Publications by authors named "Stephan Schott"

9 Publications

  • Page 1 of 1

Identification of Arctic Food Fish Species for Anthropogenic Contaminant Testing Using Geography and Genetics.

Foods 2020 Dec 8;9(12). Epub 2020 Dec 8.

Department of Biology, Queen's University, Kingston, ON K7L 3N6, Canada.

The identification of food fish bearing anthropogenic contaminants is one of many priorities for Indigenous peoples living in the Arctic. Mercury (Hg), arsenic (As), and persistent organic pollutants including polychlorinated biphenyls (PCBs) are of concern, and these are reported, in some cases for the first time, for fish sampled in and around King William Island, located in Nunavut, Canada. More than 500 salmonids, comprising Arctic char, lake trout, lake whitefish, and ciscoes, were assayed for contaminants. The studied species are anadromous, migrating to the ocean to feed in the summers and returning to freshwater before sea ice formation in the autumn. Assessments of muscle Hg levels in salmonids from fishing sites on King William Island showed generally higher levels than from mainland sites, with mean concentrations generally below guidelines, except for lake trout. In contrast, mainland fish showed higher means for As, including non-toxic arsenobetaine, than island fish. Lake trout were highest in As and PCB levels, with salmonid PCB congener analysis showing signatures consistent with the legacy of cold-war distant early warning stations. After DNA-profiling, only 4-32 Arctic char single nucleotide polymorphisms were needed for successful population assignment. These results support our objective to demonstrate that genomic tools could facilitate efficient and cost-effective cluster assignment for contaminant analysis during ocean residency. We further suggest that routine pollutant testing during the current period of dramatic climate change would be helpful to safeguard the wellbeing of Inuit who depend on these fish as a staple input to their diet. Moreover, this strategy should be applicable elsewhere.
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http://dx.doi.org/10.3390/foods9121824DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7764770PMC
December 2020

Cooperation through Competition-Dynamics and Microeconomics of a Minimal Nutrient Trade System in Arbuscular Mycorrhizal Symbiosis.

Front Plant Sci 2016 27;7:912. Epub 2016 Jun 27.

Facultad de Ingeniería, Centro de Bioinformática y Simulación Molecular, Universidad de Talca Talca, Chile.

In arbuscular mycorrhizal (AM) symbiosis, fungi and plants exchange nutrients (sugars and phosphate, for instance) for reciprocal benefit. Until now it is not clear how this nutrient exchange system works. Here, we used computational cell biology to simulate the dynamics of a network of proton pumps and proton-coupled transporters that are upregulated during AM formation. We show that this minimal network is sufficient to describe accurately and realistically the nutrient trade system. By applying basic principles of microeconomics, we link the biophysics of transmembrane nutrient transport with the ecology of organismic interactions and straightforwardly explain macroscopic scenarios of the relations between plant and AM fungus. This computational cell biology study allows drawing far reaching hypotheses about the mechanism and the regulation of nutrient exchange and proposes that the "cooperation" between plant and fungus can be in fact the result of a competition between both for the same resources in the tiny periarbuscular space. The minimal model presented here may serve as benchmark to evaluate in future the performance of more complex models of AM nutrient exchange. As a first step toward this goal, we included SWEET sugar transporters in the model and show that their co-occurrence with proton-coupled sugar transporters results in a futile carbon cycle at the plant plasma membrane proposing that two different pathways for the same substrate should not be active at the same time.
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http://dx.doi.org/10.3389/fpls.2016.00912DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4921476PMC
July 2016

Response to Comment on "Diminishing Returns or Compounding Benefits of Air Pollution Control? The Case of NO(x) and Ozone".

Environ Sci Technol 2016 Jan 18;50(1):502-3. Epub 2015 Dec 18.

School of Public Policy and Administration, Carleton University , Ottawa, Ontario, Canada K1S 5B6.

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http://dx.doi.org/10.1021/acs.est.5b05889DOI Listing
January 2016

Diminishing Returns or Compounding Benefits of Air Pollution Control? The Case of NOx and Ozone.

Environ Sci Technol 2015 Aug 6;49(16):9548-56. Epub 2015 Aug 6.

‡School of Public Policy and Administration, Carleton University, Ottawa, Ontario, Canada K1S 5B6.

Unlabelled: A common measure used in air quality benefit-cost assessment is marginal benefit (MB), or the monetized societal benefit of reducing 1 ton of emissions. Traditional depictions of MB for criteria air pollutants are such that each additional ton of emission reduction incurs less benefit than the previous ton. Using adjoint sensitivity analysis in a state-of-the-art air quality model, we estimate MBs for NOx emitted from mobile and point sources, characterized based on the estimated ozone-related premature mortality in the U.S.

Population: Our findings indicate that nation-wide emission reductions in the U.S. significantly increase NOx MBs for all sources, without exception. We estimate that MBs for NOx emitted from mobile sources increase by 1.5 and 2.5 times, on average, for 40% and 80% reductions in anthropogenic emissions across the U.S. Our results indicate a strictly concave damage function and compounding benefits of progressively lower levels of NOx emissions, providing economic incentive for higher levels of abatement than were previously advisible. These findings suggest that the traditional perception of a convex damage function and decreasing MB with abatement may not hold true for secondary pollutants such as O3.
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http://dx.doi.org/10.1021/acs.est.5b00950DOI Listing
August 2015

Optimal Ozone Control with Inclusion of Spatiotemporal Marginal Damages and Electricity Demand.

Environ Sci Technol 2015 Jul 24;49(13):7870-8. Epub 2015 Jun 24.

Department of Civil and Environmental Engineering, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario K1S 5B6, Canada.

Marginal damage (MD), or damage per ton of emission, is a policy metric used for effective pollution control and reducing the corresponding adverse health impacts. However, for a pollutant such as NOx, the MD varies by the time and location of the emissions, a complication that is not adequately accounted for in the currently implemented economic instruments. Policies accounting for MD information would aim to encourage emitters with large MDs to reduce their emissions. An optimization framework is implemented to account for NOx spatiotemporal MDs calculated through adjoint sensitivity analysis and to simulate power plants' behavior under emission and simplified electricity constraints. The results from a case study of U.S. power plants indicate that time-specific MDs are high around noon and low in the evening. Furthermore, an emissions reduction of about 40% and a net benefit of about $1200 million can be gained for this subset of power plants if a larger fraction of the electricity demand is supplied by power plants at low-damage times and in low-damage locations. The results also indicate that the consideration of temporal effects in NOx control policies results in a comparable net benefit to the consideration of spatial or spatiotemporal effects, thus providing a promising option for policy development.
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http://dx.doi.org/10.1021/acs.est.5b01178DOI Listing
July 2015

Optimal ozone reduction policy design using adjoint-based NOx marginal damage information.

Environ Sci Technol 2013 19;47(23):13528-35. Epub 2013 Nov 19.

Department of Civil and Environmental Engineering and ‡Department of Public Policy and Administration, Carleton University , 1125 Colonel By Dr., Ottawa, ON K1S 5B6, Canada.

Despite substantial reductions in nitrogen oxide (NOx) emissions in the United States, the success of emission control programs in optimal ozone reduction is disputable because they do not consider the spatial and temporal differences in health and environmental damages caused by NOx emissions. This shortcoming in the current U.S. NOx control policy is explored, and various methodologies for identifying optimal NOx emission control strategies are evaluated. The proposed approach combines an optimization platform with an adjoint (or backward) sensitivity analysis model and is able to examine the environmental performance of the current cap-and-trade policy and two damage-based emissions-differentiated policies. Using the proposed methodology, a 2007 case study of 218 U.S. electricity generation units participating in the NOx trading program is examined. The results indicate that inclusion of damage information can significantly enhance public health performance of an economic instrument. The net benefit under the policy that minimizes the social cost (i.e., health costs plus abatement costs) is six times larger than that of an exchange rate cap-and-trade policy.
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http://dx.doi.org/10.1021/es402531nDOI Listing
July 2015

Improving NO(x) cap-and-trade system with adjoint-based emission exchange rates.

Environ Sci Technol 2012 Nov 25;46(21):11905-12. Epub 2012 Oct 25.

Department of Civil and Environmental Engineering, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario, Canada.

Cap-and-trade programs have proven to be effective instruments for achieving environmental goals while incurring minimum cost. The nature of the pollutant, however, affects the design of these programs. NO(x), an ozone precursor, is a nonuniformly mixed pollutant with a short atmospheric lifetime. NO(x) cap-and-trade programs in the U.S. are successful in reducing total NO(x) emissions but may result in suboptimal environmental performance because location-specific ozone formation potentials are neglected. In this paper, the current NO(x) cap-and-trade system is contrasted to a hypothetical NO(x) trading policy with sensitivity-based exchange rates. Location-specific exchange rates, calculated through adjoint sensitivity analysis, are combined with constrained optimization for prediction of NO(x) emissions trading behavior and post-trade ozone concentrations. The current and proposed policies are examined in a case study for 218 coal-fired power plants that participated in the NO(x) Budget Trading Program in 2007. We find that better environmental performance at negligibly higher system-wide abatement cost can be achieved through inclusion of emission exchange rates. Exposure-based exchange rates result in better environmental performance than those based on concentrations.
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http://dx.doi.org/10.1021/es302406yDOI Listing
November 2012

Exact density functional for hard-rod mixtures derived from Markov chain approach.

Phys Rev E Stat Nonlin Soft Matter Phys 2012 Apr 24;85(4 Pt 1):042107. Epub 2012 Apr 24.

Fachbereich Physik, Universität Osnabrück, Barbarastraße 7, 49076 Osnabrück, Germany.

Using a Markov chain approach we rederive the exact density functional for hard-rod mixtures on a one-dimensional lattice, which forms the basis of the lattice fundamental measure theory. The transition probability in the Markov chain depends on a set of occupation numbers, which reflects the property of a zero-dimensional cavity to hold at most one particle. For given mean occupation numbers (density profile), an exact expression for the equilibrium distribution of microstates is obtained, which means an expression for the unique external potential that generates the density profile in equilibrium. By considering the rod ends to fall onto lattice sites, the mixture is always additive.
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http://dx.doi.org/10.1103/PhysRevE.85.042107DOI Listing
April 2012

Internal friction and vulnerability of mixed alkali glasses.

Phys Rev Lett 2005 Sep 7;95(11):115901. Epub 2005 Sep 7.

Institut für Physik, Technische Universität Ilmenau, 98684 Ilmenau, Germany.

Based on a hopping model we show how the mixed alkali effect in glasses can be understood if only a small fraction c(V) of the available sites for the mobile ions is vacant. In particular, we reproduce the peculiar behavior of the internal friction and the steep fall ("vulnerability") of the mobility of the majority ion upon small replacements by the minority ion. The single and mixed alkali internal friction peaks are caused by ion-vacancy and ion-ion exchange processes. If c(V) is small, they can become comparable in height even at small mixing ratios. The large vulnerability is explained by a trapping of vacancies induced by the minority ions. Reasonable choices of model parameters yield typical behaviors found in experiments.
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http://dx.doi.org/10.1103/PhysRevLett.95.115901DOI Listing
September 2005
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