URL：https://www.researchgate.net/profile/Ekkehard-Christoffels/publication/267380090/figure/fig1/AS:295694553370624@1447510483063/Erft-River-Basin-dotted-cultivation-of-field-crops-hatched-open-pit-lignite-mines_Q320.jpg
掲載元：https://www.researchgate.net/figure/Erft-River-Basin-dotted-cultivation-of-field-crops-hatched-open-pit-lignite-mines_fig1_267380090
