Before Going to the Stream
Before Going to the Stream
Before your class goes out to the stream for your field experience, it is important to understand the vital link between land uses and water quality. We explore some questions about watersheds, land uses, water quality and pollution below.
What is a watershed?
A watershed, also known as a “drainage basin,” is the area of land and air that drains into a stream, river, or other water body. High points, or divides, determine a watershed’s boundaries. To understand what a watershed is, think about what path one drop of rain can take when it lands on the ground. It could fall on a paved surface such as a road, run down into a storm drain, through a pipe and out into a stream. Or it could soak into the earth, become ground water, and slowly make its journey towards the same stream or a different wetland or river. Ultimately, that drop of rain will makes its way to a larger body of water. This movement of water is part of the water cycle of all water we see, whether in a gas, liquid, or solid state. Water is neither created nor destroyed, but simply recycled and moved around in various forms.
[Diagram Courtesy of U.S. Forest Service]
The size of a watershed can vary greatly. It can be large like the Mississippi River watershed, which drains more than a million square miles of land from 33 states and two Canadian provinces, or as small as a creek that drains just a few acres.
In addition, all watersheds are interconnected in that they can be part of a larger watershed or have smaller sub-watersheds within them. For example, the Juniata River is a sub-watershed of the Susquehanna River watershed while the Susquehanna River watershed is a sub-watershed of the Chesapeake Bay watershed. Often citizens will look at their local watershed as well as the larger watershed when identifying issues and projects.
How are land uses and water quality linked?
Any activity that occurs on the land can affect water quality because any pollutant on land or in the air can wash into waterways when it rains. Different land-uses have the potential to cause different types of water quality degradation. For example, rain that washes over your yard can pick up excess fertilizers and pesticides and carry them into your local water body. This can also happen on farmland. When rain washes over driveways, roofs, and streets, it can pick up oil, rubber and other residues. Also, on hot days paved surfaces can heat up rain runoff that can then enter a waterway and cause elevated water temperatures.
An inventory of land uses within the boundaries of your watershed will help you locate potential sources of or threats that can cause water quality degradation in your local waterways. Refer to the “Watershed Survey” chapter in this publication for information about conducting a land-use inventory.
Sources of Pollution: Point and Nonpoint
When asked to picture in their minds pollution entering rivers, most people imagine discharge pipes from factories spewing foul-smelling chemicals into the water. These types of pollution examples are known as point source pollution because they come from a single identifiable source such as a pipe. Point sources of pollution threaten the health of rivers and are subject to federal regulations under the Clean Water Act. The National Pollution Discharge Elimination System (NPDES) requires factories and other point source dischargers to obtain permits and adhere to standards. Since its enactment, the Clean Water Act has been directly responsible for removing more than 1 billion pounds of toxic chemicals per year and more than 6 billion pounds of oxygen-depleting pollution from wastewater each year.
The major threat to today’s water quality is pollution without an easily identifiable source, or nonpoint-source pollution. Nonpoint-source pollution accounts for more than half of all surface water pollution. We all contribute to nonpoint-source pollution. Using fertilizer and pesticides on our lawns, failing to clean up after our pets, and washing our cars are all activities that cause nonpoint-source pollution. Every time it rains or snows, natural and man-made pollutants on the land are washed into streams and wetlands with the storm water. These pollutants include pesticides, fertilizers, metals, manure, road salt and motor oil that originate from farms, lawns, paved surfaces, landfills and home septic systems. In addition, air pollutants contaminate rain water.
Another significant contributor to nonpoint-source pollution is soil erosion. Although erosion is a natural process, an unnatural acceleration of this process may be caused by construction sites, dirt roads, and other land disturbances. In fact, according to the Environmental Protection Agency, eroded soil is the most widespread pollutant in rivers. Other possible sources of sediment pollution are cropland, surface mines, overgrazed pastures, landfills, logging operations and other activities that produce areas of bare soil. The texture of the soil and its potential for absorbing water, the steepness of the slope and the adequacy of protective ground cover are all factors that influence the extent of erosion.
Nonpoint-source pollution can degrade a stream quickly by introducing organic and inorganic pollutants that bury streambeds, decrease oxygen and negatively affect aquatic life. Nutrients, such as nitrogen and phosphorus, that enter streams through storm water runoff, cause excess algae growth in streams, lakes, wetlands and estuaries. When the alga dies, it decomposes, depleting dissolved oxygen required by fish and other aquatic organisms. Erosion of sediment into a stream can smother aquatic life and clog the gills of fish as well as diminish light that underwater plants need to grow. Bacteria washed into streams from septic tanks and animal waste runoff can make aquatic organisms and humans sick.
Nonpoint-source pollution problems are increased in urban and suburban areas because paved surfaces cause runoff to occur faster and in greater quantities. In a healthy and functioning watershed, pollutants are absorbed and filtered by soil and vegetation before they can reach waterways. Paved roads, parking lots and rooftops are called impervious because water is unable to penetrate these surfaces to reach the soil beneath them. In many urban areas, storm water rushes over pavement, collecting nonpoint-source pollution. This water then flows into a storm drain and shoots through an outfall pipe directly into the stream. This high volume of storm water can erode streambanks, thus increasing the problem of sediment pollution downstream. New construction sites can also lead to sediment pollution if steps are not taken to prevent erosion of exposed soil. Impervious surfaces also cause thermal pollution because rainwater flows over hot pavement before entering the stream. As urban sprawl becomes the norm, nonpoint-source pollution becomes more and more difficult to address.
The Clean Water Act also regulates nonpoint-source pollution. For more information about the legislation and how you can participate in the regulatory process, refer to “Understanding and Using the Clean Water Act” in this publication. In addition, there are many actions you can take, both as an individual and as a part of your community, to prevent nonpoint-source pollution and to alleviate its effects on local waterways.
There are choices we make every day that can affect the amount of nonpoint-source pollution entering our streams. This action kit can help you become a watershed steward by providing the tools to diagnose watershed problems and take action to improve the health of your watershed.