What a great exchange. I've been away from this board too long. You guys are great. Here's some thoughts about oaks, tannins, green wood, etc.
Tannins leach into water. Tannins are acids. If your water has no buffering capacity, pH changes dramatically. For example, where Dave's ponds are, the soils are rocky, sandy loam, with red clay underneath. No buffering capacity. Look at it this way, tannins are similar to indigestion. Rolaids solve the indigestion. Acids, even mild ones like tannic acid, can wreak havoc in water that isn't buffered. But, add a few rolaids to acidic water, and the problem dissolves. (please forgive the pun). So, if you want to use green oaks, have your water tested for buffering capacity. Check pH. A pH of 7 is neutral. Lower than 7, water is acidic, higher than 7 is basic. Look at calcium carbonate, or lime, levels. If you have levels high in lime, green oaks cause less problems, because lime buffers acid. If lime levels are low (less than100ppm), plan to add lime to your pond, preferably before it fills.
Here's the bottom line....aglime "kills" tannic acid, renders it harmless. So, I would be tempted to treat the water rather than remove the trees.
