Publication No. 10761
Why Is the Water Green?
Student Laboratory Kit
Materials Included In Kit
Bristol’s prepared algae media concentrate, 100X, 100 mL
Additional Materials Required
Algae culture, 400 mL
Set up the stock algae culture by obtaining 400–500 mL of algae from a local pond, aquarium, or purchase a stock algae culture, such as Desmids, available from Flinn Scientific, Catalog Number LM1045. (Try to get a concentrated sample—the greener the water the better). A purchased culture is typically about 150 mL. Since 400 mL of culture is required for this lab, dilute the culture to reach the necessary volume with spring or dechlorinated tap water. If time allows, let the culture sit in sunlight for a few days before beginning the activity.
The algae cultures, nitrate and phosphate solution are not considered hazardous but always use safe laboratory practices. Remind students to wash their hands thoroughly with soap and water before leaving the laboratory. Please consult current Safety Data Sheets for additional safety, handling and disposal information.
Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. Algae cultures, including those containing nitrates and phosphates, may be poured down the drain with an excess of water according to Flinn Suggested Disposal Method #26b. The microscope slides and coverslips should be thrown away in a glass disposal bin only. The snap-top containers maybe saved for future use.
Correlation to Next Generation Science Standards (NGSS)†
Science & Engineering PracticesAsking questions and defining problems
Analyzing and interpreting data
Planning and carrying out investigations
Engaging in argument from evidence
Disciplinary Core IdeasMS-LS2.B: Cycle of Matter and Energy Transfer in Ecosystems
HS-LS2.B: Cycle of Matter and Energy Transfer in Ecosystems
Cause and effect
Scale, proportion, and quantity
Energy and matter
HS-LS2-4. Use mathematical representations to support claims for the cycling of matter and flow of energy among organisms in an ecosystem.
Answers to Prelab Questions
Thick blankets of algae block out sunlight needed by other photosynthetic life below the surface.
Bacteria levels therefore increase to decompose the plants and other organisms killed directly, or indirectly, by the lack of sunlight. In turn, dissolved oxygen levels decrease as bacteria populations increase.
Lack of dissolved oxygen can be detrimental to larger life forms (e.g., fish, turtles and amphibians) and indirectly can even affect humans.
Counts will vary with species used.
Answers to Questions
The control sample did not receive any “runoff” chemicals and provides a baseline level of growth for comparison with the samples that did receive nitrates and phosphates.
The nitrate and phosphate combination culture. Although the same amount of nutrient was added, the combination nutrient of yields higher growth than samples containing a single nutrient. Note: Some species may yield the highest growth in the phosphate only culture.
Chlorophyll, which is the site of photosynthesis, creates the green coloration of both the green algae this experiment and in plants.
Student sketches will vary.
Typically the nitrate and phosphate combined culture have the highest microscopic algal count.
Student answers will vary depending on algal cell counts.
Yes. The “greenest” culture also yielded the highest microscopic algal cell count.
Why Is the Water Green?
Ever notice how bodies of water differ in color, odor and clarity? Algae are among the most abundant life forms present in all bodies of water, saltwater and freshwater alike and are a major contributor to water quality.
Algae are a special group of organisms that can be found nearly everywhere—in saltwater, freshwater, damp soil, ice, on rocks, lichens and even in the air. Considering that algae are photosynthetic organisms, they can basically survive anywhere moisture, essential nutrients and sunlight are present. Algae are responsible for production of a large portion of the Earth’s atmospheric oxygen and marine and aquatic food chains rely greatly on their presence. Algae are broadly defined by their pigment color, which are often described in color terms (e.g., blue-green, green, brown, red, brown-yellow). Algae come in many sizes from single-celled organisms to very large seaweed varieties.
In this lab, algae cultures will be treated with nitrates and phosphates to simulate bodies of water that have been contaminated with chemical runoff. Will algae bloom in these microenvironments?
Wear chemical splash goggles whenever working with chemicals, heat or glassware. Wash hands thoroughly with soap and water before leaving the laboratory. Please consult current Safety Data Sheets for additional safety, handling and disposal information.
Student Data Table 1. Observations of Algal Growth
Tint—Slight green algae growth
Student Data Table 2. Algae Cell Counts