KANSAI Close-up

[Columns]Notorious water hyacinth: a new attraction?

This autumn, pretty, pale purple flowers on the surface of water at many spots in the southern central part of Lake Biwa delighted visitors (photo). They were the common water hyacinth, an introduced species long considered a nuisance because of the threat it poses to the natural environment. At the same time, other alien species of aquatic plants and fish have begun to proliferate in Lake Biwa recently, as if induced by the abnormal weather. This is causing quite a headache for people and local governments wishing to protect the environment as they mull how to get rid of them or whether there are ways of coexisting with them.
The water hyacinth is an aquatic plant belonging to the scientific family Pontederiaceae. It is called 'hotei-aoi' in Japanese because the round bulge at the base of a leaf looks like Hotei (a potbellied god). It was introduced to Japan during the Meiji era (1868-1912) for ornamental purposes.
Today, however, they proliferate in reservoirs, canals and lakes in warm regions because they are very strong, clogging the flow of water or preventing the sunlight from reaching into water. They tend to be viewed as a 'harmful plant' because of such damage.

Serious damage
In fact, actual damage has been reported in Lake Biwa. In 2003, the plant showed abnormal proliferation in the Konohama-naiko lagoon in Moriyama city, causing a lack of oxygen near the water surface, abnormal water quality triggered by death of the plant, and death of crucian carp in fish preserves due to oxygen deprivation. It is also feared that the proliferation of introduced plants and animals with very strong reproductive capacity in themselves may have an adverse effect on the entire ecosystem of the area.
Therefore, the city and other local governments along the shore of the lake are working on measures to rid it of water hyacinth. Damage is also reported in Hyogo, Wakayama and some other prefectures, while other warm and temperate regions in China and Africa are also reporting similar troubles.

Redeeming qualities
However, this 'harmful plant' also has some redeeming qualities and admirers. These people plan to take advantage of its strong reproductive capacity that enables it to proliferate even in extremely polluted water and use it to purify water in lakes and ponds. For example, the Hotei Club in Seiwa Village, Mie Prefecture, is growing water hyacinth in idle rice paddies for viewing. The Nara Prefectural Agricultural Technology Center gives high ratings to the plant's capacity to absorb a large amount of nitrogen and phosphorus and plans to use it for water purification. It is also proposing to use dead plants as an organic fertilizer.
In Lake Biwa, other adventive creatures have been discovered, including mizu-himawari (Gymnocoronis spilanthoides), a plant of South American origin with a ferocious reproductive capacity, and the channel catfish, a carnivorous fish in the same family as catfish of North American origin. There was also mass proliferation of water lettuce, which grew in the Yodo River. These all involve the risk of causing a great deal of damage to the ecosystem as well as human lives and they are officially designated as 'invasive alien species' whose growing, cultivation and import are regulated.
It is not certain how the abnormal weather conditions affect them. However, the Lake Biwa Museum of Shiga Prefecture says that at this moment there are no signs of water hyacinth proliferating to the extent of causing great damage to fishing and other activities in the lake. Though there appears to be a little too much of it, there seems to be a little room for the water hyacinth, which blossoms from late summer through mid-October, to give a person like me ... an avid flower-enthusiast ... a chance to enjoy 'flower viewing in autumn.' (Kagami)

 
image