Life in a Lake: Modeling the effects of phosphorus on aquatic organisms
Environmental Science, Chemistry, Biology
High School: 9-12 grade
Project 2061 Benchmarks NAS Science Standards or NCTM Standards supported by this activity:
Content Standard A – Science as Inquiry
- Ask a question about objects, organisms, and events in the environment
- Plan and conduct a simple investigation
- Employ simple equipment and tools to gather data and extend the senses
- Use data to construct a reasonable explanation
- Communicate investigations and explanations
Content Standard C – Life Science
- Life cycles of organisms
- Organisms and their environment
Content Standard E – Science and Technology
- Identify a simple problem
- Propose a solution
- Implementing proposed solutions
- Evaluate a product or design
- Communicate a problem, design, and solution
Content Standard F – Science in Personal and Social Perspectives
- Personal Health
- Types of Resources
- Changes in environments
- Science and technology in local challenges
The purpose of this activity is to get the students engaged in understanding the effects of water pollution in the form of phosphorus addition to a lake. We did this lesson after testing several water quality parameters in streams near the school. Students could talk about the exact values they have found, however have difficulty understanding what this value meant in terms of it’s effect on the surrounding fauna. Students will learn the concepts of eutrophication, population fluctuations, and environmental problem solving. Students will also learn how to conduct a scientific inquiry-based experiment and will collect, graph, examine, and report data.
Context (Background information for teacher):
Prior to this activity students should understand basic water quality measurements taken in aquatic systems (eg. phosphorus, nitrogen, oxygen, pH, temperature) by either lectures or actual field activities. Students should know that when a lot of nutrients are in an aquatic system, it is known as being eutrophic. Students should understand that many of these nutrients are added to water bodies through non-point and point sources. Point source pollution can be identified and has a particular discharge location (factory outflow, waste water plant discharge, storm sewer pipes). Nonpoint source pollution is contributed over an extended area and cannot be traced to a single point (farm field, lawn, parking lots, runoff). They should also be familiar with ways to decrease input of nutrients into water bodies. Students should have some background about aquatic organisms such as phytoplankton, zooplankton, and fish and also knowledge about food-chains. Phytoplankton are photosynthetic free-floating algae and are found in the water column. Phytoplankton are a food source for zooplankton and their growth is usually limited by phosphorus in freshwater systems. Once the phytoplankton die they sink to the bottom, where bacteria decompose them and consume oxygen while doing so. Zooplankton are tiny free-floating animals in aquatic systems, and feed on phytoplankton. Small fish feed on the zooplankton in many lakes. Lastly, students should be able to design a scientific experiment by following the scientific method, understand independent and dependent variables, and be able to graph and examine scientific data.
This lesson is part of a water quality unit.
- EcoBeaker program for High School Students produced by Simbiotic Software; http://simbio.com/
- Have EcoBeaker installed on computers
- Have practice with software
Reflective discussion of our water quality testing results, begin to discuss what affects these water quality parameters have on aquatic organisms. Discuss point source/non-point source pollution, and ways to decrease nutrient inputs to lakes.
Describe the lesson:
- Students will be placed into four groups and assigned computers.
- Students will then design their own experiment to test the effects of phosphorus on a lake system. They will be told that each model simulation should last 52 weeks, or one year. They will also be told that they need at least 3 different phosphorus treatments and 3 replicates of each treatment.
- Once they have their experiment designed (question, hypothesis, and phosphorus treatment levels) they will have a teacher check it before starting actual model simulations.
- Before they begin their experiment they will have a few minutes to familiarize themselves with the program and how to run the model simulations using Procedure one on the assignment.
- They will then run their experiment using Procedure two on the assignment. They will set the first phosphorus level chosen (kg/acre/day) and let the program run for one year. At that time they will record the length of experiment, and the number of individuals for phytoplankton, zooplankton, and fish. They will run the same phosphorus level at least three times to get replicate samples. Then they will run the other treatments designed prior to experimentation. They will calculate averages of phytoplankton, zooplankton, and fish for each phosphorus level.
- After they are finished conducting all of their model simulations they will graph their results. For each response variable (phytoplankton, zooplankton, or fish) they will create a bar graph and plot the averages with phosphorus level on the x-axis.
- They will then have questions to answer relating the results of the experiment to their prior understanding of nutrient addition to water bodies.
- Students will work on graphing the results and lab questions as a group.
- Lastly they will present to the class their question, hypothesis, experimental design, and results to the class, and questions 1 and 4 from the worksheet.
- Participation in activity
- Experimental Design
- Worksheet questions and graph (Download the worksheet: .doc or .pdf)
Students can also monitor oxygen levels at the bottom of the lake at different phosphorus levels. This can then be related to the population dynamics of the phytoplankton, zooplankton, and fish.