I’m on the Eastern Shore of Maryland, near Denton, standing in a forested wetlands surrounded by miles of corn and soybean fields. Here, in this little island of biodiversity, sweetgum trees and bald cypresses rise up from coffee-colored water.A gentle wind sways the branches, leading spots of light and shadow in a dance over the surface of the water, illuminating tufts of grasses and rotting logs that are home to salamanders and frogs.This place is what is called a “Delmarva Pothole” or “Delmarva Bay.” They are small, isolated, fresh water wetlands that are connected only beneath the ground to nearby streams and rivers.Although few outsiders have ever heard of them, biologists say these potholes – which locals call “whale wallows” -- provide invaluable ecological services for the Chesapeake Bay by filtering runoff pollution being washed by rain off of farm fields.