Act to save our lakes, rivers and fish

This is because ecosystems evolve, along with the animals and plants that make up the system. If some species has to become fast growing or fast breeding, a matter that consumes vast quantities of energy and is not therefore a natural survival trait, it is because lots of other things want to eat it.

But when that fast growing plant or fast breeding animal is introduced into a new ecosystem, without all the things that eat it, populations can explode. And that is what has happened to water hyacinth in every warm or hot ecosystem outside South America.

Water hyacinth is a tough, fast growing and fast spreading water weed. It has pretty flowers for those who like that sort of thing, and is easy to grow. So some nurseries imported it for ponds. And it escaped, into the wild waterways of many other countries in Asia, North America and, pertinently for our readers, into Africa.

Since the Second World War dam after dam and river after river in much of Southern Africa has become clogged with this terrible weed.

One small plant will breed to cover a large lake in a few years, and regrettably most lakes are now contaminated outside South Africa where freezing winters will kill the plant.

Authorities around the world have tried herbicides, defoliants and other chemicals, for only short term effects and creating dangers that in some cases are now, in light of extra knowledge, considered unacceptable.

Manually scooping up the weed and dragging it the banks works, but is slow, labour intensive and expensive. But most authorities, trying to keep waterways and fishing grounds open, have resorted to this.

In the long term biological control is obviously a better solution. Water hyacinth does not clog the Amazon and other South American rivers. This is because there are a lot of things there that eat it.

But there is a double problem. First of all scientists have to do intensive research on the plant in its natural ecosystem to see just what does it, and then they have to do more applied research to see what else those things eat before introducing them into the mats of weed in Africa. It is no good, for example, to introduce some insect that really prefers to eat maize.

Fortunately the South America and African ecosystems are not that far apart. The two continents only separated after the first primates evolved and so there is a good chance that the predators that exist in South America will not explode and cause an even bigger problem in Africa.

This is not the case for North America. That continent separated from Africa a lot earlier and only collided with South America in very recent times.

So biological control in Africa is a distinct possibility, but once again this brings up the need for a combined research effort.

Only South Africa could possibly do this alone, in the first place, and South Africa is not hard hit by water hyacinth. So on practical grounds a joint effort is required. Secondly it is no good Zimbabwe making a unilateral decision to introduce some sort of weevil and Zambia and Namibia rejecting it. These sort of things do not obey international frontiers. Any decision to introduce a natural control must be basically unanimous, and that means the overwhelming majority of the region’s experts in this sort of research must give a thumbs up.

Mechanical removal can continue. Water hyacinth is not totally evil. It takes nutrients out of the water, usually there in the first place because of fertilizer leaching or inadequate sewage processing. If the plant is then taken out of the water these extra nutrients come with it, and if the heaps are left to compost a decent natural fertilizer is the result.

But there is no way that something the size of Lake Victoria can be cleared manually. All that manual methods can do is clean out odd pockets once a natural ecosystem has been established with an introduced feeder of hyacinth.

We hope that the resources, and the transnational teams of scientists, will now be assembled to make a major assault on this menace, before we lose our lakes, rivers and fish forever.

January 2007
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