TÔGBLÉ

Background
The scourge of the water hyacinth
"The water hyacinth is a freshwater plant, floating and invasive of Lake Nokoué. This plant forms a dense vegetal carpet making it impossible to transport by boat and a fortiori to fish. Depending on the environmental conditions, a carpet of water hyacinths can double in size in 6 to 18 days. It represents a real threat for the biodiversity of the environment
invaded environment. Indeed, since it occupies the surface of water, it :
- blocks the exchanges between the atmosphere and the water and thus the oxygenation of the water, thus endangering the aquatic animal life.
- prevents the light rays from reaching the immersed plants, thus killing these plants and the aquatic animals that feed on them.
This plant has two modes of reproduction. When the conditions of life are favorable, it reproduces by vegetative multiplication. When the bad season arrives (high salinity or low temperature for example), the fruits of the water hyacinth fall into the water with their seeds. During all this bad season, the seeds remain in hibernation in the mud. When the good season returns, these seeds germinate and give birth to new plants.
The proliferation of water hyacinths, by the congestion that they create in the aquatic systems, makes difficult the catchment of water. In addition, navigation becomes difficult, which limits the transport activities of users. On Lake Nokoué, access to lake villages such as Ganvié becomes difficult and limits tourist activities. The water hyacinths in these lakeside villages and those in the neighborhoods bordering the lake become ideal habitats for mosquitoes responsible for malaria.

The solution
Mechanical harvesting of hyacinths is considered the best short-term solution to control the proliferation of the plant. This requires relatively heavy amphibious equipment (harvesters of 13 and 16 meters long, working like a harvester, conveyor belts, boats & belts and conveyors, ...) for the collection of plants in the water for their transport on the bank and their routing to a waste treatment center. The advantage of this method is that almost all water hyacinths are removed massively and quickly in one go This method is very rigorous even if sometimes some disadvantages make that other vegetable species are removed with this cursed plant.
Opportunities of its economic valorisation
"Perennial water hyacinths can weigh up to 50 kg/m² (90% water). This represents a colossal mass of organic matter potentially recoverable in many ways. Three distinct parts make up this plant: the roots, the leaves and the flower. Its invasive character and its fast proliferation pushed the local populations to find activities of valorization such as:
- the manufacture of threads and ropes (leaves)

- the development of basketry, baskets and mats (leaves)
- the development of charcoal briquettes obtained by the pyrolysis of water hyacinth (leaves, flower, roots)
- water treatment or phytodepuration (root system but need of the plant as a whole)
Water purification by phytodepuration
- animal nutrition (leaves)
- production of biogas (leaves)
- creation of fertilizer or mulching of crops (leaves, flower and roots)
- the production of absorbent fibers to face oil spills (roots)
Overview of its presence in Lake Nokoué
"The climate of Lake Nokoué induces a certain periodicity in the presence of the water hyacinth on the lake. Rainfall and its impact on the salinity of the lake water is the major factor influencing its (non) proliferation. This plant expands most during the fresh water period, i.e. from the end of July to October. Then, the decrease of the rainwater supply reduces the flow of the rivers that feed the lake with fresh water. The level of the lake goes down. This level approaches that of the ocean, the water of the lake becomes more brackish. As a consequence, the water hyacinth
develops at a slower speed from December and ends up dying around mid-February when the salinity becomes too high.