Notwithstanding the acquisition authority contained in subsection (a) of this section, any lands, waters, or interests therein, which are owned wholly or in part, by or which hereafter may be owned by, or under option to, the National Park Foundation, The Nature Conservancy (including any lands, waters, or interests therein which are designated as “Nature Conservancy Lands” on the map referred to in section
410ff of this title) or any similar national, nonprofit conservation organization, or an affiliate or subsidiary thereof shall be acquired only with the consent of the owner thereof: Provided, That the Secretary may acquire such property in accordance with the provisions of this subchapter if he determines that the property is undergoing or is about to undergo a change in use which is inconsistent with the purposes of this subchapter.