Environmental Engineering Reference
In-Depth Information
10
Management of invasive aquatic plants
Julie A. Coetzee and Martin P. Hill
10.1 Introduction
Aquatic ecosystems throughout the world are continually threatened by the pres-
ence of invasive aquatic plants, both fl oating and submerged (Table 10.1), which
cost governments vast sums of money every year to control. These invasive plants
are predominantly anthropogenically spread, and their presence is usually a symp-
tom of the enrichment of waters through pollution, as a result of increasing urban-
ization, industry, and agriculture. These plants have signifi cant ecological impacts
on the environment, and associated cascading socioeconomic effects.
Dense impenetrable infestations restrict access to water, negatively impacting
fi sheries and related commercial activities, the eff ectiveness of irrigation canals,
navigation and transport, hydroelectric programmes and tourism (Navarro and
Phiri 2000). Poverty-stricken rural communities whose livelihoods depend on
access to clean freshwater waterways are arguably the most negatively impacted
communities. Ecologically, increased biomass and dense canopy production of
aquatic plant infestations aff ect water quality, especially dissolved oxygen, which
signifi cantly reduces benthic and littoral diversity (Masifwa et al . 2001; Toft et al .
2003; Midgley et al . 2006), and infestations are also associated with increases in
the populations of vectors of human and animal diseases, such as bilharzia, mal-
aria, elephantiasis, encephalitis, and cholera (Pancho and Soerjani 1978; Creagh
1991/1992; Harley et al . 1996). For these reasons, invasive aquatic plant infest-
ations need to be controlled to mitigate their negative impacts on ecosystems,
livelihoods, and economies.
10.2 Plant characteristics important in management
Invasive aquatic plants display variable growth forms, and may be free-fl oating (e.g.
water hyacinth, Eichhornia crassipes ), attached and emergent (e.g. alligator weed,
Alternanthera philoxeroides ), or submerged (e.g. spiked water milfoil, Myriophyllum
spicatum ). The degree to which these species rely on sexual or vegetative modes of
reproduction, or both, is also highly variable. Because of this variability in growth
form, mode of reproduction, and the impacts that they have on systems, there is
no uniform method for the control of invasive aquatic species.
 
 
 
 
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