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

Permafrost aggradation reduces peatland methane fluxes during the Holocene

Methane emissions from northern high latitude wetlands are one of the largest natural sources of atmospheric methane, contributing an estimated 20% of the natural terrestrial methane emissions to the atmosphere. Methane fluxes vary among wetland types and are generally higher in peatlands, wetlands with > 40 cm of organic soil, than in wetlands with mineral soils. However, permafrost aggradation in peatlands reduces methane fluxes through the drying of the peat surface, which can decrease both methane production and increase methane oxidation within the peat. We reconstruct methane emissions from peatlands during the Holocene using a synthesis of peatland environmental classes determined from plant macrofossil records in peat cores from > 250 sites across the pan-arctic. We find methane emissions from peatlands decreased by 20% during the Little Ice Age due to the aggradation of permafrost within peatlands during this period. These bottom-up estimates of methane emissions for the present day are in agreement with other regional estimates and are significantly lower than the peak in peatland methane emissions 1300 years before present. Our results indicate that methane emissions from high latitude wetlands have been an important contributor to atmospheric methane concentrations during the Holocene and will likely change in the future with permafrost thaw

The Use of Assisted Reproductive Technology by European Childhood Cancer Survivors

CCS often wish to have biological children yet harbour concerns about fertility impairment, pregnancy risks and the general health risks of prospective offspring. To clarify these concerns, health outcomes in survivor offspring born following ART (n = 74, 4.5%) or after spontaneous conception (n = 1585) were assessed in our European offspring study by descriptive and bivariate analysis. Outcomes were compared to a sibling offspring cohort (n = 387) in a 4:1 matched-pair analysis (n = 1681). (i) Survivors were more likely to employ ART than their siblings (4.5% vs. 3.7%, p = 0.501). Successful pregnancies were achieved after a median of one cycle with, most commonly, intracytoplasmic sperm injection (ICSI) using non-cryopreserved oocytes/sperm. (ii) Multiple-sibling births (p < 0.001, 29.7% vs. 2.5%), low birth weight (p < 0.001; OR = 3.035, 95%-CI = 1.615-5.706), and preterm birth (p < 0.001; OR = 2.499, 95%-CI = 1.401-4.459) occurred significantly more often in survivor offspring following ART utilisation than in spontaneously conceived children. ART did not increase the prevalence of childhood cancer, congenital malformations or heart defects. (iii) These outcomes had similar prevalences in the sibling population. In our explorative study, we could not detect an influence on health outcomes when known confounders, such as multiple births, were taken into account

Decadal-scale hotspot methane ebullition within lakes following abrupt permafrost thaw

Thermokarst lakes accelerate deep permafrost thaw and the mobilization of previously frozen soil organic carbon. This leads to microbial decomposition and large releases of carbon dioxide (CO2) and methane (CH4) that enhance climate warming. However, the time scale of permafrost-carbon emissions following thaw is not well known but is important for understanding how abrupt permafrost thaw impacts climate feedback. We combined field measurements and radiocarbon dating of CH4 ebullition with (a) an assessment of lake area changes delineated from high-resolution (1–2.5 m) optical imagery and (b) geophysical measurements of thaw bulbs (taliks) to determine the spatiotemporal dynamics of hotspot-seep CH4 ebullition in interior Alaska thermokarst lakes. Hotspot seeps are characterized as point-sources of high ebullition that release 14C-depleted CH4 from deep (up to tens of meters) within lake thaw bulbs year-round. Thermokarst lakes, initiated by a variety of factors, doubled in number and increased 37.5% in area from 1949 to 2009 as climate warmed. Approximately 80% of contemporary CH4 hotspot seeps were associated with this recent thermokarst activity, occurring where 60 years of abrupt thaw took place as a result of new and expanded lake areas. Hotspot occurrence diminished with distance from thermokarst lake margins. We attribute older 14C ages of CH4 released from hotspot seeps in older, expanding thermokarst lakes (14CCH4 20 079 ± 1227 years BP, mean ± standard error (s.e.m.) years) to deeper taliks (thaw bulbs) compared to younger 14CCH4 in new lakes (14CCH4 8526 ± 741 years BP) with shallower taliks. We find that smaller, non-hotspot ebullition seeps have younger 14C ages (expanding lakes 7473 ± 1762 years; new lakes 4742 ± 803 years) and that their emissions span a larger historic range. These observations provide a first-order constraint on the magnitude and decadal-scale duration of CH4-hotspot seep emissions following formation of thermokarst lakes as climate warms

The effect of elevated CO2 on the production of C- and N- based defense compounds in tomato (Lycopersicon esculentum).

Since tomato contains both C- and N-based chemical defense compounds, we were able to monitor the effect of elevated CO2 in a single species, eliminating the need to compensate for interspecific differences. In this study we asked: 1) What effect does eCO2 have on constituitive concentrations of tomatine and of various phenolic compounds within the leaves and stems of tomato plants? 2) Can production of either group of compounds be systemically induced by mechanical damage. 3) If so, does eCO2 affect induction?http://deepblue.lib.umich.edu/bitstream/2027.42/55047/1/3491.pdfDescription of 3491.pdf : Access restricted to on-site users at the U-M Biological Station

Methane Emissions from Northern Wetlands During the Holocene : A Synthesis Approach to Account for Wetland Expansion and Fen-Bog-Permafrost Transitions (Invited)

Methane emissions from northern high latitude wetlands constitute a major uncertainty in the atmospheric methane (CH4) budget during the Holocene. To reconstruct northern wetland methane emissions, we used an empirical model based on syntheses of observations of peat initiation from more than 3600 radiocarbon-dated basal peat ages, plant-macrofossil-derived peatland type from more than 250 peat cores from sites across the northern high latitudes, and observed CH4 emissions averaged from modern-day wetland types in order to explore the effects of wetland expansion and changes in wetland type. Peatland basal ages and plant macrofossil records showed the widespread formation of fens in major northern wetland complexes before 8000 BP. After 8000 BP, new fen formation continued, but widespread peatland succession (to bogs) and permafrost aggradation also occurred. Reconstructed CH4 emissions from peatlands increased rapidly between 10,600 BP and 6900 BP due to fen formation and expansion, then stabilized after 5000 BP at 42 ± 25 Tg CH4 y-1, as high methane-emitting fens transitioned to lower methane-emitting bogs and permafrost peatlands. Permafrost formation in northern peatlands after 1000 BP decreased CH4 emissions by 20% to 34 ± 21 Tg y-1 by the present day. Warming temperatures, changes in peatland hydrology, and permafrost thaw will likely change the magnitude of northern peatland emissions in the future

Radiocarbon dates of peatland initiation across the northern high latitudes

A compilation of basal dates of peatland initiation across the northern high latitudes, associated metadata including location, age, raw and calibrated radiocarbon ages, and associated references. Includes previously published datasets from sources below as well as 365 new data points

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

New compilation of formation dates, origins and fates for lakes within the Last Glacial/Permafrost Maximum domain of the Northern Hemisphere

Global lake distribution datasets show that a vast majority of Earth’s lakes by number and area are located in the high latitudes of the Northern Hemisphere. Lakes abundance in these regions has been linked to histories of glaciation, permafrost, and peatlands (Smith et al., 2007). Although well-dated sedimentary lake records are regularly used for the reconstruction of paleoenvironmental conditions and landscape dynamics, so far no consistent panarctic database exists on the age and origin of northern high latitude lakes. Lake cores, peat cores and exposures detailed in primary literature sources often provide a complete picture of how and when lakes formed. Here, we compile an extensive dataset of 1154 unique lake basal and minimum ages from both past and extant lakes within the domain of glaciation and permafrost extent during the Last Glacial/Permafrost Maximum [Lindgren et al. 2015] collected primarily from detailed literature descriptions. We distinguish ten distinct classes of lake origin after Vincent & Laybourn-Parry [2008] and include information on the fates (both mechanism and timing) of non-extant lakes described in peat cores and exposures. Analysis of the dataset reveals an increase in rates of northern hemisphere lake formation beginning ~14,500 cal. yr BP that was sustained, with a short lull during the Younger Dryas, until it began to generally decrease after ~ 10,500 cal. yr BP. Peak lake formation in regions where ice sheets were present into the early and mid-Holocene occurred later. Formation frequencies for lakes of glacier-dependent origin (i.e. kettle, moraine-dammed, glacial scour) and glacier-independent origin (e.g. oxbow, thermokarst, coastal uplift) coincided, suggesting that climatic factors were driving processes such as glacial retreat and permafrost degradation responsible for lake formation simultaneously. The dataset also reveals a weak correlation (R2 = 0.26) between the timing of lake drainage or terrestrialization and the timing of lake establishment. Although highly variable, the average length of lake persistence on the landscape determined from non-extant lake records was 5460 years. Lindgren, A., Hugelius, G., Kuhry, P., Christensen, T.R., Vandenberghe, J., 2015. GIS-based Maps and Area Estimates of Northern Hemisphere Permafrost Extent during the Last Glacial Maximum. Permafrost and Periglacial Processes, n/a-n/a. Smith, L.C., Sheng, Y., MacDonald, G.M., 2007. A first pan-Arctic assessment of the influence of glaciation, permafrost, topography and peatlands on northern hemisphere lake distribution. Permafrost and Periglacial Processes 18, 201-208. Vincent, W. F. & J. Laybourn-Parry (Eds.) (2008). Polar Lakes and Rivers. New York, NY: Oxford University Pres