Any lands acquired by the Secretary of the Interior under the terms of this section and section 666d of this title, if located within or adjacent to an existing wildlife refuge or reservation, immediately shall become a part of such refuge or reservation and shall be administered under the laws and regulations applicable thereto, and, if not so located, may be administered as a migratory-waterfowl management area, refuge, reservation, or breeding ground in accordance with the provisions of the Act of August 14, 1946 (60 Stat. 1080), and Acts supplementary thereto.