IMO, knowledge, & experience aeration is a complex topic due to numerous variables such as size & depth of pond, pond configuration and bathymetry of the basin, trophic (nutrient-BOD) state of the pond which changes, size of the aeration system and how quickly it can turn the water column, regional (climate) location, water temperature, type and efficiency of the diffusers, water quality, fishery type, and goals for the pond, etc. Aeration generally reduces chances of DO problems which is why it has proven popular for benefiting ponds. With all these variables occurring,,,, each pond is truly unique, thus the default aeration method is to aerate 24/7 to compensate for all the variables since very few pond owners and sellers have the ability to test DO, evaluate BOD, and determine needed operation time for each pond. Simple is often easiest. Under sized or minimally sized aerators need to be run 24/7 to get the pond turned over adequately.
IMO Snrub's rational is sound -""During daylight the upper layer of water gets super saturated (on a sunny day) with O2 by algae production. At night the opposite happens. So why would a person want to bring up lower level water (lower in O2 to begin with) to the upper level where O2 is also dropping? I understand the water/air interface is adding O2 to low DO water. But would you not want to bring low O2 water up during a period of maximum O2 production rather than at night when only the air/water interface can add O2?""
Short answer is yes, ideally you want to force the best quality water to the bottom and the best quality water is usually at the surface. However in most cases anytime you can dilute the worst water quality with better quality water, this is good. In most, not all situations as long as you are mixing daily, the differences between the two techniques is not significant enough to cause DO problems. The discussion is often or becomes academic - a mater of degree.
There are two main goals involved in this discussion: A. most efficient DO adding aeration method, and B. provide cooler water for the fishery. Each requires different aeration periods.
We also have to account that the bubbling action of the diffusers will add as much or more DO to the rising water column as simple atmospheric diffusion which according to text books is stated as very inefficient for adding DO to the water. Wave action improves atmospheric O2 diffusion. Note: bubbling from aeration adds a lot less DO to the water compared the the millions of algae cells per ounce of water during daylight.
Normally DO is consumed most rapidly at the mud water interface and at depths where light does not penetrate. This DO loss is primarily by bacterial respiration during decompostion. Normally there are lots of bacterial in the water column, but many more at the mud water interface where decomposition is most abundant. A good example of this IMO is in winter during ice cover when DO is lost first in the surface mud and then progresses upward as winter progresses. Final DO loss is then at the near surface under the ice/snow cover. Fish will move upward in the water column as this process progresses.
During summer and warm temperatures water is only able to hold about 1/2 as much DO as during 39F water. Plus all biological & chemical DO absorbing activities occur faster in warmer water. So DO can be consumed quicker in summer compared to winter, thus the greater need for aeration in summer.
In most ponds whenever low DO water is brought to the surface it gets infused with higher DO water, degassed, and pushes, pulls, or moves better water to the depths. In most cases there is not enough DO degradation to cause problems because of the high amount of DO in the surface layer and generally there is enough DO to satisfy the needs of the entire pond. Exceptions occur after several cloudy rainy days when algae production is reduced, turbid or low water clarity occurs, and when low algae production is present for various reasons.
Last edited by Bill Cody; 03/30/18 11:14 AM.
