A Lesson Plan from the Virginia State Parks'
Your Backyard Classrooms

Where Has All The Top Soil Gone?

Grade Levels

6 - 9

Objectives

    Students will investigate changes caused by water flowing over soil by:

Standards of Learning

Science:

    Students study sediment load of local water sources, devise and conduct experiments to test the effect of Best Management Practices on erosion control.

Background

    Erosion is the natural process by which soil and rocks are moved by wind or water along the earth's surface. As fertile topsoil is eroded, land productivity decreases. The eroded particles, which eventually settle out of the air or water during sedimentation, alter the environment on which they land. In the Chesapeake Bay or its tributaries,, the suspended particles block light energy, thereby reducing photosynthesis in Bay vegetation. As particles settle, bottom organisms are covered and channels are filled with sediment. In addition, the particles can adsorb chemicals including fertilizers, pesticides, heavy metals and other toxics and carry them to the Bay. Most sediments come from non point sources, such as bare fields, housing projects, construction sites and cities

    Commercial fertilizers and animal manure supply nutrients to improve crop productivity and urban landscapes, but not all of the fertilizer stays on the land. Nitrogen, important for leaf and stem growth, is water soluble and easily leaches into ground water supplies or is carried in surface runoff.

    Nitrogen and phosphorus, when transported into the Bay in unnaturally large quantities, contribute to nutrient over enrichment. Phytoplankton, which thrive on increased nutrient levels, multiply rapidly, clouding the water, and reducing sunlight penetration. Without sufficient sunlight, much of the phytoplankton eventually dies, settling to the bottom, where bacteria (decomposers) consume it. The bacteria do not need sunshine, but they do need oxygen. During the summer, much of the Bay's deep waters are oxygen-stressed because oxygen demand is high and the warmer water cannot hold as much oxygen as colder water can. This situation sometimes results in fish kills, and occasionally in the spectacle of crabs leaving the water.

    A variety of agricultural practices, called Best Management Practices (BMP's), are being used extensively in the Bay region and elsewhere to reduce soil erosion. Some BMP's divert and control runoff, while others slow the water flow so that more water is absorbed into the soil. BMP's include strip cropping (planting different coops in alternating rows across the slope), terracing (stair-stepping the land's slope with terraces), contour plowing (plowing with the land's contour), no-till or minimum-till systems (leaving most crop residue on the field and preparing the soil and planting in one operation), crop rotation (following one crop with another to eliminate bare fields and provide natural soil enrichment), establishing permanent seed cover in highly erodible areas, and leaving natural plant growth, or "buffer" zones, along river and stream banks. An additional practice is the use of manmade soil erosion and sediment control structures to contain sediments.

Materials

Per group:

Resources:

Extension services of the Chesapeake Basin.
Best Management Practices for Nutrient Uses in the Chesapeake Basin. 1984-85. Bulletin 308.

Capper, J., G. Power, and F. Shivers. 1983.
"Chesapeake Waters." Tidewater Publishers. Centerville, MD.

Environmental Protection Agency. Washington, D.C.
"Chesapeake Bay: Introduction to an Ecosystem." 1982

DuMont, P., T. Kupelian, and T. Levermann. 1989.
"Know Your Soil." Science Scope. Volume 12, Number 7. National Science Teachers Association.

Fox, B. 1987.
"The Water Sure Looks Muddy This Year." The Story of Soil Erosion Around the Chesapeake Bay (4-H manual). Virginia Cooperative Extension Service.

Fox, B. 1988.
"It's Green Green, It's Green They Say." The Story of Nutrient Enrichment of Chesapeake Bay (4-H manual). Virginia Cooperative Extension Service.

U.S. Government, Department of Agriculture, Soil Conservation Service.
(The local office is listed in the phone book under County or U.S. Government).

Virginia Division of Soil and Water.
(*04) 786-2064 for information; (804) 786-3334 for audio-visual materials.

Welbrich, T. and G. Smith. 1969.
"Agricultural Practices and Water Quality." Iowa State University Press, Ames.

Procedure

Before the Trip:

  1. To determine if the school grounds are suitable farm land, students take several soil samples from four or five locations by digging small holes about four inches deep in several places and removing about a 1/2 cup of clean soil from the bottom of each hole.

  2. Combine the samples and mix thoroughly. Place the mixed sample in a sealed plastic bag and take it to the local Virginia Extension Office (look under the County Government section in the phone book) for analysis. Allow one week for processing of the sample, longer in the spring when demand is high. The extension Office will provide information on the suitability of the soil sample for farming, and can answer any questions.

  3. To investigate the sediment load in local water sources, students first must decide how to get consistent results from their sampling methods. Together, discuss the variables that must be controlled in order to have results that can be compared fairly (e.g. same size and shape of containers, same volume). Determine the volume of water to be collected, and collect similarly sized and shaped clear containers.

  4. Students collect the water samples in the containers from a variety of local water sources such as streams, lakes, rivers, and ditches. The best time to collect samples is following a rainy period. Be sure that students identify the location sampled and collect water from the water body itself, not from bottom material.

  5. After students bring samples to school, they gently shake each jar and compare the color and clarity of the samples, predicting how much sediment will settle out of each. After the particles settle overnight, students compare the amount of sedimentation to their predictions.

  6. After receiving the soil sample analysis, discuss the report, the importance of soil nutrients to plant growth, and the effect of sediment load and nutrient enrichment on the Chesapeake Bay.

  7. Divide the class into groups of four or five students. Distribute two aluminum foil roasting pans to each group. The groups cut a V-notch, about two to four cm deep. in the middle of one short side for a water spout. Prepare one extra set of pans for teacher demonstrations.

  8. Discuss the Best Management Practices that are being used throughout the Bay region to reduce agricultural runoff.

  9. After discussing the practice of establishing permanent crop cover the practice of establishing permanent crop cover to reduce erosion, solicit suggestions of ways to model the procedure using the set of teacher demonstration pans. One way to carry out the procedure is to fill both pans with soil, cover one with sod cut from grass, elevate one end, pour water simultaneously over both pans and collect the runoff in a cup at the notched spout.

  10. Discuss variables in the experiment and how to control them. Students may suggest that the pans must be tilted equally, equal amounts of water must be poured from the same height and at the same rate of flow.

  11. Several students should conduct the experiment and discuss the results by comparing the amount and clarity of the water that flows off each pan.

  12. Once everyone understands how to control for variables, each group chooses one BMP to model using their pans. Groups should discuss their plans with the teacher before actually conducting their tests. BMP's that are easiest to model include terracing, mulching, planting across the slope, and establishing a buffer zone. Sod will be needed to model crops and plantings. Each team could bring in their own materials or the teacher may furnish them.

  13. Each group explains its model and discusses the results of its experiment. Discuss:

At the Park:

  1. Collect samples from creeks and rivers to check for sediment load as students did at school. (Note: The accessible river and creeks at Chippokes will not reflect the effects of BMP's at Chippokes since these are tidal waters and are carrying sediments and runoff from other farms and the river bottom.

  2. Lead the students on a tour of the farm and look for no-tillage fields, the buffer zone between farm land and the river and the man-made sediment control structures. Look for evidence that these methods are having some impact.

Where in the Park?

Chippokes Plantation State Park.

Check with park staff about the best access to river and creeks. Chippokes is the only park with farmland for observing BMP's.

When

At the Park:

1/2 to 1 hour, any time of day.

Time of Year:

Any time of year is suitable. Turn-around time for soil sample analysis is considerably longer during the spring.

Extensions

  1. Students select a site with erosion problems on the school grounds and devise and implement a strategy for correcting the problem.

  2. Students look for BMP's and WMP's (Worst Management Practices) as they ride back to school.

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