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
