In this extended experiment, students explore the effects of algal blooms on dissolved oxygen levels of water in a system by growing their own algae blooms in water bottles. They also connect excess nutrients to excess algae growth. This will prepare them for understanding how nutrient pollution affects the Chesapeake Bay.

Approximate Time: 2 class periods + intermittent time to collect visual and dissolved oxygen data

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Objectives:

• Students will perform an experiment to determine the effects of excess nitrogen in natural bodies of water

• Students will understand that eutrophication, nutrient pollution (specifically nitrogen), and dead zones are all connected

Materials:

• Materials for Algae in a Jar experiment (see below)

• Dissolved oxygen test kit

• Additional glassware (ex test tubes) so multiple students can test at the same time

• For clues wall: “Lots of algae in the Bay before fish died”

• Algae in a Bottle Teacher Guide

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Handouts:

• Algae in a Bottle experiment procedure

• Data collection sheet

• Analysis & summary sheet

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DCI: LS2.C: Ecosystem Dynamics, Functioning, and Resilience

SEP: Planning & Carrying Out Investigations, Constructing Explanations & Designing Solutions

CCC: Cause & Effect

What kinds of living things are in the Chesapeake Bay? Don’t forget living things that are not animals!

• The purpose of this warmup is to connect with the previous day’s activity, and to determine whether students remember that algae live in the Bay.

Tell students that you have another clue about the dead fish in the Bay. Before the dead fish appeared, scientists noticed that there was something strange about the water. It looked like this (show picture below). They thought there might be a connection between the color and the dead fish, but they had to find out for sure. We are going to start an experiment today to see what might cause this color in the Bay, and whether that might have caused the fish to die.

Ask students what they notice about the color in the picture. Key things for them to see are: it is a green color, it is closer to the shore than the center of the Bay, it seems almost like it is in waves. Ask students if they have any ideas what this color might be. Use questioning to help them realize that what they are looking at is a large quantity of algae. Lead a short discussion to see if/what students already know about algae. Then show them these pictures:

Ask if any students have seen anything like the first picture. Tell them that the first picture shows algae growing in a pond. When this happens, it is called an algae bloom. The second picture shows what some algae look like under a microscope. Ask if students know why they have a green color. Use questioning to help students recognized that they can make their own food like plants (you don’t need to discuss photosynthesis and chloroplasts). Students will learn more in depth about algae in Activity 4. Add the clue “Lots of algae appeared in the Bay before the fish died” to your clues board and have students add it to their sheets.

Tell students that they are going to be performing an experiment to see if the algae are causing the fish to die. To do that, they are going to grow their own algae to observe what happens. Collaborate with students to develop a research question such as “How do algae affect the water they are growing in?” Hand out the “Algae in a Bottle Experiment Procedure” to students, and have them write the research question in the space at the top.

Have students read through the materials first. When they get to the fertilizers, tell them that the different fertilizers will help the algae to grow. You don’t need to go into detail at this point about why you are adding these particular fertilizers, but students will begin to understand in later activities in the module.

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Read through the procedure with students and check to make sure they understand what each of the bottles is for. When students are ready to begin, divide them into groups and have them complete the Setup Day portion of the procedure. Make sure that students make observations of their bottles on Day 1. Since all their data will be the same, you can test the dissolved oxygen on the first day together to teach students how to use the kits. Use a mix of pond water and bottled water like in their experiments. Before testing, briefly explain to students what “dissolved oxygen” means (they will learn more about this in Activity 4).

At regular intervals (ex. every two days), have students make observations of their bottles. Halfway through the experiment, have students test for dissolved oxygen in each of the bottles and record the data on their data sheets. On the last day of the experiment, have them test the dissolved oxygen one more time.

By the end of 14 days, the bottles will look something like this:

Have students graph their data for dissolved oxygen (you may choose to have them pool their data first). Discuss with students what kind of graph would be most appropriate. In this case, a line graph works best to show the change over time. Students should graph all their data on one set of axes to make comparison easier. They can use different colors or symbols for the different bottles. If technology is available, students can use Excel or Google Sheets to make their graphs.

Have students analyze the change in dissolved oxygen (see note below re: differentiation for different math levels), and describe the changes in the appearance of the bottles.

Lead a class discussion with students about what their data means in the context of the experiment. Use the CER below as a guide to drive the discussion.

Make sure students have already completed Activity 4 before they do this section of this activity so they can make logical deductions about what happened in each of the bottles. Have students write a claim-evidence reasoning statement explaining their results. Because of the complexity of this CER, students will likely need some scaffolding and support. A sample explanation might be:

• Claim: Algae grow fastest when there are extra nutrients in the water. The more algae there are, the more decomposers there will be to decompose them, causing the dissolved oxygen in the water to go down.

• Evidence: In the bottles with the most fertilizer, we could see the most algae growing. In the bottle with no fertilizer (control) there was only a little algae growing. The bottles with the most algae and fertilizer had the least dissolved oxygen at the end, and the bottle with the least algae (control) had the most dissolved oxygen at the end.

• Reasoning: Algae need nitrogen and phosphorus to grow. When they have extra nitrogen and phosphorus, more algae will grow. Eventually the algae die and decompose. Decomposers use oxygen to break down the algae. In the bottles with the most algae, there were more decomposers, so they used more oxygen, causing it to go down the most.