SOS Lesson Plans/Student Worksheets

Teachers Guide to Watersheds, Landuse and Pollution

Lesson Introduction

The land area surrounding a lake is called the watershed. Precipitation in a watershed will either infiltrate in the ground or runoff into local streams and rivers that feed the lake. There are a number of factors that influence how much rainfall will runoff and how much will infiltrate into the ground. The topography and elevation of the watershed will impact the speed in which runoff will reach the lake. The steeper the watershed land area, the faster the runoff. The size of the watershed will also affect the amount of runoff that leads to a lake. The greater the amount of land area in a watershed the more opportunities for runoff to reach the lake via streams. The type of land cover will also affect runoff. Watersheds covered in vegetation and forests provide a chance for rainfall to be absorbed by plants and filtered into the ground. Watersheds covered in hard or impervious surfaces cause the rainfall to runoff more rapidly because there is no plant material to stop and absorb the flow of water.

Landuse Impacts on Lakes
The landuses in a watershed can have a major impact on the amount and types of pollution that ends up in a lake. If you think of the watershed as a bowl and the lake at the center or bottom of that bowl, you can envision how any contaminants such as road salt, pet wastes, and excessive soil loss could impact and "fill-in" the bowl. The types of pollution that may enter a lake from landuses are called non-point source pollutants. They are pollutants in the watershed that may enter the lake from runoff that occurs after a rainfall.

Forested watersheds have the least impact on pollution to a lake. Rainfall that reaches a forested watershed will be captured by the trees and filtered through the soils before it reaches a stream and then finds its way to a lake. If the forest land is logged improperly however, exposed soils may runoff with the rainfall and contribute sediments to the lake. Sediments contain organic matter such as phosphorous which in turn "feeds" the lake with added nutrients. Foresters that institute best management practices can reduce the impacts of logging on a watershed.

Land that is urbanized or residential may also contribute pollutants. Urban areas have hard surfaces such as parking lots and driveways which are impervious to rainfall. Rainfall that hits impervious surfaces will pick-up pollutants and carry them to the lake via local stormdrains. Pog wastes, car oil, and road salts all make there way into the lake because of the runoff from urban or residential areas. Another source of pollution to lakes from urban and residential landuse is construction. Construction activities may cause huge losses of soil from the construction site to a local waterway. This can lead to increased turbidity of the lake and also contribute to nutrient loading from the phosphorous contained in the soil. In New York State, the Department of Environmental Conservation regulates best management practices at construction sites to protect lakes from this type of non-point source pollution.

Finally, agricultural landuses may also contribute pollutants to a lake. Agricultural practices include exposing soil, the application of fertilizers and pesticides, and for farms that have livestock, the potential for animal wastes to enter local streams. Many farms in New York State are trying to reduce the impact of agricultural practices on lakes and streams by including best management practices in their management of the farm.

Lesson Outcomes

Through this lesson and accompanying activity students will:

  • Compute the land-to-water ratios for two watersheds.
  • Learn to interpret landuse maps.
  • Develop a scale model for land-to-water volume ratios.
  • Interpret data and conduct independent research.

MST Standards

  • Standard 2 Key 1
  • Standard 6 Key 2, 3, 6
  • Standard 7 Key 1, 2

Social Studies Standards

  • Standard 3 Key 1, Key 2

Lesson Objectives

During this lesson your students will be comparing watersheds in the Finger Lakes to examine a number of questions regarding how or why these watersheds may be vulnerable to non-point sources of pollution. At the end of this activity they should have a model of the three watersheds and be able to answer questions.

To conduct this activity your students will need the following items:

  • Print out (or view of) the watershed landuse maps for Cayuga, Owasco and Skaneateles Lakes (to print the map you may need to print to fit the page margins)
  • Sugar cube
  • Paper squares (either cut up construction paper or post-it notes)

Activity

Activity - Watershed and Landuse

Answers

Procedure Answers:

  1. Determine the ratio of watershed area to lake volume for the Finger Lakes watersheds using the table below.
  2. Watershed to Water Volume

     

    Cayuga

    Owasco

    Skaneateles

    Watershed Area

    1145km2

    470km2

    153km2

    Lake Volume

    9.3 km3

    .8 km3

    1.6 km3


  3. Using the sugar cube and paper squares make a model of these watersheds. The sugar cube represents one cubic kilometer of water (km3) each paper square represents one square kilometer (km2). If you do not have enough squares to create your model be creative!! Label the squares or use different colors to represent the measurement.
  4. Note: round your ratio to the nearest number.

  5. When you have finished compare the watersheds. Which one has a greater land to water ratio?
    • Owasco Lake 587:1, Cayuga 123:1, Skaneateles 95:1
  6. Using the landuse maps, website links listed in the lesson introduction, and link to the Finger Lakes answer the following questions:
    • Which watershed do you believe is more vulnerable to non-point source pollution and why?
      • Owasco has a greater land to water ratio therefore there is a greater potential for more runoff of nps pollution reaching a lake with much less volume of water than Cayuga or Skaneateles. The more land area surrounding a watershed the greater the potential for runoff. Even though Cayuga has more land area the volume of water is greater, and the lake is deeper so dillution will play a role in offsetting the impacts of pollution to the lake.
    • What is the dominant landuse in the watersheds?
      • The dominant land use in the watersheds is broken up evenly between agriculture and forest.
    • How would these landuses potentially contribute to the non-point source pollution problems of these watersheds?
      • NPS pollution from agriculture includes fertilizers, pesticides, and sediments from agricultural operations. Forest landuse would depend on how mush is actually logged, but the impacts of logging would be runoff of sediments.
    • Name two best management practices to reduce non-point source pollution in the Finger Lakes.
      • See the links to best management practices for more information.
    • Name two economic reasons that the Finger Lakes should be protected from non-point sources of pollution.
      • The Finger Lakes are used for drinking water and they are a tourist destination, see Finger Lakes link for further info.
    • There are 11 total Finger Lakes, of these which one has a similar volume of water as Skaneateles Lake?
      • Canandaigua Lake has 429 billion gallons Skaneateles has 424

Bonus: Research and find the watershed to volume ratio for one of the Great Lakes. Write a short essay on the location and characteristics of this watershed.

For the answer see the visit the Great Lakes Atlas at the EPA website.



 

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