Soil Composition:
Most soils are commonly made up of three materials:
Clay is a type of fine-grained natural soil material containing clay minerals. Clays develop plasticity when wet, due to a molecular film of water surrounding the clay particles, but become hard, brittle and non–plastic upon drying or firing. Most pure clay minerals are white or light-coloured, but natural clays show a variety of colors from impurities, such as a reddish or brownish color from small amounts of iron oxide. Clay is formed due to chemical weathering. Chemical weathering takes place largely by acid hydrolysis due to low concentrations of carbonic acid, dissolved in rainwater or released by plant roots. The acid breaks bonds between aluminum and oxygen, releasing other metal ions and silica.
Silt is a granular material of a size between sand and clay and composed mostly of broken grains of quartz. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension with water. Silt usually has a floury feel when dry, and lacks plasticity when wet. Silt is a common material, making up 45% of average modern mud. It is found in many river deltas and as wind-deposited accumulations. It is produced in both very hot climates (through such processes as collisions of quartz grains in dust storms) and very cold climates (through such processes as glacial grinding of quartz grains.)
Sand is a granular material composed of finely divided rock and mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand soil contains more than 85 percent sand-sized particles by mass. The composition of sand varies, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal settings is silica (silicon dioxide, or SiO2), usually in the form of quartz.
Soil Texture Triangle:
A soil texture triangle gives names associated with various combinations of sand, silt and clay and is used to classify the texture of a soil.
Here’s how to read a soil texture triangle properly: https://www.youtube.com/watch?v=SXp8Lg0SFPQ
Soil Texture Test:
The Aging Process of Lakes and ponds:
Bodies of water, like many things on Earth, go through an aging process.
Oligotrophic Lakes (“young lakes”) - Over several thousands of years, shorelines of oligotrophic lakes erode and become less steep. The rocks on the lake bottom grind against each other creating sand, while more plant life emerges on the shore and in the water.
Traits of Oligotrophic Lakes:
- Steep shorelines going down to the water’s edge
- Coniferous trees (pines, etc) around the lake’s shoreline
- They are very deep (100+ feet)
- The lake bottom is mostly rocky
- The water is very clear
Mesotrophic Lakes (“middle-aged lakes”) - After several thousand more years, mesotrophic lakes gain nutrients from the fallen, decayed leaves from deciduous trees, decayed shoreline plants, decaying aquatic plants, and the remains of fish and other water creatures. The lake bottom near the shore becomes covered with silt and sediment as a result of more years of weathering and erosion.
Traits of Mesotrophic Lakes:
- Less steep shorelines
- A mixture of coniferous and deciduous trees around the lake’s shoreline
- They are less deep than oligotrophic lakes
- The lake bottom is mostly made of sand and/or clay
- The water is very clear
Eutrophic Lakes (“old lakes”) - It is the nature of all lakes to fill themselves in and become land. After several thousand more years, the lake will continue to become shallower in the center, more shoreline will erode into the water, and trees will fall in.
Traits of Eutrophic Lakes:
- Gentle, completely flat shorelines
- Mostly deciduous trees (oaks, maples, etc) around the lake’s shoreline
- They are pretty shallow
- The water is murky because of an excessive amount of planktonic algae growth
Logging Tasks:
1. At Stage One, according to the sign, freshwater wetlands typically have high ___________ ________ and poor _____ __________. Why do you think this occurs based on what you know about their soil composition in the description?
2. At Stage Two, determine what type of aging process is Bee Meadow Lake in currently? Name specific signs of this at the GZ.
3. At Stage Two, take a golf-ball-sized amount of soil (or about 25g) from the shoreline of the lake. Perform the Soil Texture Test as seen in the flow chart above. What type of soil is found in and near Bee Meadow Lake?
**When completed with this logging task, please replace the soil where you found it to minimize impact to the lacustrine environment.**
4. After determining the type of soil at Stage Two, use the Soil Texture Triangle in the description to determine the percent silt, percent clay, and percent sand of the soil.
Hint: you should get a range of percentages for each (for example, if you hypothetically found silt loam soil, it would be composed of 0%-50% sand, 0-25% clay, and 50-80% silt according to the soil texture triangle).
5. As of June 2019, earthcaches now contain required photo logging tasks. Please provide a photo of yourself, your GPSr, or a personal item that proves that you have visited this site. Please post this in your log.
Sources:
https://en.wikipedia.org/wiki/Glacial_lake
https://www.goodbyetomuck.com/wiki/everything-about-muck-in-lakes
https://en.wikipedia.org/wiki/Clay
https://en.wikipedia.org/wiki/Silt
https://en.wikipedia.org/wiki/Sand
http://www.westerville.k12.oh.us/userfiles/4148/Classes/5342/soil%20texture.pdf?id=517609
Enjoyed finding this EarthCache? Consider awarding it a favorite point!
| We have earned the Geological Society of America's highest level: |
 |
