North Carolina Department of Environment and Natural Resources
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Dirt Can Be Dirty
Did you know that the #1 pollutant in North Carolina is dirt? When soil is washed into streams and river, it smothers small animals and fish by clogging their gills. Look for bare patches of ground around your home and around your school that might add to the soil washed into waterways. Could something be planted here to keep the soil in place?

Pervious material will let water through them. Impervious materials will not. When new houses, office buildings, and shopping centers are built, the amounts of impervious surfaces often go up. The concrete and asphalt used to build roads and parking lots are impervious. Water runs on top of them, collecting pollutants as it goes. When impervious surfaces are constructed right next to streams and creeks, polluted runoff goes straight into the water.

Some builders and homeowners plant or keep what is called a buffer between developed areas and the water. A buffer is an area with plants that help do two things. First of all, they slow the water down. This makes it less likely for the soil in that area to erode, or wash into the water. Second, plants in the buffer area actually help soak up some pollutants in the runoff before they make it into the stream.

The Effect of Plants and Trees as Buffers
Erin Hancock, NCWRC
Build Your Own Buffer Gaphic
Build Your Own Buffer

You can see how buffers work by pouring water down a slanted, impervious surface like a clipboard or cookie sheet. Now, crumple up a bunch of small pieces of paper and tape them to the clipboard. Do this until the whole clipboard is covered with crumpled paper balls. Tip your new “buffer” to a slanted position again and pour the water. What do you notice that is different from the last time? How has the speed of the water changed? How much water comes off of the bottom compared to when there was no buffer? If you want, you can add “pollution” to the water, like coffee grounds or pencil shavings, and see how many are trapped by the buffer.

Coffee Grounds