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for transfer of water was mostly in place. Engineers designed a pumping station on
the bank of the Torrens River, which transferred freshwater to the southern end of
the lake by gravity. Pumping began on 23 July 2003. Two additional barge-mounted
pumps were deployed on the lake to pump high salinity water out and into the Port
River. The project was completed on 1 December 2003. Although limited mixing of
fresh and saltwater slowed progress, there was a salinity reduction at the depth where
C. taxifolia grew (Collings et al. 2004). Most locations in West Lakes went below
17 ppt for 0-30 days, although one area never dropped below 24.8 ppt. Fragments of
C. taxifolia from West Lakes tested after 3 months failed to grow, and there was no
evidence of any regrowth after salinity was increased. Within 2 weeks of refilling
from the sea, normal salinity returned to West Lakes. No C. taxifolia has been found
in West Lakes since 2003 (Collings et al. 2004).
15.5.4
Chemical Controls, Including Chlorine and Sea Salt
Many chemicals have been tested in the laboratory and in the field with C. taxifolia .
These include chlorine, copper (electrodes and cloths soaked in copper salts), hydro-
gen peroxide, and domestic herbicides known to kill nuisance freshwater algae and
angiosperms (e.g., Uchimura et al. 2000; Thibaut 2001; Madl and Yip 2005). While
some chemicals produced the desired results at high doses, toxicity extended to all
organisms in the locality. Possible exceptions included liquid chlorine (California)
and sea salt (Australia). Liquid chlorine (sodium hypochlorite) at a 12% stock solu-
tion was injected under black tarpaulins in California shortly after the infestation
was reported (Anderson 2005). Over time, liquid sodium hypochlorite was replaced
with 2.5-cm diameter, solid, chlorine-releasing tablets used for swimming pools
(Anderson 2005). Monitoring of sediments under the tarps occurred in December
2001 and August 2002 to determine if the treated sediments continued to preclude
growth of fragments of C. taxifolia (Anderson 2005). Cores from untreated areas
promoted fragment growth while none emerged in treated sediments. Anderson
(2005) did find, however, that seagrass and living invertebrates were present in all
cores. Williams and Schroeder (2004) examined the role of chlorine for eradication
of C. taxifolia in finer detail in the laboratory. They tested apical fragments at 10, 15,
50, and 125 ppm doses at three temperature regimes (7-10°C shocks, 10-11°C, 20-
23°C). At the highest temperatures, chlorine at 50 ppm killed all but one fragment of
C. taxifolia and at 125 ppm killed all fragments. Williams and Schroeder (2004)
concluded that field eradication would require a chlorine concentration of 125 ppm
for at least 30 min in the water column directly surrounding the C. taxifolia blades.
Chlorine must also penetrate a minimum of 15 cm into sediments to reach rhizoids
and buried stolons (Williams and Schroeder 2004).
Although chlorine was successful in the USA, chlorine has not been investigated
in Australia. The most popular chemical treatment in Australia has been coarse sea
salt (99.5% NaCl, mean particle diameter: 2.7 mm) and the most effective dosage was
determined experimentally to be 50 kg/m 2 (Glasby et al. 2005a). The salt dissolved
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