Environmental Engineering Reference
In-Depth Information
3. Take readings in open but shaded conditions. Turn your back to the
sun to avoid direct sunlight.
4. Carefully stir or swish the water in the bucket or bottle until it is
homogeneous, taking care not to produce air bubbles (these scatter
light and affect the measurement). Pour the water slowly in the tube
while looking down the tube. Measure the depth of the water col-
umn in the tube at the point where the symbol just disappears.
orthophosphate
Earlier we discussed the nutrients phosphorus and nitrogen. Both phospho-
rus and nitrogen are essential nutrients for the plants and animals that make
up the aquatic food web. Because phosphorus is the nutrient in short sup-
ply in most freshwater systems, even a modest increase in phosphorus can
(under the right conditions) set off a whole chain of undesirable events in
a stream, including accelerated plant growth, algae blooms, low dissolved
oxygen, and the death of certain fish, invertebrates, and other aquatic ani-
mals. Phosphorus comes from many sources, both natural and human.
These include soil and rocks, wastewater treatment plants, runoff from fertil-
ized lawns and cropland, failing septic systems, runoff from animal manure
storage areas, disturbed land areas, drained wetlands, water treatment, and
commercial cleaning preparations.
Forms of Phosphorus
Phosphorus has a complicated story. Pure, elemental phosphorus (P) is rare.
In nature, phosphorus usually exists as part of a phosphate molecule (PO
4
).
Phosphorus in aquatic systems occurs as organic phosphate and inorganic
phosphate. Organic phosphate consists of a phosphate molecule associated
with a carbon-based molecule, as in plant or animal tissue. Phosphate that
is not associated with organic material is inorganic, the form required by
plants. Animals can use either organic or inorganic phosphate. Both organic
and inorganic phosphorus can be dissolved in the water or suspended
(attached to particles in the water column).
The Phosphorus Cycle
Phosphorus cycles though the environment, changing form as it does so.
Aquatic plants take in dissolved inorganic phosphorus as it becomes part
of their tissues. Animals get the organic phosphorus they need by eating
aquatic plants, other animals, or decomposing plant and animal material.
