Background and Rationale
What exactly is phosphogypsum?FUN FACT!
FOR EVERY TON OF PHOSPHATE FERTILIZER THERE IS 5 TONS OF PHOSPHGYPSUM PRODUCED! |
Phosphogypsum, calcium sulfate dihydrate (CaSO4•H2O), is a waste by-product of phosphate fertilizer production. To obtain bioavailable phosphorous a wet process is used by crushing phosphorus containing rock and digesting it with sulfuric acid. Depending on the source rock, phosphogypsum can contain very high levels of fluoride, trace metals, and naturally occurring radionuclides (Rutherford, Dudas & Samek, 1994). Due to the these concerns phosphogypsum is usually stockpiled and monitored to decrease potential release into the environment. Although most phosphogypsum is currently stacked, around 15% is used for road foundation, construction cement, and even as a soil amendment (Korcak, 1986; Tayibi et al., 2009). |
Importance of suitable vegetation as a phosphogypsum phyto-cap
Image source: https://ncc-website-2.s3.amazonaws.com/documents/2021_Forest-Strategy-Final.pdf
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Phosphogypsum stacks without a cover system can present hazards to people and the environment through wind deposition of particles, infiltration into ground water, and release into water bodies (Komnitsas, 1999). To mitigate these effects vegetation covers (phyto-caps) have been implemented for long-term stack closure (Jackson et al., 2011). Currently, reclamation options for the closure of phosphogypsum stacks, are being examined with the intent to implement vegetation phyto-capping measures without the use of high-density polyethylene liner (Hallin et al., 2010). To successfully contain the phosphogypsum the vegetation used must decrease water infiltration, reduce erosion, and be sustainable under stack conditions. Vegetation grown on stacks must also root directly into the phosphogypsum, which is relatively nutrient poor and lower in pH (~5.0) (Komnitsas, 1999). To determine if a phyto-cap will be viable it is essential to understand the underground physical factors effecting root behavior such as root density and root impedance (Centenaro, 2018). If root systems are unhealthy, or are not establishing deep enough to support larger species they can lead to stack destabilization, and higher rates of water infiltration (Yu et al., 2007). Therefore, it is imperative to look at the physical factors which may affect root systems and overall vitality of vegetation growing into phosphogypsum.
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Part 1. Soil Core Analysis
Research Objective
To determine the rooting potential and abundance of vegetation growing on a reclaimed phosphogypsum stack we asked this question:
1. Are the soil physical parameters of bulk density, volumetric water content, and air filled porosity restricting or enhancing rooting abundance within phosphogypsum? Application Determining the physical properties of phosphogypsum and their relationship to rooting propensity can help stack closure plans that include a phyto-cap better predict the rooting depth and abundance before planting. |
Part 2. Greenhouse Experiment
Research Objective
The purpose of this experiment is to determine if changes in both bulk density and plant available water have an influence in the overall growth and rooting behavior of trees. For the purpose of this course assignment, and available data, I asked only one question:
1. Does bulk density and plant available water increase or decrease the growth and biomasses of trees (Populus balsamifera) grown in controlled conditions, and if it does by how do these factors influence above ground measurements? Application Understanding the affect of phosphogypsum physical parameters have on seedlings may help decision makers on deciding if the conditions are favourable for planting seedlings on reclaimed phosphogypsum stacks. |