Soil: who cares?
Did you know that global soils contain two (perhaps three) times the amount of carbon currently in the atmosphere? As much carbon as in permafrost? As much carbon as in remaining fossil fuel reserves? Did you know that without soil, we, along with all other living things, would simply not exist? That civilisations have disappeared because the soil disappeared? And that we are now losing soil faster than we’re making it?
If you answered ‘no’, you are not alone. Thankfully for humanity, there are those who not only know the answers, but more importantly, know to voice these questions in the first place. The British scientific community recently lost one of those voices: Dr Barry Rawlins of the British Geological Survey was a pioneering soil scientist who strove to avoid one of the commonest pitfalls of modern academe, not seeing the forest for the trees. According to his colleagues, his work was far reaching because he understood that soils do not exist in a vacuum; instead, they are surrounded by and interact with countless other environmental variables.
Dr Rawlins had, in the words of his colleagues, an ‘almost-obsession’ with soil, in particular how it relates to so many other aspects of our lives. In a conversation shortly before he died, Dr Rawlins and his colleagues discussed the magnitude of bringing together so many interconnected strands, crossing countless disciplines over widely varying spatial and temporal scales. At the end of that conversation, Dr Rawlins summed up his own view: simply, what he most wanted to know was how soil works. In particular, why does it have the properties that it does, and how do these properties allow it to provide the services that it does? Over a distinguished career, Dr Rawlins both asked and answered the question: are soils important?
Soil structure and processes
The structure of soil has wide ranging implications, including the distribution of nutrients on farmland, soil erosion, and flood management. Dr Rawlins’s work took him deep into the nano-scale structure of soils. His work on soil structure has shown that soil stability can be used as a proxy for soil health. He revealed that soils derived from calcium-rich parent materials are more stable than those originating from sandstones and clays. He also developed new techniques for identifying sources of eroded soil through a combination of Bayesian statistics and geochemical analyses. This work is allowing better land-use management to ensure that soils maintain their ability to perform essential functions (e.g., store nutrients, provide pathways for water runoff, support plant roots).
Using cutting-edge X-ray computer tomography at the Diamond Light Source synchrotron, Dr Rawlins generated fine-scale 3D models of organic matter, pores, and minerals within soils; the aim was to investigate how organic matter distribution impacts on soil microbes, which consume the carbon in organic matter and then release CO2. Given rising atmospheric CO2 levels and the consequences for global climate change, better understanding of this process is critical, especially because soils are currently a greater reservoir of carbon than the atmosphere. Dr Rawlins’s work at Diamond was truly ground-breaking.
Carbon sequestration within soil
Dr Rawlins did not just consider soil carbon as a simple system; rather he took pains to place it in the wider natural context. For example, he connected the soils that cover our hillslopes to the rivers that transport materials released from within those soils. To this end, he tackled the rate at which CO2 is emitted from river waters in the UK, generating a national model of riverine CO2 flux. This work will have important consequences for the calculation of global-scale CO2 emissions, because his team were able to demonstrate that riverine emissions are highly dependent on the state of water turbulence, a factor not yet incorporated into global emission models.
Soil interacts dynamically with the environment across different spatial and temporal scales, and there is a growing need to assess how these interactions will be impacted by a changing global climate. Dr Rawlins approached this from a large-scale perspective, collating a global dataset on soil change and using it to consider the impact of environmental change on different soil ecoregions.
He also considered the role of other elements in the soil system, in particular phosphorus, which enters into soils owing to widespread use of phosphate fertilisers. His landscape-scale work showed that phosphorus content in soils is controlled by soil concentrations of iron-oxide and organic carbon; mineral surface area; and bedrock geology. This work is helping us to develop more effective remediation approaches for polluted soils.
National assessment of soils
Dr Rawlins’s best-known work was on the variation of soil at regional to national scales, motivated in part by the 2008 Climate Change Act, which requires the UK government to assess the stocks and flows of carbon within the landscape. In general, national scale mapping of soil properties has been limited to government-based surveys. Dr Rawlins recognised the potential of the British Geological Survey’s Geochemical Baseline Survey of the Environment (G-BASE) as a source of data to examine variations in the signature of the soils’ parent material across the landscape. Such a database opens access to understanding anthropogenic impacts. Most recently, Dr Rawlins examined the use and strength of additional data sources, including commercial data and data from farmers, collected on a routine basis (for unrelated issues). Dr Rawlins developed statistically rigorous guidance to help policy makers and regulators make best use of these data, alongside carefully designed surveys. This data synthesis has had an immediate impact, filling significant data gaps and reducing the need for expensive soil surveys.
With more people than ever living in cities, Dr Rawlins turned his attention to urban soils, in particular how projected changes in climate will impact their functions. This work exposed issues surrounding ground movement in response to changing soil structure, and the implications for property damage (both practical and economic), as well as changes in infiltration rates and the corresponding impacts on the runoff of surface waters, especially after extreme rainfall. He also identified issues surrounding land management, which in urban areas is undertaken on very small scales, making coordinated strategies challenging.
Dr Rawlins was fundamental to the success of the UK Soil Observatory (www.ukso.org) and the mySoil smartphone app (www.bgs.ac.uk/mysoil). His collaborative work with CEH, Cranfield University, James Hutton institute and Rothamsted made him the ideal science lead for BGS on these projects. He helped create a strong working group with the sole aim of making national soil data more visible and readily accessible than ever before. He always understood the importance of raising the profile of soil science to a wider audience, championing the use of social media, as well as smartphone-app and web content. His models for the Advanced Soil Geochemical Atlas of England and Wales (National Soil Inventory) are very popular downloads from the observatory and exemplify his skill in bringing together different experts, across multiple institutions to share knowledge and data to the benefit of all.
A lasting legacy
While strongly grounded in science, Dr Rawlins never forgot that he was a public servant. He carefully ensured that his research had practical significance and wide societal impact, typified by the work on contaminants and CO2 and urban soils. His work was often tethered to governmental policy and decision-making. In coming years, Dr Rawlins’s legacy will live on, both within the vast body of his work, and through the policies that this work helped to shape.
So, are soils important? Barry Rawlins had no doubt.
In your opinion, which aspect of Dr Rawlins work will have the most significant long-term impacts on society?
Probably his work on national aspects of soil quality, as his work with the farmers’ data, for example, will be a huge cost saving for DEFRA. It’s not the most exciting of his work, perhaps, (that would be the synchrotron work) but it is going to make a day-to-day difference straight away, as indeed you stated. But of course, you rightly ask about the longer-term impact, and although that’s always hard to anticipate, it’s likely to be the synchrotron work, because knowing how carbon is structurally stored within soil aggregates has implications for how mobile it might be (in the context of CO2 emissions) and how recalcitrant it can be (important for soil health). The impact of that work will take a little time to mature, as it was published only recently.
Globally, where is soil loss most acute?
Well, there are many places where it’s acute, but sub-Saharan Africa, or more specifically the Sahel, is often regarded as the most critical. The vulnerability there is largely erosion of poorly managed land coupled to increasing droughts and therefore loss of protective vegetative cover. But soil loss is possibly more acute in places where the land has multiple uses, where the “loss” is not so much that the soil disappears (as it does in the Sahel) but that it becomes inaccessible. These places include the rural environments that surround large urban areas (megacities or soon-to-be megacities), because that land is wanted by industry, or by commercial agriculture (e.g., palm oil), or it’s bought up in speculative deals and simply not used for agriculture (legal land grabbing), or it’s converted to urban development (i.e., housing). And then we need to add to that category the related one of sinking deltas. All of the world’s largest deltas (most of which are in the developing world) are critically important for providing food for their hinterlands, and almost all of them are sinking. They are sinking because the sediment that feeds them is sequestered behind dams, and they are also subsiding because of unremitting pumping of either groundwater (for crops) or hydrocarbons.
Are there any places where soil production is growing?
No, none that I know of. I suppose strictly speaking, soil is being recovered in areas where permafrost is thawing, but those soils are not going to be useful for production for a long time, and so the real answer is no.
Does farming help or hinder soil production and soil quality?
Both. Modern commercial farming tends to reduce the bacterial diversity in soils and it impoverishes the balance of macronutrients (hence the need for synthetic and other fertilisers). Certain types of farming (e.g., lumber) and agricultural practices can significantly alter the ability of soils to be resilient to running water and wind, and it’s well known that poor farming can and does lead to significant soil loss and impoverished soil quality.
Soil production depends largely on the availability of water near the rock-soil boundary zone. Poorly managed agriculture leads to soil loss through erosion and reduces the transmission of water to rocks below (through compaction), so to that extent, the rate of soil production must be negatively impacted. We know that on average, soil production keeps pace with soil erosion (prior to humans and agriculture) or else we would not have any soil left to talk about. And we know that soil loss is generally amplified by poor land management, and so in general, soil is not being replaced as quickly as it’s being lost.
Barry Rawlins led the Sustainable Soils team at the British Geological Society and collaborated across a wide range of areas. Colleagues from the British Society of Soil Science remember his greatest contributions to science, to policy, and to enriching the lives of those around him.