The main pollutants in the Chesapeake are nutrients. The two primary nutrients are nitrogen (N) and phosphorus (P). Nitrogen and phosphorus are essential for life, and both of them occur naturally in soil, water, and air. There's also lots of N and Pin human sewage and farm animal manure. Plant fertilizer used on lawns and farm fields are made of nitrogen and phosphorus. If nutrients are required for life, then how can too many nutrients cause problems for the Chesapeake?

When the Bay receives too many nutrients, the system gets out of balance (see Figure 10). Single celled plants, called algae, are present in all water systems. These essential plants are the first link in the food web. However, excess algae cause two major problems for other life in the Bay. When the Bay receives excess nutrients, algae bloom, or become too abundant. Because there are so many algae the color of the water turns brownish or greenish. These algal blooms block sunlight from reaching beds of submerged aquatic vegetation or SAV. SAV provides excellent habitat and food for many Bay animals, but SAV can die when light is reduced. The second problem occurs after the algae bloom. Large masses of algae die, sink to the bottom, and decay. The bacteria that break down the dead algae use large amounts of oxygen. With less oxygen in the water, fish, crabs, and other aquatic life are greatly affected.

Objective:
To perform an experiment that simulates conditions in the Chesapeake Bay

Skills:
scientific method, mathematics, predicting, interpreting

Vocabulary:
food web

Overview:
This simple experiment is an excellent way to show the effects of over-enriching a water system with nutrients. The experiment should help the students visualize how lawn and farm fertilizers can have a negative impact on the Bay.

Materials:

• four 1-liter beakers (you can substitute equal size jars or bottles)
• a small amount (a few tablespoons) of commercial lawn fertilizer (Caution: do not use a fertilizer with weed control since these types contain a herbicide)
• a bucket of water from a pond, stream, or from the Bay
• a scale to measure the fertilizer
• paper and pens to make a chart

Procedure

Divide the group into teams of two to four students. For more advanced groups you may want to give the students all the materials and challenge them to design their own experiment to test the effect of fertilizers(nutrients).

1. Fill each jar with 750 ml of water.

2. Weigh and then add 10 mg. of fertilizer to one beaker. Weigh and then add 25 mg. of fertilizer to a second beaker. For a concentrated, water soluble fertilizer, this amounts to a few granules. (If you use an organic based fertilizer, you may need to add more, since organic fertilizers contain less nutrients then an equal amount of inorganic fertilizers.)

3. Add 10 mg. of fertilizer to a third beaker, and completely cover it with aluminum foil (this is the control for light).

4. Don't add anything to the fourth beaker (this is the control for fertilizer).

5. Label and date each beaker, and place them on a sunny window sill.

   In about 10 days the algae should begin to grow in the beakers with fertilizer. The control should remain relatively clear. Discuss how each mini-bay relates to the Chesapeake. How does the abundance of algae affect submerged aquatic vegetation, fish, oysters, and crabs? How do nutrients get into the Bay? Where do they come from? How can we reduce our inputs of nutrients to the Bay?

Other options for this activity:

Obtain some Elodea from a tropical fish store. Elodea is a type of freshwater SAV. Place a piece of Elodea in each beaker and monitor its growth. Initially, the Elodea may grow well, but eventually the algae growth should overwhelm the Elodea and cause it to die. Students can monitor the growth of Elodea over time. Students can also measure oxygen, pH, nitrogen, and phosphorus levels in each beaker. Students can design a chart, collect data over a 4- to 6-week period, and interpret the data.