Teacher’s Instructions:

1) Hand out a copy of pages 2-6 to each student.2) Have students read page 2 and complete the tasks.3) Provide each student with a copy of the Answer Key for Map 1 (page 7) and have them correct their own map.4) Provide each student with a copy of pages 8 and 9 and have them complete the assignment.5) Collect the assignments and correct them using the answer key on pages 10 and 11.

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Factors That May DisturbBiogeochemical Cycles

Algae

Factors That May DisturbBiogeochemical Cycles

Objective:To learn about the factors that may disturb biogeochemical cycles.

Tasks:1) Recall what you’ve learned about biogeochemical cycles.2) Use Map 1 (page 3) to draw a line that encompasses all the rivers and tributaries that feed into Lake Winnipeg. This is Lake Winnipeg’s watershed.3) Once you have completed your watershed, check your map against the answer key map (page 7). Make any necessary adjustments.4) Read the background information (pages 4 and 5).5) Using your knowledge of biogeochemical cycles, the background information and the map, answer the questions in the assignment (pages 8 and 9).

Key Terms:

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- watershed: the region draining into a river, river system, or other body of water- leaching: penetrating gradually- legumes: peas or beans- manure: any animal or plant material used to fertilize land such as the contents of stables and barnyards, decaying animal or vegetable substances, etc.- bale: a large package of material (straw) tightly bound with twine or wire and often wrapped

Round straw baleLegumesLeaching

MAP 1

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Background:

Crop Rotation

To help maintain nitrogen cycles in their soil, farmers can use a variety of farming practices. Some of these practices are more environmentally friendly thanothers and the cost of each practice varies greatly.

The quickest (but more expensive) way to increase the nitrogen content in soil is to apply chemical fertilizers. Farmers can spread or inject these fertilizers on or into their soil. Farmers should get their soil tested first to ensure the correct amount of nitrogen is added. When too much chemical fertilizer is applied to a field it has agreater chance of running off or leaching into ground water, rivers and lakes duringa heavy rain. Many of these rivers and lakes are areas where fish live.

Farmers can also use crop rotation to help increase nitrogen in the soil. Croprotation is when farmers plant a different crop in the same field each season. Somecrops (like legumes) are nitrogen fixers and increase the amount of nitrogen in thesoil. This farming practice is very inexpensive.

Farmers can also leave one or two fields as summer fallow. This means that no crop is planted for at least one season. The soil is allowed to “rest” and the nitrogencontent will increase naturally due to the bacteria in the soil and especially if there is some organic material such as straw or manure present.

Spreading Fertilizer

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Spreading Manure

Harvester/Combine

Straw

Tilling/Cultivating

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Spreading or injecting animal manure on or in a field will also increase the soil’snitrogen content. However, the smell can be very unpleasant and farmers shouldtake care that a nearby town or neighbour is not down wind during manureapplication. Injecting manure will lessen the smell more than spreading it on thesurface. Farmers would need to rent or purchase the spreading or injecting equipment but the cost of manure would be minimal if the farmer has livestock on his or her farm.

During harvest, farmers can choose to spread the straw of the crop on the soil. Then, the straw and stubble is worked into the field during tilling. Adding this plantmaterial to the field will increase the nitrogen content of the soil as it decays. Sometimes farmers need to bale the straw and take it off the field so that they can use it as bedding for their cattle. In this case, the remaining stubble is worked into the soil. The costs associated with this practice are minimal.

The nitrogen cycle is very important. All living things need nitrogen to grow.However, the nitrogen cycle may become disrupted and there may be too much nitrogen available. When there is too much nitrogen in our water it may lead to algal blooms and an over-growth of water plants.

POSSIBLE EFFECTS ON FISH

Excessive plant growth and algal blooms may affect the fish that live in the water.The water may become less or more suitable for certain species of fish. As these plants grow and then die and decay, they use up oxygen in the water. This leaves less oxygen for the fish. This may cause the fish population to decrease. An algal bloom may block sunlight from penetrating the water. Thus, plants below the water’s surface may not be able to perform photosynthesis and they may die. Again, this may decrease the amount of oxygen in the water which may in turn cause a decrease in the fish population. Alternatively, an increase in vegetation may provide a benefit to some species offish. Fish also use plants for shelter and protection. An increase in plant growth would increase the amount of protective shelter for fish.

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Algae

Lake Winnipeg Watershed (light gray)Area used for agriculture (dark gray)

Answer Key: Map 1

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Assignment: (23 marks)

Questions:

1) Using the map, estimate the percentage of the watershed that is used for agriculture. (1 mark)

__________

2) Recall the nitrogen cycle. List the nitrogen inputs and outputs for the following two systems: a) pasture of cattle (4 marks)

b) field of grain (4 marks)

3) What methods do farmers use to help maintain the nitrogen cycles in their soil? (5 marks)

Using your knowledge of biogeochemical cycles, the background informationand the maps, answer the following questions.

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4) What impact could a flood in the Red River valley have on the nitrogen cycle in Lake Winnipeg? And, how may this affect fish in Lake Winnipeg? (4 marks)

5) What other circumstances may affect the nitrogen cycle of Lake Winnipeg? (2 marks)

6) Use the decision making process to determine what could be done by farmers to decrease the impact of fertilizers on Lake Winnipeg? (3 marks)

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Answer Key:

Questions:

1) Using the map in the answer key, estimate the percentage of the watershed that is used for agriculture. (1 mark)

__________

2) Recall the nitrogen cycle. List the nitrogen inputs and outputs for the following two systems: a) pasture of cattle (4 marks)

b) field of grain (4 marks)

3) What methods do farmers use to help maintain the nitrogen cycles in their soil? (5 marks)

Using your knowledge of biogeochemical cycles, the background informationand the maps, answer the following questions.

50% - 60%

Outputs:- plants use N to grow- cattle use N from plants to make protein- cattle take N with them when they are sold

Inputs: -some N is returned through their wastes andwhen the plants decay

Outputs:- plants use N to grow- N leaves when grain and straw is taken from the field

Inputs:- some is returned when straw decays- fertilizer or manure can add N

- apply chemical fertilizers or manure- leave straw on field to decay- leave fields as summer fallow- crop rotation

Assignment: (23 marks)

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Answer Key:

- top soil and nutrients (nitrogen) would be moved intothe lake - causes an increase in plant growth or analgae bloom- there would be more food for fish but less oxygen, especially as the plants die and decay- less oxygen would mean that more fish would die

- chemical spill- drought- increase/decrease in fish population- increase/decrease in decaying organic matter- raw sewage spill

Students should consider the costs and environmentalbenefits of each farming practice. Ideally, they wouldcome up with ideas to encourage farmers to use themost environmentally friendly practice.

For example, students could suggest that the governmentprovide the farmers with a subsidy if they leave one or two fields as summer fallow (to help off set the loss of income).

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4) What impact could a flood in the Red River valley have on the nitrogen cycle in Lake Winnipeg? And, how may this affect fish in Lake Winnipeg? (4 marks)

5) What other circumstances may affect the nitrogen cycle of Lake Winnipeg? (2 marks)

6) Use the decision making process to determine what could be done by farmers to decrease the impact of fertilizers on Lake Winnipeg? (3 marks)