Pond Boss Forums AERATION Systems questions Water Temp Survey

I've decided I would like to do a reasonably good temperature survey of my pond and have begun to play around with the idea. Here is a graph of some data I collected this past weekend. I wanted to see what impact my winter time aeration had on water temps. So I got two digital thermometers with remote probes and took some data. Note that my pond is completely frozen over. We just ended a cold spell last week in which we had 21 days in a row with night time temps below zero. When this happens my aerator which only runs two 4 hours shifts a day does not keep the pond open. I really wanted to know what was happening down there. I drilled a hole about 10 feet from the aerator and dropped two probes. I put one probe about 6 inches above the bottom and the other just below the ice. My aerator runs for 4 hours starting at midnight and again at noon. I measure water temps just before the aerator started at noon. Those are the measurements at time 0 in the graph. For the first 15 minutes I measuring the top and bottom temps every minute. Then I measured every time I could take a break from cutting fire wood. These points are each time you see a change in slop of the graph. The last data point was taken a little over 30 minutes after the aerator shut down. I must say I see some expected results and some unexpected. The temperature just under the ice took some time to get going but eventually started to rise. It had a unexplained drop after 165 minutes but then rose again. The weird thing is then it began to drop again and continued down even after the air was shut off. The temperature near the bottom as one might expect began to drop slowly but then to my surprise it began going back up and continued more steeply after the air was shut off. Anybody care to explain my data? This raised enough interesting questions that I think I'm going to by a temperature logger and get some good accurate data over long periods of time.

Very nice, bz! Just like an engineer!

Is there some water deeper than where you dropped the thermometers? I wonder if the circulation reached out and moved some deeper water that was warmer, and your bottom temp headed up toward the 39F that might have been in a deeper spot?? Just guessing.

When my wife gives me that "just like an engineer" comment it's not always a compliment, but I'll take yours Dave as positive. Yes, there is deeper water close to the aerator. Below is a contour map of my pond. The aerator is in the deepest part of the pond (second section from the left) but is located in 7 feet of water right adjacent to the 8 foot deepest spot. I was measuring the temps about 10 feet from the aerator closer to shore towards the bottom of the map in about 5 feet of water. So as you move out from shore you have the location I'm taking temps in about 5 feet of water, then you have the aerator further out in 7 feet of water, then the 8 foot hole even further out. It sounds plausible that in the first two hours cold water was moved from under the ice toward shore, it would then turn about and go deep and wash the bottom with colder water. The aerator could be pulling warmer water up from 7 feet and washing it under the ice it would explain the upper temperatur rising during this same period. Then after two hours enough of the deeper warmer water had made the circuit and thus began warming the bottom area. I can't explain the surface temp beginning to drop while the bottom temp rises but maybe if I think about it some more. It was also interesting that several times I dropped the surface sensor down to mid depth and usually found some 39 deg. water there. I think I've convinced myself that I do have some degree of supercooling going on in this area of the pond. Notice that the starting temp near the bottom was only about 36 deg. This may be because I was not at the very deepest area but it may also be because this section of pond gets aerated regularly and the whole area is cooler than it should be. I've suspected this for some time since I have noticed that fish don't live in the aerated pond section during the winter. I did drill some holes in the far left and far right sections of pond. In both of these areas I had 46 degrees near the bottom in the deepest spots. I knew when I started this that I should be measuring the 8 foot area to be most meaningful but I couldn't do that given the thin ice in that area caused by the aerator. I am intrigued enough now that I'm going to find some temp data loggers to get lots of accurate data. Dave, can you suggest a source for inexpensive devices. I've found some submerible ones that sell for about $100 including software but if I can get the cost down perhaps I can afford 3 units or 3 channels so I can simultaneously measure top, middle, and bottom. The ones I'm looking at can store enough data that I should be able to run them for several days. I think that data will be interesting.

BZ - we do use some relatively inexpensive temperature loggers. I'm not at the office, and won't be back until the middle of next week. I'll try to remember to find the source for you, and send you the details. If you don't hear from me, please excuse my old-guy memory, and send me an email reminder.

BZ - here are moderately priced, underwater temp loggers. I'll check with the students to see if they know of other companies (they buy them, not me ).

http://www.1800loggers.com/solutions/products/loggers/_loggerviewer.php5?pid=158

http://www.1800loggers.com/solutions/products/loggers/_loggerviewer.php5?pid=443

Here is one that we are using down in the Nebraska Sandhills.

http://www.benmeadows.com/search/optic+stowaway/2277/

I have a temp data logger called IButton which costs $25 It connects to your computer via a usb adapter. This allows you to set the logging interval.

see http://www.maxim-ic.com/products/ibutton/products/ibuttons.cfm#dataloggers

Frank

I just found that you can get the HOBO loggers for as little as $39 (8K memory) or $49 (64K memeory). They apparently are so inexpensive because they are "only" waterproof to 30 meters, which of course is plenty for most ponds. They come with waterproof cases, and download vis USB interface (as Frank mentioned). YOu do have to pay for the software, though.

www.hobologgers.com/pendant

Thanks guys. I had been gone for a while and this thread dropped off the radar screen so I had forgot about it. I did look at the HOBO but don't think I found them that cheap. Great, I'll check these out. Next thing I'll want is to survey O2. That's going to cost I know.