Central Arizona Project manages a 330 mile long system of concrete lined canals,
inverted siphons, tunnels, pumping plants and pipe lines which bring water from
the Colorado River, on Arizona’s western border, across the state to the canal terminus
near Tucson. Quagga mussels have been present in the source waters of the aqueduct
(Lake Havasu and Lake Pleasant) for a minimum of two years. In 2008 live veligers,
at various stages of development, were observed in plankton samples taken at numerous
points of the aqueduct. Despite such observations, very few settled adults were
found anywhere in the aqueduct.
Based on the data collected during the 2009 environmental monitoring program, the
lack of settled adults in the aqueduct may be due to fortunate combination of environmental
factors. This situation may not persist in the future. Central Arizona Project may
require a control program which would minimize mussel settlement in the canal and
associated structures. One such method of control would be the depression of the
pH of the water which is being transported in the canal.
A proof of principle experiment was conducted in 2009, using Lake Ontario water.
Veliger rich water was pumped to a flow-through field laboratory. At the laboratory,
the pH of the incoming water was adjusted using phosphoric acid to pH 7.3, 7.1 and
6.9. Three replicates of each pH resulted in 9 treatment tanks and three control
tanks. The experiment started on June 16, 2009 and it was terminated on November
15, 2009. Adult mortality of almost 40% was recorded at pH 6.9 after 10 weeks of
exposure. Analysis of weight/length relationship of adult mussels confirmed that
for any given length the mussels were significantly lighter at all three pH levels
when compared to the controls. New settlement was essentially prevented at pH of
7.1. Calculations of projected acid use have shown that if sulphuric acid was used,
the entire aqueduct could be protected for approximately $10 million in annual chemical
costs. There is an opportunity to lower this cost further by treating for only 3
months rather than year around. This would bring the annual cost of chemicals down
to $2.5 million.
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