Embedded Files
In order to better understand soil horizons and the conditions under which they formed, we dug a soil pit in the woods behind UVM's Delehanty Hall.
Burlington Area with the soil pit site marked.
Our site was located at 44.4834˚N, -73.1943˚W. It was just off of a trail on a relatively flat surface. The image below is a zoomed in image of Burlington with the site marked.
Figure 1: Before the pitThis is the area where we dug our pit. The land was flat, forested, and looked undisturbed. It's mid-October, so there are quite a few leaves on the ground from the surrounding trees.
Figure 2: A first look at the pitOur pit was approximately 72 cm deep and we observed three distinct layers that were characterized by depth, color, and texture.
Figure 3: A closer lookThe measurements and change of colors are slightly easier to see in this close up image.
How did each horizon form?
How did each horizon form?
Physical and chemical weathering processes that contribute to pedogenesis occur at both the top of the soil at earth's surface as well as below the surface at the parent material. Because a wide variety of processes and factors contribute to pedogenesis, different soil horizons are formed. The soils behind Delehanty Hall most closely resemble forest soils, as the area has been covered by trees for hundreds if not thousands of years.
The O Horizon was formed by the decomposition of organic material, a majority of which is leaf and needle litter, trees, and animal remains.
The A Horizon formed through the mixing of the organic matter and the mineral soil below. Oxygen and carbon dioxide are able to reach this layer, along with rainwater. These substances can cause a variety of chemical reactions which help break down the organic matter and incorporate mineral soil.
The B Horizon has its characteristic golden brown/red appearance from the leaching of minerals from above. The color can be attributed to the iron oxides and lack or organic matter. The pebbles towards the bottom of the horizon were likely contributed by the horizon below.
The C Horizon, or the parent material, was thought to be glacial till. Rounded pebbles of various sizes and types were found in the densely packed horizon, suggesting the former presence of glaciers.
Was this soil natural or impacted by humans? How do we know?
Was this soil natural or impacted by humans? How do we know?
Given this specific soil profile, it's safe to say that it's natural and has not been significantly altered due to human influence. The first indication of this that can be interpreted even before digging the pit is the presence of the surrounding trees. They provide a likely indication that the area has been forested for years. When humans alter a landscape, it is often for the purpose of building or agriculture. If the area had been cleared for building, the O and A Horizons would be much smaller, as there would not be as much organic material to decompose and contribute to the thickness of the horizon. If the area had been used for agriculture, the topsoil would have been mixed frequently and disturbed. This could also induce the formation of a new horizon, created from the mixing of material that may not frequently touch. Based on the undisturbed horizons we saw, it is unlikely that humans altered the composition.
***I worked with Remy Farrell and Mark Hehlen to dig and interpret the soil pit described above***
Page updated
Google Sites
Report abuse