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Definition:
Nutrients
are elements that are needed by plants and animals for growth.
Why
does it cause pollution?
When
people discuss water quality and nutrients that cause pollution, they
are usually talking about nitrogen and phosphorus.
Most other nutrients, like calcium, magnesium, sodium, and
potassium are naturally in high abundance in nature.
Nitrogen and phosphorus are said to be “limiting
nutrients.” This means
that these are the hardest nutrients for some plants and animals to
come by and are the only nutrients that are limiting their growth.
So, their growth is often directly related to the amount of
these limiting nutrients that they are able to get.
Generally
speaking, phosphorus is a limiting nutrient in freshwater systems and
nitrogen is a limiting nutrient in saltwater systems.
So, back to our fundamental
question, “Why do nutrients cause pollution?”
Limiting nutrients cause pollution when they enter waterbody in
relatively high amounts. If
the conditions are right, where there is a lot of sunlight, the water
is clear, and the temperature is high, nutrients cause algae to grow. When this happens, the algae use the sunlight to make food
for themselves and increase their numbers.
This is called an algae bloom.
Algae blooms can result in large floating “mats” of algae.
When the algae die, however, they sink and become organic
matter. Organic matter on
the bottom of the water column is used by bacteria for food.
In order for the bacteria to break down the organic matter they
use dissolved oxygen. This
can lead to hypoxia and fish kills.
How
does it get into water?
Farmers
and homeowners use nutrients in the form of inorganic fertilizers to
make plants grow. Farmers
use fertilizers to produce food and fiber crops; whereas homeowners
use fertilizers to make their grass greener and richer growth.
However, when it rains excess applied nutrients can dissolve in
the rainwater and runoff the land and into the nearest bayou or
stream.
Untreated sewage runoff is
also a large source of nutrients.
Before modern, man-made inorganic fertilizers people in
agriculture would use animal waste or manure to fertilize their
fields. Human waste is no
exception. It is high in
nutrients, including phosphorus and nitrogen.
Municipal sewage systems and individual home sewage systems
contribute large amounts of nutrients to waterways each year.
What
land uses are the source of this type of pollution in the B-T Basin?
This
type of pollutant does not cause documented problems in the Barataria
and Terrebonne Basins. In some other places, nutrient pollution
might be caused by urban
or agricultural runoff.
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