Environmental Engineering Reference
In-Depth Information
be sources of pollution in local waters. Thousands of fish con-
centrated in open net pens produce tons of feces. Combined
with uneaten food, this waste sinks to the bottom and affects
the local environment, polluting the water and smother-
ing plants and animals on the seafloor below the cages. For
example, the nutrients in unused fish feed and fish feces can
cause local algal blooms, which lead to reduced oxygen in
the water, which in turn can lead to the production of ammo-
nia, methane, and hydrogen sulfide, which are toxic to many
aquatic species. Low oxygen can also directly kill marine life.
Many types of aquaculture use chemical treatments such as
antibiotics or antiparasite chemicals for a successful harvest.
The amount of these chemicals released into the environment
determines their effects on other organisms. A wide range of
chemicals is currently used in the aquaculture industry—pri-
marily pharmaceuticals such as antibiotics and antiparasitic
chemicals, and antifouling agents such as copper for the cages.
In some areas, such as Southeast Asia and South America,
overuse of antibiotics has led to increased resistance of bacte-
ria to treatment, which can make them much more harmful to
the cultured species and potentially to other species, includ-
ing humans.
Once in the water, what happens to the pollutants?
Ocean currents and organisms may redistribute pollutants
considerable distances. However, sediments tend to bind met-
als, and many organic contaminants concentrate in the bot-
tom sediments. The historic use of some chemicals that are no
longer manufactured in the United States (e.g., DDT, PCBs) has
left a legacy of contamination in the sediments, which remain
contaminated with these persistent chemicals that continue to
cycle through the environment and affect marine life decades
after their input has ceased. Contaminated sediments also
pose a problem for dredging operations, because the dredg-
ing process can release the contaminants from the sediments
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