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The section on aquatic ecosystems mentioned a key term to the functioning of any waterway: watershed. This section will give you more specifics about what a watershed is and what impact it has to the water system. Specifically you will learn:
What is a Watershed?
What does this term mean, and how does the watershed work?
Often called a drainage basin, the watershed is the area in which water, sediments, and dissolved minerals drain from higher elevations to a larger body of water, such as a stream, river, lake, estuary or ocean. Because any body of water is a product of the elements in its watershed, the watershed is essential to the health of the ecosystem.
To underscore the importance of the watershed, let's look at the ecosystem of a healthy lake.
Soil on the land contains natural minerals and nutrients from dead plant life and animal excretions.
During a rainstorm, some of the soil travels to a nearby marsh or other wetland.
The wetland (watershed) absorbs the excess nutrients from the soil and releases the correct amount to a stream.
When too much of a good thing is not a good thing
While people scan the ingredients of packages of food to compare which one will give them more nutrients, the life in an aquatic ecosystem has a limit to the amount of nutrients it can digest. While more nutrients are better for people, they are not necessarily better for fish.
Nature balances each aquatic ecosystem to perfection. During different times of the day, algae and other aquatic plants feast on a selection of food in the form of chemical nutrients, such as nitrate and sulfate. Every day, some of those plants die, but others are "born" to take their place. The fish in the ocean have enough oxygen to breathe and food to eat.
When a man-made chemical substance like fertilizer is introduced into the system, it breaks down into individual chemicals as it seeps into the soil and eventually into the water. Some of those chemicals, like nitrate and sulfate, are already present in the water as nutrients. The chemicals add extra nutrients that the watershed must try to absorb, and when it reaches its loading capacity, the watershed allows the excess nutrients to spill into the ocean. The water is now loaded with nutrients.
Too many nutrients causes a chain reaction that eventually ends in death. More nutrients mean more algae. Algae die in mass amounts, multiplying bacteria that feed on detritus (decaying matter). As the bacteria deplete the oxygen, the fish begin to suffocate and eventually die. The decomposition of the dead algae and fish causes the foul odor people smell at a fish kill area.
Nutrient loading is typically caused by human interference in the ecosystem. Besides chemicals in man-made substances, nutrients and contaminants exist in auto exhaust, roads, parking lots, rooftops and other man-made structures.
Respecting the Watershed
The Highway Signs
When you see a sign on a road or a highway telling you that you're approaching a watershed, what do you do? The highways are cluttered with so many signs that most people have never noticed one sign that can make a difference to a fish: a watershed sign. To a person driving on a highway, a sign saying, "Haw River Basin" or "Approaching Neuse Watershed" may be confusing. After all, every other sign tells drivers what to do (like a speed limit sign) or informs them of something they might need (like a blue information sign). So what is a driver to do in response to a watershed sign?
Just like the information signs tell you that you are approaching a rest area or an exit with gas stations or restaurants, watershed signs tell you that you are approaching a watershed. Why? To raise awareness that everyone lives in the watershed or river basin, to encourage people to take care of the river basins by cleaning up litter and using natural products at home, and to remind people that their actions at work, at home and on the road affect the water quality.
These signs also inform the public that the NC Department of Environment and Natural Resources (NCDENR) and the NC Department of Transportation (NCDOT) are committed to preserving wetlands and controlling water pollution. Like the agricultural and construction industries, any new transportation or road project requires a NPDES permit before any work can be done. In fact, NCDOT has a wetland and stream restoration program that creates wetlands wherever a highway project will impact a wetland or watershed site. You can find out more about this project by viewing the NCDOT Soil and Water Engineering Section site. You can find out more about the partnership between NCDOT and NCDENR by reading the River Basin Web page.
Are construction companies and highway planners the greatest offenders of polluting the watershed? Watershed sizes vary. Some include several streams and rivers feeding into one large water source, and others surround only one source, fed by an underground spring. In general, large watershed areas typically are not as clean as smaller watershed areas. That is because the more area feeds into a single lake, the more chance each part of that area has to pick up sediment and pollution.
In addition, larger watershed areas have more likelihood of becoming part of a construction site. In many cases, before the foundation is laid for a road or business and housing development, trees in the area are cut and the ground is leveled, so that any cavities, including wetlands, may be filled in.
Both large public construction companies as well as private builders make these mistakes. But if concrete or asphalt replaces a wetland, the wetland is no longer available to absorb the sediment and nutrients from the soil before they travel to their next destination. Rain cannot be absorbed by the nonporous surface and so carries everything directly to the nearest water source.
Every industry associated with building projects must follow regulations established by the Environmental Protection Agency and carry a NPDES permit for point-source pollution. Typically a licensed industry will replace wetlands and control for sediment runoff into the water. However, homeowners building additions on their own property are not governed by these regulations and usually are not even aware that they are affecting the water quality.
Just replacing a roof increases the rate at which phosphorus dumps into the water. If the roof is sloped, the amount of phosphorus that escapes into the water is even greater. That is why laws prohibit building anywhere within miles of watershed property.