The role shallow ponds play in relation to climate change would likely be the algae. Decades ago it was argued that oceanic algae produce more oxygen and scrub more carbon that the forests do. Grass carp are a very common means of controlling unwanted aquatic vegetation (including algae) in the Western Hemisphere. As Kepis said though, your bureaucracy would be very difficult to overcome if possible at all. Yes, I have two small ponds of my own. Each less than a half acre. Kepis is entirely correct that runoff fertilizer is a very, VERY common cause of algae and that it does play a part in the food chain to the larger fish. So much so that most elementary school books list it as the base of the food chain and most farmers here periodically deliberately fertilize their multi use ponds if their isn’t enough runoff.