Activity

Stream Chemistry

Summary
Students collect water from a stream and use colorimetric tests to measure dissolved oxygen and pH, then use their readings to determine if the stream is healthy.
Science content
Biology: Features, Adaptations of Living Things (K, 1, 3, 7)
Biology: Food Webs, Ecosystems, Biomes (3, 4)
Chemistry: Atoms, Molecules (3-7)
Materials
  • tubes for dissolved oxygen measurement
  • dissolved oxygen tablets and colour chart (e.g. La Motte)
  • tubes for pH measurement
  • pH indicator solution and colour chart
Procedure

Introduction: the chemistry of the stream water determines how much life can grow in it. First we will measure how much oxygen is in the water (http://www.lamotte.com/pages/common/pdf/instruct/5963.pdf). Like us, the living things in the stream need oxygen. We breathe oxygen in from the air. Animals that live in the water use oxygen that is dissolved in the water. (http://tellus.ssec.wisc.edu/outreach/teach/ideas/kotoski/Minifact_Sheet…). Second, we will measure the pH of the water (or how acidic it is). If the water is too acidic (or too much in the other direction, too alkaline) living things will die (http://tellus.ssec.wisc.edu/outreach/teach/ideas/kotoski/Minifact_Sheet…).

Within a designated area, students explore the stream to find landmarks (e.g. waterfall, bridge), then choose a part of the stream that they would like to sample. First they collect water in a tube for dissolved oxygen testing, and then collect the tablets from an adult. While these tablets are dissolving, they can collect a second tube of water from the same place for pH testing, and then get a drop of pH indicator solution.
Students record their pH and their dissolved oxygen level for the area of the stream that they tested. Students can draw a map of the stream, with landmarks, and mark where they sampled from. They can also mark the location and readings obtained by a friend.
When all the students have made their measurements, the group hears all the readings and then discusses how healthy the stream is for living things. (In this class: dissolved oxygen was 4ppm -sufficient for some, but not all, life; pH varied from 6.5 to 7.5 - able to support a variety of living things).

Extension of experiments on dissolved oxygen - use the tablets to measure the dissolved oxygen in a sample of pond water, and track the reduction in dissolved oxygen as it is used by the living things in the pond water (experiment suggestions in ref 4)

Notes

This activity requires purchasing chemical test kits from a biological supply company or a water testing company. To simplify, just do the pH test, which is cheaper and more readily available.

Grades taught
Gr 1
Gr 2
Teaching site
Weir Elementary