Not just the U.S. There are more trees today worldwide than 200 years ago. And fyi; trees aren't the only oxygen producers. Shrubs, grass, seaweed, moss, pretty much anything green.
Please correct me if I am wrong, but I learned that large water bodies tends to capture large amounts of CO2, not produce oxygen. Aquatic flora and fauna do play a large part in the production of oxygen but trees make most of it (the Amazon rain forest makes around 30% alone).
Large water bodies containing phytoplankton (tiny plants that drift around near the surface) both absorb CO2 AND produce large amounts of oxygen.
"In the process of photosynthesis, phytoplankton release oxygen into the water. Half of the world's oxygen is produced via phytoplankton photosynthesis."
http://news.nationalgeographic.com/news/2004/06/0607_040607_phytoplankton.html
FYI the ammount of o2 in the atomsphere is in high enough quantities that if all o2 ceased to be produced, there would be no real problem for something like 200 years. VSause did something on it
"In the process of photosynthesis, phytoplankton release oxygen into the water. Half of the world's oxygen is produced via phytoplankton photosynthesis."
http://news.nationalgeographic.com/news/2004/06/0607_040607_phytoplankton.html