The combined impact of salinity and water table on Juncus balticus growth: Implications for fen construction in the Athabasca Oil Sands Region
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Date
2022-08-05
Authors
Wang, Tianshi
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Publisher
University of Waterloo
Abstract
Oil sands mining destroys peatlands by removing all vegetation on the ground and digging up to 75 m deep to reach the oil. To investigate methods to return peatlands to the post-mining landscape, a fen reclamation project was launched to build a new peatland using salvaged peat according to hydrological design and vegetation reintroduction. However, salt contamination is a concern for growth and physiology of plants because salts in mine waste materials are transported into the fen through groundwater. A salinity-tolerant plant community with Baltic rush (Juncus balticus) dominant was planted in 2013 but cover has decreased over time. The response of the plant community to continued salinization under a range of hydrologic conditions remains unclear. This thesis investigated the combined influence of soil salinity and water availability on J. balticus growth and ecophysiology under a controlled greenhouse experiment and in the field, which can be used to predict whether this species can continue to survive in the constructed fen in the future.
In the greenhouse experiment, J. balticus seedlings were grown in a full factorial experiment with seven salinity levels and two soil water table levels for 14 weeks. Plant growth and stress were assessed based on leaf photosynthetic parameters, plant height, above and belowground biomass, and leaf and root sodium (Na+) and potassium (K+) concentrations. Photosynthesis rates decreased when Na+ concentrations exceeded 2300 mg L-1, while this response was not observed in the aboveground or belowground biomass. Noticeably, biomass and photosynthesis rates were always lower in the wetter treatments, regardless of salinity. Plant height did not have significant relationships with either salinity or water table levels. Leaf and root Na+ concentrations increased with salinity but were similar in roots between 2300 and 4600 mg L-1 treatments. Leaf and root K+ concentrations decreased as salinity increased. This result indicates that J. balticus is relatively resilient to the Na+ concentration currently in the fen, and the salinity is not a stress to this species even in the future. However, the salt stress in J. balticus would be more severe under the wet condition. Therefore, it is necessary to maintain some dry microsites to support this saline species in the fen construction project.
In the field, gas exchange, biomass, and elemental content of J. balticus was measured at eleven sampling sites in the constructed fen from mid-June to late-August. Water table was measured with each gas exchange measurement, while salinity of the pore water was measured once after collecting the biomass at the end of the field season. An increasing water table (wetter) could promote the root growth of J. balticus between the range of -70 and -10 cm. However, the growth of shoots was inhibited when the water table was close to the surface. Correspondingly, GEP decreased under high water table (wet condition). In the element content analysis, Na:K was lowest at the water table between -40 and -20 cm, which indicated J. balticus could have better performance to deal with Na+ in their leaves at this range of water table. Na+ concentration between 113 and 238 mg L-1 did not have noticeable effect on Juncus growth. In addition, age of the plant is another independent variable that had a negative impact on GEP per aboveground biomass.
Together, results from the greenhouse experiment and the field collection demonstrated that salinity had limited impact on J. balticus growth, while water table had closer relationship with its performance. When the water table was lower than -10 cm (-70 ~ -10 cm), this factor had the positive relationship with growth parameters, while if the water table is higher than -10 cm, or inundated, it would negatively impact J. balticus growth. Moreover, shallow water table interacted with salinity causing additional stress under high Na+ concentration in wet conditions. In the future, the impact of water table and salinity on the whole plant community composition and function could be studied. Furthermore, sulphate could be another element that could threaten the health of plants in constructed fens and should be studied further.
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Keywords
Oil Sands, Juncus, Water Table, Salinity