CSDMS meeting 2026 by Kyungsoo Yoo

Thank you so much for uh the opportunity to share my um work and some salt and see. So I'd like to start with uh the soils as a component of shaping the morphology of the landscapes. As you see here um you have a soil covered hill slope and the soil basically overlies the underlying uh bedrock and then if you want to um you know follow the trajectory of the ground surface elevation that elevation is basically on changing according to the change of elevation at the sole bedrock boundary and also the sickness of the source. So at the boundary of the soil and bedrock that elevation is going to be affected by omnip rate and the soil production but at the same time the mass of the soils will be determined by the balance of soil production and then the mass loss by uh so erosion and chemical weathering. Okay. uh but if I go to uh you know uh other conferences like so science society of America or ecological society of America or most of uh you know our department seminars and I start uh talking about soils as a carbon reservoir and the soil is such a very important reserve of carbon that has a big impact on the global carbon cycle. So within this community of soil carbon cycle, the big question is how much of a soil carbon is actually associated with the minerals. And if you dig up the source and look at the organic matter, you will quickly find that some organic matter are not really combined with the minerals, but there also significant P of organic matter that are tightly combined with the minerals by basically being sobbed onto the mineral service or by being accruded in the aggregates. Um so they also have their own models. So this is a very uh simple and incorrect in many ways uh view of the so organic carbon. So uh so organic carbon can be considered as a sum of particulate organic carbon which is uh described as PC here and also mineral associated carbon which is described MAOC and they have their own uh their own inputs and their own uh decay rates but it's al often very hard to really differentiate uh the two and then it's very hard to really uh define where those two are clearly split. So many of the experimental work to uh to quantify those separate pools and depend on very operational uh experimental measurement and then those two pools are also connected because of the microbes. So here some of the particular organic pool uh carbon will be consumed by microbes and the microbes die and then some of those dead masses or alive mees biomasses of microbes can be sequestered into the mineral associated to carbon. So uh in my talk today I like to make a two argument and the first argument is that this uh so carbon cycle actually matters uh to the elevation of the ground surface. So uh the morphology of the landscape is somehow connected to what is happening to the organic matter in the source. That's the first argument I like to make. And the second argument I'm going to make is that ours really highlighted. So you can see this uh example of connection between carbon cycle and the ground surface elevation through the action of the earths and see so uh I'm going back to uh about you know 10,000 years when the glacier covered much of the North America. So when the glacia retreated and you know uh forest and uh pretty uh followed um and then this is uh what the forest floor used to look like before aromes caught up. So if you go into the curious forest that are very common in Minnesota like a sugar maple or basswood forest then you will see that uh there is tons of understory plants and as you walk in you'll also find that ground surface is very soft because they are covered with a s uh o horizon. What's going on here? Okay. But once or arrive then much of the those understory plants disappear and then being replaced by gramminoid and grass types of plants and then uh also the o horizon or the lip layer quickly disappears. So and this is the two data from a very different environment. The top one is from uh Abbyiscoco, Sweden, the first national park in the country and the second one is from uh North Central forest in Minnesota. So here in the accesses you see the distance. So that's basically distance from the point where we believe were introduced into the forest. So are moving into the forest. In the Minnesota case it has advanced about 200 meter. In abisco aiscoco case it has advanced about one kilometer and then there are two y-axis and the green one showing the lip sickness or lip biomass and the dark one is showing uh the ursome biomass. So here are the dark forces and eating into the forest and consuming the organic layer. So by uh monitoring this speed and also by uh dividing the length of our invasion chronos sequence uh by the speed of their movement we can also tell how long this site has been invaded. So among you know from those research we know that uh you know if they're left alone they advance about you know five to 10 meter per year. So from here and most to the end of this uh you know classroom. So uh if you multiply 10,000 years uh with the dead rate you can go about 50 kilometer to 100 kilometer. So it's very insignificant in the scheme of the continent. So much of the uh North America basically stayed uh without native for last uh 10,000 years. So, so when I first studying uh there was some invasion in Minnesota. I met with uh you know with tribe people in the liter lake and some of the young pe uh one of the young people there told me that his grandfather uh grandfather had told him that came in the white people. So they had been uh aware of this for a long time but now his scientists arrived and then got surprised. So then uh I was very curious about whether uh OG language actually record anything about it. And so before our last Oj linguist retire uh I asked John Nicol who used to be in the uh American Indian department here you know whether Oz language has any t for u thems but then he also told me that you know uh he had been always curious why language doesn't have a tongue forums and then when He heard this from uh those descriptive words and his uh kind of conjecture was that probably was invasive species or someone introduced the species but he couldn't believe it uh himself. So uh going back to our uh questions. So let's think of uh soul sickness and then being governed by those uh factors. So let's say you know or just arrive then what do you think is going to happen? Do you expect expansion of the soil or do you expect collapse of the soil? So do you see epsilon as a positive sign or negative sign? So so keep your thinking and you may write down and uh whether you will be surprised or not. So uh one thing that is really surprising about this earths is that wherever they invade they basically do the same thing and over and over again and then that is that basically they remove the organic horizon the lift layer and then they create this top soil in a mineral rich but also organic rich uh in top soil which we call a horizon. So another way of saying it is that they replace the O horizon with a horizon and that seems to be happening everywhere from Sweden and Finland in Minnesota and Alaska everywhere that uh we have visited. So if you think of this from you know carbon perspective and then you can uh see two things you know one is and very contrasting things you can see as very uh vigorous detore and then they come and they arrive and then they remove that litter layer within a matter of five years to a decade. So they turn soil into carbon source by removing the O horizon. But that's when you really focus on the little layer. But let's say you don't care about the oil horizon, but you care about the mineral soil. Then you are going to see the opposite thing. So you will see as animal that are very strong biotopators and the mixing organic matter and the minerals together and create what we like to see the mineral associated organic carbon that turnover slowly. So then we may you will be tempted to say the ors are probably helping source to uh sequest the carbon. So uh here is the carbon uh concentration data from different parts of the world uh you know boreal arctic and temperate and then you know you may see the decrease of the carbon concentrations from pre-invasion to post invasion but uh but you are not actually seeing the decrease of the carbon storage here because you're only seeing the decrease of carbon concentration to really get the storage you have to multiply ly those concentration by the bur density. So and also there's a horizon changes. So those white circles uh which describe the normal situation uh you have very high uh carbon concentration and making them all horizons and those horizons will be later replaced by a horizon. Now uh they taking the surface of the soil their carbon concentration is uh smaller but there are denser. So you can see this again uh depending on whether you look at the O horizon or a horizon you can see it as a you know carbon sink or carbon source. So now let's look at the burket density. So uh here uh there's a really a nice relationship between uh organic matter fraction in the source and the burka density. So but uh wherever we go and wherever we collect organic matter fractions and the bur density data uh they follow this uh nice nonlinear f uh trend that you reduce the organic matter content then you increase the bur density and then we find this from several different invasion chronos and but also uh another thing that is important is that it also O matches with much larger collection of the data that shows the relationship between organic matter fraction and the B density. So here uh basically uh I'm not really telling you which direction the system is moving because that also depends on whether you look at the O horizon or you know a horizon. So if you're looking at the O horizon you will see the organic matter fraction decrease and the burk density increase but if you look at the a horizon then your organic matter fraction will increase and the burk density will decrease. So uh there are both directions uh in this diagram. So the one way to resolve this to really focus on uh the volutric changes uh is to normalize all the concentrations to something immobile that we trust that this particular element doesn't get uh washed down by le or doesn't get introduced into the soil by biological and carbon cycles and one of those candidate is zerconium. So by combining uh zerconium concentrations in the soil uh versus the apparent material and also by comparing the burke densities uh that we can calculate uh epsilon which is uh volutric uh deation um uh factor. So if epsilon is zero that means your soil has no has gone through no change in volume uh during the formation and in comparison to the parent material. But if epsilon is eight that means soil is basically containing 800% of the volume that it parent material used to have. So if it is minus one then basically volume has disappeared. So here uh so uh the x-axis is the cylum values and the y-axis is soil and then there are three categories you know pre-invasion and intermediate invasion and then also intensively invaded the region. So before uh the earth invasion because of the or horizons that you have a dramatic uh expand uh dramatically volutrically expanded the source so it's a 800% volumetric expansion but then once um arrive then the volumetrication decreased quite dramatically to 100%. So um kind of going back to earlier question. So uh ORS you know uh they tend to uh decrease the existing volumetric expansion before their arrivals. But uh but this is just one example because depending on which stage of invasion your sample and also depending on what kind of ursomes invading at the place and you may have different signs. So this is just a take uh take this as one uh possible outcomes of the volumeatic uh volumeatic change in the soil uh due to swim invasion here. Okay. Uh so now I'm going to uh do a very simple experiment a simple uh mass balance modeling to you know test or highlight the idea that the carbon cycle and then which is in this case strongly mediated by earth invasion has a big capacity to modulate the sickness of the source and by also by doing so the elevation of the ground surface. So there's a two uh scenarios here. You know one scenario is that or some are really strong so they get rid of all horizons that that's the model focus. The second case uh it focus on the scenario that are actually uh more than that they actually create a significant mineral associated organic cut. So uh under the hood of the models there is uh three horizons and then O horizons and also the root rayer and the mineral horizon that is going to turn to a horizon and thenomes are being introduced at certain point of the time and then uh they eat some of the plant leaf litter and then they also eat some of the fine roots and then they transfer those carbon into the soil and at the same time they partition the carbon into two different poles that are turning at different speed and also there is a bioteation happening uh between uh the root layer and the underlying middle source. So two scenarios uh so uh you know x-axis here is time relativity invasion. So we are only simulating a 50 years because that's how much we know about uh what is happening in the uh the field and the y-axis shows basically the entire soil carbon pool. So if you have uh osomes as deadly bores uh uh okay uh scenario one which is red then your carbon storage is decrease quite rapidly and then uh by 20 years you lose most of the carbon in the system but if you have ursomes as you know producer of the mineral associated carbon that is turning over slowly then your total carbons to will increase but that's not really surprising because that's how we uh you know set up the model. But now uh let's think about some difference between uh geocchemist or ecologist and um and gemophologist in my view and the geocchemist are very much concerned about how much uh things are here at certain location. So we care about the mass of something per square. But if I talk to germaphologist and they care about the elevation. So they care about the volume of the materials uh per uh given areas and then so we if we want to go back and forth uh we need a conversion factor. We need a conversion factor that uh makes us to do the unit change and in this case the burket density is that uh the key. So I'm going back to this one. So we have a really nice relationship between organic matter fraction and bal density which means that if I can track down how the organic matter concentration in the soil change then we can simulate how the burka density will change and by doing so then I can change the mass carbon per square or mass soil per square meter to the thickness of that layer and which can lend me to to the elevation of the ground surface. So uh so this is the result. So if you look at the uh earth surface again land surface elevation in comparison to the preosome invasion and depending on you know whether you have earths as dribbles or you have ursomes as a creator of the min associated carbon your ground surface uh will evolve differently you know plus minus uh 10 or 20 cm in 20 years or 50 years and that is a lot faster than millimeter per year or uh you know meter per million years. So but then we don't really know how long it will last but kind of going back to the burka density we can go a little further. Uh so when you combine a burka density with the particle density of the minerals and the particle density of organic matter then you can calculate the porocity. So you can also model how the porocity will evolve with uh the invasion of the earths and then this is the results. So two scenarios again at the time zero uh those two scenarios kind of converge and then as time goes on by 10 years those two two scenarios diverse and then the red line which simulate the earths as deadly bors showing the uh the senos soil and then less porosity. But in contrast where your ursomes create the mineral associated carbon uh you uh have a sickening soil but also it porosity uh increased quite dramatically. So here um I showed you uh modeling result uh only up to 50 years which is really uh short uh time compared to the most presentation we have seen uh so far and the reason being um that we don't really know what is going to happen after 50 years of earth invasion. So there could be a very different scenarios. You know, for example, the biomass of biomass of the European ors we see in Alaska and Minnesota are way higher than those uh biomass uh in their origins like a southern Europe. And then we also have a new invasion of jumping and those are of Asian origin. And then they really uh change the souls within couple of years. And then they also show tremendously higher uh population density uh than those they show in their kind of home countries like you know China or Korea and Japan. So we don't really know whether they their population level will uh slow down and we also don't know uh how their perturbation of biochemistry by accelerating organic matter can change the nitrogen cycle or phosphorus cycle. In the case that they can help the slow release of the nitrogen, they may solve the problem with light nitrogen limitation for certain s certain time and boost the plant production which will bring in a more li into the soil and then that will lead to the more organic matter in the soil and also we have a very limited data that stretches beyond in 30 years and then those limited data seem to suggest that osomes are getting more effective in creating a mineral associated organic carbon but that we we don't really know uh you know what is really truly happening beyond the 50 years I think that is a fair assessment so here um I hope I convinced you that uh the arsomes are important and in that uh their kind introduction into a system can change the porocity and also uh the volume at volume of the source uh quite dramatically enough to uh change the elevation of the ground surface and that also has uh implications uh for uh so erosion because the first thing is that uh when ours arrive uh they can lead up you know over horizons which means you're uh they are getting rid of this protective layer that protect the mineral surface from the rain or from the uh the overand flow. So, so they may have a negative impact or kind of accelerate the soil erosion and also u this modeling and our some field data show that you know or some uh in certain cases can they can dramatically decrease the porocity of the source which may uh elevate occurrences of the overend flow that can also uh acceler leading to accelerate the erosion. So uh Nate my students presented the poster. So if you have visited with the Nate that uh you know Nate had some uh some data to show you uh the erosion rate change with ursomes. So uh I will leave you with some uh potential discussion topics and I also also like to acknowledge uh my graduate students Nund and and Adrien W Sarah Bower, Tyler Bowman, K Restno and Amy Little who all contributed to uh understanding the impact of ours in the poorest Minnesota and Alaska and thank There.