Stormwater Runoff - Soil

Loose soil, whether from construction sites or lack of plant root systems, is easily picked up and transported by stormwater runoff. Excess soil in bodies of water is a Nonpoint Source Pollutant.

Mud shakes: Soil Profile in a Bottle

Materials needed

• Clear container with a lid (bottle or jar)

• Garden trowel

• Marker

• Soil

• Water

Procedure

1. Fill the jar ⅓ full of the soil to be tested.

2. Fill the remainder of the jar with clean water, but leave some space at the top.

3. Cap the jar and shake vigorously until the soil turns into a uniform slurry.

4. Set on a level surface and time for one minute.

5. Place a mark the outside of the jar, showing the coarse sand layer settled at the bottom of the jar.

6. Leave the jar in a level spot for 2 hours.

7. Mark the top of the next settled layer with the permanent marker. This is the silt layer.

8. Leave the jar on a level spot for 48 hours.

9. Mark the top of the next settled layer with the permanent marker. This is the clay layer that has settled on top of the silt layer.

Look at the marks you made on the jar. Which layer is the largest? Which is the smallest? Why do the larger particles settle out first? What is the stuff floating in the jar? What is the composition of your soil? How do you think this soil affects water quality?

Repeat the experiment with soils from different areas of your yard. Look for bare spots nearby. How does the soil in this area compare to soil with vegetation? How might water move in the bare area compared to the vegetated area?

Soil Vocabulary

The particles that make up soil are categorized into three groups by size – sand, silt, and clay. Sand particles are the largest and clay particles the smallest. Most soils are a combination of the three.

Sand: Sand particles are the largest and heaviest soil particles. Sand also has larger spaces between particles, and so is less compact than clay or silt. Sandy soils feel gritty to the touch. Sand is porous and usually holds less water for plants and animals than other soil types. Soils with large amounts of sand can dry out easily and are not as useful for growing most plants.

Silt: Silt particles are of middle size and weight. Silt feels smooth and slippery to the touch when wet. Silty soils hold both nutrients and water well, which can make them good soils in which to grow plants.

Clay: Clay particles are the smallest and lightest soil particles. Clay soils are generally highly compact, with little space between particles. This can make it difficult for many plants to thrive in soil containing a high level of clay, since it is harder for roots to grow and for circulating air to reach the roots. Clay feels sticky to the touch when it is wet but can harden and crack when it gets dry and hot. Clay also tends to hold more water.

Loam: a mixture of sand, silt, and clay

Organic Matter: Organic Matter is very light and tends to float to the top. Organic matter comes in a variety of sizes and colors. Organic matter is comprised of dead plant and animals and adds nutrients back into the soil when it decomposes. Because organic matter decomposes over time, it must be replenished.

*Save your mud shakes to use with Unit 3 Protecting Our Watersheds.