I’ve been writing about water, the stuff without which we would have no ponds. Their meager depth hides the complexity of water in vernal pools. I’ll provide one last bit of data from our studies in Oklahoma and then give my take on the relevance for everywhere else.
My first post on this topic includes a photograph of a student standing in a turbid pond. This is the common appearance of ponds in that part of the country. As we were studying the vertical profile of many water parameters we included total suspended solids, a measure of turbidity. I was surprised by the results – ponds are not uniformly turbid. As you can see from the graph they are actually less turbid at the top and more turbid as you descend. Given that the Secchi disc depth (a measure of water clarity used by aquatic scientists everywhere – see the photo) was measured in centimeters as opposed to meters as it is in clear lakes, I never would have guessed that the water is even more turbid at depth.
Secchi disc - and this water isn't particularly turbid!
The explanation is pretty simple. Heavier particles settle leaving lighter particles suspended in the water. The soils of Oklahoma contain lots of clay that is made up of exceptionally small particles that settle slowly so the water stays turbid. What about the winds sweeping down the plains and keeping the water mixed? Just as I showed in the graphs of my last post, the wind doesn’t make any difference. The reason for this is not anything revolutionary. The closer you get to the ground, the slower the wind speed. For ponds to mix, the winds would have to be howling. It is windy for sure at head level but your feet rarely sense it. Ponds don’t get disturbed by the wind enough for much to happen to the layers established by changes in temperature.
My guess for the global significance of our results? Ponds in New England are probably stratified more than people have previously expected. A single scoop of water from a pond is in no way adequate to tell what is actually going on in the water at the scale that organisms experience the water. Ponds in the woods, sheltered from the wind are probably even more stratified than those in the middle of the plains making that scoop of water particularly meaningless, again at the appropriate scale. I could be wrong but until there is adequate data in opposition to what I suggest I think I have hit on a great, unexplored area of vernal pool studies.
Finally, I wrote a number of posts about how water serves as a medium to transmit messages between predator and prey and within species populations as well. These organisms have poorly developed sight and rely on water to carry information about their surroundings. It should come as no surprise that habitats with compromised waster quality, not necessarily toxic but enough to screw up signals, can lead to all sorts of problems for pond inhabitants. I’d like to tell you some stories proving this point but unfortunately, I don’t know any. Perhaps one of the readers of this post can pass along such a story to me. I know they are out there but the number of people looking at vernal pool water chemistry is small and finding these stories may be difficult. But incredibly important.
I’ll tell what I think is a great story about the response of populations to differing water chemistries tomorrow. These differences are natural but point to the types of intricate responses we miss by ignoring the base of the food web.
