Pond Boss Forums AERATION Should I aerate? Does aeration allow higher stocking rates?

Does using aeration allow to stock more fish? It would seem since there is more usable water space that more fish could be added to ones pond. I'm sure there are a lot more factors involved, but thought by increasing aeration alone it would allow somewhat more fish to be added.

Hey there Heybud! Yes, I have heard that once aerated a pond can support a significantly larger carry capacity. Don and Barry at American Sportfish told me a few years ago how much they were able to increase the carrying capacity, I don't remember how much so, but the answer to your question is yes.

Heybud,

A thermocline can be a physical barrier for fish. Some fish cannont tolerate the colder water or the lower dissolved oxygen levels that often accompanies that deeper, colder water. They simply won't go down there. A bottom-laid aerator which breaks up that thermocline will intuitevely increase habitat which you mentioned. Of course this is a generality as pond dynamics vary from one to the next based on several factors. Maybe a fisheries biologist could chime in here.

As important, an aerator will help the pond assymilate the wastes produced by a larger population/community of fish. This will keep your water quality better and your fish happier.

There is not much published on how much destratification by aeration can increase carrying capacity (cc). It will depend on several if not numerous factors. Generally destratification will increase the invertebrate community that inhabits the benthic zone in the pond bottom that would normally be anoxic. One of the main factors is how much this will increase cc is what portion (%) of the pond bottom now becomes aerobic to support invertebrates.
Another big factor is amount of pond fertility which very few have a good estimate of this number or where their pond is located on the fertility or nutrient scale.

Another factor that I think enters this discussion is the compositon of the fish community. The more herbivores and ominvores there are present the more the cc will be increased.

One has to remember that the destratifiation is affecting primarily the invertebrate community of the pond's food web-chain. For a wild guess I would say the cc increase of fish would be on the order of 10%-25%. This assumes the entire pond is now destratified and in some instances this is not true due to undersized or inefficient aeration units leaving some parts of the sediment water interface still anoxic or without adequate DO to support most larger bottom dwelling invertebrates.

If you were talking about surface aeration in commercial fish ponds then it's a given that aeration can increase the carrying capacity of a pond. However commercial fish grow out ponds are rarely very deep.

The first limiting factor in these commercial fish ponds is oxygen with the second ammonia.

Will a well designed aeration system eliminate the entire thermocline in a pond? I'm sure the answer is going to be it all depends.

Usually a well designed bottom diffuser aerator will destratify the entire pond. Situations where destratification tends to be more of a problem are ponds with islands, L shaped ponds, ponds with bays and fingers, long narrow ponds, S shaped ponds and ponds with unevenly shaped bottoms or with holes or pockets.

IMO before installing an aeration system one should know the depth of natural mixing of the pond or lake. Then aeration of these areas or sections (usually shallow) that are not stratified, do not need to be artificially mixed. Depth of natural mixing is usually the depths shallower than where the thermocline forms. However in special situations where clear, high visibility water is present natural oxygenation can occur below the thermocline.

Aeration of only a portion of a pond is probably better than no aeration. Some or partial destratification will make the stratification less stable and improve at least some areas of the pond bottom. Unstable stratification has its pros and cons.

I have a follow up question to Larry's. If you could completely eliminate the entire thermocline in a pond, would it be a desirable thing to do? Don't fish need some measure of temperature differential in order to regulate their own temperature? (This is not very well worded, hopefully you understand what I'm asking).

JeffHAP, It depends on the fish species. Generally for warm water fish no problem for not having a cool area or temperature differential. Remember we are talking about cold blooded animals. Generally the only time the lack of a cool water refuge or temperature differential is with cold (trout) or cool water (yellow perch) fish. And more so with cold water fish than cool water fish.

For deep ponds (>25ft) that stratify and loose DO in the deep zone there are hypolimnetic aerators that can oxygenate the deep cold water zone/layer and not destratify the pond/lake.

That makes sense, thanks Wild Bill.

And in a pond with creek arms of a depth up to 8' - what does one do in this scenario? I have around 2.5 acres main body, but another acre in creek arms running up to 300' and 40' wide. Would one place diffusers in the creek arms also, or just let those fish figure out where the "better" water is?

Hey TJ,

As Bill was stating, we would place diffusers in areas that natural aeration is non-existant. For example if wind and wave action is bringing oxygen saturated water to a level of 4' then we would want to circulate the area of 4' and deeper. So, yes, we do place diffusers in canals or we also use our bottom circulators to push water out and bring water in.

All diffusers have a % of OTR (Oxygen Transfer Rates). In an aquaculutre setting and large capacity fish farms, this is a very important number to know. For example, the 9" stone diffusers used by Aquatic Eco in an "H" pattern could support up to 5,000# of warmwater fish. That was back in 1998. They have since improved stones and membrane diffusers so the same set up may be able to support a greater amount of fish.

Aeration in the matter we use it in normal home ponds should be termed "Circulators" in that we are using the bubbles as a lifting apparatus opposed to bubble oxygen transfer efficeincy. It has been said by the late Bob Heideman with Aquatic Eco Systems that the bubble transfer is less than 5% when using compressed atmospheric air. Heck that is only 20% oxygen anyway.

This is why it is important to know what the oxygen levels are at a minimum during the am hours and what they are through out the day and best option during a full month before sizing an aeration system. This will allow us pros to look at data "we love data and graphs" and design a system that will meet the oxygen demand the pond has both for worst case scenerio and shock load. The term turnover rates is ambiguous and is very broad. We found that many pond owners did not know what the oxygen levels were so we had to make assumptions to what they may be and match a turnover rate to meet that assumed oxygen demand.

Now that test kits, meters and informed pondowners exist, we as pros need to get back to the specfics of aeration design and literally custom design a system to meet those demands and provide the OTR and SAE (Standard Aeration Efficiency) for each system. OK off my soap box.

TJ - If the creek arms of a pond have inflow all summer then the stratificaion in those arms will probably be minimal or only temporary. However if the inflow is very intermittent then stratification will probably occur whenever the inflow is not occurring. Very low inflows will probably not have a strong impact on destratification. DO and or temperature vertical profile tests would have to be made in these areas to provide specifics about each area.

This is great feedback guys. One creek arm will fluctuate with flows, one will maintain a fairly steady flow.

I obviously don't want to invest more than needed in terms of diffusers, at the same time risking water quality is not acceptable either. Am I oversimplifying the solution by saying: "My main BOW is well aerated, if DO levels drop in the creek arms that are not aerated the fish will naturally find their way to the main BOW with better water conditions - so diffuser placement in the arms is superfluous?"

TJ -"..so diffuser placement in the arms is superfluous?" IMO you are basically correct. The degree of benefit putting diffusers in the arms is probably not real noticable on the fishery. The mixed layer of water in the "arms" is very likely 5-7ft thick. This is probably a large protion of the arm leaving a low percentage of the deepest part of the basin anoxic for a few months (for NE prob. Jul-Sep). The fish will still use the oxygenated layer of the arms for feeding and growth. Performing a few water temperature measurements to locate the thermocline in the arms next year during Jul-Sept will give you a good idea of just how big of a bottom area becomes anoxic in summer for your pond/sm lk. I would be interested in seeing this data. This info would make a very good short story for PBoss mag. If needed, I can help you with advice for this project.

TJ - Another thing to take into consideration when placing diffuser stations is that they will help keep sediment that is brought in by your streams suspended in the water column if they are placed too close to the mouth.

If your streams bring in moderate to high amounts of suspended particulate, and you place your diffuser stations too close to the mouth of them, particulate that is suspended will be kept in supsension much longer by the uplift and circulation of a poorly placed station, and add to any clarity issues you may have, or present you with a clarity issue if you don't already have one.

I would stay out of the stream arms. This will give suspended particulate more time to settle, instead of being circulated into your pond's main body water column.

I just revisited this case study on reservoir destratification and came across some good info on destratification and the effects on fish/invertebrate distribution.

http://content.cdlib.org/view?docId=kt8p...ere&anchor.id=0

The entire 97 page case study which has a ton of good info on the effects of destratification is available at http://escholarship.org/uc/item/2dk2m8tm

That is a very good short description of aeration effects on a system. Will look at the long version when time allows. Thanks for posting that info.