Now a "bio-disaster" in
China Tackles the
by John Dawes
United Kingdom & Spain
Click images to enlarge
The beautiful water hyacinth (Eichhornia crassipes) --
popular as an aquarium plant, but more so as a year-round decorative
plant for ponds in warmer parts of the world and summer pond
decoration in northern climates
as well as a natural spawning
medium in commercial fish breeding farms and home aquaria --
is causing major problems in many countries, among them, China.
However, it is not the pond/water gardening hobby or aquatic
industry that are responsible for the eco-disaster created by
this deceptively delicate-looking plant. This article is aimed
at informing about the spread of the plant in China, at placing
the sources of the problem in some form of perspective, and at
highlighting some of the attempts being made to tackle the "spreading"
Water hyacinths being used
as a spawning medium in a Singapore
ornamental fish farm. The plants also keep the water "sweet".
Despite its attraction as an aquarium, pond and fish-spawning
plant, the water hyacinth was first imported into China in 1901,
not as an ornamental plant, but as cattle fodder. In fact, by
the 1950s and 1960s, it was distributed for this purpose throughout
most Chinese provinces. It was also used -- to a lesser extent
- as fertiliser and, up to the 1980s, it was used to manufacture
Its first introduction as an ornamental plant, i.e. destined
for aquaria and ponds, was in 1903 when specimens were introduced
into Taiwan "from Southeast Asia". While this source
sounds somewhat vague -- in view of the large area covered by
Southeast Asia -- it, nevertheless, confirms that this South
American species was already in the region more than 100 years
Clump of deceptively
During the 1970s, water hyacinths were transplanted and mass
reared in many areas, and began causing significant damage from
the 1980s onwards. Today, the plant is officially recorded as
established and reproducing in no fewer than 17 Chinese provinces.
In Guangdong, Yunnan, Fujian, Zhejiang and Taiwan, it is now
regarded as a "bio-disaster". Hyacinths are also present
in several other (colder) provinces, where it is used mainly
as animal fodder, but where it dies during winter.
An idea of the scale of the problem is provided by Shanghai.
In 2002, 1.68 million tons of water hyacinths were removed from
the Huangpujiang River and other bodies of water in Shanghai,
with the operation costing US$10 million. Since then, Shanghai
has invested over US$1.2 million on a project of integrated management
of water hyacinth.
These water hyacinths were photographed
on the banks of the Pearl River that
runs through Guangdong Province
in southern China.
The threat posed by the water hyacinth is multi-faceted. The
most obvious of these is that it competes for space and nutrients
with native plants. But this is only the beginning. In some sites
in southwestern China, for example, it has "greatly reduced"
native plant diversity, not just through direct competition,
but through water pollution after hyacinths die and sink. In
Coohai, the number of native plant species dropped from 16 in
1960, to just three in 1990. If the plants are collected and
piled up on land, this, too, causes heavy pollution and environmental
degradation when the plants decay and the runoff finds its way
into the local water courses, ponds and lakes.
The water hyacinth has also been implicated in human health
because dense mats of the plant create ideal conditions for mosquitoes
and flies. Even public security appears to be affected because
it is claimed that "dense and high water hyacinth plants
provide a nice place for criminals to hide."
In terms of control methods, physical removal, which now costs
over US$12 million per year, is considered uneconomic and ineffective
and cannot provide long term control. This method is therefore
only practised in a few places these days.
Dense clumps of water hyacinths
can cause health problems.
The use of chemicals also has its problems, especially in areas
where the water colonised by the hyacinths is also used by people
and their animals. Chemicals also have the disadvantage that,
while they may effectively control the weed, their effectiveness
results in the death of such high numbers of plants that low
dissolved oxygen levels result, which, of course, are harmful
There is, however, a ray of hope on the chemical front. A
chemical compound (KWHO2) has recently been developed which inhibits
asexual reproduction in the water hyacinth. This method of reproduction,
in which plants produce large numbers of offsets throughout the
growing season (about six every 26 days), is the fastest way
in which the water hyacinth spreads.
KWHO2 inhibits the formation
of offsets produced
by water hyacinths
It has been found in experiments carried out in concrete pools
that KWHO2 inhibits asexual reproduction (reducing it by up to
70%). Since the treatment does not result in the death of the
plants, the water pollution problems encountered with mass eradication
chemical treatments do not arise. Further, toxicity tests reveal
that KWHO2 can be categorised as a low-toxicity herbicide. Indeed,
skin and eye irritation tests showed no negative effects. Finally,
KWHO2 decomposes rapidly in water, thus posing no risk of long
term accumulation. The herbicide has now been used around Shanghai
as part of an integrated management programme and has "gained
Another component of these integrated programmes includes the
use of the weevil Neochetina eichhorniae, which has a
voracious appetite for water hyacinths, but not for other plants.
A success rate of around 90% has been obtained under experimental
conditions, making the weevil a good candidate for use as a biological
control agent. Presumably, any fears associated with potential
problems caused by the weevils once the hyacinths are controlled
or eliminated are minimised by the weevils' very specific hyacinth-based
A further line of control is also now being followed. As from
2000, research has been carried out at Shanghai Jiao Tong University
to control water hyacinths using micro-organisms. So far, nine
species of fungus have been isolated from water hyacinths and
these show varying effects on the growth of the plant. Further
research is, obviously, necessary, but the evidence obtained
so far indicates that this line of enquiry could yield valuable
The battle against the exotic and impressive water hyacinth
is, obviously, receiving a great deal of attention, and achieving
some notable victories, in China. Important lessons are also
being learned which will, hopefully, help other countries and
regions to tackle this spectacular pest.
NOTE: While there are quite a few scientific
papers dealing with the problems faced by China with regard to
the water hyacinth, a particularly useful (and brief) recently-published
report is the following: Chu Jian-jun, Ding Yi and Zhuang Qi-jia
(2006), Invasion and control of water hyacinth (Eichhornia
crassipes) in China. Journal of Zhejiang University SCIENCE
B, Vol. 7 (8): 623-626.
This paper can be accessed via www.zju.edu.cn/jzus. This will take you to
the Journal homepage. Click on the JZUS Archives in the menu
list and then simply key in: water hyacinth in the search box
and click. This will take you to the available pages in the archives
dealing with water hyacinths.
This "meadow" with a small lake
in the background is not a meadow at all, but a
hyacinth-smothered lake in Sri Lanka.