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FishinDaddy

D.O. in rainwater?

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I have heard, both on here and from someone at the Teneroc ranger station, that rainwater has low Dissolved Oxygens levels.  True or False?  It seem to me that falling rainwater would serve as an aerator on the surface on the lake...but what do I know.

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I think it may be low levels because of the amount of acid in the rainfall. I wouldn't think that acid would be good for the fish, but I would also think that it would areate the surface of the water like you say, because it inverts it if the rainfall is hard enough, and I think that may also be the reson that fish feed on top more when it's raining, the areated water starts to move down in the water column and the fish search for the fresher water which brings them to the surface. Thats just my thoughts, anyone feel free to correct me.

                                                                    Ian

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I have always been told that rain puts oxygen in the water.

Have you ever seen the big water sprays in office park ponds?  They are there to aerate the water and to put oxygen in the ponds for good pond management.

I would hope Micro would put in his input on this subject as he would know.  ;)

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Rain areates the water by cooling it (cooler water holds mor O2) and by churning the surface.

D.O. does not fall down the water column. That would require the warm water above the thermocline, to sink, which isn't going to happen (until turnover any way).

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If equipment to test DO concentration (meter or test kit) is not available, the following observations and conditions can be used to anticipate oxygen depletion:

     Fish swim at or near the surface gulping air (piping).

     Fish suddenly stop feeding.

     There is a rapid change in water color to brown, black or gray, signifying loss of an algal bloom.

     A putrid odor arises from the water.

     There has been an extended period of hot cloudy weather.

     There is a heavy summer wind and a rainstorm.

Emergency aeration should be applied whenever fish show signs of oxygen depletion or when dissolved oxygen drops below 4 mg/L.

Many recreational pond owners purchase aerators and place them on electric timers. Proper use of the timer should have the aerator turn on during the late evening (10 p.m. to midnight) and turn off after daylight (7-8 a.m.). Using an aerator is not a complete substitute for monitoring DO concentrations and an oxygen depletion event resulting in a fish kill may still occur. However, use of an aerator is recommended and will prevent many problems.

Summary

Dissolved oxygen (DO) is oxygen gas (O2) that is dissolved in water. Most DO in ponds is produced during photosynthesis by aquatic plants and algae. For this reason DO increases during daylight hours, declines during the night, and is lowest just before daybreak. Dissolved oxygen concentrations below 5 mg/L may be harmful to fish and piping (gulping air at the surface) may be observed when DO falls below 2 mg/L. Low levels of DO are most frequently associated with hot, cloudy weather, algae die-offs, or heavy thunderstorms. Dissolved oxygen can be monitored using an electronic oxygen meter or chemical test kit. Emergency aeration should be supplied whenever DO falls below 4 mg/L or environmental conditions favor an oxygen depletion event.

1. This document is Fact Sheet FA 27, one of a series of the Department of Fisheries and Aquaculture, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. First published: September 1992. Reviewed: May 1997, February 2003. Please visit the EDIS Web Site at http://edis.ifas.ufl.edu.

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I would say that light rain would probly not have much effect on the DO in a body of water. The results of a heavy storm may be from the introduction of dead organic material that is washed in and muddy water. The dead organic material consumes O2 when it decomposes and the darker water may inhibit sunlight and the ability of plants to photosynthesize and the darker/warmer water will not hold O2 as well. Just my 2 cents.

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