Having wrtitten about biological aspects of shallow waters for the first 31 posts, I thought I’d switch and write about another critical aspect of these habitats, water. There is no pond,lake or river without the stuff so understanding it is pretty important. No water, no pond, no salamanders, toads or zooplankton. The formal study of water is called limnology. Although I have taught limnology for a long time (it was the first independent class I ever taught) I am not a limnologist. I am an aquatic ecologist but there is just way too much specialized knowledge for me to call myself a limnologist. This was made clear to me during the 18 months I spent at the now defunct Kinneret Limnological Lab in Israel. They had real limnologists there and I wasn’t one of them.
Not know much about a topic never stopped me from having an opinion so sometime during the 1980’s I decided that shallow waters were not anything like lakes but behaved in some unique way that required special understanding that limnologists did not give to ponds and pools. When I finally had the opportunity to collect limnological data, I of course discovered that I was absolutely wrong. What threw me off initially was scale. Everything that happens in the water of a lake happens in shallow waters but in a much compressed way.
My graduate students at Oklahoma State came across a pond a few miles from campus that became our limnology study site. A typical sampling scheme for a lake depends on a mechanism whereby water is collected at specific depths and then brought to the surface for analysis. There are Nansen Bottles and Van Dorn collectors (similar items at http://www.aquaticresearch.com/discrete_point_water_samplers.htm) designed to sample discrete masses of water. These devices work fine in meters of water but less well in centimeters of water. They were originally designed for ocean studies and work well there but ponds are different, obviously,
The first challenge was to come up with a mechanism that would allow us to collect unique samples of water that were centimeters apart. I think we came up with a good system. In the pond we placed a ringstand to which was attached a meters stick (to accurately measure the depth of the water). The assembly was carried into the pond and placed as upright as possible. After waiting a short time the meter stick assembly was slowly lowered through the water column by a grad student standing nearby (photo at left show Chad Boeckman who collected most of the data you’ll be reading about; he changed projects so the data has been dormant for a few years). We were able to clearly see differences at distances only a 2 cms apart. You can see from the photograph that the typical central Oklahoma pond is rather turbid and this makes for some interesting differences between Oklahoma and ponds in New England where turbidity is usually absent .
Attached to the meter stich was a length of Tygon tubing that had a horizontal fitting on the end for collecting water at a specific depth (at left). By placing holes throughout the end we hopefully disturbed upper and lower water as little as possible.
The assembly in the pond was connected by a long length of tubing to an assembly on shore that consisted of a an automated water tester attached to a special sampling vessel and a hand operated pump. Normally the device would be lowered through the water of a lake or ocean but these systems are much too shallow so we brought the water to the unit. Turbidity was determined by weight in the lab so a measured aliquot of water from each depth was brought back to lab.
I know all of this seems like a great deal of trouble but as you’ll see in the next post or two it revealed some neat things about vernal ponds inn Oklahoma which should translate into ponds everywhere.
