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• Tree areas of agroforestry systems (AFS) stored more C than adjacent herblands. • Surface organic horizon contained 10% of the C stored in the tree area of AFS. • C storage in surface organic horizon was positively related to tree age. • Establishing AFS can be an effective strategy for climate change mitigation. Agroforestry systems (AFS) are increasingly being recognized as sustainable land-use systems that can increase carbon (C) sequestration and improve food security. However, the relative contributions of various C pools to the overall C stock of AFS and their dependence on factors such as tree age, species diversity and density is still unclear in many regions. Using an equivalent soil mass approach, we investigated the effect of three different AFS (hedgerow, shelterbelt, and silvopasture) and their component land-use types (treed areas and adjacent cropland/grassland) on various C pools across 36 sites in central Alberta, Canada. On average, the treed area within AFS stored 178.5 t ha−1 more C relative to adjacent cropland or grassland, although the total C stock did not differ among the three AFS types. Most of the C in the treed area of AFS was stored in the mineral soil (61%), overstory trees (28%), and the LFH (litter, partially decomposed litter and humus, 10%) layer, while midstory trees, shrubs, and understory vegetation together accounted for the remaining 1% of the C storage. The C stock size in the treed area was closely associated with tree stand characteristics of the three AFS, with the C pool size in the LFH positively related to tree age. Our results highlight that the amount of C stored in the LFH layer is substantial and should be considered when assessing C storage within AFS and suggest that investing in AFS can be an effective strategy for meeting part of Canada's C reduction goals to mitigate climate change. [ABSTRACT FROM AUTHOR]

Abstract: This study presents a computational methodology to estimate the maximum probable leakage of CO2 along old wells in a geological sequestration operation. The methodology quantifies the maximum probable CO2 leakage as a function of the statistical characterization of existing wells. We use a Monte Carlo approach based on a computationally efficient simulator to run many thousands of realizations. Results from the Monte Carlo simulations are used to determine maximum leakage rates at 95% confidence. Uncertainty in the analysis is due to leaky well parameters, which are known to be highly uncertain. We consider a wide range of parameter values, with our focus on assignment of effective well permeability values and the correlation of those values along individual wells. We use a specific location in Alberta, Canada, to demonstrate the methodology using a hypothetical injection and an assumed probability structure for the well permeabilities. We show that for a wide range of parameter values, the amount of leakage is within the bounds suggested as acceptable for climate change mitigation. [Copyright &y& Elsevier]

Abstract: Large stationary CO2 emitters are located in central Alberta with cumulative annual emissions in the order of 30 Mt CO2. This includes four coal-fired power plants in the Wabamun Lake area, southwest of Edmonton with emissions between 3 to 6 Mt/year each. The study will perform a comprehensive characterization of large-scale CO2 storage opportunities in the Wabamun area and analyze any potential risks. As a benchmark, the project will examine the feasibility of storing 20 Mt- CO2/year for 50 years within 30 km of Wabamun. This gigaton-scale storage assessment project is one to two orders of magnitude larger than the commercial projects now under study. It will fill a gap between Canadian province-wide capacity estimates (which do not involve site specific studies of flow and geomechanics etc.) and the detailed commercial studies of small CO2 storage projects currently underway. Unlike the commercial projects, this project is planned as a public non-confidential project lead by the University of Calgary (U of C). The study will first assess the possible injection formations within the area based on storage capacity, ease of injectivity, leakage likelihood, and interference with current petroleum production. Then a few (1–3) specific targets will be selected for more detailed studies. The detailed studies will evaluate how the injected CO2 moves and reacts within the reservoir, the storage integrity of the over and underlying shaly aquitard, leakage risks of CO2 along existing wells and a preliminary well injection design. Finally, the study will do a preliminary assessment of currently available options for monitoring such large scale injection of CO2. Since the project is planned to develop a realistic scenario we will add an economic evaluation of the total project costs downstream of the capture and pipeline transportation components. Furthermore, the study will outline the necessary next steps to close any remaining knowledge gaps before planning and conducting the actual injection phase of the project. [Copyright &y& Elsevier]