Water balance of a hybrid poplar phytocap on a reclaimed phosphogypsum stack

• Author / Creator

  Kravchinsky, Gleb

• Phosphogypsum (PG) is a by-product of phosphorus fertilizer production and is piled into large stacks that eventually require reclamation. The first step in the reclamation process is constructing a topsoil cap to facilitate revegetation. An alternative to traditional topsoil caps underlain with synthetic liners are phytocaps, which effectively reduce deep drainage through canopy interception of rainwater, temporary water storage in the root zone, and evapotranspiration. The objective of this study was to assess the risk of deep drainage below a phytocap of fast-growing poplar trees was established on a PG stack at a former phosphorus fertilizer plant in Fort Saskatchewan, Alberta, in 2015, by measuring and modelling its water balance.Components of the soil water balance – root zone soil water storage, precipitation, transpiration – were measured on-site with soil moisture sensors, meteorological station, soil moisture sensors and heat ratio sap flow sensor measurements scaled by leaf area. Runoff was assumed to be negligible, and surface/canopy evaporation was estimated by comparing measured changes in soil moisture storage following precipitation events during the growing season. Deep drainage below the root zone was then estimated as the value required balance with the water inputs and losses with measured changes in root zone soil water storage. Because transpiration was not measured over the entire growing season, empirical models were developed to fill in gaps in the transpiration using other meteorological variables. Average deep drainage estimates for the 2019 and 2020 growing seasons were 10 mm and -47 mm, respectively. Based on these results, the hybrid poplar phytocap apparently minimized or eliminated deep drainage during the growing season and even offset the positive deep drainage that occurred during snowmelt in the spring of 2020 when the trees were not actively transpiring. The clay liner at the base of the PG stack (up to 30 m below the surface) is likely key to retaining deep drainage from spring snowmelt within the stack that can be accessed by the poplars later in the growing season. Because the water balance of only two growing seasons was measured and only one spring snowmelt recharge event, it is suggested that deep drainage risks over the long term be further informed by further measurements and/or simulation models.

• Subjects / Keywords

  • phosphogypsum
  • hybrid poplar
  • model

• Graduation date

  Fall 2024

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-jtr1-5t23

• License

  This thesis is made available by the University of Alberta Library with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.