The Water Hyacinth
1st October, 2003
This beautiful but deadly plant proliferates in lakes across Africa – choking everything in its path. Why, asks Tom Hargreaves, have all attempts to manage it failed?
Originating in Latin America, the beautiful water hyacinth is believed to have been introduced to Africa in the 19th century by Belgian colonialists who wanted to adorn ponds with it. Today, it proliferates across the lakes and rivers of central and eastern Africa, causing serious social and economic problems.
• The plant has a high demand for oxygen and starves all other marine life of the gas, which leads to depletion of fish stocks.
• Its large leaves block out sunlight for other aquatic plants, preventing photosynthesis. And the high rate at which the leaves evapotranspire (release water vapour) aggravates water loss. Thanks largely to the hyacinth, Lake Victoria is described as being on the verge of ‘ecological collapse’.
• Local communities have been forced to migrate because the hyacinth has stopped them anchoring near to their settlements. This makes fishing impossible.
• The hyacinth has spread behind the huge dam on Lake Kariba in Zambia, disrupting the electricity supply by clogging the turbines and reducing water flow. Yet another overpriced and oversized development brought to its knees by nature.
Water hyacinths never used to be a problem, but their growth has mushroomed since WWII as an abundance of nutrients – derived from loose topsoil – has been washed into the waterways. This process is exacerbated by industrial agriculture, deforestation and dams.
Industrial Agriculture – Encouraged by World Bank subsidies and structural adjustment programmes, agricultural systems in east and central Africa have been profoundly changed over the last 50 years. There has been a shift from small-scale subsistence farms growing a range of crops to large-scale monocultures that demand costly applications of fertilisers and pesticides to fend off disease. The modern approach has caused a massive increase in soil erosion, which has been compounded by overgrazing.
Deforestation – Vast areas of forest have been cleared in recent years to make way for this intensive agriculture. Yet forests are essential to maintaining good soils. The roots of the trees act as the soil’s natural binding mechanism, while the canopy serves as a windbreak and prevents the topsoil from being blown away.
Big Dams – The construction of large dams throughout the region in the 1960s and 1970s resulted in huge lakes building up behind the dams, and slowed the flow of rivers downstream. These vast expanses of still and slow-moving water provide the perfect environment in which the hyacinth can prosper.
Clumsy attacks on the Hyacinth
The usual techniques for tackling a problem posed by nature have been tried – basically, attempting to destroy the hyacinth by whatever means necessary.
Chemical – The most common strategy has been to cover the water hyacinth with herbicides. This has had little to no effect as the hyacinth has a 15-year germination period. Thus, not only the leaves but also the roots and seeds must be destroyed for effective removal. What has happened, however, is that the herbicides deployed have destroyed entire aquatic ecosystems and the livelihoods that depend upon them.
Biological – In Uganda, the Central American Weevil Beetle (which feeds on the hyacinth) has been introduced into Lake Kyoga. Applying this technique on a large scale would require billions of beetles to be imported, and the introduction of another ‘alien’ species will almost certainly cause further imbalances in the ecological system.
Mechanical – To date, the most effective technique for managing the problem has been the manual destruction of the hyacinth and part of its root network. In Zimbabwe 200 full-time workers are paid the minimum wage to keep the hyacinth population around Harare in check. This is effective but also expensive – costing over $100,000 a year even before the cost of transporting the cut plant matter out of the region is added.
None of these attempted solutions has halted the proliferation of the water hyacinth. The reason for this is that, as with other traditional ‘pest’-control programmes, the symptoms are being targeted instead of the root causes.
By thinking in a more systemic way a problem has been converted into a fantastic opportunity. This systemic approach prevents soil erosion, saves trees, reduces the hyacinth problem, provides jobs and creates five sources of either feed or revenue where before there were none.
Nothing is wasted in nature, and the water hyacinth is nature’s attempt to recover the nutrients that would otherwise be lost as a result of topsoil erosion.
By seeing the plant as an opportunity instead of a problem, the hyacinth can be managed more sustainably.
Hyacinth biomass is a very fibrous material and cannot be fed to livestock as it would harm their digestive systems. However, it is excellent for growing mushrooms in. Indeed, mushrooms spore spontaneously on dried piles of water hyacinth waste awaiting disposal.
Early experiments in growing mushrooms from dried water hyacinth substrate yielded fantastic results, with a first crop produced after just 30 days, and second and third batches within another 10 days.
Conventional mushroom farming incurs 60-80 per cent of its costs in the preparation of substrate and in the use of energy needed to kill microbial organisms, which compete with mushroom spores. In the hyacinth system the substrate is free, and locally-sourced biogas fuel saves energy costs. Furthermore, water hyacinth substrate actually outperforms traditional substrates like sawdust, producing 1.1 tons of mushroom per ton of substrate. And the oyster and straw mushrooms grown are particularly rich in potassium, magnesium, iodine and calcium – all of which are crucial to a healthy diet.
The system is therefore ideal for microfinance initiatives, costing an individual farmer only US$500 to start up, with the first mushroom stock being sold after only 1 month and other revenue streams following on soon after. From the 200 unskilled workers clearing the hyacinth on a minimum wage in Zimbabwe (Z$16.10), it is estimated that 1000 jobs could be created by mushroom cultivation. At present, mushrooms sell for around 11 Zimbabwean dollars per kilo and, when supplemented with the other revenue streams, this process could provide wages as high as Z$200 in the long term.
2 Earthworms – Humus
Mushroom cultivation breaks up the ligno-cellulose in the water hyacinth and leaves a residual substrate that can be put to excellent use in cultivating earthworms. The earthworms in turn produce high-quality humus that can then be applied to the soil as fertiliser.
The worms also provide an ideal high-protein chicken feed, and the chicken manure contributes to the generation of electricity from biogas.
The rest of the residual mushroom substrate can be used as a source of feed for cattle, whose manure is also used to generate biogas.
Cattle and chicken manure is channelled into a ‘digester’. The methane contained in the manure is used as fuel, thus reducing the need to cut down trees for firewood.
This article first appeared in the Ecologist October 2003