Thesis

Understanding the feasibility of growing reed canary grass on a historic mine site for phytostabilisation

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Awarding institution
  • University of Strathclyde
Date of award
  • 2022
Thesis identifier
  • T16402
Person Identifier (Local)
  • 201894764
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Department, School or Faculty
Abstract
  • Historic mining tailings and spoil are typically too physically, chemically and biologically deficient for spontaneous vegetation regrowth, allowing for the redistribution of contaminated material. The use of contaminated land, such as historic mines, to grow bioenergy crops could increase the sustainability of bioenergy resulting in an increase in land available for agriculture and the remediation of degraded soils. The aim of this study was to understand the feasibility of growing a novel energy crop grass species in mine soils amended with two organic waste soil amendments (OWSA) used to promote plant growth and decrease the bioavailability of potentially toxic elements (PTE) for the purposes of remediation. The organic waste amendments used in this study were green waste compost (GWC) and drinking water treatment residue (DWTR). Reed Canarygrass (RCG) (Phalaris arundinacea), a perennial grass species and novel energy crop able to rapidly colonize and establish on contaminated soils whilst not (usually) accumulating high levels of PTE, was the plant species used throughout this study. The approach that was taken involved both field and pot trials with soils from a historic Pb-Zn mine site in the North East of England. Soils from this mine site were found to have very low levels of nutrients and very high levels of PTE (Pb and Zn >13000 mg/kg). The application of the BCR sequential extraction on the unamended pot trial mine soils found that many of the PTE analysed for were mostly in bioavailable fractions. The same analysis on the soils amended with the OWSA found a significant decrease in the bioavailability of Pb and Cu (P < 0.05) after plant growth. The field trial involved 648 pre-grown RCG plants planted-out into mine soils amended with either one of the two OWSA or a combination of the two, all at a target rate of 30% (amendment weight/ soil weight). A quarter of the planted soils were left unamended as a control. Three cultivars of RCG, each bred for a different commercial use, were planted. Biomass production was assessed by sampling all above ground material and measuring dry weight. The mobility of PTE was assessed by biomass digestion and analysis (ICP-MS), and through the imaging of the biomass with x-ray computed tomography (XCT). Results from field trial sampling showed plant survival rates of above 97%. Cultivars bred for greater biomass (SW RF5004 and SW RF5032) presented statistically significant increases (P < 0.05) in dry mass. Both amendments and the combination of the two had significant positive effects on biomass production compared to the control in the following order GWC, DWTR+GWC, DWTR (P < 0.05). Analysis of the biomass showed very high concentrations of PTE found within the biomass, particularly Pb (500 -7500 mg/kg). The application to soil of GWC was found to significantly lower Cu and Zn biomass concentrations (P < 0.05) however the effect of the two amendments on concentrations of PTE in biomass was generally ambiguous. High Pb concentrations found in biomass were investigated further using XCT and was found to be from a combination of particulate surficial contamination and plant uptake. The results suggest that RCG is a viable remediation option on even highly contaminated soils when grown with appropriate OWSA and that further work should be undertaken to gain a better understanding of the location and nature of PTE within the biomass.
Advisor / supervisor
  • Lord, Richard (Senior lecturer in engineering geoscience)
  • Davidson, Christine M.
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Note
  • This thesis was previously held under moratorium until 14th October 2022 until 14th October 2024.
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