What Is That Ooze On The Lake?

Introduction:

Excess nutrients that are dumped into our lakes and streams can have a very bad effect on them.  When certain materials, known as phosphates, are dumped into lakes they impact the plant and animal life that live in that environment by causing algal blooms, certain microorganisms grow out of control when there are excess nutrients in the lake.  Unfortunately, people are often to blame for putting these extra nutrients into our water supply.  One of the focuses of our lake research was to see how excess phosphorus affects the growth of cyanobacteria in the lake environment.  Excess cyanobacteria can be a health concern.  Types of cyanobacteria have been linked with hepatotoxins and neurotoxins, all of which can make humans and other animals very sick. 

National Standard Addressed:

This activity involves an experiment and can develop Abilities Necessary to do Scientific Inquiry.  It also can be a background for introducing issues of Natural Hazards and Personal Health.

The concept of  Populations and Ecosystems is a standard under the concept of Life Science.  This activity shows how populations in an ecosystem are greatly influenced by outside factors entering the environment.

Objectives and Benchmarks:

Find the effects of different water on the growth of cyanobacteria.  Students will observe the growth of cyanobacteria for four days in different nutrient levels.

Materials:

Baby food jars                           Fish tank (lake) water                          Distilled water            1x phosphorus solution                       2x phosphorus solution            Cyanobacteria solution                          Graduated cylinder

Advanced Preparation:

Collect cyanobacteria and mix the 1x and 2x solutions.  First make the stock solutions listed at the top of the table.  Then make each variety of the complete nutrient solution by adding the amounts across the table to enough distilled water to make one liter.

Procedure:

Label four baby food jars with the following: fish tank water, distilled water, 1x solution, and 2x solution.  Place ten mL of Cyanobacteria solution into each of the four baby food jars.  Place 190mL of fish tank water, distilled water, 1x solution and 2x solution into the four jars.  Observe the amount of cyanobacteria in each jar.  Place the jars either in a bright sunlit window or in front of a high watt light bulb for four days.  Observe the growth of Cyanobacteria and compare it to the first days observation.

Things to Consider:

Focus on why some of the Cyanobacteria grows faster than others.  Also note how the amount of light affects the growth of the Cyanobacteria.

Critical Concepts:

Cyanobacteria            Populations and Ecosystems            Growth and Adaptation