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Objective Students will learn about the nutrient cycle and how nutrients affect water quality and the aquatic ecosystem. They will be given the opportunity to develop hypothesis and verify their hypothesis. Growth of all organisms is dependent on receiving sufficient nutrients. The primary nutrients are carbon, nitrogen, and phosphorous. We receive our nutrients from the plants and other animals we consume. Plants also depend on these nutrients. Because of the relative abundance of carbon dioxide in the atmosphere, carbon is generally not a nutrient that limits plant growth. In rivers, lakes, and ponds phytoplankton and other plants are generally limited by the amount of nitrogen and phosphorous found in the water. The ratio of nitrogen (N) to phosphorous (P) in the water indicates which nutrient will be the limiting nutrient. N: P ratios are generally greater than 10, and thus are phosphorous limited. Because lakes are generally
phosphorous limited, a number of detergents, fertilizers, etc. have been
blamed for the eutrophication of lakes and streams. Most detergents today
are labeled as being phosphorous free due to industry attempts to rectify
eutrophication problems. Activity
Collect pond water that contains algae from your local pond. This water can then be placed in different beakers or jars with different concentrations of nitrogen and phosphorous added.
The above table illustrates how to set up a matrix to test the effect of different concentrations of nitrogen and phosphorous on algal growth. Growth will take around one week or more and can be measured visually, or by using a spectrophotometer. Record your results after one week and discuss how surface water runoff could effect the color, smell, and vitality of neighborhood lakes, streams, and ponds. Primary sources of external nutrients are: 1. Municipal wastes
Have students check for phosphorous content in their household detergents, soaps, etc. Visit your local streams and note the change in algae growth as a function of the seasons. There is usually a late spring bloom, followed by summer decay, and then a fall bloom as falling leaves decay. Have students evaluate which possible inputs will effect their local water body. Have students maintain a log of their bottle ecosystem. They can record water appearance, smell (a balanced system will not smell like rotten eggs (H2S), plant growth, etc. Have them compare their bottle ecosystems with other classmates and draw conclusions. DID YOU KNOW? Lake Erie is a well known example of a system that became eutrophic (nutrient rich); algae flourished and then decayed, oxygen levels plummeted, and fish died. The Clean Water act of 1970 mandated secondary wastewater treatment and Lake Erie has made a comeback. #4.3 Students know major sources of water, its uses and importance, and its cyclic patterns of movement through the environment. #5 Students know ways that science, technology, and human activity have an impact on the world and its resources. Return to top
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