I became curious so I checked Wikipedia. Along with other classifiactions, pH is indedd one factor for classification. "A bog or mire is a wetland type that accumulates acidic peat" according to the Wikigod. "Fens are characterized by their water chemistry, which is neutral or alkaline." "A salt marsh is a type of marsh that is a transitional intertidal between land and salty or brackish water..." Interesting stuff in math books!