NEW WORLDS - The New Wild: Why Invasive Species will be Natures Salvation - page 21

dramatically in the intervening months was the quality of the lake's water. It had been flushed clean, and
with that the weed had departed.
This lends credence for a theory that the real problem in Lake Victoria was never so much the weed
itself as the choking pollution. Over the years during which the weed had taken hold, the lake and the
rivers that delivered water to it had filled with sewage from cities such as Kampala and Kisumu. Efflu-
ent from sugar factories, paper mills, tanneries, and breweries proliferated across the lake's catchment,
and silt washed into the lake as forests were chopped down and soils eroded. This pollution had turned
a once-clear, well-oxygenated lake into a muddy body with no oxygen in its bottom layers. Water hy-
acinth, raised in the fetid swamps of the Amazon, loved it. But then things abruptly changed.
In 1998, there was a major El Nino event in the Pacific Ocean. It caused unusual weather around
the world, including massive and unseasonal rains in East Africa. During my visit that year, much of
Nairobi had been flooded. Rivers brought torrents of fresh water that cleansed the lake of its accumu-
lated pollution, says Lawrence Kiage, a Kenyan researcher now at Georgia State University. 29 The weed
was suddenly starved of the rich soup of nutrients on which it depended.
The story fits, as do subsequent events. There has been no big new El Nino since 1998 and no ex-
ceptional rains to flush the lake clean. The pollution is building up again, and in 2013 the hyacinth was
advancing once more, the bays and beaches covered in weed. The weevils, if they were still around,
were not keeping it back. Fishers were again abandoning their boats. It appears that blaming the alien
weed—and seeking solutions to the lake's problems by trying to remove it—has been the wrong dia-
gnosis, leading to the wrong treatment. Lake Victoria remains sick. It may never be freed of weeds until
its wider ecological problems are solved. That, as I hope to show, is a lesson relevant to many other
infestations of alien species.
Casting the weed as an environmental villain has also meant that water managers and conservation-
ists alike have been blind to the idea that water hyacinth might be a resource of some value. It might be
used and harvested—even valued as a crop, under the right conditions. The evidence for this heretical
thought comes from China, which deliberately introduced it in the 1930s as a way of absorbing heavy
metals in water bodies and as a livestock fodder crop. It continued to do so until the 1970s, when mount-
ing pollution from the fast-growing city of Kunming caused the weed to take over Dianchi Lake, China's
sixth biggest lake. But Chinese scientists didn't give up. In 2010 they began planting water hyacinth in
artificial enclosures in the lake to soak up nutrients. They harvested the weed and processed it to pro-
duce biogas and organic fertilizer for local farms. The result was both an economic benefit and a cleaner
lake.
Zhi Wang of the Kiangsu Academy of Agricultural Sciences in Nanjing claims the experiment “sug-
gests a tremendous potential for the utilization of water hyacinth for nutrient removal.” Maybe Lake
Victoria, which is two hundred times the size of Dianchi, is too big to achieve similar results, but the
Chinese findings do suggest a creative solution that could work in many places “infested” with the
weed. Perhaps we should try this trick more often with other alien species—thinking about their vigor-
ous growth as a potentially valuable resource rather than a threat. 30
Lake Victoria has another widely touted environmental villain. The Nile perch ( Lates niloticus ) was
introduced to the lake by British colonialists in the 1950s, initially for sportfishing. 31 The fish is a giant.
It grows up to six feet long and has a prodigious appetite. It has become one of Uganda's most valuable
exports, but it is also blamed for the extermination of around half of the five hundred species of small
bony cichlid fish that once lurked in the muddy lake depths. Cichlids are widely kept in home aquari-
ums. The species include angelfish and oscars. In Lake Victoria, they have been a uniquely dominant
presence. Most of the species there evolved in the lake itself and are found nowhere else. They once