Water Chemistry
• Water quality of ecosystems is dependent
on chemical, physical, and biological
factors.
• When substances in water are harmful to
the organisms that live there, the water is
considered polluted.
Dissolved Oxygen (Chemical)
• This is the most important
chemical requirement for
aquatic organisms.
• Diffusion
• Water mixes with air
when it falls over rocks
and waterfalls increasing
the level of D.O.
• Standing or slow moving
bodies of water have less
D.O. than fast moving
water bodies.
DO Continued
• Photosynthesis increases D.O. as respiration by
aquatic animals decreases it. (remember the
carbon-oxygen cycle?)
• Water polluted with organic matter has less D.O.
than clean water because decomposers of the
organic matter use up the D.O.
• Most fish cannot live with D.O. less than 5
ppm.
• 0-5 ppm low 6-10 ppm medium 11-15 ppm
high
Temperature (physical)
• As temperature increases less D.O. can
be held in the water.
• Trout require high levels of D.O. which is
why they live in coldwater streams.
Temperature Con’t
• Thermal
pollution occurs
when industries
(power plants)
use water for
cooling. The hot
water is
dumped into
aquatic systems
raising the
temp.
Turbidity (Physical)
• It is the measure of the amount of light
scattered or absorbed by particles in water
(cloudiness).
• eroded soil in water increases turbidity,
clog fish gills, and smothers aquatic
insects.
pH (Chemical)
• Few aquatic organisms can live
in water with pH lower than 4 or
higher than 9.
• Best range: fish 6.7 - 8.6
pH
• CO2 produced from decaying organisms
forms carbonic acid decreasing pH.
• sulfuric acid in water comes from acid
mine drainage and acid rain (burning fossil
fuels) decreasing pH.
• alkaline industrial waste (bleaching plant)
can increase pH.
Patagonia acid mine after a storm
Hardness (Chemical)
• Water with many minerals is considered hard.
• Water containing calcium and magnesium is
said to be hard.
• The minerals in hard water can buffer acidic rain
water.
• Calcium is needed for clams, snails, and other
shelled organisms.
• 0 - 60 ppm soft 60 - 120 med. 120 - 180 hard
Nitrites/Nitrate (Chemical)
• Runoff of fertilizers, animal
wastes, and sewage are the
major sources.
• EUTROPHICATIONExcessive nitrogen causes
algae population to explode
(algae bloom).
• Most nitrogen is constantly
used up in the system. More
than 1 ppm. indicates
excess.
• When the algae dies it
decomposes using up the D.O.
• high nitrogen harms animals - causes
methemoglobinemia (blue babies) (look it
up pg. 311 in text).
Phosphates (Chemical)
• Comes from the same sources as nitrogen
as well as some industrial processes.
• also causes algae blooms.
• not as harmful to humans or animals as
nitrogen.
• More than 0.5 ppm. indicates excess.
Hurricane Floyd
2.5 bil gallons hog/poultry waste
Dead Zones