Ships leaving the Argentine agricultural ports hub of Rosario on the Parana River are having to reduce cargos by thousands of tonnes due to low water levels, the local head of logistics said on Wednesday, amid growing environmental concerns.Dryness in Brazil, where the Parana originates, has diminished cargo traffic and sparked worries by environmentalists about dredging the river below certain depths. The dryness has reduced the amount of cargo that can be carried by ships at the height of the Argentine corn and soy export season."Handymax ships are leaving port with 9…