- Title
- The response of soil organic carbon to climate variability and change
- Creator
- Gibson, Abraham
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2021
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Reversing the depletion of soil organic carbon (SOC) in agricultural soils is seen as a potential climate change mitigation strategy. As SOC is an important attribute for soil health this can also increase the productivity of soils to feed growing populations. These strategies require carbon to be stored on medium to long term timescales to be successful. Therefore, the response of SOC to climate variability and change must be understood. Drought is of particular interest, as it represents periods of limited water availability and increased temperatures. These conditions are not favourable for SOC development and may reduce SOC. The aim of this thesis is to assess the response of SOC to climate variability and potential climate change using field and modelled datasets. The response of SOC to drought for a catchment in the Upper Hunter region of New South Wales, Australia is examined using field data collected in 2006, 2014 and 2018. For this comparison, a historical climate record for the study area was created to quantify drought severity and duration. It was found that the droughts presented severe deficits in rainfall and warmer than average temperatures (i.e., conditions not favourable for SOC), however the catchment did not show lasting drought impact. As droughts occurred on timescales shorter than SOC turnover times, there were no impacts to SOC. Modelled SOC from the BIOS2) model (national-scale data), over a period of 1911 to 2015, also showed SOC stability, despite these oscillations between wet and dry conditions. This indicates that over the short-term, increasing SOC to sequester carbon may be a successful due to the insensitivity of SOC to natural climate variability. Field data collected across a climate gradient for continental Australia was used to analyse the potential response of SOC to climate change, with samples were collected across a range of Köppen-Geiger climate zones. SOC concentrations for the 12 sites were compared with soil properties, climate variables and vegetation measures. Temperature was found to be a major control on SOC for the sites. In addition to this, the climate classes of the sites showed a shift to warmer and drier categories for 2070–2090 under RCP 8.5. As a result, long-term increases in temperature may be a barrier to sequestration of carbon as SOC. As field data is often limited in availability, methods for estimating SOC in lieu of this were also explored. This is because the ability to accurately characterise baseline SOC is crucial to understanding temporal fluxes in SOC and developing sequestration strategies. SOC estimates for the BIOS2 model are validated against field data prior to their application. Estimates of SOC from the Soil Landscape Grid of Australia are also compared to field data. The two datasets captured the mean state of SOC across the various field sites, however, point scale variability of SOC was not captured. The effect of local topography on moisture accumulation, insolation as well as soil erosion and deposition may be a factor in point-scale variability not being captured in the SOC estimates. This was explored by comparing relationships between topographic attributes and SOC across various digital elevation model and sampling scales. At large scales, climate attenuated the effect of topography on SOC, with high resolution SOC and elevation data required to identify these relationships. Processes impacting the carbon cycle that are driven by topography (e.g., soil erosion) are being increasingly recognised as important fluxes of SOC. These impact its temporal stability and are uncertainties not captured in estimates of SOC. These need to be accounted for in methods used to estimate SOC for sequestration. Overall, SOC has been stable to natural climate variability, indicating that sequestration efforts may be successful in the near term. However, further into the future, increasing temperatures with climate change, leading to reduced SOC, may need to be considered when developing sequestration strategies to potentially mitigate climate change. Additionally, there are point scale variabilities and processes that are not well constrained in current SOC modelling and accounting methods. Through identifying this response of SOC to climate variability and these uncertainties, this will lead to the development of sequestration measures that are potentially robust to climate change.
- Subject
- soil organic carbon; drought; climate change; agriculture; soil science
- Identifier
- http://hdl.handle.net/1959.13/1426881
- Identifier
- uon:38484
- Rights
- Copyright 2021 Abraham Gibson
- Language
- eng
- Full Text
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| Thumbnail | File | Description | Size | Format | |||
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| View Details Download | ATTACHMENT01 | Thesis | 7 MB | Adobe Acrobat PDF | View Details Download | ||
| View Details Download | ATTACHMENT02 | Abstract | 414 KB | Adobe Acrobat PDF | View Details Download |