Source: http://memoirepfe.fst-usmba.ac.ma/get/pdf/Substance%20d%26%2339%3Binteret%20socio-economique%20d%26%2339%3Bune%20ressource%20naturelle_%20l%26%2339%3Barganier%20-%20ELHAOURI%20Doha_3833.pdf