What is oxygen made up of? molecules or atoms, if molecules, what atoms are present?

Well, since Oxygen is an element on the periodic table, and elements are the types of atoms there are, then I would go with molecules because it can't be an atom if it is what makes up an atom.

Wetlands form where water and land meet. a lake with a wetland fringe can fill in with decayed plant and animal material to become a wet meadow. a pond can fill in to become a bog or fen. sediment can fill in a river marsh to become a swamp.flooding of coastal lowlands from rising sea levels has created broad coastal marshes that are protected from wave action by barrier islands or reefs. coastal wetlands also form when rivers deposit sediment as they reach the ocean. plants then take root and hold the soil firm against the forces of tides and waves.