Sponge it Up!

Objectives: Students will understand how glaciers act as hydrologic buffers for river flow.
Related Web-Activity: Thirsty River
Subjects: Geology, Hydrology
ELRS: Science 1.2, 1.3
Size: Whole class to group
Setting: Outside
Duration: 15 minutes
Materials: One yard of 2 inch diameter PVC pipe, > 2 inch cube sponge, water

Background

In all ecosystems buffers exist that help minimize the impact of challenging environmental conditions. Glaciers, for example, minimize the impact of summer drought to areas downstream in a watershed by slowly releasing water into the river during warm, dry summers. There are many other examples of buffers:

• Riparian forests anchor soil in the ground with plant roots and act like buffers when floods occur, so topsoil is not washed away by turbulent waters.
• The thick bark on Douglas-fir trees acts as a buffer when fires race through the understory of forests and protects these trees from being consumed by flames.
• Lichens use much of their energy to produce secondary compounds that buffer them (and others nearby) from invading bacteria and microbes.

Much of the time, buffers are examples of how short-term efficiency of an ecosystem or a species is compromised in order to protect other processes in the long term. For example, it takes extra energy for Douglas-firs to make thick bark. But in the long-term making extra-thick bark benefits the tree species as a whole. Indirectly, the thick bark helps other species survive; a surviving Douglas-fir tree will also provide habitat and shelter for wildlife after fires pass through.

How do you compromise efficiency in your life in order to buffer yourself and others from the challenges of the future?

Procedure

Teachers, demonstrate to students the concept of glacial hydrologic buffers by inserting a cube of sponge into a PVC pipe and pushing it at least halfway through the length of the pipe. The sponge must fit snugly and fill the diameter of the pipe completely. Have one student hold the PVC pipe vertically as another student pours a cup of water into the top. (You may wish to do this outdoors.)

Before the demonstration, talk about the materials and their analogous counterparts:

1. PVC pipe = watershed
2. Sponge = glacier
3. Cup of water = snow and rain on the glacier

The two phases of the experiment represent the two primary seasons in Northwest hydrologic systems:

 a) Releasing of water into the PVC pipe = winter rain/snow season,
 b) The time after water is released = summer dry season.

Discuss with your class the following questions:

1. How would ecological systems downstream of glacial watersheds be affected if glaciers did not exist?
2. What are other hydrologic buffers that you find in your area?