Erosion and Sedimentation
Have you ever seen the red
clay washing into a stream? Chances are high if you
live in the Triangle. Man-made land disturbances such
as home, road, and office construction, elimination
of vegetation, and poor farming practices all contribute
to erosion. Erosion occurs when soil washes away because
the plant roots that would ordinarily bind the soil
together have been destroyed. The washed away sediment
must go somewhere, and often that happens to be a
stream, river, lake, or ocean (sedimentation).
How bad could soil washing into a water body be? While
it may not seem like a big problem, sedimentation
is the number one water quality problem in the United States,
and therefore a core concern for the Richland Natural
Area. Soil contains large amounts of naturally occurring
and human-applied nutrients such as nitrogen and phosphorous.
Once in the water, these nutrients stimulate algal
growth. (cultural eutrophication). Algae adds oxygen
to the water in the beginning through photosynthesis.
But at night and during decay, algae consumes more
oxygen than it produces. Additionally, decomposers
utilize much oxygen, leaving little for other organisms
like fish. This creates a low-oxygen environment,
which can lead to the death of many organisms.
Sedimentation also increases the cloudiness, or turbidity,
of the water, creating complications for aquatic plants
that need sunlight, and for aquatic animals whose
gills become clogged with sediment.
Added soil also alters the physical streambed and
course of a stream. It decreases a lake’s water
capacity, which has tremendous implications for flood
control, as in the case of Richland Lake.
Protecting the stream and lake banks in the Richland
Natural Area are vital for maintaining good water
quality for plants, aquatic animals, as well as recreational
and drinking water.
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Impervious Surfaces
Concrete, asphalt, or any other
material that does not allow water to pass through it
is an impervious surface. These surfaces affect water
quality by increasing the volume and speed of runoff.
Roads, sidewalks, and buildings increase the volume
of water flowing into streams and lakes because they
cannot absorb it. The speed of it is also increased
since the water encounters few obstructions on these
smooth surfaces and is not absorbed. The combination
of increased speed and volume speeds the rate of erosion
of natural surfaces adjacent to these impervious surfaces.
Certain structures can be built to mediate the problems
associated with these surfaces. Retention ponds hold
water, slowing it down before it enters the waterway.
Rain gardens use plants to naturally filter the sediments
and pollutants running off from impervious surfaces.
Limiting the amount of impervious surfaces in the Richland
Natural Area as well as employing rain gardens and other
devices will assist in ensuring good water quality.
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