Thanks, that is encouraging!
It is hard to grow terrestrial plants on hard, packed clay. I transferred that expectation to aquatic plants. Sometimes it is good to be wrong!
Get the soil tested for nutrients/pH, etc., etc. Just like a farmer would test their crop field soil. You might be surprised at what the test results are.
Your hard packed clay on land, - how much water does it have to grow plants?
I have many places on the farm where there is 1-3' of top soil with excellent organic matter. That top soil then grades into sandy loam or clay loam subsoils. I then hit almost 100% clay at depths of 6-8'.
This area was 8-12" of good top soil with prairie grass roots and lots of other organic activity. The soil profile then went almost straight into hard-packed clay with very little transition zone. I only had a 6100# mini-excavator, but I could not even dig this stuff effectively. I am used to digging wet clay where you get a bucket-full and then push the break-out limits of the equipment. This was the opposite - I would scrape and scrape and barely get the bucket teeth to bite. It got a little better at depth when there was a tiny bit of residual moisture in the clay. I could scrape partial buckets in that stuff.
There is essentially zero penetration of my deep-root species of prairie grass into this clay. I don't know if the problem is poor soil quality of the type that might show up in a soil testing analysis as you suggested above, or if this clay is just too dense for the roots to penetrate? The bluestem and switch grass roots go to 6-8' depth in the other areas of the farm with loose, sandy soils.
The NRCS data says our average precipitation is 25-33" per year. The grass in this area is just barely observably thinner than the grass in the areas of deeper soils. Our blend of native prairie grasses is just mind-boggling (to me at least) at how efficient it is in capturing and utilizing the limited water it receives. I really couldn't believe how well the grass was thriving on this ground on such a thin layer of "usable" soil.
That is my expanded analysis of how my terrestrial plants are doing. I wouldn't even call the material that will form the bottom of a pond in this location a "soil". I would call it a clay horizon above bedrock. (No idea of the depth to bed rock. I have never hit bedrock in any of my test pits.)
I just have zero experience if that type of material would grow aquatic plants, so I have zero confidence on the plant cycle development in that type of pond!
Any more advice from you (or others) would still be greatly appreciated.
