Salinization of soil over saline-sodic overburden from the oil sands
Transcription
Salinization of soil over saline-sodic overburden from the oil sands
Salinization of soil over saline-sodic overburden from the oil sands in Alberta Sophie Kessler1, S. Lee Barbour2, Ken C. J. van Rees3, and Bonnie S. Dobchuk1 1 Can. J. Soil. Sci. Downloaded from pubs.aic.ca by Ms Amy Heidman on 01/09/13 For personal use only. O’Kane Consultants Inc., 2312 Arlington Ave., Saskatoon, Saskatchewan, Canada S7J 3L3 (e-mail:[email protected]); 2College of Engineering, University of Saskatchewan, 57 Campus Dr., Saskatoon, Saskatchewan, Canada S7N 5A9; and 3College of Agriculture and Bioresources, University of Saskatchewan, 51 Campus Dr., Saskatoon, Saskatchewan, Canada S7N 5A8. Received 28 January 2010, accepted 20 August 2010. Kessler, S., Barbour, S. L., van Rees, K. C. J. and Dobchuk, B. S. 2010. Salinization of soil over saline-sodic overburden from the oil sands in Alberta. Can. J. Soil Sci. 90: 637647. Saline-sodic mine overburden (also referred to as spoil) removed to access the oil sands in the Athabasca region of Alberta is used as backfill in open pits and is also placed in large upland structures. These deposits are reclaimed with a soil cover to support re-vegetation. The chemistry within reconstructed soil profiles over saline-sodic overburden was investigated to determine the nature and spatial distribution of salts in the soils. Four reclamation treatments were compared: three layered covers (35, 50 and 100 cm thick) and one non-layered cover (100 cm thick). Salts have accumulated in the cover soils 15 to 20 cm above the overburden, raising the electrical conductivity in the lower part of the soil to between 4.5 and 6.0 dS m 1, which is beyond the acceptable value for vegetation growth. Salt redistribution was not related to slope position and the pattern of salt ingress suggests that diffusion has been the main mechanism driving salt migration into the soils during the initial 4-yr period following placement. Cover thickness did not affect the extent of salt migration, but the overall quality of the thinner covers (35 and 50 cm) for vegetation growth was compromised by the increased salinity levels. Key words: Saline/sodic overburden, landform salinity, soil cover salinity, salt migration, salt diffusion, oil sands reclamation Kessler, S., Barbour, S. L., van Rees, K. C. J. et Dobchuk, B. S. 2010. Salinisation des sols sur les morts-terrains salins-sodés des sables bitumineux de l’Alberta. Can. J. Soil Sci. 90: 637647. Les morts-terrains salins-sodés retirer des mines de l’Athabasca, en Alberta, pour accéder aux sables bitumineux sont employés comme remblais dans des dépotoirs à ciel ouvert et de vastes ouvrages sur les plateaux. On restaure ces dépôts en les recouvrant de sol sur lequel la végétation pourra pousser. Les auteurs ont étudié la chimie des profils de sol rebâtis sur les morts-terrains salins-sodés afin de déterminer la nature et la répartition du sel dans le sol. Ils ont comparé quatre traitements de restauration: une couverture faite de couches multiples (de 35, de 50 ou de 100 cm d’épaisseur) et une couverture d’une seule couche (de 100 cm d’épaisseur). Le sel s’accumule dans le sol de couverture, soit 15 à 20 cm au-dessus des morts-terrains, si bien que la conductivité électrique dans la partie inférieure du profil s’établit entre 4,5 et 6,0 dS m 1, ce qui dépasse le seuil acceptable pour la croissance de la végétation. La redistribution du sel ne dépend pas de la pente et sa pénétration laisse croire que la diffusion est le principal mécanisme expliquant sa migration dans le sol au cours des quatre premières années suivant les travaux. L’épaisseur de la couverture n’affecte pas le degré de migration du sel, mais la plus forte concentration de sel dans les couvertures moins épaisses (35 et 50 cm) empêche la croissance des plantes. Mots clés: Morts-terrains salins-sodés, salinité du relief, salinité de la couverture de sol, migration du sel, diffusion du sel, restauration des sables bitumineux Oil sands mining operates under the condition that reclaimed landscapes will have a land capability equivalent to, or better than, that which existed prior to disturbance. Current reclamation practices involve the capping of mine spoil with reclamation material, selectively salvaged from the original landscape, with the characteristics required to support self-sustaining vegetation covers (Sandoval and Gould 1978). The overburden removed to access the oil-bearing formation at the Syncrude Canada Ltd. (SCL) Mildred Lake Operation belongs geologically to the Clearwater formation, which is of marine origin (Stott and Aitken 1993). The overburden is used as backfill in the open pits Can. J. Soil Sci. (2010) 90: 637647 doi:10.4141/CJSS10019 and is also placed in large upland structures. Approximately one-third of the final reclaimed landscape at SCL Mildred Lake operation will be underlain by such material (Marty Yarmuch, SCL Research and Development, personal communication 2010). Geochemical characterization (Wall 2005) has shown that these shales are pyritic and can undergo oxidation when exposed to atmospheric conditions, as occurs during mining. The chemical reactions associated with Abbreviations: SCL, Syncrude Canada Ltd.; EC, electrical conductivity; TDS, total dissolved solids; SAR, sodium adsorption ratio 637