Environmental Engineering Reference
In-Depth Information
North Africa, but becoming increasingly problematic in North America. It pro-
duces large, sinking nuts, with barbed spines that cling to moving objects, includ-
ing the plumage of geese, mammal fur, human clothing, nets, wooden boats,
construction equipment, and other vehicles (Hummel and Kiviat 2004).
Most invasive aquatic plants have been introduced to areas outside of their native
range via the horticultural and aquarium trades, and continue to spread in this
fashion. Water hyacinth is indigenous to South America but has been spread
throughout the world because its fl owers are attractive to gardeners. Similarly,
the beautiful yellow water lily (
Nymphaea mexicana
), native to Florida, has been
introduced to new habitats for ornamental purposes (Capperino and Schneider
1985). The majority of submerged invasive plants, such as hydrilla in the USA
and lagarosiphon in New Zealand, were introduced via the aquarium trade as
ornamental aquarium plants (Schmitz
et al
. 1991), and continue to be sold
despite their status as declared invaders in many countries, particularly via the
internet (Kay and Hoyle 2001). Recently, in 2006, hydrilla was discovered from
one water body in South Africa, and it is likely that it too was introduced via
the aquarium trade. Genetic analysis of South African hydrilla revealed that it
is most closely related to hydrilla from Malaysia and Indonesia (Madeira
et al
.
2007), and reportedly, the majority of aquarium plants imported into South
Africa originate from Singapore and Malaysia (N. Stallard, pers. comm.). There
are fears that it will spread to other water bodies via recreational boaters and fi sh-
ermen who frequent the dam, as this is the main mode of spread of the weed in
the USA (Langeland 1996).
Other invasive aquatic species, such as water chestnut, have been introduced
for agricultural purposes, making their eradication and control di cult due to
confl icting interests. An interesting case of confl ict of interests is that of alligator
weed in Australia. Here it is placed in the top 20 weeds of National Signifi cance
because of the negative ecological and economic impacts it has on the environ-
ment (h orp and Lynch 2000). It was accidentally introduced into New South
Wales, Australia, in ship ballast in 1946 (Hockley 1974) and has subsequently
spread throughout the country, producing dense mats that disrupt the ecology
of riparian areas, stream banks, and water bodies (Sainty
et al
. 1998). h e main
mode of spread is via boat transport between water bodies and the transportation
of contaminated turf, soil, and sand from infested to uninfested locations (Julien
and Bourne 1998). However, between 1995-2000, it was discovered that alligator
weed was being cultivated in gardens as a leafy vegetable by the Sri Lankan com-
munity all over Australia, but predominantly in Victoria (Gunasekera and Bonila
2001), because it had been mistaken for a popular leafy vegetable, sessile joy weed
(
Alternanthera sessilis
). Following these discoveries, it became clear that alligator
weed had been widely distributed by hand and post to many parts of Australia,
