Identifying temporal patterns and controlling factors in methane ebullition at Sallie\u27s Fen, a temperate peatland site, using automated chambers

Despite leading to a potentially significant positive climate feedback, the processes controlling wetland methane fluxes remain relatively poorly understood. Automated chambers were employed in a temperate peatland site to quantify the timing and magnitude of methane ebullition (bubbling), one of the three pathways for wetland methane flux. The resulting datasets offer high temporal coverage of both components of this flux pathway, allowing for the first analysis of ebullition variability on seasonal, synoptic and diel timescales. The seasonal peak in ebullition occurred in August, likely due to high methane production rates and low methane solubility, both driven by temperature. Synoptic scale variability was driven by hydrostatic pressure variations due to water table position. A daily pattern in ebullition was identified, with peaks at night. Several potential mechanisms for this pattern were explored. The cumulative contribution of ebullition to total methane flux during the summer was estimated to be 2--12%

Magnitude and controls on the net carbon balance of a New Zealand raised bog

Peatlands play an important role in the Earth system as both persistent carbon dioxide (CO₂) sinks and methane (CH₄) sources. However, large uncertainties remain in our understanding of peatland carbon cycle – climate feedbacks. The majority of research has been conducted in the Northern Hemisphere as most of the global peatland area is located there. Few data have been collected in Southern Hemisphere peatlands and there is a limited basis for predicting how these systems will respond to changing climatic drivers and other anthropogenic forcings such as drainage for agriculture. Furthermore, it is unclear whether our knowledge of peatland functioning and carbon (C) cycling from the Northern Hemisphere translates to systems that have developed under different climatic and hydrologic settings with unique vegetation. To gain a better understanding of peatland carbon and greenhouse gas exchange in a globally distinct and unique peatland type, I used eddy covariance to measure net ecosystem CO₂ exchange (NEE) and CH₄ flux (FCH₄) in an undisturbed New Zealand raised bog over ~2.5 years. The overarching goals of this research were to determine magnitudes of the main components of the ecosystem C budget, gross primary production (GPP), ecosystem respiration (ER), and FCH₄, and their sensitivity to environmental and physical drivers. With respect to CO₂ exchange, high VPD periods restricted the light-saturated photosynthetic capacity during clear sky days. Elevated VPD was also the only condition that led to reductions in daily total GPP, a response likely triggered to reduce transpiration water losses. These results have important implications for the future C sink strength of New Zealand peatlands given a trend toward drier summers with clearer skies and higher VPD. With respect to FCH₄, a severe drought during summer 2013 allowed me to explore the interacting controls of temperature and water table depth. During 2012, a relatively average meteorological year, annual total FCH₄ was 21.5 g CH₄⁻ C m⁻² yr⁻1, whereas total FCH₄ during the drought year (2013) was 14.5 g CH₄⁻C m⁻² yr⁻¹. I found that water table depth was the most important overarching control on FCH₄ over various timescales from weekly to inter-annual. Water table depth regulated the temperature sensitivity of FCH₄, which was highest when the water table was within 50 – 80 mm of the surface. This depth range corresponds to the relatively shallow rooting zone of the dominant vegetation, which may provide much of the substrate for methane production. Kopuatai bog was a very strong C sink compared to Northern Hemisphere bogs and fens. Despite the elevated ER during the drought year, Kopuatai was a sink of 74.5 gC m⁻², which is at the high end of published Northern Hemisphere estimates. The more average meteorological year (2012) resulted in a much larger sink of 152 gC m⁻². This work has revealed the importance of atmospheric controls on plant CO₂ uptake and hydrologic (i.e. water table) effects on ecosystem respiration and FCH₄, when considering the overall C balance. These effects imply that the future C sink capacity of Kopuatai bog may be reduced due to the long-term trend toward drier, sunnier summers and more frequent droughts in the region

Climate and Land-Use Controls on Surface Water Diversions in the Central Valley, California

California’s Central Valley (CV) is one of the most productive agricultural regions in the world, enabled by the conjunctive use of surface water and groundwater. We investigated variations in the CV’s managed surface water diversions relative to climate variability. Using a historical record (1979−2010) of diversions from 531 sites, we found diversions are largest in the wetter Sacramento basin to the north, but most variable in the drier Tulare basin to the south. A rotated empirical orthogonal function (REOF) analysis finds 72% of the variance of diversions is captured by the first three REOFs. The leading REOF (35% of variance) exhibited strong positive loadings in the Tulare basin, and the corresponding principal component time-series (RPC1) was strongly correlated (ρ > 0.9) with contemporaneous hydrologic variability. This pattern indicates larger than average diversions in the south, with neutral or slightly less than average diversions to the north during wet years, with the opposite true for dry years. The second and third REOFs (20% and 17% of variance, respectively), were strongest in the Sacramento basin and San Francisco Bay−Delta. RPC2 and RPC3 were associated with variations in agricultural- and municipal-bound diversions, respectively. RPC2 and RPC3 were also moderately correlated with 7-year cumulative precipitation based on lagged correlation analysis, indicating that diversions in the north and central portions of the CV respond to longer-term hydrologic variations. The results illustrate a dichotomy of regimes wherein diversions in the more arid Tulare are governed by year-to-year hydrologic variability, while those in wetter northern basins reflect land-use patterns and low-frequency hydrologic variations

Mass fluxes and isofluxes of methane (CH4) at a New Hampshire fen measured by a continuous wave quantum cascade laser spectrometer

We have developed a mid‐infrared continuous‐wave quantum cascade laser direct‐absorption spectrometer (QCLS) capable of high frequency (≥1 Hz) measurements of 12CH4 and 13CH4 isotopologues of methane (CH4) with in situ 1‐s RMS image precision of 1.5 ‰ and Allan‐minimum precision of 0.2 ‰. We deployed this QCLS in a well‐studied New Hampshire fen to compare measurements of CH4 isoflux by eddy covariance (EC) to Keeling regressions of data from automated flux chamber sampling. Mean CH4 fluxes of 6.5 ± 0.7 mg CH4 m−2 hr−1 over two days of EC sampling in July, 2009 were indistinguishable from mean autochamber CH4 fluxes (6.6 ± 0.8 mgCH4 m−2 hr−1) over the same period. Mean image composition of emitted CH4 calculated using EC isoflux methods was −71 ± 8 ‰ (95% C.I.) while Keeling regressions of 332 chamber closing events over 8 days yielded a corresponding value of −64.5 ± 0.8 ‰. Ebullitive fluxes, representing ∼10% of total CH4 fluxes at this site, were on average 1.2 ‰ enriched in 13C compared to diffusive fluxes. CH4 isoflux time series have the potential to improve process‐based understanding of methanogenesis, fully characterize source isotopic distributions, and serve as additional constraints for both regional and global CH4 modeling analysis

Southern Hemisphere bog persists as a strong carbon sink during droughts

Peatland ecosystems have been important global carbon sinks throughout the Holocene. Most of the research on peatland carbon budgets and effects of variable weather conditions has been done in Northern Hemisphere Sphagnum-dominated systems. Given their importance in other geographic and climatic regions, a better understanding of peatland carbon dynamics is needed across the spectrum of global peatland types. In New Zealand, much of the historic peatland area has been drained for agriculture but little is known about rates of carbon exchange and storage in unaltered peatland remnants that are dominated by the jointed wire-rush, Empodisma robustum. We used eddy covariance to measure ecosystem-scale CO₂ and CH₄ fluxes and a water balance approach to estimate the sub-surface flux of dissolved organic carbon from the largest remaining raised peat bog in New Zealand, Kopuatai bog. The net ecosystem carbon balance (NECB) was estimated over four years, which included two drought summers, a relatively wet summer, and a meteorologically average summer. In all measurement years, the bog was a substantial sink for carbon, ranging from 134.7 gC m⁻² yr⁻¹ to 216.9 gC m⁻² yr⁻¹, owing to the large annual net ecosystem production (−161.8 to −244.9 gCO2-C m⁻² yr⁻¹). Annual methane fluxes were large relative to most Northern Hemisphere peatlands (14.2 to 21.9 gCH4-C  m⁻² yr⁻¹1), although summer and autumn emissions were highly sensitive to dry conditions leading to very predictable seasonality according to water table position. The annual flux of dissolved organic carbon was similar in magnitude to methane emissions but less variable, ranging from 11.7 to 12.8 gC m⁻² yr⁻¹. Dry conditions experienced during late summer droughts led to significant reductions in annual carbon storage, which resulted nearly equally from enhanced ecosystem respiration due to lowered water tables and increased temperatures, and from reduced gross primary production due to vapor pressure deficit-related stresses to the vegetation. However, the net C uptake of Kopuatai bog during drought years was large relative to even the maximum reported NECB from Northern Hemisphere bogs. Furthermore, GWP fluxes indicated the bog was a strong sink for greenhouse gases in all years despite the relatively large annual methane emissions. Our results suggest that adaptations of E. robustum to dry conditions lead to a resilient peatland drought response of the NECB

Creating an Online CME Module: Early Detection and Diagnosis of Dementia and Alzheimer’s Disease

Introduction. The number of individuals living with dementia and Alzheimer’s disease (AD) in the United States is growing annually; only 40% are properly diagnosed. Primary care providers should identify individuals with cognitive impairment and provide options for care; early diagnosis of dementia and AD helps patients and families plan for the future, increases quality of life, and allows for treatment options.https://scholarworks.uvm.edu/comphp_gallery/1192/thumbnail.jp

Determinants of penetrance and variable expressivity in monogenic metabolic conditions across 77,184 exomes

Hundreds of thousands of genetic variants have been reported to cause severe monogenic diseases, but the probability that a variant carrier develops the disease (termed penetrance) is unknown for virtually all of them. Additionally, the clinical utility of common polygenetic variation remains uncertain. Using exome sequencing from 77,184 adult individuals (38,618 multi-ancestral individuals from a type 2 diabetes case-control study and 38,566 participants from the UK Biobank, for whom genotype array data were also available), we apply clinical standard-of-care gene variant curation for eight monogenic metabolic conditions. Rare variants causing monogenic diabetes and dyslipidemias display effect sizes significantly larger than the top 1% of the corresponding polygenic scores. Nevertheless, penetrance estimates for monogenic variant carriers average 60% or lower for most conditions. We assess epidemiologic and genetic factors contributing to risk prediction in monogenic variant carriers, demonstrating that inclusion of polygenic variation significantly improves biomarker estimation for two monogenic dyslipidemias

Using atmospheric observations to quantify annual biogenic carbon dioxide fluxes on the Alaska North Slope

The continued warming of the Arctic could release vast stores of carbon into the atmosphere from high-latitude ecosystems, especially from thawing permafrost. Increasing uptake of carbon dioxide (CO2) by vegetation during longer growing seasons may partially offset such release of carbon. However, evidence of significant net annual release of carbon from site-level observations and model simulations across tundra ecosystems has been inconclusive. To address this knowledge gap, we combined top-down observations of atmospheric CO2 concentration enhancements from aircraft and a tall tower, which integrate ecosystem exchange over large regions, with bottom-up observed CO2 fluxes from tundra environments and found that the Alaska North Slope is not a consistent net source nor net sink of CO2 to the atmosphere (ranging from −6 to +6 Tg C yr−1 for 2012–2017). Our analysis suggests that significant biogenic CO2 fluxes from unfrozen terrestrial soils, and likely inland waters, during the early cold season (September–December) are major factors in determining the net annual carbon balance of the North Slope, implying strong sensitivity to the rapidly warming freeze-up period. At the regional level, we find no evidence of the previously reported large late-cold-season (January–April) CO2 emissions to the atmosphere during the study period. Despite the importance of the cold-season CO2 emissions to the annual total, the interannual variability in the net CO2 flux is driven by the variability in growing season fluxes. During the growing season, the regional net CO2 flux is also highly sensitive to the distribution of tundra vegetation types throughout the North Slope. This study shows that quantification and characterization of year-round CO2 fluxes from the heterogeneous terrestrial and aquatic ecosystems in the Arctic using both site-level and atmospheric observations are important to accurately project the Earth system response to future warming.</p

Cold season emissions dominate the Arctic tundra methane budget

Arctic terrestrial ecosystems are major global sources of methane (CH4); hence, it is important to understand the seasonal and climatic controls on CH4 emissions from these systems. Here, we report year-round CH4 emissions from Alaskan Arctic tundra eddy flux sites and regional fluxes derived from aircraft data. We find that emissions during the cold season (September to May) account for >= 50% of the annual CH4 flux, with the highest emissions from noninundated upland tundra. A major fraction of cold season emissions occur during the "zero curtain" period, when subsurface soil temperatures are poised near 0 degrees C. The zero curtain may persist longer than the growing season, and CH4 emissions are enhanced when the duration is extended by a deep thawed layer as can occur with thick snow cover. Regional scale fluxes of CH4 derived from aircraft data demonstrate the large spatial extent of late season CH4 emissions. Scaled to the circumpolar Arctic, cold season fluxes from tundra total 12 +/- 5 (95% confidence interval) Tg CH4 y(-1), similar to 25% of global emissions from extratropical wetlands, or similar to 6% of total global wetland methane emissions. The dominance of late-season emissions, sensitivity to soil environmental conditions, and importance of dry tundra are not currently simulated in most global climate models. Because Arctic warming disproportionally impacts the cold season, our results suggest that higher cold-season CH4 emissions will result from observed and predicted increases in snow thickness, active layer depth, and soil temperature, representing important positive feedbacks on climate warming.Peer reviewe