Pond Boss Forums INTRO Questions & Observations hypolimnetic aeration

I heard about this type of aeration at a pond seminar this past weekend and I'm curious if anyone has any experience with it. Basically it's aeration the water below the thermocline without disturbing the thermocline. I have a small deep pond and with conventional aeration, last season it mixed well. For whatever reason I never picked up any fish in the deeper water using the fishfinder. I did however have O2 levels over 6 ppm all summer at depth. So it seems the bass and bluegills are going to inhabit the shallow waters anyway, if hypolimnetic aeration is effective at oxygenating the deep section and it stays cold, why can't I keep trout in the deep and warm water fish in the shallows? These units are pricey so I'd have to build my own but the potential seems worthy. Any experience out there or opinions?

Two-tiered fisheries are an extra bonus for those who can maintain them. Your thinking is very sound, as always. Hypolimnetic systems have been in operation in Lake Ogallala, Nebraska for years to maintain trout fisheries during the hot Nebraska summer. One thing that a biologist told me is that just because you bring oxygen to the hypolimnion, you aren't necessarily going to have a great environment for trout. You'd also have to evaluate other parameters such as other gasses that are present that fish don't thrive in, or bacterial decompositional byproducts that might alter pH or general habitability for trout. You're definitely right about the cost of the systems. They can be pricey. I don't know of anyone who used a system in a private pond. Interesting experiment. I wish you would come up with an economical way for a pond owner to do this because I would follow your model.

Would you like me to find the name of a biologist who is assigned to the Lake Ogallala project? The information may also be available on line because the Feds are involved in the funding.

How do they aerate hypolimnetically (hypnotically)?

Two tiered fishery, I like the sound of that, better yet it's a great use of space. The lecturer only touched briefly on the subject because he installed one in a large reservoir which releases cold water to a trout containing river. His concern was not aeration but hydrogen sulfide gas removal from sewage discharged from all of the houses on the perimeter of the reservoir. So this system does have the capacity to strip off organic products of decomposition as well as aerate. The schematic he showed can be found if you Google "hypolimnetic aeration LIMNO" the system is shaped like a huge R2D2 and vents gasses to the surface. Buying one would un-doubtedly break the bank (or the marriage) but building one is feasable.

The reason that it became necessary at Lake Ogallala is because historically this lake derived it's water source from The upper third of Lake McConaughy, which was well oxygenated. About twenty years ago the overflow structure was altered so that the water that came from Lake McConaughy was derived from the lower third which was anoxic. The water was plenty cold, but even spraying it into Lake Ogallala did not impart enough O2 to support what was once a world class trout fishery. Hypolimnetic aeration systems were installed, and I believe have been a pretty good success. I have queried the forum at Nebraska Game and Parks Commission to see what the consensus is as to the success of the system.

What do the fish below the thermocline eat if hypolimnetic aeration is effective at oxygenating the deep section and it stays cold? I assume they do not cross the thermocline to the surface to forage where the food is.

Surprisingly, Eric, cool and cold water species will readily cross into the epilimnion for short periods of time to feed, provided the temperature differential isn't too great. As Cecil, often reminds us, it's usually the lack of oxygen that kills a trout before the greater temperature. Higher temperature water, as you know contains less oxygen at saturation, but a trout will stray a few degrees from ideal to grab an easy snack.

A true "two-tiered" fishery will have prey items that also favor the cooler, now oxygenated water. I think some northern lakes almost act like a lake on top of a lake and have lake trout/cisco communities in the hypolimnion and muskellunge/sucker communities in the epilimnion. It sure gives fisherman extra options and also takes advantage of greater usable water volume.

Thanks Bruce. Absent large lake feeding communities is there enough food in ponds below the thermocline when added to short shallow foraging actions across it to support a trout population?

My personal theory, is that the hypolimnetic system would have to be in operation for a year, during which you could feed trout early in the morning on the surface, when they could come up to feed with minimal stress. During this time, the bottom community could establish with organisms that thrive in cooler, oxygenated water. Certain species of nymphs and dragonfly larvae should do quite well in the cooler bottom water.

I like your pics. They gave me an idea. What about using it to do as stated above but have it reinject the water just above the thermocline so it would sink through it and remove the barrier in total. This should give both sets of fish easy access to both zones only inhibited by temps.

Interesting thought!! Sounds like a masters thesis to me.

So where does the aeration come from? You guys(ya'll) nearly had Meadowlark and myself convinced several months ago that bubbles dont aerate the water very much, but the forced subjection of the water to air at the surface is where a vast majority of the transfer takes place.

You're listening way too close, burgermeister!!

I think it has to do with the size and quantity of the bubbles. In order to provide fish with oxygen, the bubbles have to be extremely numerous because the cumulative surface area is so much greater for the same volume of air. I think that is one of the reasons the system is so expensive because it requires large volumes of air in the form of extemely tiny bubbles. The bubbles essentially stay entrained in the hypolimnion because each individual buble is so small. You don't get the added benefit of air/water interface from traditional airlift diffusion.

P.S. That might be the biggest B.S. answer ever given on the forum. :p

I think the concept can be adapted to smaller ponds that are pretty deep and have a hypolimnion thickness of at least 10ft deep or greater. My term paper for limnology class was about hypolinmetic aeration. I currently can not find the paper.

burgerm wrote: "You guys(ya'll) nearly had Meadowlark and myself convinced several months ago that bubbles don't aerate the water very much, but the forced subjection of the water to air at the surface is where a vast majority of the transfer takes place. You have to put the amount of oxygenation of water by bubbles into context. Bubbles do not put very much oxygen into water COMPARED to photosynthesis and surface agitation. But bubbles can and do oxygenate water significantly under certain conditions such as long contact time of bubbles with water and if the volume of water to be oxygenated is not great. Continual bubbling of smaller volumes with fine bubbles puts dissolved oxygen into water. Usually the volume of the hypoliniion is small in deep, kettle basin, morphometric shaped pond basins compared to the volume of the epilimnion. Thus a smaller amount of dissolved oxygen is necessary compared to the amount needed by the epilimnion. Plus the hypolimnion is cooler and oxygen consumption is less compared to epilimnion demands.

A prototype of Bruce's example above would consist of a vertical pipe (4"-10"dia)anchored at the base and held upright with a float. The side arms should probably come off the side at a downward 45 deg angle and at a depth just below the thermocline. The upper dome (placedat bottom of thermocline) would have a narrow diameter (3/8"-1/2") vent pipe to vent excess air from the diffuser and hypolinmetic gasses. Air diffuser would be at bottom of vertical pipe. Rising water would be oxygenated somewhat as it rises in the pipe and then discharged downward at a 45 deg out the side arms below the thermocline. Continual recirculation of the hypolimnetic water would accumulate oxygen at a rate that is hopefully greater than the BOD of the hypolimnion.

I will look again for my Limnlogy Hypolimnetic Aeration term paper but I am running out of places to look.

...brilliant

Bill, your explanation makes much more sense(thanks) but, I have to admit, I liked Bruce's better. It made me LMAO. Bruce, go have another JD and reread your post. :rolleyes:

Here's the answer from Nebraska Game and Parks Commission. I'm "aquaman".

http://www.ngpc.state.ne.us/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=2&t=010078#000002

I think I'm going to have to moderate myself.

In order to produce small enough bubble size to promote good O2 tranfer without creating a rapid rise to the surface and promote mixing of the two layers, you will likely have to create an air saturation tank with several minutes residence time with at least 60-80 psig. This air water mix is then subjected to a quick pressure drop across a mixing valve. This is similar to design for a flotation device used in conventional waste water clarification through flotation ( look for dissolved air flotation design) The effect is tryue dissolved air, unlike diffused air, that looks like milk when 1st allowed through the mixing valve.

Bill, perfect description of a Hypo system.

Because the hypo water is so low in oxygen, it has a desire to off-gas the hydrogen sulfide and carbon dioxide gases and absorb oxygen. The vent tube allows the off gas and at the top there is usually a stair case type aparatus for the water to trickle down and gravity feed back to the bottom.

Another type of hypo system would be to have a pump on shore pulling water into an oxygen cone from the top. An oxygen generator would be pumping pure O2 in the bottom of the cone. As the water falls down inside the cone, it mixes with the pure oxygen and gravity feeds back to the hypo at a super saturated level of about 20-30 ppm.

Just an invention while sipping my JD.

I think I'll step out now that the big dogs are here.

Cary, I'd join you in a shot of JD and talk hypo/epilimnion any time you wanted!

Cary's idea of having the unit on shore and pumping water from the pond bottom up to it may be the easiest and most efficient way for a small pond. Air compressors will produce more CFM when they don't have to pump deep and the residence time of the water in the reactor can be controlled by the inflow rate. The trout farming industry uses tanks with inverted funnels to re-oxygenate water before returning it to rivers and it's application would do the same in this case. The weight of the water will return it to depth through a long enough pipe. You can pump from one end of the pond and return to the other. Testing the DO of the effluent will help determine the flow rate.

PaPond...I think we have a new invention that I need to work on!

I think I will call it the "Transducermodulator" (Marvin the Martian from Warner Bros.)

Although coldwater forage fish are optimum, in our northern lakes that have a "two tiered fishery" aka two story lakes, the trout feed on a lot of invertebrates on the bottom and surprisingly even the larger fish are good zooplankton filterers in the water column.

Yes if the stocking rate is kept fairly low. I don't have the literature in front of me as I sent it to another member here to copy but there are guidelines for stocking ponds when they are not fed pellets.