH4 emissions by 20% to 34 ± 21 Tg y-1 by the present day

Perceptions of wood in rivers and challenges for stream restoration in the United States

This article reports a study of the public perception of large wood in rivers and streams in the United States. Large wood is an element of freshwater aquatic ecosystems that has attracted much scientific interest in recent years because of its value in biological and geomorphological processes. At the heart of the issue is the nature of the relationship between scientific recognition of the ecological and geomorphological benefits of wood in rivers, management practices utilizing wood for river remediation progress, and public perceptions of in-channel wood. Surveys of students' perceptions of riverscapes with and without large wood in the states of Colorado, Connecticut, Georgia, Illinois, Iowa, Missouri, Oregon, and Texas suggest that many individuals in the United States adhere to traditionally negative views of wood. Except for students in Oregon, most respondents considered photographs of riverscapes with wood to be less aesthetically pleasing and needing more improvement than rivers without wood. Analysis of reasons given for improvement needs suggest that Oregon students are concerned with improving channels without wood for fauna habitat, whereas respondents elsewhere focused on the need for cleaning wood-rich channels for flood risk management. These results underscore the importance of public education to increase awareness of the geomorphological and ecological significance of wood in stream systems. This awareness should foster more positive attitudes toward wood. An integrated program of research, education, and policy is advocated to bridge the gap between scientific knowledge and public perception for effective management and restoration of river systems with wood

Explaining the Relationship Between Sexually Explicit Internet Material and Casual Sex: A Two-Step Mediation Model

Despite increasing interest in the implications of adolescents’ use of sexually explicit Internet material (SEIM), we still know little about the relationship between SEIM use and adolescents’ casual sexual activities. Based on a three-wave online panel survey study among Dutch adolescents (N = 1079; 53.1% boys; 93.5% with an exclusively heterosexual orientation; Mage = 15.11; SD = 1.39), we found that watching SEIM predicted engagement in casual sex over time. In turn, casual sexual activities partially predicted adolescents’ use of SEIM. A two-step mediation model was tested to explain the relationship between watching SEIM and casual sex. It was partially confirmed. First, watching SEIM predicted adolescents’ perceptions of SEIM as a relevant information source from Wave 2 to Wave 3, but not from Wave 1 to Wave 2. Next, such perceived utility of SEIM was positively related to stronger instrumental attitudes toward sex and thus their views about sex as a core instrument for sexual gratification. Lastly, adolescents’ instrumental attitudes toward sex predicted adolescents’ engagement in casual sex activities consistently across waves. Partial support emerged for a reciprocal relationship between watching SEIM and perceived utility. We did not find a reverse relationship between casual sex activities and instrumental attitudes toward sex. No significant gender differences emerged