Frost Tube Program

Soil Frost Tube Protocol  (DRAFT)

Purpose

The purpose of this activity is to monitor the depth of freezing in soil.  Depth of freezing reflects surface conditions such as snow depth, moss thickness, organic layer depth and soil moisture content.  Changes in frost depth, (depth to which water in soil is frozen), timing of freezing, and length of freezing period  is important because of their effects on plant growth and stability of permafrost ( permanently frozen ground) in taiga or boreal forest and tundra biomes.

Levels

Primary through secondary

Overview

Students auger a hole in an undisturbed and uncompacted soil. Students create a frost tube that is inserted into the soil.  At least four times a year, students measure the depth at which water in the frost tube has frozen.

Student Outcomes

Students will collect and analyze data related to soil freezing

Students will be able to apply data on depth of freezing in soil to understand how soil temperature and moisture coincide with changes in seasons across different biomes.  This information can also be used for testing and driving computer models of soil/ecosystem dynamics, and, hydrologic computer models for flood forecasting by the National Weather Service.

Science Concepts

Earth and Space Sciences

• Some biomes of the world have freeze/thaw cycles and these occur seasonally.  Other biomes do not have these cycles as the soil never freezes or thaws.
• Water infiltrates into the soil and freezes at certain depths during the seasonal cycles.
• Depending on the geographical location of the soil being tested, some water may never thaw or freeze.
• Water circulates through soil changing the properties of both the soil and the water.

Scientific Inquiry Abilities

·        Use appropriate tools and techniques including mathematics to gather, analyze, and interpret data.

• Develop descriptions and explanations using evidence.
• Communicate procedures and explanations.

Time

After initial set up and installation, five minutes daily as part of the atmosphere protocol

Frequency:

Depth of soil freezing is measured at the same time each day (preferably within one hour of solar noon) between the autumnal equinox and the vernal equinox.  Measurements are continued after the vernal equinox until there are three weeks in a row of no ice in the frost tube. 

Prerequisites

Basic Atmosphere protocol (GLOBE)

Soil Characterization protocol (GLOBE)

Materials and Tools (See figure 1 for graphic of tubing and other materials)

• Soil auger or post digger  or 1/2” (12 mm) steel pipe driven into the ground and jacked up to make hole 
• 12 mm (1/2”)CPVC Pipe  (2.50m) 
• 10 mm (7/16”) O.D. Tubing (2.50 m)
• Ground cover, cap, or other material to keep water and cold air out.
• Food coloring (or  flourescein dye) and water
• Funnel
• Black waterproof marker
• Meter stick with cm markings
• CPVC pipe glue

Recommended

Basic Atmosphere protocol air and soil temperature, precipitation

Soil Characterization protocol

Preparation

Site Location

1.  Select a site for installing your frost tube. Ideally, the site should be in relatively undisturbed and uncompacted soil and within 30 meters of your atmosphere study site.  Check with appropriate authorities for safety in digging in soil at the selected site.  

2. Obtain a GPS reading of the frost tube protocol study site.

Construction of Frost Tube

1. The length of the outer pipe/tube and flexible inner tubing depends on the depth of active layer (the layer  that seasonally freezes and thaws). You can check active layer thickness using steel stick (thaw probe) at the end of the summer).  Your frost tube should be this deep into the ground. Also remember that a part of the tube must stick up above the surface of the ground in order to be found in the snow. The ideal height of the CPVC pipe above the ground is 1 m.  This will keep the top of the pipe above snow for most areas and yet be accessible to students.  
2. Attach (CPVC pipe glue) the CPVC cap to bottom end of the CPVC pipe.
3. Seal (by heating with match or lighter) one end of the flexible inner tubing. 
4. Fill the flexible tube with water and food coloring (or dye) using a funnel.
5. After the flexible tube is filled up to 15 cm from the top, seal the top end of the tube.
6. Make 1 cm marks using a permanent marker on the outside of the flexible inner tubing, starting with ground level down to the bottom end of the flexible tubing.
7. The flexible tube should now be able to slip into the CPVC tube so that it extends to the bottom.

Installing Frost Tube

1. Use a soil auger to dig the hole into which the frost tube will be placed. If possible, perform the soil characterization protocol on the soil that is removed from the hole (see GLOBE Soil Characterization protocol using an auger profile). Save the soil that is removed trying to maintain it based on the depth from, which it was removed.
2. Place the frost tube (flexible inner tubing and outside tube) into the hole.
3. Mix the removed soil with a little water and then use this paste to fill in any gap between the frost tube and the surrounding soil. If possible, try to place the different kinds of soil back into the gap in the order in which it was removed. Gently work the soil into the gap with a stick, trying to eliminate any air pockets.
4. Note how far the ground level is from the top of the CPVC outer tube. Raise the flexible inner tube and mark that place with a permanent marker on the outside of the tube. Using the meter stick as a guide, continue to mark each centimeter below that line until you get to the bottom. Indicate every 10 cm with a number next to the mark.  Return the flexible tube to the installed CPVC tube and leave until measurement day.
5. Cover the top of the outside tube with a CPVC cap (Do Not Glue)  to minimize the chance of cold air or water getting down into the space between the flexible tube and the CPVC tube.

Measurement Procedures

1.      Students walk to the frost depth measurement site at the same time every week ideally within one hour of solar noon. And raise the flexible inner tube.

2.      Try to not disturb snow condition.  Student should walk the same path as much as possible in approaching frost tube.

3.      Lift the frost tube (inner tube with water and food coloring or dye)

4.      Students note the depth where the water is frozen (frozen water in inner tubing is clear; unfrozen water will have the color of whatever food coloring or dye you added in the frost tube) and count the number of centimeters down from the soil surface that the freezing (thawing) extends.

5.      Students return the inner tube to the structure and record their measurement on the frost depth measurement data sheet.

6.      Measurements are continued weekly. 

Questions for Further Investigation

How will frost depth differ in different biomes across the globe?

What would cause the depth of freezing in soils to change from one year to another?

How does the depth of frost affect vegetation phenology in a biome? Any  relationship to freshwater ice phenology?

What other parts of the ecosystem are affected by the timing and depth of soil freezing?