Thread: Two Questions

Great explanation guys! It sounds like y'all have done your homework. I could not have explained it better. Maybe y'all should have gone to School to be limnologists or fisheries biologists. I think y'all would have done well. Fisheries Biologist don't get rich but the career is awsome!

To continue this discussion the next related topic is lake/pond turnover. It involves the thermocline, water density, water temp, and dissolved oxygen (DO). As y'all have explained, due to density and temperature differences a thermocline develops with more dense, colder, and low oxygen water on the bottom (hypolimnion) and less dense, warmer, high oxygen water on the surface (epilimnion). The reason why the hypolimnion is low of oxygen is due to the decomposing organic material that settles in the bottom of lakes and pond. This decomposition uses up oxygen. Also the phytoplankton that is in the hypolimnion is producing oxygen during the day. The phytoplankton is only found where light penetrates the water column (not in the hypolimnion). All ponds and lakes that have a thermocline and turnover eventually. The bad turnovers happen on small ponds during the summer. When a summer pop up storm rolls over one of these ponds, the strong wind and cool rain that that falls on the pond causes the turnover. The cool, more dense rain that falls on the pond begin infiltrating the water column. This causes the mixing of the layers to begin. If there is strong wind, that causes turbulence on the water surface, the pond turns over. The strong wind combined with cool, heavy rain is the nail in the coffin. When a pond turns over all of the decaying organic material that has settled to the bottom, along with the low DO water mixes with the epilimnion. When this happens the DO plunges, the water will often turn a dark brown, rusty color and the fish die to lack of oxygen. Unfortunately this is pretty common. We have received 6 turnover calls on ponds already this year in D-10. I'm sure there are more to come. The the only thing you can due to prevent this from happening is have an oxygen diffuser or water fountain that pulls water off the bottom and mixes it with the surface. These kind of systems need to be put in pond before the thermocline sets up. As long as you have enough mixing, the thermocline will not develop very strong and a turnover will not occur.

On large lakes that are deep enough for a thermocline to develope, turnover occurs when the epilimnion cools due to cooler air temps. This is a gradual process and doesn't result in fish kills normally. It happen so slow that fish have a chance to adjust to their invironment. Large and small lakes/big ponds are less susceptible to turnover during the summer because they are so large. I have not seen a pond turnover that was larger than 4 acres. Hopefully this wasn't too long winded and I didn't bore y'all too much.

k, thanks.