A cross-disciplinary soil-proteomics and modelling approach for predicting switches between hydrophilic and hydrophobic soil surface responses

A strange property of many soils is that they do not readily wet on contact with rain, which has many implications for soil management. Although these soils may not be especially hydrophobic, wetting is slower than would be inferred from the sizes of their pores. This property is usually defined as sub-critical water repellency. Where water repellency is high (critical repellency), it causes ponding of water at soil surfaces. Water repellency affects the routes through which water and dissolved or suspended chemicals drain through the soil profile, leading to preferential surface run-off, infiltration paths resulting in serious erosion events, and flooding.
Soil water repellency may be influenced by both natural and man-made events. It is known that cycles of heating and drying (amongst many other factors) may produce quite dramatic changes in this soil property. Soil water repellency results from interactions between microbial activity and physico-chemical structure, but their complexity is such that at present they are only understood on an empirical and anecdotal basis. The purpose of this project is to develop a theoretical basis to understand soil water repellency and to predict some of its consequences. The practical implications of such an understanding are profound and widespread, since they may guide land management practice and flood prevention.
The three soils selected for study will be; (i) Malvern Hill clay loam, found in a previous study to exhibit extreme hydrophobicity under moderately moist summer conditions and also following air-drying in the laboratory, (ii) Gower silt loam, used in our NERC-funded proof-of-concept proteomics study and found to display up to medium levels of hydrophobicity, and (iii) Rothamsted Research Park Grass plot 3 silt loam, presently the subject of the large-scale soil metagenomic sequencing project 'Terragenome', and subcritically hydrophobic.
Soil water content will be adjusted to (i) just above and (ii) just below the Critical Soil-water Content, i.e. the content at which there is a transition between hydrophobic and hydrophilic behaviour. Further perturbations will include further drying at different temperatures to water contents simulating soil conditions that may be experienced during extreme drought periods, which are likely to cause further increases in hydrophobicity.
Information relating to water repellency will be obtained by the examination of soil properties at various scales of size (from nanometres to centimetres). We will establish the role of proteins in the development of water repellency using metaproteomics and specific hydrophobic protein isolation approaches. Atomic force microscopy (AFM), only recently applied to soil particles, will be used to examine their surface geography, hardness, stickiness and water repellency at this small scale. This technique combined with laser scanning microscopic techniques will be used to examine the water repellency of soil microbial proteins labelled with fluorescent dyes. Water repellency at two coarser scales will be examined using a water contact angle technique and penetration times using very small drops of water.
These estimates of water repellency and soil particle properties will be incorporated into a detailed computer model of soil structure, which will be used to predict the consequences of water repellency at the decimeter scale in soil, and will be compared with laboratory measurements of the wettability of cores of a few centimeters in diameter.
When the model is calibrated and validated, we will be able to use it, together with the experimental data, to predict how the perturbations change wettability. These effects will be incorporated into an existing climate model used by the Met Office, called JULES, so that predictions can be made about the likely effect of climate change. Then we will be able to suggest ways to manage UK and other soils to minimize run-off, erosion and flood risk.

The project has many facets, from strictly basic research contributions to more pragmatic environmental management applications on a landscape scale. Therefore the beneficiaries of our efforts will range widely and include: fellow scientists, water quality managers, soil, environmental and materials scientists, irrigation and global change specialists, environmentally sustainable materials manufacturers and the general public.
A prime beneficiary is the MetOffice, who maintain and develop further the simulation package JULES (Joint UK Land Environment Simulator). The MetOffice is interested in incorporating into JULES a new climate-dependent hydrology module based on our project's parametrised output. This will enable JULES to better predict climate change-induced soil hydrological changes at the catchment and regional scale, including estimating the risks of flooding and runnoff, which will be of benefit to those concerned with larger scale land management and with global climate change.
The PoreXpert model (www.porexpert.com) is being extensively tested by 5 disparate users prior to release. Current industrial applications include the characterisation of graphite porosity to enable the longer safe running of the UK's AGR nuclear power stations, ultra high speed ink-jet paper coatings, and filter efficiency prediction. Wide academic interest is shown by 3 academic sales 3 months before its release date. Novel proteins could also be used for innovations in materials sciences.
Soil and environmental scientists, irrigation specialists and water quality managers will benefit from the better understanding in underlying molecular-level processes by offering a better prospect for developing methods of ameliorating and reducing the adverse effect of soil hydrophobicity on site productivity and environmental degradation.
The wider life and soil science community will benefit through gaining an understanding of which elements of the entire genetic potential of one of the tested soils (Rothamsted Grass plot 3) is expressed under different climatic conditions via functional ecosystems genomics by comparing our metaproteomic datasets with the publicly available metagenomic data sets from the Metasoil project.
Other beneficiaries includes the specific landowners of our sites of study (National Trust and Rothamsted Research), but other landowners, local/regional/national authorities (eg Water industry, Environment Agency, SEPA, Defra), farmers and their organisations (eg Potato Council) may also benefit, via gaining a better insight of environmental conditions that liely induce hydrophobicity and its potential impacts, for improvement of, eg monitoring policies. Other beneficiaries such as managers and specialists dealing with irrigation and water transmission and quality, especially passage of fertilisers and other amendments into and through the soil, will benefit from project results at the particulate-core scale. The rapid transfer of solutes from amendments via 'finger flow' in repellent soils, adversely affects water quality by faster movement of nutrients and contaminants into the groundwater. The quality of waterways is also affected by soil hydrophobicity through increased overland drainage of soil and nutrients via surface runoff, especially after periods of intense precipitation. More complete insight to movement of these contaminants could lead to more efficient application of soil management practices which would minimise the adverse environmental consequences of soil repellency.
The general public is also a likely beneficiary through a better understanding and interpretation of their environment and the phenomena occuring within it (eg water infiltration issues).
The UK will also benefit from the project through professional training and skills base development of the PDRAs. They will experience working in an interdisciplinary project, with close links to non-academic organisations, with many networking opportunities.