Karen Cambre, Sharpe, Kenneth W.
News article for August 28, 2017
As we know all too well, we are in the peak of hurricane season and Harvey has brought our preparedness to a heighten state.
There's not much preparation that we can do for farm ponds, but in the wake of tropical systems, ponds can go awry.
Oxygen levels in a pond are critical and at their lowest levels during the heat of summer. In a hurricane or tropical storm it is not unusual to see fish kills in area lakes, bayous and ponds. There are a number of factors but one of the main reasons is the wind mixing the oxygen and non-oxygen layers of water together which reduces the available oxygen for fish. The net result is a fish kill and it will be obvious as the fish will be floating on top of the water.
This same mixing action can occur when you get a cool, quick thunderstorm during the hottest parts of summer. As you know, heat will rise so when you get a cooler layer of water on top of the warm pond water the warmer water can roll to the top. The result is the less oxygenated water from the pond goes to the top and the more oxygenated water goes to the bottom. You get a similar situation when the first cold fronts arrive in the fall. Again you have a mixing of the oxygen and the result is a fish kill.
Another reason that oxygen levels are low during a tropical system is the absence of sunlight. We can have days of cloudy weather. Oxygen is produced in a pond or water body by sunlight interacting with single celled algae that are suspended in the water column. These microscopic plants give the water its green tint. During several days of cloudy weather oxygen levels drop drastically and if you have a high stocking rate of fish, you can easily reduce oxygen below what is needed to support fish. With low oxygen you will usually see dead fish early in the morning because no oxygen is being produced during the night.
Another component of fish kills relates to the decomposition of organic matter such as leaves, weeds, grasses, etc. The decomposition of organic matter is an oxygen consuming process. You can have a lot of organic debris blown into a pond during a tropical system and this can also be caused by killing weeds in the pond or introducing hay in the pond (not recommended).
Your first clue that you have a problem with low oxygen in a pond is that all of the fish appear right on the surface of the water and are gasping at the surface and are very sluggish. Usually larger fish of the same species will be affected first and will be the first to die.
Adding oxygen to the pond is your only solution. Start when you first see fish gasping for air. Your objective is to try to create a safe zone for your fish before they get too weak to move to the area with higher oxygen levels.
The easiest way to add oxygen is to recirculate water from the pond up into the air and break the water up into small droplet sizes so oxygen from the air will attach to each water droplet. Attach a ball or gate valve to your water source pipe and then close the valve until it will spray water into the air. A large column of water, even from a well or municipal source, will add very little oxygen. You need to break the water up to create more surface area.
Usually the pond will stabilize in 4 to 5 days. If you have a fish kill, removing the dead fish will help as their decomposition will also consume oxygen and add to the problem.