• A watershed is an area of land over which water drains into a body of water.

Mapping a watershed is crucial in managing the land sources of pollution that drain into an aquatic ecosystem.

It is also important to understand the effects of human activity on the flow of water in the watershed.

• A healthy riparian area (land adjacent to a stream) provide many benefits.

Plant roots absorb water and nutrients.

Roots also stabilize banks, slowing flow of water.

Decreased water flow allow water to infiltrate the ground and replenish groundwater.

Trees shade and cool the water; cooler water temperatures hold more dissolved oxygen.

Leaf litter provides food and habitat for aquatic organisms.

• The leading source of water pollution in the U.S. is pathogens from sewage and animal waste.

Industrial activity can release metals and chemicals such as PCBs.

Runoff can contaminate water with pesticides, sediments and nutrients that cause hypoxia.

Worldwide, the major source of water pollution is nutrients, leading to algal blooms such as the "dead zone" in the Gulf of Mexico.

• The Chesapeake Bay shows typical sources of nitrogen pollution in watersheds.

Forested areas release little nitrogen to streams since roots absorb water and nutrients.

Suburban areas have faster water flow due to impervious surfaces, leading to more runoff.

Agricultural areas have highest nitrogen input and also highest runoff to streams.

• Aquatic ecosystem can be degraded by runoff and experience eutrophication: explosive algal growth that leads to depleted oxygen levels.

1. Terrestrial runoff adds excess nutrients (nitrogen and phosphorous) and cause exponential growth of algae (bloom).

2. Algal blooms block sunlight.

3. Decreased underwater photosynthesis leads to decrease in dissolved oxygen.

4. Algae eventually die and are decomposed by bacteria through respiration, further depleting oxygen levels.

The decrease in dissolved oxygen levels is called hypoxia and leads to decline of aquatic organisms.

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Smart land use in riparian area
Human use such as residential and agriculture is confined to upland regions. Excess nutrients flow down toward stream.	Zone 3: a narrow strip of light agriculture with minimal chemical use absorbs flow.	Zone 2: a managed forest with controlled harvesting further absorbs runoff.	Zone 1: an undisturbed forest, preferably planted with native riparian trees, provide habitat for the stream.

• Strategies to reduce pollutants in streams include slowing down water flow across land surfaces and federal regulations.

• Deep-rooted vegetation absorbs water and excess nutrients.

• Permeable pavers allow water to infiltrate into the ground.

• The Clean Air Act of 1972 helped reduce atmospheric nitrogen from automobile and factory emissions.

• The Clean Water Act of 1972 established pollution standards of pollutants released into the water.

• These are some methods that slow down water movement to increase infiltration of stormwater and reduce runoff.

• Green roof planted with shallow-rooted vegetation absorbs water - and cools the house.

• Rain barrel stores excess rain that can be used for watering later.

• Redirected downspout channels rainwater to vegetated areas.

• Permeable pavers allow water infiltration.

• Rain garden planted with water-loving vegetation absorbs water in low-lying areas.

• Curb cutouts divert street runoff - provided there is nearby vegetation.