Soil Characteristics in the Pantanal!

 Last Spring Quarter I took EESS 155 (The Science of Soils) with Scott Fendorf. It’s a funny class because when you tell people you are taking it they always respond with some incredulous comment along the lines of “you’re taking a class about dirt?” but the truth is that soil is actually super cool and important. I wrote a blog post a little while ago about soil carbon in the Pantanal and how it connects with some of my research interests, but I thought I would write a little more here about soil characteristics in the Pantanal so we can get excited to get our hands dirty while we are there!

In general, as you might imagine with such a diverse mosaic of micro-ecosystems within the Pantanal, the soils in the region exhibit a wide range of diversity in terms of their physical, chemical and mineral characteristics. As you can probably also guess, however, all the soil processes in the area share similarilities in that they are affected by the seasonal flux of flooding that brings water to these soils every year. This hydromorphism leads to a couple of interesting features.

One of these features, which you can actually experience first-hand if you go out and dig a pit in our local wetland (Lake Lag!), is signs of redox reactions taking place in the soil due to cyclical wetting and drying of the soil. As a quick reminder of some chemisty you might have forgetten, redox reactions involve the transfer of electrons between different compounds. For soils in particular this usually involves reduction or oxidation of Iron and Manganese, which results in the soils having red or dark gray mottled colors where water infiltrated the soil and resulting in these reactions taking place. In the Pantanal, redoxomorphic processes in the soil are some of the most important for soil formation, leading to a lot of the soils taking on this grey mottled look and falling under the soil taxonomic classification of Gleysols.

Another interesting component to thing about is the size of soil particles. Soils are classified based on their make-up of three sizes of particles. Sand particles, the largest, silt particles, in the middle, and clay particles, the smallest, all combine in various ways to form a variety of soil types from Sandy Clay to Silty Clay Loam to Loamy Sand. In the Pantanal it can be seen that smaller particle clay soils exist in the beds of some lakes, which makes sense because these small particles allow water to infiltrate into the soil much less quickly that larger soil particles. In contrast, much of the alluvial river floodplains are composed of very sandy soils, with large particles that get carried along and deposited during the river flood period. These soils drain much more quickly than the clay bottom lakes.

When we visit, hopefully we will see of these different features and we can stick our hands in the dirt to investigate! Usually you can actually feel a substantial difference!

Cole