WMOD00569

• Title: Snowpack, Cloud Seeding and the Colorado River
• Date: 1/1/1974
• Weather Modification - Doc Type: Report

ENVIRONMENTAL EFFECTS

mosquitos can be expected, as well as more ticks, and other in-
sects. Mosquitos, ticks, and flies spread disease, so that increases
in their numbers could contribute to a higher incidence of
disease.

Silver Iodide in the Environment

A full-scale )VOSA program in the Upper Colorado River Basin
will use, on the average, an estimated 8,000 pounds of silver
iodide per winter season. All of this is released to the atmosphere
in the form of a smoke that is widely dispersed by the winds.
Silver iodide dissolves only to a very minute extent in
water. It decomposes in sunlight to form metallic silver and
elemental iodine. Iodine can be a hazard if the concentrations
are high enough. The iodine vapor concentration in the air
around the silver iodide generators, where it would be expected
to be highest, is estimated to be below the accepted safe level
for humans. Ho\vever, "'Ie don't kno\IJ \vhat the long-term levels
of both silver and iodine might be in these areas, or how con-
tinued exposure to them might affect plants and animals.
Harmful effects in living things can result only from soluble
forms of silver (silver ions). Even though both metallic silver
and silver iodide are extremely insoluble in water, soluble or-
ganic forms of silver might develop as a result of biological
processes in the bottom muds of lakes, streams, and reservoirs,
as it does for mercury. At present no soluble organic forms of
silver are known to occur in nature at the normal water tem-
peratures of lakes, streams, and reservoirs.
Some materials that are present in water in low concen-
trations can build up to dangerous levels in moving up through
the food chain. A single-cell organism may metabolize silver
rather than being killed by it. A kind of insect feeding mostly
on that organism would absorb the metabolized silver, and fish
that feed on that insect might have a high level of silver in their
flesh. This is how the mercury level can become dangerously
high in tuna or swordfish, for example. It is known that a, num-

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SNOWPACK, CLOUD-SEEDING, AND THE COLORADO RIVER

freeze over, smothering fish and damming the channel so that
water cannot get downstream. This exposes downstream fish,
fish eggs, and aquatic animals to suffocation and freezing.
Anchor ice also can damage stream life forms. Anchor ice is a
spongy mass of ice crystals that forms on stream beds during
cold clear nights in water that is not frozen over. The sun melts
anchor ice just enough to detach it and it carries away life forms
that dwell on the stream bottom. Snow accumulations might
help to prevent damage from anchor ice.
The high mountain streams are fed mainly by snow, so that
they run fullest in mid-spring. WOSA would extend the period
of high meltwater runoff into late spring or early summer, and
shorten the period of low flows. Flows would also be higher
during the snowmelt season. The effects of WOSA on aquatic
lifeforms would be potentially more severe in the headwater
streams, because the effect on flows is greatest there.
The high spring stream flows tend to wash things down-
stream, such as algae, silt, aquatic insects, young fish, and fish
eggs. These life forms are carried downstream to locations that
may be less suitable for their survival.
In addition, the greater the volume of water moving down-
stream at anyone time, the greater the scouring action on the
stream bed. Loose material needed by aquatic insects for shelter,
or by egglayers to anchor their egg masses may be swept away.
WOSA could also lower the average water temperature in the
high mountain headwater streams and high mountain lakes.
Differences of only a few degrees may alter the distribution of
the various life forms within a stream. The breeding seasons, the
ability to complete a normal life cycle, the rate of growth, and
ability to develop to normal maturity may all be affected.
High inflows and outflows of meltwater tend to replace the
surface layers of lakes with water that is poor in the nutrients
needed by aquatic plants. This can affect the production of
adequate aquatic food organisms later in'the year.
.C?n the aver~ge, WOSA wou~d re~ult in generally wetter
condItIons that eXIst for longer penods In the mountains. More

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