Dwight do you see a groundwater effect and if so what aspect of the data is it effecting now ?
The ground water effect is seen in the water temperature on the bottom. You would expect that the most dense water at 39F degrees would be on the bottom. The ground water temperature remains at a relatively steady 41-42F degrees year around. As this warmer water flows through the pond it fights a losing battle with the colder pond water. At the bottom this warmer water isn't diluted as easily with colder pond water and therefore a layer of warm water remains at the bottom. There also may be some heating at the bottom from the hydraulic friction as the ground water circulates up and out of the pond sand and gravel bottom.
The bottom DO is affected by this warmer water as well. As we have noted warmer water holds less DO and ground water will have less DO then the pond water with it's oxygen producing plant life.
I think that there are other things going on with the "flow" such as stratification prevention, filtering, transferring of decaying material into the ground water table.
