The commissioner, by rule, may exempt from local implementation under this title those freshwater wetlands which, by reason of their size or special characteristics of unique environmental value or by reason of common characteristics, are appropriately to be administered pursuant to this article by the department alone. Such rule, based upon findings of fact made after public hearing, may relate to classes of wetlands based on size or particular characteristics, or to particular wetlands the characteristics of which make them subject to the exercise of the commissioner's discretion pursuant to this section. The commissioner shall make an order to such effect in each such instance and send a certified copy thereof to the executive officer of each local government affected thereby within ten days of his signing the same; such order shall not take effect until forty days after such signing.