Carolyn Smyth

An inventory-based analysis of Canada's managed forest carbon dynamics, 1990 to 2008.

Canadas forests play an important role in the global carbon (C) cycle because of their large and dynamic C stocks. Detailed monitoring of C exchange between forests and the atmosphere and improved understanding of the processes that affect the net ecosystem exchange of C are needed to improve our understanding of the terrestrial C budget. We estimated the C budget of Canadas 2.3 × 106 km2 managed forests from 1990 to 2008 using an empirical modelling approach driven by detailed forestry datasets. We estimated that average net primary production (NPP) during this period was 809 ± 5 Tg C yr−1 (352 g C m−2 yr−1) and net ecosystem production (NEP) was 71 ± 9 Tg C yr−1 (31 g C m−2 yr−1). Harvesting transferred 45 ± 4 Tg C yr−1 out of the ecosystem and 45 ± 4 Tg C yr−1 within the ecosystem (from living biomass to dead organic matter pools). Fires released 23 ± 16 Tg C yr−1 directly to the atmosphere, and fires, insects and other natural disturbances transferred 52 ± 41 Tg C yr−1 from biomass to dead organic matter pools, from where C will gradually be released through decomposition. Net biome production (NBP) was only 2 ± 20 Tg C yr−1 (1 g C m−2 yr−1); the low C sequestration ratio (NBP/NPP=0.3%) is attributed to the high average age of Canadas managed forests and the impact of natural disturbances. Although net losses of ecosystem C occurred during several years due to large fires and widespread bark beetle outbreak, Canadas managed forests were a sink for atmospheric CO2 in all years, with an uptake of 50 ± 18 Tg C yr−1 [net ecosystem exchange (NEE) of CO2=−22 g C m−2 yr−1].

Wave Friction Factors in Nearshore Sands

Abstract Wave friction factors are estimated from vertical profiles of near-bed turbulence and horizontal velocity spanning the wave bottom boundary layer. Measured values are partitioned by bed state, which ranged from irregular ripples to flat bed, and are examined as a function of two traditionally selected parameters—physical bed roughness and outer flow Reynolds number. The measurements are from two field experiments in very different nearshore environments: a relatively protected unbarred pocket beach and a linear barred beach exposed to the open shelf (Duck). Measured wave friction factors are remarkably similar for the two beaches and are highest for low-energy rippled beds and lowest for the high-energy flat bed conditions. The reduction in the friction factor for high-energy conditions corresponds to a decrease in the physical roughness of the bed as wave energy increases. As a function of relative roughness, measured friction factors are generally consistent with previous laboratory results and...

The carbon implications of large-scale afforestation of agriculturally marginal land with short-rotation willow in Saskatchewan.

Afforestation with short‐rotation coppice (SRC) willow plantations for the purpose of producing bioenergy feedstock was contemplated as one potential climate change mitigation option. The objectives of this study were to assess the magnitude of this mitigation potential by addressing: (i) the land area potentially available for SRC systems in the province of Saskatchewan, Canada; (ii) the potential biomass yields of SRC plantations; and (iii) the carbon implications from such a large‐scale afforestation program. Digital soils and land‐use data were used to identify, map, and group into clusters of similar polygons 2.12 million hectares (Mha) of agriculturally marginal land that was potentially suitable for willow in the Boreal Plains and Prairies ecozones in Saskatchewan. The Physiological Principles in Predicting Growth (3PG) model was calibrated with data from SRC experiments in Saskatchewan, to quantify potential willow biomass yields, and the Carbon Budget Model of the Canadian Forest Sector (CBM‐CFS3), was used to simulate stand and landscape‐level C fluxes and stocks. Short‐rotation willow plantations managed in 3 year rotations for seven consecutive harvests (21 years) after coppicing at Year 1 produced about 12 Mg ha−1 yr−1 biomass. The more significant contribution to the C cycle was the cumulative harvest. After 44 years, the potential average cumulative harvested biomass C in the Prairies was 244 Mg C ha−1 (5.5 Mg C ha−1 yr−1) about 20% higher than the average for the Boreal Plains, 203 Mg C ha−1 (4.6 Mg C ha−1 yr−1). This analysis did not consider afforestation costs, rate of establishment of willow plantations, and other constraints, such as drought and disease effects on biomass yield. The results must therefore be interpreted as a biophysical mitigation potential with the technical and economic potential being both lower than our estimates. Nevertheless, short‐rotation bioenergy plantations offer one potential mitigation option to reduce the rate of CO2 accumulation in the earths atmosphere and further research is needed to operationalise such a mitigation effort.

Estimating product and energy substitution benefits in national-scale mitigation analyses for Canada

The potential of forests and the forest sector to mitigate greenhouse gas (GHG) emissions is widely recognized, but challenging to quantify at a national scale. Mitigation benefits through the use of forest products are affected by product life cycles, which determine the duration of carbon storage in wood products and substitution benefits where emissions are avoided using wood products instead of other emissions‐intensive building products and energy fuels. Here we determined displacement factors for wood substitution in the built environment and bioenergy at the national level in Canada. For solid wood products, we compiled a basket of end‐use products and determined the reduction in emissions for two functionally equivalent products: a more wood‐intensive product vs. a less wood‐intensive one. Avoided emissions for end‐use products basket were weighted by Canadian consumption statistics to reflect national wood uses, and avoided emissions were further partitioned into displacement factors for sawnwood and panels. We also examined two bioenergy feedstock scenarios (constant supply and constrained supply) to estimate displacement factors for bioenergy using an optimized selection of bioenergy facilities which maximized avoided emissions from fossil fuels. Results demonstrated that the average displacement factors were found to be similar: product displacement factors were 0.54 tC displaced per tC of used for sawnwood and 0.45 tC tC−1 for panels; energy displacement factors for the two feedstock scenarios were 0.47 tC tC−1 for the constant supply and 0.89 tC tC−1 for the constrained supply. However, there was a wide range of substitution impacts. The greatest avoided emissions occurred when wood was substituted for steel and concrete in buildings, and when bioenergy from heat facilities and/or combined heat and power facilities was substituted for energy from high‐emissions fossil fuels. We conclude that (1) national‐level substitution benefits need to be considered within a systems perspective on climate change mitigation to avoid the development of policies that deliver no net benefits to the atmosphere, (2) the use of long‐lived wood products in buildings to displace steel and concrete reduces GHG emissions, (3) the greatest bioenergy substitution benefits are achieved using a mix of facility types and capacities to displace emissions‐intensive fossil fuels.

Climate change mitigation potential of local use of harvest residues for bioenergy in Canada

We estimate the mitigation potential of local use of bioenergy from harvest residues for the 2.3 × 106 km2 (232 Mha) of Canadas managed forests from 2017 to 2050 using three models: Carbon Budget Model of the Canadian Forest Sector (CBM‐CFS3), a harvested wood products (HWP) model that estimates bioenergy emissions, and a model of emission substitution benefits from the use of bioenergy. We compare the use of harvest residues for local heat and electricity production relative to a base case scenario and estimate the climate change mitigation potential at the forest management unit level. Results demonstrate large differences between and within provinces and territories across Canada. We identify regions with increasing benefits to the atmosphere for many decades into the future and regions where no net benefit would occur over the 33‐year study horizon. The cumulative mitigation potential for regions with positive mitigation was predicted to be 429 Tg CO2e in 2050, with 7.1 TgC yr −1 of harvest residues producing bioenergy that met 3.1% of the heat demand and 2.9% of the electricity demand for 32.1 million people living within these regions. Our results show that regions with positive mitigation produced bioenergy, mainly from combined heat and power facilities, with emissions intensities that ranged from roughly 90 to 500 kg CO2e MWh−1. Roughly 40% of the total captured harvest residue was associated with regions that were predicted to have a negative cumulative mitigation potential in 2050 of −152 Tg CO2e. We conclude that the capture of harvest residues to produce local bioenergy can reduce GHG emissions in populated regions where bioenergy, mainly from combined heat and power facilities, offsets fossil fuel sources (fuel oil, coal and petcoke, and natural gas).

Acoustic observations of vertical and horizontal swimming velocities of a diel migrator

Astrong sound scattering layerwhich underwent diel verticalmigrationwas observed over 176 days using a bottom-mounted 600 kHz ADCP at a depth of approximately 285 m on the upper continental slope. Average observed descent times of the scatterers were within 12 minutes of sunrise and average ascent times were within 13 minutes of sunset. Average ascent speeds progressively increased away from the bed and approached6 cm/s.Average descent speeds similarly reached amaximumof∼6 cm/s. Horizontal velocities of the scatterers during vertical migration were found to be smaller than ambient velocities (by up to 3 cm/s), and it is inferred that the migrators were swimming horizontally against the flow. Horizontal velocities of the scatterers during time intervals when the layer was near the seafloor were found to be southwest (up to 3 cm/s), and onshelf (up to 1.7 cm/s) relative to the flow above the layer. Swimming velocities were independent of alongshelf flow direction, counter to the hypothesis that the scatterers sought to maintain their position by swimming against the flow.

A systems approach to assess climate change mitigation options in landscapes of the United States forest sector

BackgroundUnited States forests can contribute to national strategies for greenhouse gas reductions. The objective of this work was to evaluate forest sector climate change mitigation scenarios from 2018 to 2050 by applying a systems-based approach that accounts for net emissions across four interdependent components: (1) forest ecosystem, (2) land-use change, (3) harvested wood products, and (4) substitution benefits from using wood products and bioenergy. We assessed a range of land management and harvested wood product scenarios for two case studies in the U.S: coastal South Carolina and Northern Wisconsin. We integrated forest inventory and remotely-sensed disturbance data within a modelling framework consisting of a growth-and-yield driven ecosystem carbon model; a harvested wood products model that estimates emissions from commodity production, use and post-consumer treatment; and displacement factors to estimate avoided fossil fuel emissions. We estimated biophysical mitigation potential by comparing net emissions from land management and harvested wood products scenarios with a baseline (‘business as usual’) scenario.ResultsBaseline scenario results showed that the strength of the ecosystem carbon sink has been decreasing in the two sites due to age-related productivity declines and deforestation. Mitigation activities have the potential to lessen or delay the further reduction in the carbon sink. Results of the mitigation analysis indicated that scenarios reducing net forest area loss were most effective in South Carolina, while extending harvest rotations and increasing longer-lived wood products were most effective in Wisconsin. Scenarios aimed at increasing bioenergy use either increased or reduced net emissions within the 32-year analysis timeframe.ConclusionsIt is critical to apply a systems approach to comprehensively assess net emissions from forest sector climate change mitigation scenarios. Although some scenarios produced a benefit by displacing emissions from fossil fuel energy or by substituting wood products for other materials, these benefits can be outweighed by increased carbon emissions in the forest or product systems. Maintaining forests as forests, extending rotations, and shifting commodities to longer-lived products had the strongest mitigation benefits over several decades. Carbon cycle impacts of bioenergy depend on timeframe, feedstocks, and alternative uses of biomass, and cannot be assumed carbon neutral.

Coherent Doppler profiler measurements of near‐bed suspended sediment fluxes

Vertical profiles of vertical turbulence intensity and vertical sediment fluxes were collected by an acoustic Coherent Doppler Profiler during two experiments: at Queensland Beach, NS and SandyDuck97. Measurements are investigated as a function of bedstate from low energy vortex ripples to high energy flat bed. Ensemble‐average vertical turbulence intensity profiles exhibit a peak within the wave boundary layer at heights of O (1 cm) above bottom for all bedstates. Peak average turbulence intensities are relatively independent of bedstate, varying by no more than 50% despite a factor of 7–10 variation in average wave energy. This otherwise remarkable observation can be understood from the corresponding decrease in the physical roughness of the bed, associated with the different observed bedstates. Estimated wave friction factors are highest for low energy rippled beds and smallest for flat bed conditions. Estimates of the vertical suspended sediment flux partitioned into mean, wave, and turbulent componen...

Coherent Doppler profiler measurements of near‐bed suspended sediment fluxes for different bed states

Vertical profiles of vertical turbulence intensity and vertical sediment fluxes were collected by an acoustic coherent Doppler profiler at two locations: Queensland Beach (Nova Scotia), and Duck (North Carolina). Observations of the turbulence intensity over different bed states (irregular ripples, cross ripples, linear‐transition ripples, and flat bed) reveal that the near‐bed turbulence levels are strongly affected by bed forms. This study examines the mechanisms of distributing suspended sediments and generating near‐bed turbulence for the four bed states based on the characteristics of two previously observed mechanisms: diffusion and vortex shedding. Wave‐phase averages of turbulence intensity, suspended sediment concentration, and suspended sediment fluxes are compared to vortex shedding and diffusion signatures. Evidence of vortex shedding is found for the low‐energy ripples, but no signatures of diffusion are observed. Two diffusion models including a bed stress model, and an eddy diffusion model ...