Publications

Symbiotic relationships between N₂-fixing prokaryotes and their autotrophic hosts are essential in nitrogen (N)-limited ecosystems, yet the importance of this association in pristine boreal peatlands, which store 25 % of the world’s soil (C), has been overlooked. External inputs of N to bogs are predominantly atmospheric, and given that regions of boreal Canada anchor some of the lowest rates found globally (~1 kg N ha⁻¹ year⁻¹), biomass production is thought to be limited primarily by N. Despite historically low N deposition, we show that boreal bogs have accumulated approximately 12–25 times more N than can be explained by atmospheric inputs. Here we demonstrate high rates of biological N₂-fixation in prokaryotes associated with Sphagnum mosses that can fully account for the missing input of N needed to sustain high rates of C sequestration. Additionally, N amendment experiments in the field did not increase Sphagnum production, indicating that mosses are not limited by N. Lastly, by examining the composition and abundance of N₂-fixing prokaryotes by quantifying gene expression of 16S rRNA and nitrogenase-encoding nifH, we show that rates of N₂-fixation are driven by the substantial contribution from methanotrophs, and not from cyanobacteria. We conclude biological N₂-fixation drives high sequestration of C in pristine peatlands, and may play an important role in moderating fluxes of methane, one of the most important greenhouse gases produced in peatlands. Understanding the mechanistic controls on biological N₂-fixation is crucial for assessing the fate of peatland carbon stocks under scenarios of climate change and enhanced anthropogenic N deposition.

Keywords: Biological N₂-fixation, Boreal peatlands, Carbon, Nitrogen, Sphagnum, Methanotrophs

The Athabasca Oil Sands Region (AOSR) in northeastern Alberta, Canada has attracted much international attention in recent years due to the increased level of oil sands operations. A passive sampling program was initiated in 1999 to monitor ozone (O₃), nitrogen dioxide (NO₂) and sulfur dioxide (SO₂) in the AOSR for the estimation of the exposure of the forest monitoring sites and the characterization of temporal trends. Since 1999, highest concentrations of O₃ and NO₂ occurred in April and winter, respectively. The observed spring O₃ maximum is common in the northern hemisphere. The higher winter-time NO₂ concentrations were due to low atmospheric mixing height, stable atmosphere, and higher emissions during winter.

Sen-Theil trend analysis, a non-parametric analysis for temporal trending, determined that O₃ concentrations from 2000 to 2009 did not change. NO₂ concentrations increased slightly at three sites, and significantly increased at two sites closer to stationary and mobile sources. SO₂ concentration was increasing at JP107 and was decreasing at JP101. SO₂ concentrations did not increase at 4 other sites close to the major emissions. This suggests that SO₂ emissions were likely stable.

Spatial analysis was conducted to characterize the concentration distribution in the region. The O₃ concentrations were low near the emission sources (9.4 km) likely due to local O₃ titration. Highest NO₂ and SO₂ concentrations were measured near the main source area. Generally, passively measured monthly average concentrations of O₃, NO₂ and SO₂ stabilized at 20, 48 and 48 km from the main source area suggesting NO₂ and SO₂ emission influences were limited to < 50 km away from the major sources. However, one site (JP107) located near the Athabasca River Valley, 94 km north of the main source area, had higher SO₂ and NO₂ concentrations. This could be attributed to influence of valley flow, and/or to additional sources added in the region since 2007.

Keywords: Trend; Athabasca oil sands region; Passive sampler; Ozone; Sulfur dioxide; Nitrogen dioxide.

A portable dilution sampling and measurement system was developed for measuring multipollutant emissions from stationary and mobile sources under real-world operating conditions. This system draws a sample of exhaust gas from the source, dilutes it with filtered air and quantifies total volatile organic compounds (VOCs), carbon monoxide (CO), carbon dioxide (CO₂), nitric oxide (NO), nitrogen dioxide (NO₂), sulfur dioxide (SO₂), oxygen (O₂), particle size distribution, particle number and mass concentrations, and black carbon (BC) concentration at 1–6 sec interval. Integrated samples by canisters and filter packs are acquired for laboratory analyses of VOC speciation, particle mass concentration, light absorption, elements, isotopes, ions, ammonia (NH₃), hydrogen sulfide (H₂S), sulfur dioxide (SO₂), carbon, and organic compounds. Experiments were carried out to evaluate this system. The accuracy of key real-time instruments were found to deviate < ± 12% from references. CO₂ was used as the tracer gas to verify the concentration uniformity in the three measurement modules and relative concentration difference was < 5.1%. Instrument response time was tested by emissions from lighting and burning matches. The DustTrak DRX and optical particle counter (OPC) had the fastest response time, while other instruments had 3.5–21.5 sec delay from the DustTrak DRX and OPC. This system was applied to measure emissions from burning pine logs in a wood stove. The real-time data showed flaming, transition, and smoldering phases, and allowed real-time emission ratios to be calculated. Combing real-time data and laboratory analysis, this measurement system allows the development of multipollutant emission factors and source profiles.

Keywords: PM_2.5; Emission factor; Source profile; Biomass burning; Source characterization.