Crossword puzzle clue "describes some soils and sloughs"

(Arabic) a substance which, dissolved in water, forms a solution containing hydroxyl ions and with a pH of more than 7

BOG, to sink into a bog

FEN, wet land with alkaline, neutral, or only slightly acid peaty soil

MERE, to mark off, divide, also MEARE, MEER

MIRE, to sink in mud

MOLT, to shed feathers or fur, also MOULT

MORASS, a very wet or muddy area of ground