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Growth and physiological parameters were examined in rat root (Acorus americanus Raf.) plants grown under controlled environment conditions in hydroponics and subjected to different pH and salinity treatments to determine whether these environmental factors may contribute to poor establishment of A. americanus in oil sands constructed wetlands. When A. americanus plants were subjected to a root zone pH ranging from 6.0 to 9.5, the plants that were growing at pH 7.0 showed the highest relative growth rates and chlorophyll concentrations compared with lower and higher pH levels. The greatest inhibition of growth occurred at pH ranging from 8.0 to 9.5. High pH also triggered significant reductions in tissue concentrations of N, P, and microelements, whereas the concentrations of Mg increased at pH >8. When NaCl (25, 50, and 100 mmol L^sup -1^) was added to the nutrient solution at pH 7.0 and 8.5, higher mortality and greater tissue concentrations of Na and Cl were measured in plants growing at pH 8.5 compared with pH 7.0. The results show that A. americanus plants growing at the optimum pH of 7.0 can better tolerate salinity compared with plants exposed to high root zone pH. Both pH and salinity may present important environmental constraints to growth and establishment of A. americanus plants in oil sands constructed wetlands.
Abbreviations: dry weight, DW; EC, electrical conductivity; RGR, relative growth rate.
Mining of the Athabasca oil sands deposits near Fort McMurray in northeastern Alberta, Canada, involves open-pit mining operations for oil recovery that may extend as deep as 250 m below the ground surface (Bauman et al., 2000). Oil sands contain a heavy type of petroleum, referred to as bitumen, which occurs in a mixture of sand and clay. The extraction of bitumen from the ore is based on a modified ver- sion of the Clark Hot Water Process combining the use of steam and NaOH (Kasperski, 2003). The process of extraction requires large amounts of process water, which results in large volumes of solid (tailings sand) and aqueous (fine) tailings. One of the present options for tailings management involves their treatment with g ypsum and the deposition of tailings water into tailing ponds, where the g ypsum can settle the solid particles of the fine tailings and make the...