SOS Lesson Plans/Student Worksheets

Watersheds, Landuse and Pollution Student Worksheet

Lesson Introduction

he 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. Pet 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 and nitrogen 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 Objectives

During this lesson you 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 you should have a model of the three watersheds and be able to answer questions.

Activity

Activity - Watershed and Landuse



 

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