Germination, growth and gas exchange of selected boreal forest seedlings in soil containing oil sands tailings

Greenhouse experiments were conducted to determine the effects of soil enriched in fine tailings (FT), produced by the oil sands extraction, on germination, seedling growth and physiology of several plant species of the boreal forest. The germination of seeds was initially delayed by 15% FT in dogwood (Cornus stolonifera Michx) and jack pine (Pinus banksiana Lamb) but not in white spruce [Picea glauca (Moench) Voss]. In the second set of experiments we showed that all dogwood seedlings survived 6 months of treatment with 15% FT while the survival rates of raspberry, jack pine and white spruce seedlings were reduced to 44, 55 and 94%, respectively. FT reduced root and shoot dry weights in raspberry seedlings and the number of lateral shoots in jack pine and white spruce seedlings. In raspberry and jack pine seedlings, reductions of gas exchange were recorded. The results of our study suggest that the modifications of soil chemistry, texture and structure by FT may all contribute to the observed phytotoxic effects.     

Effects of consolidated tailings water on red-osier dogwood (Cornus stolonifera Michx) seedlings

As part of their tailings management, the oil sand industries plan on producing consolidated (composite) tailings (CT), in which an inorganic coagulant aid (gypsum) is added to create a non-segregating deposit. The water associated with this treatment contains potentially phytotoxic levels of sodium, sulfate, chloride, boron, aluminum, fluoride and strontium. Since CT water is expected to saturate deposits in the reclamation areas, it may affect successful reclamation of these sites. Red-osier dogwood (Cornus stolonifera Michx) was demonstrated to be relatively salt resistant and to have high potential for the reclamation of mining areas. In the present study, we used red-osier dogwood to examine the effects of CT water on the accumulation of ions within plant tissue, growth, gas exchange, water potentials and chlorophyll concentration. CT water reduced shoot lengths and dry weights in treated plants. The roots of treated plants accumulated higher concentrations of sodium and chloride than did shoots. The accumulation of sodium and chloride was accompanied by an increase in magnesium and calcium and a decrease in potassium in the roots, while the levels of potassium increased in the leaves. CT water altered gas exchange and water potentials in seedlings, and resulted in a decrease in chlorophyll's a and b. The results suggest that the mechanisms of salt resistance in red-osier dogwood seedlings involve the restriction of sodium transport from roots to shoots.     

Jack pine growth and elemental composition are affected by saline tailings water

In the processing of oil sands from Alberta's Athabasca formation, large quantities of alkaline, saline tailings and associated process-affected waters are produced. These waters may have a negative effect on plants used in reclamation of mined areas in this region of the northern boreal forest. In the present study, we examined the effects of process-affected water on the growth and elemental composition of jack pine (Pinus banksiana Lamb.) seedlings. Seedlings were grown in sand culture, and treated with tailings water to which mineral nutrients had been added. One-month-old seedlings were treated for 14 d, and all measured growth parameters were reduced. Growth and shoot elemental composition were also measured in seven-month-old seedlings that were treated for 10 wk with process-affected water. Shoots had significantly elevated levels of Na, Cl, S, P, B, and Sr, and significantly reduced levels of Fe, Mo, Ba, and K. The relationships between elemental composition and seedling growth and injury were examined using multiple regression. Growth rates, dry weights, and carotenoid content were reduced, but were not related to shoot elemental composition. Needle necrosis was positively related to tissue Na and Cl. Results indicate that reclamation planning must consider substrate Na and Cl levels when planting jack pine on tailings-affected sites.     

The effect of salinity on the emergence and seedling growth of Picea mariana, Picea glauca, and Pinus banksiana

Mining operations in areas of the boreal forest have caused salinity issues to be a major concern for reclamation. One of the factors determining successful reclamation is the ability of species to self-propagate. The effects of salinity on the seedling emergence and early growth of three boreal forest conifers: Picea mariana, Picea glauca, and Pinus banksiana were determined. Seeds were planted in sand moistened with solutions of various concentrations of sodium chloride or sodium sulfate. Seedling emergence was monitored on a daily basis and growth parameters assessed after 6 weeks. The emergence of Pinus banksiana seedlings was least affected by salinity, and at certain concentrations, emergence even appeared to be stimulated by the presence of salt. Picea glauca was the most sensitive of the species studied. Hypertrophia was observed in all species at high concentrations of Na2SO4, and an increase in salt levels caused a corresponding reduction in seedling height and weight, root length and number of lateral roots.     

Responses of red-osier dogwood to oil sands tailings treated with gypsum or alum

The application of composite or consolidated tailings (CT) technology provides Alberta's oil sands industry with a means of reducing the volume of the fines fraction in extraction tailings and allows for faster reclamation and revegetation of mining sites. This study examined the effects of coagulant aids (gypsum and alum), used in the production of CT, on the ion content, growth, and survival of greenhouse-grown red-osier dogwood (Cornus sericea L. subsp. sericea). Seedlings were planted in gypsum-CT and alum-CT substrates, and compared with those planted in reclamation material (salvaged peat and till). The seedlings were bottom-watered with one of the following: (i) Hoagland mineral solution prepared in deionized water (Epstein, 1972); (ii) Hoagland solution in gypsum-based CT release water; or (iii) Hoagland solution in alum-based CT release water. Pore water of CT substrates and CT release waters had similar chemical characteristics, including salinity levels. However, plants in CT substrates had higher concentrations of ions (particularly Na and B), reduced growth, and higher mortality than plants in reclamation material and treated with CT waters. The presence of H2S indicated low-oxygen conditions in the CT substrates, while in the reclamation materials with CT release water treatments, no evidence of sulfides was observed. Low-oxygen conditions in the CT substrate treatments may have interfered with plant exclusion mechanisms for Na and B. Therefore, substrate properties may modify responses of reclamation plants to pore water chemistry due to the effects on oxygen availability to roots.