Water Quality
Dissolved Oxygen
And
Turbidity
Indicators of Water System Health
• Water quality, or water health is determined
by testing physical factors such as
1. Temperature
2. Dissolved oxygen
3. pH
4. Turbidity
5. Bio-indicators
6.Presence of nitrates
Physical Indicators
• Water is considered healthy if the following
conditions are met:
1) moderate to cool temperatures
2) high dissolved oxygen
3) neutral pH (between 6.5-7.5)
4) clear water (low turbidity)
Oxygen in Water
• Oxygen dissolves in water from the atmosphere
and from photosynthesis from plants in the
water.
• Wind, waterfalls, rapids and waves also help add
oxygen to water.
• It is important because aquatic organisms need it
to breath.
• The higher the dissolved oxygen level in water,
the higher the biodiversity.
• COLD WATER CAN HOLD MORE OXYGEN THAN
WARM WATER and MOVING WATER HOLDS
MORE OXYGEN THAN STILL WATER.
Oxygen and Temperature
• As water temperatures increase, the dissolved
oxygen levels decrease.
• This can cause stress to fish and other water
organisms.
• Dissolved oxygen levels can change
throughout the day and with the seasons.
• Oxygen levels are usually lowest in the
morning and increase during the day. This is
because plants have stopped the production
of oxygen over night.
pH
• High or low pH readings are signs of an
unhealthy water system.
• Neutral water has a pH of 7.
• Most aquatic life functions best in water at a
neutral or slightly basic (8.0 to 9.0).
• Water can become acidic from acid rain and
can become basic from an overgrowth of
algae.
Turbidity
• Turbidity is a measure of how clear the water
is.
• High turbidity, or cloudy water, is a sign of
unhealthy water.
• Causes of turbidity include silt and sediment
from run-off. This includes mud.
• Algal blooms, or rapid growth of algae
because of too many nutrients in the water,
can also cause high turbidity.
Turbidity
• High turbidity is harmful because it can cause
the following:
1. Increase in water temperature which will cause
dissolved oxygen levels to drop.
2. Reduce sunlight which will prevent or slow down
photosynthesis and cause decreased dissolved
oxygen.
3. Too many particles in the water can also clog the
gills of fish and cause fish kills.
Chemical Indicators-Nitrates
• Nitrates and phosphates are compounds used for
growth by plants and algae.
• Fertilizers contain nitrates and phosphates and can
enter the water by run-off from farm fields, golf
courses, or lawns.
• Too many nitrates can cause algal blooms in water,
which are harmful.
• Algal blooms cause high turbidity and lower the
dissolved oxygen levels in the water.
• The overgrown algae starts to die and decompose,
which will take even more oxygen from the water.
• This process is called eutrophication.
Eutrophication – Bad!
• Eutrophication – Excess (too many) nutrients
being put into the water!
– Fertilizers
– Industrial Waste / Sewage
– Run-off
• Natural or
artificial ways
Eutrophication – Bad!
• Eutrophication – Excess (too many) nutrients
being put into the water!
– Fertilizers
– Industrial Waste / Sewage
– Run-off
• Natural or
artificial ways
Eutrophication
Bio-Indicators
• Bio-indicators are organisms or parts of organisms that
are used to assess aquatic ecosystem health.
• Organisms that are sensitive to water quality are called
intolerant and can be used to determine water health.
• Trout, shellfish, amphibians such as salamanders are
good indicators of healthy water.
• Macroinvertebrates are organisms without backbones
that can be seen by eye and are used as indicators of
water quality. Intolerant species are mayflies,
stoneflies, and dragonfly larvae.
• The presence of tolerant organisms such as leeches,
rat-tailed maggots, and midge larva indicate poor
water quality.
Bio-Indicators for Water Quality
Water Pollution
• Pollution can be one of two
types:
– Point Source
– Non-point Source
• Point Source – Can trace
exact location. Can point to
single source of pollution.
• Non-Point Source – Unknown
origination (start). Comes
from lots of different places.
Cannot point to just one
single source.