Nothing in this Act or other existing law shall be construed as necessarily prohibiting or mandating the development of agricultural potential within the Yukon Flats National Wildlife Refuge pursuant to existing law. The permissibility of such development shall be determined by the Secretary on a case-by-case basis under existing law. Any such development permitted within the Yukon Flats National Wildlife Refuge shall be designed and conducted in such a manner as to minimize to the maximum extent possible any adverse effects of the natural values of the unit.