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[ABIDJAN] Former fishermen around Africa's shrinking Lake Chad have adapted to their changing surroundings by taking up farming. But a recent study indicates this may not be sustainable if high water levels do not return.

Lake Chad, bordered by Cameroon, Chad, Niger and Nigeria, has a maximum depth of only 11 metres and has shrunk considerably in the last 40 years, largely because of a decrease in rainfall in its southern basin.

A study by researchers from France and Niger, published in the journal Regional Environmental Change, undertook soil, hydrological and groundwater surveys. The scientists also conducted interviews with farmers as well as members of local administrations and projects to find out how the Mober people of eastern Niger have adapted to this significant environmental change.

They found that the rich soil reclaimed from the shrinking lake has enabled the Mober people to grow crops such as cowpea, maize, rice and green peppers without using fertilisers or irrigation.

Jean-Marie Ambouta Karimou, a researcher at Abdou Moumouni University, Niger, told SciDev.Net that, until the 1970s when lake levels were at their highest, "fishing would provide both food and income to the lakeside populations, thanks to the exportation of smoked or dried fish".

He said the former fishermen "have consequently and progressively turned into farmers and cultivated the lake shores". The crop yields in these areas are superior to those of rain-fed crops. This has contributed significantly to food security and the improvement of living conditions.

The authors warned that, if the lake level does not rise, there is a risk of soil exhaustion.

"In the absence of the return of the waters of the lake, the exhaustion of the soils in the lakebed is foreseeable … A series of rainy years will induce the rise of the water level in the southern pool and the return of water in its northern basin.

"The maintenance of the agronomic qualities of the soils that are not regularly covered by the high waters of the lake is a real gamble in the short term."

The authors cited the example of one area of exposed land where there is already little organic matter and warned that, without flood, this will decrease further.

They said that the evolution of the living conditions of the Mober people needs to be monitored carefully over the coming decades.Before he precised that, in spite of the small surfaces which were exploited by the farmers, for reason of poverty, the crops yields are highly superior to those of rain crops.