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Journal of Chemistry
Volume 2017, Article ID 8175631, 19 pages
https://doi.org/10.1155/2017/8175631
Research Article

Understanding the Spatial Heterogeneity of CO2 and CH4 Fluxes from an Urban Shallow Lake: Correlations with Environmental Factors

1Key Laboratory of Integrated Regulation and Resource Development on Shallow Lake of Ministry of Education, College of Environment, Hohai University, Nanjing, Jiangsu 210098, China
2Department of Plant, Soil, and Microbial Sciences, Michigan State University, East Lansing, MI 48824, USA
3School of Earth Sciences and Engineering, Nanjing University, Nanjing 210093, China

Correspondence should be addressed to Zhenhua Zhao; moc.621@0004hzz

Received 19 May 2017; Revised 9 September 2017; Accepted 12 October 2017; Published 19 November 2017

Academic Editor: Davide Vione

Copyright © 2017 Zhenhua Zhao et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Linked References

  1. Intergovernmental Panel on Climate Change, Climate Change 2013—The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, T. F. Stocker, D. Qin, G.-K. Plattner, Eds., Cambridge University Press, Cambridge, UK, 2013. View at Publisher · View at Google Scholar
  2. G. Yvon-Durocher, A. P. Allen, D. Bastviken et al., “Methane fluxes show consistent temperature dependence across microbial to ecosystem scales,” Nature, vol. 507, no. 7493, pp. 488–491, 2014. View at Publisher · View at Google Scholar · View at Scopus
  3. E. Sanhueza, Y. Dong, D. Scharffe, J. M. Lobert, and P. J. Crutzen, “Carbon monoxide uptake by temperate forest soils: The effects of leaves and humus layers,” Tellus B: Chemical and Physical Meteorology, vol. 50, no. 1, pp. 51–58, 1998. View at Publisher · View at Google Scholar · View at Scopus
  4. M. J. Prather and J. Hsu, “Coupling of nitrous oxide and methane by global atmospheric chemistry,” Science, vol. 330, no. 6006, pp. 952–954, 2010. View at Publisher · View at Google Scholar · View at Scopus
  5. H. J. Smith, “Greenhouse gases drove African rainfall,” Science, vol. 346, no. 6214, pp. 1195–1195, 2014. View at Publisher · View at Google Scholar
  6. M. U. M. Anas, K. A. Scott, and B. Wissel, “Carbon budgets of boreal lakes: State of knowledge, challenges, and implications,” Environmental Reviews, vol. 23, no. 3, pp. 275–287, 2015. View at Publisher · View at Google Scholar · View at Scopus
  7. K. Sturm, A. Grinham, U. Werner, and Z. Yuan, “Sources and sinks of methane and nitrous oxide in the subtropical Brisbane River estuary, South East Queensland, Australia,” Estuarine, Coastal and Shelf Science, vol. 168, pp. 10–21, 2016. View at Publisher · View at Google Scholar · View at Scopus
  8. IPCC, IPCC, Geneva, Switzerland, 2014.
  9. J. Jauhiainen, H. Takahashi, J. E. P. Heikkinen, P. J. Martikainen, and H. Vasander, “Carbon fluxes from a tropical peat swamp forest floor,” GCB Bioenergy, vol. 11, no. 10, pp. 1788–1797, 2005. View at Publisher · View at Google Scholar · View at Scopus
  10. J. Le Mer and P. Roger, “Production, oxidation, emission and consumption of methane by soils: A review,” European Journal of Soil Biology, vol. 37, no. 1, pp. 25–50, 2001. View at Publisher · View at Google Scholar · View at Scopus
  11. D. Bastviken, J. Cole, M. Pace, and L. Tranvik, “Methane emissions from lakes: Dependence of lake characteristics, two regional assessments, and a global estimate,” Global Biogeochemical Cycles, vol. 18, no. 4, pp. 1–12, 2004. View at Publisher · View at Google Scholar · View at Scopus
  12. T. Delsontro, D. F. Mcginnis, S. Sobek, I. Ostrovsky, and B. Wehrli, “Extreme methane emissions from a swiss hydropower Reservoir: Contribution from bubbling sediments,” Environmental Science & Technology, vol. 44, no. 7, pp. 2419–2425, 2010. View at Publisher · View at Google Scholar · View at Scopus
  13. S. Li, R. T. Bush, N. J. Ward, L. A. Sullivan, and F. Dong, “Air-water CO2 outgassing in the Lower Lakes (Alexandrina and Albert, Australia) following a millennium drought,” Science of the Total Environment, vol. 542, pp. 453–468, 2016. View at Publisher · View at Google Scholar · View at Scopus
  14. S. Xiao, D. Liu, Y. Wang, Z. Yang, and W. Chen, “Temporal variation of methane flux from Xiangxi Bay of the Three Gorges Reservoir,” Scientific Reports, vol. 3, article no. 2500, 2013. View at Publisher · View at Google Scholar · View at Scopus
  15. L. Liu, M. Xu, M. Lin, and X. Zhang, “Spatial variability of greenhouse gas effluxes and their controlling factors in the Poyang lake in China,” Polish Journal of Environmental Studies, vol. 22, no. 3, pp. 749–758, 2013. View at Google Scholar · View at Scopus
  16. Y. Xing, P. Xie, H. Yang, L. Ni, Y. Wang, and K. Rong, “Methane and carbon dioxide fluxes from a shallow hypereutrophic subtropical Lake in China,” Atmospheric Environment, vol. 39, no. 30, pp. 5532–5540, 2005. View at Publisher · View at Google Scholar · View at Scopus
  17. B. A. Tangen, R. G. Finocchiaro, R. A. Gleason, and C. F. Dahl, “Greenhouse Gas Fluxes of a Shallow Lake in South-Central North Dakota, USA,” Wetlands, vol. 36, no. 4, pp. 779–787, 2016. View at Publisher · View at Google Scholar · View at Scopus
  18. H. Song and X. Liu, “Anthropogenic Effects on Fluxes of Ecosystem Respiration and Methane in the Yellow River Estuary, China,” Wetlands, vol. 36, pp. 113–123, 2016. View at Publisher · View at Google Scholar · View at Scopus
  19. P. A. Raymond, J. Hartmann, R. Lauerwald et al., “Global carbon dioxide emissions from inland waters,” Nature, vol. 503, no. 7476, pp. 355–359, 2013. View at Publisher · View at Google Scholar · View at Scopus
  20. D. Bastviken, A. L. Santoro, H. Marotta et al., “Methane emissions from pantanal, South America, during the low water season: Toward more comprehensive sampling,” Environmental Science & Technology, vol. 44, no. 14, pp. 5450–5455, 2010. View at Publisher · View at Google Scholar · View at Scopus
  21. H. Marotta, L. Pinho, C. Gudasz, D. Bastviken, L. J. Tranvik, and A. Enrich-Prast, “Greenhouse gas production in low-latitude lake sediments responds strongly to warming,” Nature Climate Change, vol. 4, no. 6, pp. 467–470, 2014. View at Publisher · View at Google Scholar · View at Scopus
  22. C. Palma-Silva, C. C. Marinho, E. F. Albertoni et al., “Methane emissions in two small shallow neotropical lakes: The role of temperature and trophic level,” Atmospheric Environment, vol. 81, pp. 373–379, 2013. View at Publisher · View at Google Scholar · View at Scopus
  23. J. L. Riera, J. E. Schindler, and T. K. Kratz, “Seasonal dynamics of carbon dioxide and methane in two clear-water lakes and two bog lakes in northern Wisconsin, U.S.A.,” Canadian Journal of Fisheries and Aquatic Sciences, vol. 56, no. 2, pp. 265–274, 1999. View at Publisher · View at Google Scholar · View at Scopus
  24. R. B. Peixoto, H. Marotta, D. Bastviken, and A. Enrich-Prast, “Floating Aquatic Macrophytes Can Substantially Offset Open Water CO2 Emissions from Tropical Floodplain Lake Ecosystems,” Ecosystems, vol. 19, no. 4, pp. 724–736, 2016. View at Publisher · View at Google Scholar · View at Scopus
  25. R. Bolpagni, E. Pierobon, D. Longhi et al., “Diurnal exchanges of CO2 and CH4 across the water-atmosphere interface in a water chestnut meadow (Trapa natans L.),” Aquatic Botany, vol. 87, no. 1, pp. 43–48, 2007. View at Publisher · View at Google Scholar · View at Scopus
  26. S. Kosten, M. Piñeiro, E. de Goede, J. de Klein, L. P. M. Lamers, and K. Ettwig, “Fate of methane in aquatic systems dominated by free-floating plants,” Water Research, vol. 104, pp. 200–207, 2016. View at Publisher · View at Google Scholar · View at Scopus
  27. D. F. McGinnis, N. Bilsley, M. Schmidt et al., “Deconstructing Methane Emissions from a Small Northern European River: Hydrodynamics and Temperature as Key Drivers,” Environmental Science & Technology, vol. 50, no. 21, pp. 11680–11687, 2016. View at Publisher · View at Google Scholar · View at Scopus
  28. T. Delsontro, M. J. Kunz, T. Kempter, A. Wüest, B. Wehrli, and D. B. Senn, “Spatial heterogeneity of methane ebullition in a large tropical reservoir,” Environmental Science & Technology, vol. 45, no. 23, pp. 9866–9873, 2011. View at Publisher · View at Google Scholar · View at Scopus
  29. J. A. Harrison, B. R. Deemer, M. K. Birchfield, and M. T. O'Malley, “Reservoir Water-Level Drawdowns Accelerate and Amplify Methane Emission,” Environmental Science & Technology, vol. 51, no. 3, pp. 1267–1277, 2017. View at Publisher · View at Google Scholar · View at Scopus
  30. S. Wang, C. Liu, K. M. Yeager et al., “The spatial distribution and emission of nitrous oxide (N2O) in a large eutrophic lake in eastern China: Anthropogenic effects,” Science of the Total Environment, vol. 407, no. 10, pp. 3330–3337, 2009. View at Publisher · View at Google Scholar · View at Scopus
  31. R. Gonzalez-Valencia, A. Sepulveda-Jauregui, K. Martinez-Cruz, J. Hoyos-Santillan, L. Dendooven, and F. Thalasso, “Methane emissions from Mexican freshwater bodies: Correlations with water pollution,” Hydrobiologia, vol. 721, no. 1, pp. 9–22, 2014. View at Publisher · View at Google Scholar · View at Scopus
  32. M. L. Pace, J. J. Cole, S. R. Carpenter et al., “Whole-lake carbon-13 additions reveal terrestrial support of aquatic food webs,” Nature, vol. 427, no. 6971, pp. 240–243, 2004. View at Publisher · View at Google Scholar · View at Scopus
  33. L. J. Tranvik, J. A. Downing, J. B. Cotner et al., “Lakes and reservoirs as regulators of carbon cycling and climate,” Limnology and Oceanography, vol. 54, no. 6, pp. 2298–2314, 2009. View at Publisher · View at Google Scholar · View at Scopus
  34. P. Kortelainen, M. Rantakari, H. Pajunen et al., “Carbon evasion/accumulation ratio in boreal lakes is linked to nitrogen,” Global Biogeochemical Cycles, vol. 27, no. 2, pp. 363–374, 2013. View at Publisher · View at Google Scholar · View at Scopus
  35. L. Liu and M. Xu, “Microbial biomass in sediments affects greenhouse gas effluxes in Poyang Lake in China,” Journal of Freshwater Ecology, vol. 31, no. 1, pp. 109–121, 2016. View at Publisher · View at Google Scholar · View at Scopus
  36. X. Cheng, Y. Luo, Q. Xu et al., “Seasonal variation in CH4 emission and its 13C-isotopic signature from Spartina alterniflora and Scirpus mariqueter soils in an estuarine wetland,” Plant and Soil, vol. 327, no. 1, pp. 85–94, 2010. View at Publisher · View at Google Scholar · View at Scopus
  37. A. P. Schrier-Uijl, A. J. Veraart, P. A. Leffelaar, F. Berendse, and E. M. Veenendaal, “Release of CO2 and CH4 from lakes and drainage ditches in temperate wetlands,” Biogeochemistry, vol. 102, no. 1, pp. 265–279, 2011. View at Publisher · View at Google Scholar · View at Scopus
  38. J. F. Magenheimer, T. R. Moore, G. L. Chmura, and R. J. Daoust, “Methane and carbon dioxide flux from a macrotidal salt marsh, Bay of Fundy, New Brunswick,” Estuaries and Coasts, vol. 19, no. 1, pp. 139–145, 1996. View at Publisher · View at Google Scholar · View at Scopus
  39. P. Yang, C. Tong, Q.-H. He, and J.-F. Huang, “Diurnal variations of greenhouse gas fluxes at the water-air interface of aquaculture ponds in the Min River estuary,” Huanjing Kexue, vol. 33, no. 12, pp. 4194–4204, 2012. View at Google Scholar · View at Scopus
  40. A. Tremblay, J. Therrien, B. Hamlin, E. Wichmann, and L. J. LeDrew, “GHG Emissions from Boreal Reservoirs and Natural Aquatic Ecosystems,” in Greenhouse Gas Emissions — Fluxes and Processes, Environmental Science and Engineering, pp. 209–232, Springer Berlin Heidelberg, Berlin, Heidelberg, 2005. View at Publisher · View at Google Scholar
  41. S. Juutinen, M. Rantakari, P. Kortelainen et al., “Methane dynamics in different boreal lake types,” Biogeosciences, vol. 6, no. 2, pp. 209–223, 2009. View at Publisher · View at Google Scholar · View at Scopus
  42. T. Diem, S. Koch, S. Schwarzenbach, B. Wehrli, and C. J. Schubert, “Greenhouse gas emissions (CO2, CH4, and N2O) from several perialpine and alpine hydropower reservoirs by diffusion and loss in turbines,” Aquatic Sciences, vol. 74, no. 3, pp. 619–635, 2012. View at Publisher · View at Google Scholar · View at Scopus
  43. Apha, Standard methods for the examination of water and wastewater, American Public Health Association, Washington, USA, 2005.
  44. S. Sun, D. Xing, and L. Zhang, “Determination of nitrate-N in Water by 2-isopropyl-5-methyphenol spectrophotometry,” Journal of Environment and Health, vol. 24, no. 4, pp. 256-257, 2007. View at Google Scholar
  45. C. Ter Braak and P. Smilauer, CANOCO reference manual and Cano Draw for Windows user's guide: Software for canonical community ordination (version 4.5), Microcomputer Power, NY, USA, 2002.
  46. B. Angers, P. Magnan, M. Plante, and L. Bernatchez, “Canonical correspondence analysis for estimating spatial and environmental effects on microsatellite gene diversity in brook charr (Salvelinus fontinalis),” Molecular Ecology, vol. 8, no. 6, pp. 1043–1053, 1999. View at Publisher · View at Google Scholar · View at Scopus
  47. D. Moreira and J. C. M. Pires, “Atmospheric CO2 capture by algae: Negative carbon dioxide emission path,” Bioresource Technology, vol. 215, pp. 371–379, 2016. View at Publisher · View at Google Scholar · View at Scopus
  48. P. Casper, S. C. Maberly, G. H. Hall, and B. J. Finlay, “Fluxes of methane and carbon dioxide from a small productive lake to the atmosphere,” Biogeochemistry, vol. 49, no. 1, pp. 1–19, 2000. View at Publisher · View at Google Scholar · View at Scopus
  49. A. Ojala, J. L. Bellido, T. Tulonen, P. Kankaala, and J. Huotari, “Carbon gas fluxes from a brown-water and a clear-water lake in the boreal zone during a summer with extreme rain events,” Limnology and Oceanography, vol. 56, no. 1, pp. 61–76, 2011. View at Publisher · View at Google Scholar · View at Scopus
  50. L. Liu, M. Xu, R. Li et al., “Timescale dependence of environmental controls on methane efflux from Poyang Hu, China,” Biogeosciences, vol. 14, no. 8, pp. 2019–2032, 2017. View at Google Scholar
  51. J. F. Harley, L. Carvalho, B. Dudley, K. V. Heal, R. M. Rees, and U. Skiba, “Spatial and seasonal fluxes of the greenhouse gases N2O, CO2 and CH4 in a UK macrotidal estuary,” Estuarine, Coastal and Shelf Science, vol. 153, pp. 62–73, 2015. View at Publisher · View at Google Scholar · View at Scopus
  52. E. M. Baggs and H. Blum, “CH4 oxidation and emissions of CH4 and N2O from Lolium perenne swards under elevated atmospheric CO2,” Soil Biology & Biochemistry, vol. 36, no. 4, pp. 713–723, 2004. View at Publisher · View at Google Scholar · View at Scopus
  53. H. Marotta, C. M. Duarte, S. Sobek, and A. Enrich-Prast, “Large CO2 disequilibria in tropical lakes,” Global Biogeochemical Cycles, vol. 23, no. 4, Article ID GB4022, 2009. View at Publisher · View at Google Scholar · View at Scopus
  54. S. Sobek, L. J. Tranvik, and J. J. Cole, “Temperature independence of carbon dioxide supersaturation in global lakes,” Global Biogeochemical Cycles, vol. 19, no. 2, Article ID GB2003, pp. 1–10, 2005. View at Publisher · View at Google Scholar · View at Scopus
  55. N. R. Bates and L. Merlivat, “The influence of short-term wind variability on air-sea CO2 exchange,” Geophysical Research Letters, vol. 28, no. 17, pp. 3281–3284, 2001. View at Publisher · View at Google Scholar · View at Scopus
  56. A. Tremblay, L. Varfalvy, C. Roehm, and M. Garneau, Greenhouse gas emissions-fluxes and processes. Hydroelectric Reservoirs and Natural Fnvironments, Springer-Verlag, Berlin/Heidelberg, 2005. View at Publisher · View at Google Scholar
  57. X. Li, W. Hu, L. Yang, F. Zhang, and Z. Hu, “Diurnal variation of carbon dioxide flux on water-air interface of Meiliang Bay, Taihu Lake in wintertime,” Chinese Journal of Ecology, vol. 24, no. 12, pp. 1425–1429, 2005. View at Google Scholar · View at Scopus
  58. G. Algesten, S. Sobek, A.-K. Bergström, A. Jonsson, L. J. Tranvik, and M. Jansson, “Contribution of sediment respiration to summer CO2 emission from low productive boreal and subarctic lakes,” Microbial Ecology, vol. 50, no. 4, pp. 529–535, 2005. View at Publisher · View at Google Scholar · View at Scopus
  59. D. E. Allen, R. C. Dalal, H. Rennenberg, R. L. Meyer, S. Reeves, and S. Schmidt, “Spatial and temporal variation of nitrous oxide and methane flux between subtropical mangrove sediments and the atmosphere,” Soil Biology & Biochemistry, vol. 39, no. 2, pp. 622–631, 2007. View at Publisher · View at Google Scholar · View at Scopus
  60. R. G. Striegl, P. Kortelainen, J. P. Chanton, K. P. Wickland, G. C. Bugna, and M. Rantakari, “Carbon dioxide partial pressure and 13C content of north temperate and boreal lakes at spring ice melt,” Limnology and Oceanography, vol. 46, no. 4, pp. 941–945, 2001. View at Publisher · View at Google Scholar · View at Scopus
  61. G. Huimin, C. Lu, Y. Yifan et al., “Advances in methane emission and emission reduction in rice field,” Chinese Agricultural Science Bulletin, vol. 31, no. 3, pp. 160–166, 2015. View at Google Scholar
  62. T. Hosono and I. Nouchi, “The dependence of methane transport in rice plants on the root zone temperature,” Plant and Soil, vol. 191, no. 2, pp. 233–240, 1997. View at Publisher · View at Google Scholar · View at Scopus
  63. J. Wilkinson, A. Maeck, Z. Alshboul, and A. Lorke, “Continuous Seasonal River Ebullition Measurements Linked to Sediment Methane Formation,” Environmental Science & Technology, vol. 49, no. 22, pp. 13121–13129, 2015. View at Publisher · View at Google Scholar · View at Scopus
  64. S. W. A. Naqvi, H. W. Bange, L. Farías, P. M. S. Monteiro, M. I. Scranton, and J. Zhang, “Marine hypoxia/anoxia as a source of CH4 and N2O,” Biogeosciences, vol. 7, no. 7, pp. 2159–2190, 2010. View at Publisher · View at Google Scholar · View at Scopus
  65. G. Antler, A. V. Turchyn, B. Herut, A. Davies, V. C. F. Rennie, and O. Sivan, “Sulfur and oxygen isotope tracing of sulfate driven anaerobic methane oxidation in estuarine sediments,” Estuarine, Coastal and Shelf Science, vol. 142, pp. 4–11, 2014. View at Publisher · View at Google Scholar · View at Scopus
  66. L. Kuangfei, X. Yaling, J. Dabing et al., “Study on methane emission and control measures of paddy field in Hubei area,” Agriculture Environmental Protection, vol. 19, no. 5, pp. 267–270, 2000. View at Google Scholar
  67. H. Kludze and R. D. DeLaune, “Gaseous exchange and wetland plant response to soil redox intensity and capacity,” Soil Science Society of America Journal, vol. 59, no. 3, pp. 939–945, 1995. View at Publisher · View at Google Scholar · View at Scopus
  68. P. Kankaala, J. Huotari, E. Peltomaa, T. Saloranta, and A. Ojala, “Methanotrophic activity in relation to methane efflux and total heterotrophic bacterial production in a stratified, humic, boreal lake,” Limnology and Oceanography, vol. 51, no. 2, pp. 1195–1204, 2006. View at Publisher · View at Google Scholar · View at Scopus
  69. C. Huai, Z. Shun, and W. Ning, “Advance in studies on production, oxidation and emission flux of methane from wetlands,” Chinese Journal of Applied & Environmental Biology, vol. 12, no. 5, pp. 726–733, 2006. View at Google Scholar
  70. R. Osudar, A. Matoušů, M. Alawi, D. Wagner, and I. Bussmann, “Environmental factors affecting methane distribution and bacterial methane oxidation in the German Bight (North Sea),” Estuarine, Coastal and Shelf Science, vol. 160, pp. 10–21, 2015. View at Publisher · View at Google Scholar · View at Scopus
  71. L. M. Stapleton, N. M. J. Crout, C. Säwström et al., “Microbial carbon dynamics in nitrogen amended Arctic tundra soil: Measurement and model testing,” Soil Biology & Biochemistry, vol. 37, no. 11, pp. 2088–2098, 2005. View at Publisher · View at Google Scholar · View at Scopus
  72. D. Weixin and C. Zucong, “Effects of nitrogen fertilization on methane production in wetland soils,” Journal of Agro-environmental Science, vol. 22, no. 3, pp. 380–383, 2003. View at Google Scholar
  73. J. T. Huttunen, J. Alm, A. Liikanen et al., “Fluxes of methane, carbon dioxide and nitrous oxide in boreal lakes and potential anthropogenic effects on the aquatic greenhouse gas emissions,” Chemosphere, vol. 52, no. 3, pp. 609–621, 2003. View at Publisher · View at Google Scholar · View at Scopus
  74. C. A. Kelly and D. P. Chynoweth, “The contributions of temperature and of the input of organic matter in controlling rates of sediment methanogenesis,” Limnology and Oceanography, vol. 26, no. 5, pp. 891–897, 1981. View at Publisher · View at Google Scholar · View at Scopus
  75. S. Weiwei, W. Dongqi, C. Zhenlou et al., “The dissolved CH4 and N2O concentration and their emission flux in Yangtze river delta plain river network,” Science in China (Series B:Chemistry), vol. 39, no. 2, pp. 165–175, 2009. View at Google Scholar
  76. R. C. Upstill-Goddard, J. Barnes, T. Frost, and S. Punshon, “Methane in the southern North Sea: Low-salinity inputs, estuarine removal, and atmospheric flux,” Global Biogeochemical Cycles, vol. 14, no. 4, pp. 1205–1217, 2000. View at Publisher · View at Google Scholar · View at Scopus
  77. G. Abril, M.-V. Commarieu, and F. Guérin, “Enhanced methane oxidation in an estuarine turbidity maximum,” Limnology and Oceanography, vol. 52, no. 1, pp. 470–475, 2007. View at Publisher · View at Google Scholar · View at Scopus
  78. N. Linto, J. Barnes, R. Ramachandran, J. Divia, P. Ramachandran, and R. C. Upstill-Goddard, “Carbon Dioxide and Methane Emissions from Mangrove-Associated Waters of the Andaman Islands, Bay of Bengal,” Estuaries and Coasts, vol. 37, no. 2, pp. 381–398, 2014. View at Publisher · View at Google Scholar · View at Scopus