The Effect of Fertilizer on Algae

Transcription

1 Name The Effect of Fertilizer on Algae Problem Why is the water green and how do we fix it? Introduction As primary producers, algae form the base of the food web in the upper layers of the ocean and in freshwater lakes and ponds. The term algae is used to describe a range of organisms from the large brown kelp found attached to rocks at the seashore to the tiny green algae found in fish tanks. Like other plants, green algae need nitrogen and phosphorous in order to grow. All two nutrients must be available for the algae to thrive and reproduce. Have you ever seen a pond or lake with a thick, green layer of algae on its surface? This layer is a sign that the homeostasis of the ecosystem has been disturbed by the presence of too much nitrogen or phosphorus in the water. Fertilizers and animal waste contain these nutrients, which can be transferred to bodies of water when rainfall flows downhill from farms. In this lab, you will work with Chlorella, a type of algae that is commonly found in ponds and aquariums. You will develop a question and experiment to try and figure out why the water is green. You and your group pick one out of the three questions to base your experiment on 1. Is nitrogen, phosphorus, or both the limiting nutrient for algae growth? 2. Does increasing the nitrogen amount lead to larger algae growth? 3. Does increasing the phosphorous amount lead to larger algae growth? Materials for your group to choose from 4 test tubes glass marking pencil test tube rack 4 dropper pipettes algae culture ( Chlorella ) 25 ml graduated cylinder spring water 2 different fertilizers (High Nitrogen and/or High Phosphorous) 4 cotton balls grow light

2 Safety Wear safety goggles and plastic gloves when handling cultures. If you have glass test tubes or cylinders, check for cracks or chips. Alert your teacher if you break a glass object. Wash your hands thoroughly with soap and warm water before leaving the lab. Pre Lab Questions 1. What is the independent variable in this experiment? (What are you actually controlling what goes in each tube) 2. What is the dependent variable in this experiment? (What is changing from your independent variable) 3. Which tube will be your control and what will be in that tube? (think of what you want to use as the comparison) 4. What is your hypothesis and why do you think that? Use the pictures to write down/draw: 1) What type of liquid/fertilizer(s) is in each tube 2) How much of each fertilizer (in drops) will be in each tube 3) What organism and its quantity (in drops) will be in each tube. 4) Label your control tube

3 Procedure Write down in your procedure and check the boxes off when you include them: What is in each tube and how much (in drops)? Are all the tubes in sunlight? Where will each tube be placed? How long will you be measuring algae growth? How will you measure algae growth? (Remember the colorimeter PowerPoint slide) Include all of the the materials you circled on the previous page Data Collection: Write down what is in each tube underneath Tube 1, Tube 2, and Tube 3 Absorbance (in Abs) Day Tube 1: Tube 2: Tube 3: Remember, a higher absorbance means more algae growth

4 Data Analysis 5. Label the amount of days you collected the absorbance for your tubes on the x axis and your absorbance levels as the y axis. Do not forget your label your units! Do not forget to make symbols for each tube and to label them in your legend. Analyze and Conclude 6. After graphing your absorbance data, compare your three tubes. Which tube had the lowest amount of absorbance after 3 days? Which tube had the highest absorbance after 3 days? 7. Does having a higher absorbance have more or less algae growth? 7. Based on what you answered for Question 6 and Question 7, what can you conclude about how your chosen variables (nitrogen or phosphorus) affect algae growth?

5 8. Looking back at your hypothesis in Question 4, does your data support or not support your hypothesis? How? 9. Where could there have been error involved in your experiment? What could you have done differently in this experiment to come up with even better data and conclusions? 10. In 2 3 sentences, develop an explanation to explain your data and conclusions. Use what you know about nutrients, limiting nutrients, and algae to help you come up with an explanation. 12. What future research/questions could you ask or perform based on your conclusions? Post Lab Questions Situation: The City of Richfield recently passed a new bill stating that city residents can use unlimited fertilizer on their lawns whenever they want called the Green Water Bill. After a couple of months, you noticed that Richfield Lake s water has a greenish color to it and that resident s pets that lived close to the lake are getting sick and dying. You, being the intelligent biologist you are, saw this coming from a mile away because of your experiment. You recently got asked to present an explanation of this phenomena to the Minnesota Congress and how to fix this problem. You decided to ask yourself questions that you believe Congress will ask you and are preparing answers for them.

6 13. What has your research shown could, specifically in the fertilizer, be causing this greenish water color in Richfield Lake? Please reference your data and graph. 14. How does an algal bloom affect the primary producers that live at the bottom of the lake? (Think about what algal blooms block from reaching producers in the lake and what producers need to create energy?) 15. How does the excess algae affect first level consumers that feed on algae? What effect do you think this will have on the other organisms in the lake ecosystem? 15. Thinking back to the nitrogen and phosphorus cycle, what benefits do fertilizers bring to the environment? 16. With what you said for Questions 14 and 15, what risks do fertilizers bring to lake ecosystems? 17. Using your data from the experiment, what should we change with our fertilizer to make sure when we use fertilizers, we reduce the chance of an algal bloom in Richfield Lake? (Think about if we should use less nitrogen or phosphorus in the fertilizers)

7