The Effect of Nitrates on Water Quality

The Effect of
• If your lake or stream tests positive for
nitrates, this does not necessarily mean that
there is a problem with the water quality.
• High levels of nitrates in water can create
conditions that make it harder for aquatic
insects or some species of fish to survive.
• Algae and other aquatic plants use nitrates as
a source of food. If algae have too many
nitrates available, they will grow fast and
• So what is the problem with that?
• Large amounts of algae can cause large
variations in the amount of dissolved oxygen
in the water.
• Photosynthesis by algae and other plants
generates oxygen during the day. However, at
night, dissolved oxygen may decrease to lower
levels because of higher levels of oxygen
consuming bacteria that feed on dead or
decaying algae and other aquatic plants.
Taken from:
• Most people who have a well know to test for
the presence of nitrates. In drinking water it is
much more critical than in your lake or
• If you drink water that has a high level of
nitrates, it can interfere with the ability of
your red blood cells to transport oxygen.
• Infants who drink water high in nitrates may
turn "bluish" and appear to have difficulty in
breathing since their bodies are not receiving
enough oxygen.
• Methaemoglobinaemia is caused by the
decreased ability of blood to carry vital oxygen
around the body. One of the most common
causes is nitrate in drinking water. Controlling
nitrate levels in drinking water sources to
below around 50mg/litre is an effective
preventive measure.*
*Taken from the World Health Organization
• Why do we need nitrogen? What are the
sources of nitrogen?
• Nitrogen is essential for all living things, this includes
both plants and animals. If you look at what makes
up DNA in cells and what is found in proteins, you
will find the presence of nitrogen. Animals get
nitrogen by eating plants and other animals.
• Plants need nitrogen for growth. Unlike animals,
they can’t get their nitrogen by eating proteins.
Plants get nitrogen from water and from the soil.
They absorb nitrogen in the form of nitrates and
ammonium ions.
• The following picture was taken from
• Aquatic organisms excrete wastes that contain
ammonia. When these organisms die they
create ammonia.
• Different types of bacteria in the water change
the ammonia produced during decomposition
to produce nitrite which is then converted by
other bacteria to nitrate . (NO3-)
• Although nitrates occur
naturally in soil and water,
high levels of nitrates are
usually considered to be
a contaminant of ground
and surface waters.
• Many sources of excess nitrates come from
human activity. These can sometimes be traced
to agricultural activities, human wastes, or
industrial pollution.
• Nitrogen based fertilizers are often applied to
fields, yards, and golf courses to help with the
growth of plants.
• Manure is also used as a fertilizer to promote
plant growth.
• Rainwater can wash some of these nitrates
into streams and rivers or the nitrates can
seep into the ground water.
• Untreated human sewage can also contribute
to nitrate levels in surface and ground water.
• Leaking septic systems or septic systems that
are not functioning properly can be a source
of nitrates.
• And while city sewage treatment plants treat
sewage to make it non-hazardous, these
plants still some release nitrates into
• Not all excess nitrates are from human
• If a lake has the presence of large numbers of
birds, their excretions that get into the water
can create higher levels of nitrates.
• Higher levels of nitrates can mean more
aquatic plants.
• An excess in the growth of plants and algae
can create an unstable amount of dissolved
• A fluctuation of dissolved oxygen between
daytime and nighttime amounts can create
stressful conditions for fish.
• If they are stressed for a significant part of the
day, it will affect their normal eating patterns
and their reproductive patterns.
• Excess algae or plant growth is a problem for
• If you've ever been to a beach where mats of
rotting algae wash up on shore or the bottom
of the lake is teaming with weeds, it's could be
because excess nitrates are available for plant
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