Soil is not something I spent a lot of time thinking about before starting to work for DeepRoot. But in that time, I’ve come to see and appreciate soil as an almost-magical substance.
Soil is foundational to so many things: the biological processes of billions of organisms, carbon sequestration, plant life, and the built environment itself. Yet most of us know almost nothing about it.
Human activity has a huge and direct impact on soil. All the disturbance and compaction that comes with development impairs two of the functions soil performs best: (1) supporting plant life, and (2) absorbing water runoff from impervious surfaces like streets, roads, and parking lots. It’s easy to forget that all the things that happen above ground influence what goes on below.
This week’s podcast guest, Jonathan Russell-Anelli, is a pedologist who studies soil. He examines questions related to the composition and behavior of soils so that we can manage them better.
What is the difference between forest soils and urban soils? Is there really such a thing as bad soil? Should we regulate soil quality the same way we do air and water? These are just a few of the topics we discuss in this wide-ranging episode.
Leda Marritz | Creative Director, DeepRoot
TRANSCRIPT: Undiscovered country
GUEST: Jonathan Russell-Anelli, Pedologist (Cornell University)
Humans have been fertilizing the world for a very long time, with all different kinds of stuff. At this point I don’t think there’s any landscape of the world, or waterscape of the world for that matter, whether it’s soil or otherwise, that really has not been impacted to some point by humans.
Soils are a particular case study because soils are really an overlooked feature of our landscape. It’s something beneath our feet; we don’t really pay that much attention to it, and if we’re in urban environments it’s often paved over or armored in some way. Which is unfortunate because all the things that we’re doing aboveground are really affecting what’s going on down below.
My name is Jonathan Russell-Anelli, I’m a pedologist. A pedologist is a soil scientist who looks at the form and function of soil. I’m a faculty member at Cornell University.
This is Remarkable Objects, a podcast from DeepRoot about the intersection of nature and the urban environment. I’m Leda Marritz.
Soil is everywhere, and hugely important to humans and other living things.
Did you know that it can take up to a thousand years to form just one centimeter of topsoil? Or that five thousand different types of bacteria can be found in one gram of soil? Or that soils are a critical part of the carbon cycle, helping us to mitigate and adapt to climate change?
These are incredible statistics that should have a direct impact on how we treat this material – yet, as Jonathan said, we often don’t even know soil is there. Most of us don’t pay much attention to it, particularly in the built environment.
If anything, soil in the city is often viewed as a nuisance or assumed to be a health hazard. Its care and preservation are rarely considerations in the development process. Yet human activity has a huge and direct impact on soil. All the disturbance and compaction that comes with development impairs two of the functions soil performs best: supporting plant life and absorbing water runoff from impervious surfaces like streets, roads, and parking lots.
Jonathan is thinking about questions related to the composition and behavior of soils all the time so that we can manage them better – because soil is the foundation of everything from our food security, to creating resilient cities where nature is a thriving element of the urban fabric. I talked to Jonathan about the difference between forest soils and urban soils, whether we should think of soil as a resource or as infrastructure, and his possibly unpopular view that we should consider legislation to regulate soil quality.
I think everyone learns in school that soil is a living substance, but when you look at it, it doesn’t necessarily seem like a lot is happening. We know that soil is full of organisms, though, so what can you tell us about the biological processes are occurring in soil?
Many of the dynamics of the soil system are in fact driven by organisms. The nutrient recycling and the nutrient storage are pretty much driven by microorganisms decomposing, or worms decomposing, material – organic material – and recycling it. So as living things die, that material gets decomposed and gets put back into the system.
Soil happens to be an ideal media for that to happen because it has a lot of, sort of, niches for these organisms to survive in. The soil also operates as a media for plant growth – so, photosynthesis as well as the sort of nutrients then being taken up, that were decomposed and released by these organisms, being taken up and sort of stored in the plant material, as well as the soil particles themselves basically acting to hold onto these nutrients and slowly releasing them over time as demands of the system, primarily plant demands, take these nutrients and put them into biomass.
We think of soil as a thing, or an object, but it sounds like it’s more like an environment.
It’s probably better to think of soil as a volume rather than a thing, because with soil we’re really concerned about the whole volume. It’s not just the solids that are in there that are important to us, but it’s also the void spaces – the spaces where air and water move. The reality with soils, the things that are driving soils and the functions that soils provide, are really the interchange between those solids and that void space, where the air and water are interacting with the solids.
Soils act as an interface between four of the major earth’s systems: the first one is the atmosphere, then there’s the hydrosphere, which is the water system, then there’s lithosphere, which is sort of the rocks and the geology, and finally the biosphere – which is the living organisms. Of all the systems, or all the locations on the planet earth, soil is the only one that actually all four of those major systems interact with consistently.
Why is that important, that interface?
It has to do with a concept we call, sort of, edge effect – edge effect is this idea that when systems interact with something, that dramatic changes happen at these interfaces between systems.
Now, a good example of this is weather. Or another good example of this is basically the interface between a forest and a grassland. If you’re a birder or anything like that, you’ll know that a lot of these birds are sitting in the forest, but they’re coming out into the grassland to do something. Or, the inverse of it. And so a lot of the dynamics of the system occur at these edges.
Because of the nature of the solid material, the mineral material and the organic material of the soil, and these void spaces where the water and the air is, there are lots of edges inside this volume of soil. It’s this interaction at these edges that drive nutrients, that drive water, that drive basically the respiration, carbon storage, the organisms that live in this soil.
It’s why with people like me, we’re very interested in the arrangement of these soils. It’s all well and good, “OK, I have this soil that’s down below me.” But I really want to know what that soil is made of so I can make predictions about, or I can make decisions about, management, or what will happen.
How does human activity, and I’m thinking particularly of development, impact soil? And how do we understand the difference between a soil that exists in a forest and one that exists in a city?
Natural soils are produced by natural processes. I know that sounds really simplistic, but when you move into urban environments, and actually in rural and agricultural environments as well, there’s a huge amount of human impact, and humans tend to concentrate their impact at the surface, because that’s what we interact more with.
There are a number of primary ways we impact the soil. One is basically through contact: you know, compression, vibration, running tillage instruments, sealing it. How that impacts the soil – humans tend to compress and compact it. We tend to make things denser because vibrations shake up the material.
As I spoke earlier, you really shouldn’t think of soil as a thing, you should think of it as a volume. Part of that volume is occupied by space, where the oxygen and the atmosphere and the water move. But when you start vibrating and compacting, what you’re going to do is you’re going to reduce the amount of that void. So infiltration rates are going to be reduced, aerobic respiration rates will be reduced because we’re going to have less oxygen moving into these soils. So we’re going to start seeing more and more anaerobic respiration, for example.
Those are sort of the primary ways that humans in urban environments interact. And then if we tarmac over we make it even harder for these natural processes, or for the soils to produce, these sort of natural processes that benefit humans, and the plants, and the other organisms that live in that environment.
If you think about an urban environment, soils are the media upon which much of our infrastructure is built. Probably not the high rises because we put foundations or pilings or something like that, but our roads, and most of our houses, and our strip malls, and our stadiums, and all that kind of stuff, are basically all built on this media, this soil medium.
I feel like what you’re saying is that there are clear benefits that we get as people, and that cities get, from modifying soils. But, what you’re describing is that treating it as a foundation for infrastructure also means sacrificing some of its other properties. So, soil and traditional urban infrastructure interact with each other in a way that is actually damaging to the soil.
That media is constantly interacting with that environment, and we are constantly interacting with that media.
So, imagine a road, and we compact the soil underneath the road so we can build a bed on top of it, so that we can then pour cement or tarmac on top of it, OK? That material underneath needs to basically be stable. Now, we start driving cars down that road and there’s vibrations. And those vibrations spread from the road to surrounding soils, and those vibrations, just by shaking something… If you shake something in a plastic jar, you notice how things settle? And that settling basically reduces the amount of void space that’s in the soil. Now, remember me saying, I want you to think of these soils as a volume. You want to actually have those void spaces in there, because those void spaces are where air and water move through the system.
So if you compact the soil, suddenly, just think about this, and suddenly there’s a big rain event and all the soil’s compacted, where is that water going to go? It’s not going to be going into the soil, some of it will be, but it won’t be going in as fast as it was before, and now we have water that’s flowing overland, and basically eroding away things, including that road we just built to move our traffic. And the traffic in turn is making the compaction in the road next to us, by the vibrations.
And so here’s very nice, sort of interactive loop. By compacting the soil, by putting roads, by putting vehicles on top of it, we then compact the dirt even more. We now prevent water from infiltrating as easily. We then concentrate water on the surface and we create problems downstream because we’re not delivering more water to the streams that were designed for less water because the ground was basically sucking up infiltration water.
Earlier you said that soil was the media upon which our infrastructure is built. If that’s true, does that make soil a form of infrastructure too – and, one that needs to be managed just like anything else?
That’s actually a really great question; it’s something I haven’t thought about before. I think of it more as water and air because it is ubiquitous, and it’s something we inherently have not made, but it’s part of the earth’s system. But the way that we use it is definitely not like water and air. We use it, we manage it, we actively as well as passively manage it much more than we do water or air.
I think, and this is a totally weenie answer, but I think I would group soils in urban environments as infrastructure because of the way we manage it and how we use it. I think that’s demeaning soil in a sense, because it’s not really infrastructure – it goes back to this, it’s part of the earth’s system, but the way we manage it, it’s definitely infrastructure.
I don’t think of it as infrastructure, but we manage it that way.
I think you’re responding to a very real, um, two very real, strong, and opposing forces around soil. One that it just be this inert substance that we can manipulate however we want or need in order to achieve our human goals. And another that we still want it to perform the function that we would expect to see in a forest or a more natural environment in terms of plant growth and containing air and water.
Right, and I would make the argument that depending upon the type of management, that management is actually keeping it as a resource or make it into an infrastructure.
I’ve made a habit of asking guests about what they see as the future of their fields, so let me ask you, in your opinion what are the frontiers for soils and soil management?
Yeah, I think sort of the frontiers for soils and certainly the frontiers for soil management – I think there’s really three things that are happening right now both intentionally and unintentionally.
I think we are continuing to fertilize the world, and that is management. It may be passive, we may not be actively doing it with intent, but we are definitely fertilizing the world and we are going to see consequences from that. In some cases it may be fairly benign, but in some cases it’s not.
So, I think we really need to start considering – this is going to seem anathema to a lot of people – but I’m almost thinking that we might want to start thinking of a Clean Soil Act. We have a Clean Water Act and a Clean Air Act… I think we need to start considering movement towards standards for soil quality. Now that’s a hard one, because what does quality really mean? Is it quality for drinking water? Is it quality for growing plants?
Yeah, what would quality mean in that context? Can we make statements about quality given how much variety naturally exists in soils?
I certainly think we can make statements about, I want to say, like, cleanliness, i.e., if a soil has x amount of lead in it then legally we need to clean this up. Now, we have recommendations for that, certainly we have all kinds of brownfield cleanup regulations about what the soil needs to be at when the brownfield has been cleaned up, before it’s certified to be used for something else.
But, if you think about what the Clean Water and the Clean Air Act did for our country – and I would say actually beyond our country, because other people look to these laws and approaches – I think a Clean Soil Act might actually be a really good idea, whether it happens or not, but certainly I think it should be part of the conversation.
Water and air, because of the way they behave in a sense, water certainly, it’s a lot easier to clean up. Soil… cleaning up soil when it’s been contaminated is not an easy task. And because we’re so intimately entwined with soil, it’s actually a really important thing to address. But because of this disconnect from soil, most people, it’s not on their radar – let’s put it that way. And so as a result, we don’t even consider, “You know what? Maybe we should be putting in regulations about how clean soil should be.”
I mean, certainly think about it from a playground perspective. Should we be able to just put a playground anywhere? And certainly in urban environments, I mean, that’s a big concern. Are we talking about lead? I mean, we have a building that’s been demo-ed, it’s in an abandoned lot, “Hey, let’s put a playground there!” Well, maybe we shouldn’t. Maybe we should think about what’s going on in that soil.
It’s a very different way of thinking about it.
It’s a different way of thinking about it, but I think it’s actually the way we’ve been thinking about the Clean Air and Clean Water Act already. But how would you apply it to something so diverse? Now, some soils are naturally contaminated; they’ve got high levels of zinc and whatever. That’s the way the soil is, so I can’t say we have to fix that soil so we bring the zinc levels down – that’s a natural soil. But on the other hand, if you’re going to be using it for certain things I think there should be some understanding about acceptable characteristics for use, which is basically what we do for water and air.
So we’re talking about soil quality here, I’m curious where do you stand on whether there is such a thing as bad soil, which is a term I hear sometimes.
I personally – this is a personal opinion – I don’t think there is anything that’s a bad soil. I think soils can be bad for a certain use, but I don’t think the soils themselves are inherently bad. I think you can think of management as, there’s some bad management because it produces something in your soil that don’t want, i.e. this compaction is a really good example. In an urban environment, compaction happens. It’s inherent to the environment, but you don’t want it to happen. So, what could you do from a management-wise to prevent that from happening?
It’s funny, because it’s everywhere, but there’s still a lot we don’t know about it, certainly for non-academics. I remember when we were talking earlier, you called it “undiscovered country.”
I think soil is undiscovered country. It’s so unfamiliar that even though it’s so commonplace, it’s this mysterious material underneath out feet. It applies to so much in our daily lives, and we don’t even know it’s there.
Remarkable Objects is produced and edited by me, Leda Marritz. You can find us online at remarkableobjects.com, and on Twitter @remarkableshow.
This podcast is a production of DeepRoot Green Infrastructure. DeepRoot provides landscape solutions and technical support services to promote mature tree growth and sustainable stormwater management in the built environment. Find out more at deeproot.com.
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