effective, oxidizing conditions must be present continually at the
water interface of the reservoir or stream site where the precipitate is
deposited.
In lakes and reservoirs containing substantial amounts of alkaline
of calcareous deposits in the drainage basin, a
earths from the
buffering action occurs based upon the equilibrium between free
calcium,
bicarbonate, carbonate, and undissociated calcium carbonate.
Free CO2 remains
in solution after this equilibrium is reached, the amount dictating the amount
also in solution. If more CO2 is added to this system the fur-
of
32
ther solution of
will occur, producing more
and little
If
is withdrawn, as occurs during extensive photosynthesis by
change.
As Wetzel (1983) has
algae and macrophytes, then
is precipitated.
pointed out, this decalcification of hard water can play a major role in regu-
lating the reservoir's metabolism since the precipitation of
will also
involve the coprecipitation of nutrients such as phosphorus and the sorption
of labile organic matter.
This reaction of
bicarbonate, and
could be used to remove
phosphorus and organic matter from incoming water, although there appears to
The effectiveness of this
be no case history of its use for this purpose.
procedure could be altered by the quantities and types of organic matter in
dissolved organic matter sorbs to
the stream.
According to Wetzel
In particular, fulvic acids, or low molecular weight
acids, seem
to repress
precipitation and allow phosphorus to remain in solution.
Effectiveness
This could prevent
from being effective in some streams.
CO2 conditions in some reservoirs.
also will be altered by the lower
These conditions would
solubilization of
and release of sorbed
materials.
The use of aluminum salts to precipitate phosphorus or to prevent its
release from reservoir sediments is a well-known in-reservoir water quality
Aluminum salts could also be added to
management procedure (see Part IV).
incoming stream water to precipitate phosphorus before it enters the reser-
voir.
When aluminum sulfate (alum) or sodium aluminate are mixed with water
with carbonate alkalinity, a visible
of aluminum hydroxide is formed to
The formation of the
may
which inorganic phosphorus is strongly sorbed.
or polymer appears to
The
also trap some particulate phosphorus.
be inert to
changes so that sorbed phosphorus will remain out of
34
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