Using the device I described yesterday we were able to get a fairly accurate picture of what happens in vernal ponds, what limnologists call a vertical profile, at least in central Oklahoma. I see no reason why these events should be different anywhere else. Using the device as pictured yesterday we determined a profile for temperature, dissolved oxygen, pH, conductivity (a measure of ions in the water), and the oxidation-reduction potential (ORP; what I was taught as the redox potential as a measure of the availability of certain substances that I can explain as we go). Using a light meter we measured light attenuation in the field and in the lab we measured total suspended solids (TSS – turbidity), total organic carbon, phosphorus and nitrogen. The impression I am trying to make is that we were fairly thorough in trying to describe what happened in the pond. And we did this for two ponds, as you’ll see in the graphs below.
I won’t bore you with all the details, just some of them, and I’ll tell you the end of the story first. My first impression, that shallow waters are not like lakes, was wrong. I had the idea that in Oklahoma, where the winds come sweeping down the plains, ponds were thoroughly mixed most of the time. Wrong. I originally thought a sample of water from anywhere in a pond would tell the entire story of the pond. Wrong. I had it all wrong and I am the first to admit it.
Ahh, but for me to be wrong there must be a good story to explain the errors of my way. As it turns out ponds are like lakes and have similar vertical profiles, just highly compressed. What occurs in meters of water in a lake, takes only centimeters in a pond. If you just see the pattern and not the scale, you wouldn’t know if you were looking at a pond or a lake. In my naiveté what I had failed to take into account was that there could be so much compression in the profile. Again, I won’t bore you with all the details but just give you a couple of examples to make my point.
Here’s the vertical profile for temperature. 
Without knowing the scale of depth you might think this is a typical lake with warmer, less dense water, on top of cooler, denser, water. Happens in lakes (and swimming pools) everywhere.
Another example would be pH. Same pattern, with more basic water on top of acidic water. The reason for this is that there is a bunch of photosynthesis going on at the surface removing carbon dioxide whose removal makes the water more basic. The amount of photosynthesis is hidden in the photographs and even standing near the ponds. But the pH profile matches the profile for chlorophyll. As it turns out these turbid systems are loaded with small algae that we can’t detect because of all the turbidity.
I’ll try and put this all together tomorrow.
