The Secretary may, within the area designated or altered pursuant to section 460m-3 of this title, acquire lands and interests therein, including scenic easements, by such means as he may deem to be in the public interest: Provided, That scenic easements may only be acquired with the consent of the owner of the lands or waters thereof: And provided further, That any parcel of land containing not more than five hundred acres, which borders either the Current River or the Jacks Fork River, and which is being primarily used for agricultural purposes, shall be acquired by the Secretary in its entirety unless the owner of any such parcel consents to the acquisition of a part thereof. Property so acquired which lies outside the boundary generally depicted on the map referred to in section 460m of this title may be exchanged by the Secretary for any land of approximately equal value within the boundaries. Lands and waters owned by the State of Missouri within such area may be acquired with the consent of the State and, notwithstanding any other provision of law, subject to provision for reversion to such State conditioned upon continued use of the property for National Scenic Riverway. Federally owned lands or water lying within such area shall, upon establishment of the area pursuant to section 460m-3 of this title, be transferred to the administrative jurisdiction of the Secretary, without transfer of funds, for administration as part of the Ozark National Scenic Riverways.