Evaluating the potential of the Normalized Burn Ratio and other spectral indices for assessment of fire severity in Alaskan Black Spruce forests.

This thesis presents an assessment of the potential of the differenced Normalized Burn Ratio (dNBR) and other spectral indices for mapping fire severity in Alaskan black. Using simple linear regression, the dNBR derived from Landsat TM and ETM+ data was correlated with ground measures of fire severity including the Composite Burn Index (CBI), depth of the organic soil remaining after the fire, reduction in the depth of the organic layer, and Canopy Fire Severity Index; these being measures of fire severity used to assess the ecological effects of fire. Regression analyses yielded weak correlations: the highest R2 for a comparison between the dNBR and CBI was 0.52, p<0.0001. However, the mid-infrared ratio showed higher potential than other spectral indices in many comparisons. Overall, these results indicate 1) validation of the dNBR is needed and 2) burn severity mapping schemes which are more comprehensive than the dNBR should be developed

Impacts of a changing fire frequency on soil carbon stocks in interior Alaskan boreal forests

Increasing temperatures and drier conditions, related to climate change, have resulted in changes to the fire regime in interior Alaskan boreal forests, including increases in burned area and fire frequency. These fire regime changes alter carbon storage and emissions, especially in the thick organic soils of black spruce (Picea mariana) forests. While there are ongoing studies of the size and severity of fire using ground- and remote-based studies in mature black spruce forests, a better understanding of fire regime changes to immature black spruce forests is needed. The goal of this dissertation research was to assess impacts of changing fire frequency on soil organic layer (SOL) carbon consumption during wildland fires in recovering Alaskan black spruce forests using a combination of geospatial and remote sensing analyses, field-based research, and modeling. The research objectives were to 1) quantify burning in recovering vegetated areas; 2) analyze factors associated with variations in fire frequency; 3) quantify how fire frequency affects depth of burning, residual SOL depth, and carbon loss in the SOL of black spruce forests; and 4) analyze how fire frequency impacts carbon consumption in these forests. Results showed that considerable burning in the region occurs in stands not yet fully recovered from earlier fire events (~20% of burned areas are in immature stands). Additionally, burning in recovering black spruce forests (~40 yrs old) resulted in SOL depth of burn similar to that in mature forests which have burned. Incorporating these results into a modeling framework (through adding an immature black spruce fuel type and associated ground-layer carbon consumption values) resulted in higher ground-layer carbon consumption (and thus total carbon consumed) for areas that burned in 2004 and 2005 than that of a previous version of the model. This research indicated that the dominant controls on fire behavior in this system were fuel type and amount, not fuel condition, and that changes in vegetation associated with more frequent fire (shift to deciduous and shrub vegetation which does not traditionally burn as readily) may represent a long-term negative feedback on burned area. These new results provide insight into the fire-climate-vegetation dynamics within the region and could be used to both inform and validate modeling efforts to better estimate soil carbon pools and emissions as climate continues to change

Analysis of the F2LR3 (PAR4) single nucleotide polymorphism (rs773902) in an Indigenous Australian population

The F2RL3 gene encoding protease activated receptor 4 (PAR4) contains a single nucleotide variant, rs773902, that is functional. The resulting PAR4 variants, Thr120, and Ala120, are known to differently affect platelet reactivity to thrombin. Significant population differences in the frequency of the allele indicate it may be an important determinant in the ethnic differences that exist in thrombosis and hemostasis, and for patient outcomes to PAR antagonist anti-platelet therapies. Here we determined the frequency of rs773902 in an Indigenous Australian group comprising 467 individuals from the Tiwi Islands. These people experience high rates of renal disease that may be related to platelet and PAR4 function and are potential recipients of PAR-antagonist treatments. The rs773902 minor allele frequency (Thr120) in the Tiwi Islanders was 0.32, which is similar to European and Asian groups and substantially lower than Melanesians and some African groups. Logistic regression and allele distortion testing revealed no significant associations between the variant and several markers of renal function, as well as blood glucose and blood pressure. These findings suggest that rs773902 is not an important determinant for renal disease in this Indigenous Australian group. However, the relationships between rs773902 genotype and platelet and drug responsiveness in the Tiwi, and the allele frequency in other Indigenous Australian groups should be evaluated

Asymptomatic people with well-controlled HIV do not have abnormal left ventricular global longitudinal strain

BackgroundPrevious studies have reported impairment in systolic and diastolic function in people with HIV (PWHIV). Our aim was to determine if echocardiographically measured left ventricular (LV) global longitudinal strain (GLS) is abnormal in asymptomatic PWHIV.MethodsA cross-sectional study of PWHIV (n = 98, 89% male, median age 53 years) and HIV-negative people (n = 50, median age 53 years) without known cardiovascular disease were recruited from a single centre. All participants completed a health/lifestyle questionnaire, provided a fasting blood sample, and underwent a comprehensive echocardiogram for assessment of diastolic and systolic LV function, including measurement of GLS.ResultsAll PWHIV were receiving antiretroviral therapy (ART) for a median of 12 years (IQR: 6.9, 22.4), the majority with good virological control (87% suppressed) and without immunological compromise (median CD4 598 cells/µl, IQR: 388, 841). Compared with controls of similar age and gender, there was no difference in GLS [mean GLS −20.3% (SD 2.5%) vs. −21.0% (SD 2.5%), p = 0.14] or left ventricular ejection fractions [65.3% (SD 6.3) vs. 64.8% (SD 4.8), p = 0.62]. Following adjustment for covariates (gender, heart rate, systolic and diastolic blood pressure, and fasting glucose), the difference in GLS remained non-significant. There were no differences in LV diastolic function between the groups. Exposure to at least one mitochondrially toxic ART drug (didanosine, stavudine, zidovudine, or zalcitabine) was not associated with impairment of LV systolic function.ConclusionNo clinically significant impairment of myocardial systolic function, as measured by LV GLS, was detected in this predominantly Caucasian male population of PWHIV on long-term ART, with no history of cardiovascular disease

Burned area and carbon emissions across northwestern boreal North America from 2001-2019

Fire is the dominant disturbance agent in Alaskan and Canadian boreal ecosystems and releases large amounts of carbon into the atmosphere. Burned area and carbon emissions have been increasing with climate change, which have the potential to alter the carbon balance and shift the region from a historic sink to a source. It is therefore critically important to track the spatiotemporal changes in burned area and fire carbon emissions over time. Here we developed a new burned-area detection algorithm between 2001-2019 across Alaska and Canada at 500 m (meters) resolution that utilizes finer-scale 30 m Landsat imagery to account for land cover unsuitable for burning. This method strictly balances omission and commission errors at 500 m to derive accurate landscape- and regional-scale burned-area estimates. Using this new burned-area product, we developed statistical models to predict burn depth and carbon combustion for the same period within the NASA Arctic-Boreal Vulnerability Experiment (ABoVE) core and extended domain. Statistical models were constrained using a database of field observations across the domain and were related to a variety of response variables including remotely sensed indicators of fire severity, fire weather indices, local climate, soils, and topographic indicators. The burn depth and aboveground combustion models performed best, with poorer performance for belowground combustion. We estimate 2.37×106 ha (2.37 Mha) burned annually between 2001-2019 over the ABoVE domain (2.87 Mha across all of Alaska and Canada), emitting 79.3 ± 27.96 Tg (±1 standard deviation) of carbon (C) per year, with a mean combustion rate of 3.13 ± 1.17 kg C m-2. Mean combustion and burn depth displayed a general gradient of higher severity in the northwestern portion of the domain to lower severity in the south and east. We also found larger-fire years and later-season burning were generally associated with greater mean combustion. Our estimates are generally consistent with previous efforts to quantify burned area, fire carbon emissions, and their drivers in regions within boreal North America; however, we generally estimate higher burned area and carbon emissions due to our use of Landsat imagery, greater availability of field observations, and improvements in modeling. The burned area and combustion datasets described here (the ABoVE Fire Emissions Database, or ABoVE-FED) can be used for local- to continental-scale applications of boreal fire science

Model comparisons for estimating carbon emissions from North American wildland fire

Research activities focused on estimating the direct emissions of carbon from wildland fires across North America are reviewed as part of the North American Carbon Program disturbance synthesis. A comparison of methods to estimate the loss of carbon from the terrestrial biosphere to the atmosphere from wildland fires is presented. Published studies on emissions from recent and historic time periods and five specific cases are summarized, and new emissions estimates are made using contemporary methods for a set of specific fire events. Results from as many as six terrestrial models are compared. We find that methods generally produce similar results within each case, but estimates vary based on site location, vegetation (fuel) type, and fire weather. Area normalized emissions range from 0.23 kg C m−2 for shrubland sites in southern California/NW Mexico to as high as 6.0 kg C m−2 in northern conifer forests. Total emissions range from 0.23 to 1.6 Tg C for a set of 2003 fires in chaparral-dominated landscapes of California to 3.9 to 6.2 Tg C in the dense conifer forests of western Oregon. While the results from models do not always agree, variations can be attributed to differences in model assumptions and methods, including the treatment of canopy consumption and methods to account for changes in fuel moisture, one of the main drivers of variability in fire emissions. From our review and synthesis, we identify key uncertainties and areas of improvement for understanding the magnitude and spatial-temporal patterns of pyrogenic carbon emissions across North America

The clinical course of acute otitis media in high-risk Australian Aboriginal children: a longitudinal study

BACKGROUND: It is unclear why some children with acute otitis media (AOM) have poor outcomes. Our aim was to describe the clinical course of AOM and the associated bacterial nasopharyngeal colonisation in a high-risk population of Australian Aboriginal children. METHODS: We examined Aboriginal children younger than eight years who had a clinical diagnosis of AOM. Pneumatic otoscopy and video-otoscopy of the tympanic membrane (TM) and tympanometry was done every weekday if possible. We followed children for either two weeks (AOM without perforation), or three weeks (AOM with perforation), or for longer periods if the infection persisted. Nasopharyngeal swabs were taken at study entry and then weekly. RESULTS: We enrolled 31 children and conducted a total of 219 assessments. Most children had bulging of the TM or recent middle ear discharge at diagnosis. Persistent signs of suppurative OM (without ear pain) were present in most children 7 days (23/30, 77%), and 14 days (20/26, 77%) later. Episodes of AOM did not usually have a sudden onset or short duration. Six of the 14 children with fresh discharge in their ear canal had an intact or functionally intact TM. Perforation size generally remained very small (<2% of the TM). Healing followed by re-perforation was common. Ninety-three nasophyngeal swabs were taken. Most swabs cultured Streptococcus pneumoniae (82%), Haemophilus influenzae (71%), and Moraxella catarrhalis (95%); 63% of swabs cultured all three pathogens. CONCLUSION: In this high-risk population, AOM was generally painless and persistent. These infections were associated with persistent bacterial colonisation of the nasopharynx and any benefits of antibiotics were modest at best. Systematic follow up with careful examination and review of treatment are required and clinical resolution cannot be assumed

2019 Scholars at Work Conference Program

Program for the 2019 Scholars at Work Conference at Minnesota State University, Mankato on March 29, 2019

Mathematical modeling of the dynamic storage of iron in ferritin

<p>Abstract</p> <p>Background</p> <p>Iron is essential for the maintenance of basic cellular processes. In the regulation of its cellular levels, ferritin acts as the main intracellular iron storage protein. In this work we present a mathematical model for the dynamics of iron storage in ferritin during the process of intestinal iron absorption. A set of differential equations were established considering kinetic expressions for the main reactions and mass balances for ferritin, iron and a discrete population of ferritin species defined by their respective iron content.</p> <p>Results</p> <p>Simulation results showing the evolution of ferritin iron content following a pulse of iron were compared with experimental data for ferritin iron distribution obtained with purified ferritin incubated <it>in vitro </it>with different iron levels. Distinctive features observed experimentally were successfully captured by the model, namely the distribution pattern of iron into ferritin protein nanocages with different iron content and the role of ferritin as a controller of the cytosolic labile iron pool (cLIP). Ferritin stabilizes the cLIP for a wide range of total intracellular iron concentrations, but the model predicts an exponential increment of the cLIP at an iron content > 2,500 Fe/ferritin protein cage, when the storage capacity of ferritin is exceeded.</p> <p>Conclusions</p> <p>The results presented support the role of ferritin as an iron buffer in a cellular system. Moreover, the model predicts desirable characteristics for a buffer protein such as effective removal of excess iron, which keeps intracellular cLIP levels approximately constant even when large perturbations are introduced, and a freely available source of iron under iron starvation. In addition, the simulated dynamics of the iron removal process are extremely fast, with ferritin acting as a first defense against dangerous iron fluctuations and providing the time required by the cell to activate slower transcriptional regulation mechanisms and adapt to iron stress conditions. In summary, the model captures the complexity of the iron-ferritin equilibrium, and can be used for further theoretical exploration of the role of ferritin in the regulation of intracellular labile iron levels and, in particular, as a relevant regulator of transepithelial iron transport during the process of intestinal iron absorption.</p