Abstract
The variation in sodium concentrations in waters of natural fens and marshes on the western Canadian landscape provides a background for choosing the appropriate plants for wetland reclamation. Broad tolerances to salinity are especially important for reclamation trials on saline-rich ‘in-pits’ that were left from open-pit oil sands mining. One such species, Carex aquatilis, has been identified as a key species in early reclamation attempts; however, at the Sandhill Wetland on the Syncrude Canada oil sands lease, this species has aggressively colonized, dominating parts of the wetland and limiting species diversity. A second species, also widespread on natural lake shores and marshes, is Carex atherodes, with field observations suggesting a broad tolerance to salinity. Here, we examine the responses of this species to a series of sodium concentrations and compare these to those of C. aquatilis. In particular, we addressed three questions: (1) How do structural attributes of C. atherodes respond to a series of Na+ concentration treatments? (2) Are different structural responses related to the functional attributes of photosynthesis, stomatal conductance, and/or transpiration rate? (3) How do these responses compare to those of C. aquatilis? We implemented a phytotron experiment to test the responses of these two species to either five or six concentrations of sodium, ranging from 20 to 3000 mg Na+ L−1. In general, structural responses of C. atherodes did not differ between 50 and 789 mg Na+ L−1, while performances of all attributes were reduced at 1407 mg L−1. Physiological attributes had high variation, but also had reduced performances at similar treatment levels. In comparison, a clear threshold was present for structural attributes in Carex aquatilis between 1650 and 2148 mg Na+ L−1, while physiological attributes were reduced between 1035 to 1650 mg Na+ L−1. These responses from C. aquatilis were similar to those previously reported. Na+ concentrations in porewater at the Sandhill Wetland in 2019 reached as high as 1200 mg Na+ L−1, with natural subsaline and sodic sites ranging much higher. Although all of the plants in the treatments remained viable at the end of the experiment, these results indicate that Na+ concentrations above 1500–2000 mg Na+ L−1 may inhibit the growth of these two species and decrease their competitive abilities.
Highlights
Oil sand deposits lie under 141,000 km2 of the landscape of Alberta, Canada and in 1967, commercial oil sands mining began in northeastern Alberta [1]
The highest biomass was produced by C. atherodes exposed to 789 mg Na+ L−1, which decreased dramatically with increasing sodium exposure (Figure 1A)
Plants exposed to 789 mg Na+ L−1 produced 1.8 times more aboveground biomass than plants exposed to 1407 mg Na+ L−1 and 5.6 times more aboveground biomass than plants exposed to 2731 mg Na+ L−1
Summary
Oil sand deposits lie under 141,000 km of the landscape of Alberta, Canada and in 1967, commercial oil sands mining began in northeastern Alberta [1]. After mining operations are concluded, these large-scale depressions, or in-pits, are refilled with a variety of tailings and process waters that have relatively high concentrations of cations and anions [4,5,6]. Reclamation of in-pit deposits is legislatively mandated to a return to equivalent land capability [7], and these sites include areas of upland and wetland vegetation that provide a new physical landscape [8]. The salinity (especially Na+) of oil sands landscapes is considerably higher than what is typical of both bogs and fens [12,16], and depending on its severity, high Na+ concentrations can provide a harsh limiting environment for many plants [19,20]. Understanding how desired plants will respond to increased Na+ concentrations is crucial to successful reclamation
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