OK, here is the story I was trying to relay. Esshup and I are working with Dwight Bremer and another pond owner in WI (forum handle is Jeff K.). All of these guys have the "pit" type, or excavated ponds that are down into the water table.
This WI pond is excavated into limestone, and is a pretty darn cool place. Very high water transparency, as you might guess -- 10 feet transparency is common.
The pond also has a spring on the pond bottom that flows directly into the pond. That spring is what is pertinent to this particular thread.
Jeff K. was doing his first dissolved oxygen (DO) measurements. Most of the pond was about 12 ppm DO. However, just above the spring hole (which is in about 5 feet of water), he only got a reading of 6 ppm.
Now, this doesn't answer the question of whether the inflowing groundwater has DO, as water with no DO quickly picks up oxygen when it has a chance, and there could be quite a bit of mixing, too. However, I thought it was very interesting that less than a foot above the spring, he could see the influence of the groundwater with that lower DO.
