Wright, Amy ORCID: 0000-0001-9333-4613 (2021) An Investigation into the Effect of Ochre Amendments on Soil Carbon Storage, Aggregate Formation and Plant Growth. MSc by research thesis, University of York.
Abstract
Ochre is an iron oxide waste that is currently stockpiled pending re-use or disposal via landfill, providing motivation to research an environmentally beneficial application for this accumulating waste product. It is known that iron oxide amendments to soils can stabilise and increase soil organic carbon content, as well as having other potential benefits to soil structure. This thesis researches whether the ochre amendments to soils could be utilised as a land-based CO2 removal method, aiding in the mitigation of climate change. It is hypothesised that additions of ochre to soils could reduce carbon availability, leading to carbon sequestration. This hypothesis is tested through an adsorption experiment which assesses whether ochre amendments to an Agricultural and Woodland Soil increase organic carbon sorption and affect phosphorus availability, metal release and soil pH. Soil incubation/plant growth experiments were also conducted which assess whether ochre amendments reduce carbon availability and affect plant growth and aggregate formation. The adsorption study concluded that the addition of the ochre to soils enhanced organic carbon sorption, reducing soil carbon availability and lability, based on the assessment of the change in quantity of carbon released into soil solution (5.89 ± 0.86 to 10.62 ± 1.29 mg/L and 7.15 ± 0.42 to 10.75 ± 3.01 mg/L for ochre amended Agricultural and Woodland Soils, respectively), relative to control soils (10.95 ± 0.16 mg/L and 13.66 ± 0.21 mg/L for Agricultural and Woodland Soil controls, respectively) (p≤0.05: ANOVA and Dunnett’s test). Ochres with a high goethite content (67.27 - 97.50 %) and a relatively low - neutral pH (4.45 ± 0.05 to 8.34 ± 0.04) were favourable in increasing soil organic carbon sorption. However, ochres with a high Na content (344 ± 159 to 846 ± 41.7 mg/kg) were found to perform less favourably. The incubation/plant growth study found a lack of difference in the extractable carbon content of ochre amended soils, compared to control soils, but found a reduction in the cold water extractable carbon content in ochre treated Woodland Incubation Soils (6.30 ± 0.96 to 14.88 ± 3.47 mg/L), indicating decreased carbon availability and increased carbon storage, relative to the Woodland Incubation control (20.88 ± 3.40 mg/L) (p≤0.05: ANOVA and Dunnett’s test). This provides motivation for further experiments to take place, requiring a longer incubation period, with thorough mixing, to ensure there is an increased opportunity of contact between the iron oxide and dissolved organic carbon. In practical applications, a solution for increasing contact chances is to plough the ochre into the soil as a slurry. Despite the addition of ochre causing there to be more fine-grained material in the soils, generally no effects on aggregate fraction size were found, implying that the fine ochres have supported the aggregation of material to form coarse, stable macroaggregates, improving soil structure. Future work should look into the organic carbon content of each aggregate size, as well as measuring changes in carbon pools, as the results of this thesis suggest there is a shift in carbon from a very labile to a less labile pool. Finally, additional experiments should analyse for potential toxic metal uptake in the plant shoot biomass, given that some of the ochre treated soils released more metals into solution than the control in the adsorption study, despite the ochre amendments having no effect on plant growth.
Metadata
Supervisors: | Mark, Hodson |
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Keywords: | Iron oxide; soil; carbon storage; adsorption; plant growth; ochre; soil aggregates |
Awarding institution: | University of York |
Academic Units: | The University of York > Environment and Geography (York) |
Academic unit: | Environment and Geography |
Depositing User: | Miss Amy Wright |
Date Deposited: | 19 Nov 2021 11:49 |
Last Modified: | 21 Mar 2024 22:55 |
Open Archives Initiative ID (OAI ID): | oai:etheses.whiterose.ac.uk:29818 |
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Description: Amy Wright MSc by Research Thesis with Corrections
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