Details of Award
NERC Reference : NE/C003985/1
Fundamental controls on soil hydrophobic behaviour: addressing the critical soil particle scale
Grant Award
- Principal Investigator:
- Professor S Doerr, Swansea University, Geography
- Co-Investigator:
- Dr C Wright, Swansea University, College of Engineering
- Co-Investigator:
- Professor R Williams, Swansea University, College of Engineering
- Co-Investigator:
- Dr R Bryant, Swansea University, College of Engineering
- Grant held at:
- Swansea University, Geography
- Science Area:
- Terrestrial
- Freshwater
- Overall Classification:
- Freshwater
- ENRIs:
- Pollution and Waste
- Natural Resource Management
- Global Change
- Environmental Risks and Hazards
- Science Topics:
- Biogeochemical Cycles
- Properties Of Earth Materials
- Hydrological Processes
- Soil science
- Abstract:
- Hydrophobicity (water-fearing) inhibits infiltration into soils that would normally be expected to wet readily under rainfall or irrigation. This phenomenon affects many soil and land use types and can occur when soil moisture falls below a critical threshold. Depending on its severity, affected soils can resist wetting for minutes or more than weeks. Hydrophobicity enhances soil erosion and leaching of contaminants, reduces plant growth, and limits soil water storage capacity, which can contribute to flooding. Climate change is expected to exacerbate these effects by prolonged droughts (promoting conditions for hydrophobicity onset) and more intense precipitation (enhancing its potential to accelerate flooding). Soil hydrophobicity originates from a coating of soil mineral particle surfaces with naturally-occurring hydrophobic organic compounds. The same compounds, however, exist in coatings in soils that do not exhibit hydrophobicity. This raises the question: which factors control the presence of hydrophobicity? Our existing knowledge is based on studies of bulk soil material, from which the effects of soil particle wettability are difficult to isolate and fundamental principles governing hydrophobicity have therefore remained largely speculative. This study will, for the first time, determine directly the fundamental physico-chemical causes and factors controlling hydrophobicity at soil particle surface scales, using an approach previously not applied in soil science. The switches between hydrophobic and wettable soil conditions, which are triggered primarily by contact with water, but are also affected by environmental factors including temperature, humidity and pH, are thought to be governed by molecular-scale morphological changes of the particle coatings. Evaluation of this and other hypotheses for soil hydrophobic behaviour directly has been limited by an inability to measure hydrophobicity and examine changes in related surface properties at the scale of particle surfaces and organic coatings. We will use Atomic Force Microscopy (AFM), to examine directly the micro- to nano-scale morphology of soil mineral particle surfaces and their interactions with water under different environmental conditions. AFM has never been applied to soil hydrophobicity, but recent advances, made primarily at the host institution, now allow us to use this technique effectively. Particles drawn from an established collection of hydrophobic and wettable soil samples, representing a variety of land uses in different countries, will be examined in air and when contacting water. Their surfaces will be re-examined following specific environmental conditioning known to affect hydrophobicity of bulk soils (temperature, humidity, pH). Model reference material such as silica particles coated with organic substances implicated in causing hydrophobicity, will also be examined, allowing comparison of well characterised model analogues with the observed behaviour of natural soil particles. Outcomes will include data at hitherto unachieved scales on (i) the morphology and spatial arrangement of organic particle surface coatings; (ii) their likely mode of attachment; (iii) effects of these coatings and of wetting, drying and environmental conditioning on the hydrophobicity of individual particle surfaces; (iv) morphological changes of the coatings associated with switches between hydrophobic and wettable states. These data will allow us to directly evaluate hypotheses regarding the physico-chemical causes and changes of hydrophobicity at soil particle scales. The knowledge gained facilitates the interpretation of the often conflicting field and laboratory observations made to date, and the development of reliable predictive models for soil behaviour and effective land use management. The expected advances in AFM techniques for studying particle hydrophobicity could be highly valuable in engineering, biological or medical applications.
- NERC Reference:
- NE/C003985/1
- Grant Stage:
- Completed
- Scheme:
- Standard Grants Pre FEC
- Grant Status:
- Closed
- Programme:
- Standard Grant
This grant award has a total value of £179,442
FDAB - Financial Details (Award breakdown by headings)
| Total - T&S | Total - Staff | Total - Other Costs | Total - Indirect Costs |
|---|---|---|---|
| £3,103 | £98,659 | £32,298 | £45,384 |
If you need further help, please read the user guide.