Ponds fulfill a lot of roles in Georgia. They provide water for thirsty crops andlivestock. They offer a cooling dunk for people and animals. And they (sometimesreluctantly) give up their fish for a summer fish fry. It’s nowonder they run short of something. “During the dog days of summer, we see many ponds become oxygen-depleted,”said George Lewis, an aquaculture and fisheries specialist with the University of GeorgiaExtension Service. “Pond owners may need to aerate (add oxygen to) their ponds toensure the pond stays healthy.”Most bodies of water that cover less than 15 acres are ponds, Lewis said. Anythinglarger is a lake. Both can become oxygen depleted, but smaller ponds are more at risk.”Ponds tend to be warm through their entire depth. Lakes probably have a layer ofcooler water near the bottom that can hold enough oxygen to support the life in it.”Ponds likely to become oxygen-starved include those near areas where a lot of organicmaterial is on or in the ground or where fertilizer is used heavily.This includes not only pastures with livestock and many farm fields, but areas aroundgolf courses or manicured suburbs, too.”Animals that graze around a pond add a huge amount of organic waste to thewater,” he said. That waste can deplete the oxygen faster.Ponds with lots of fish are good candidates for oxygen depletion, too. Fish use asurprisingly large amount of oxygen.Lewis said the oxygen isn’t depleted in just one or two days. Hot, hazy days in lateJuly and August are the most likely time the problem will start. The water is warm, so itholds less oxygen. The sun isn’t shining directly into the pond so phytoplankton aren’t producing as much oxygen.And the bacteria and fish in the water need more oxygen.”Everything is right for less oxygen to be produced,” Lewis said, “whenin fact, the pond needs more oxygen.”Oxygen depletion usually happens slowly over four or five days before obvious symptomsappear. The first symptom is usually the water changing color to a bright green. Anothersign is a fairly sudden increase in fish deaths.Whatever symptoms appear, Lewis said, the visibility in the water shows the oxygenlevel. Put something white or shiny under the water. The oxygen is probably about right ifyou can see the item 12 to 18 inches deep.”Visibility of less than 12 inches points to potential oxygen depletion,” hesaid. “You may need to aerate the water before your fish start dying.”Lewis said night aeration provides the best oxygen source for ponds. During the dayphytoplankton, microscopic plants in the water, produce oxygen through photosynthesis.At night, the sun isn’t providing the light the plants need to make oxygen, so the animals inthe water slowly use it up.”That’swhy you’ll findthe lowest oxygen levels in a pond just before sunrise,” he said. “When theproblem is getting serious, you’ll see fish at the surface literally gulping air.”Pond owners use many methods to aerate their ponds. Lewis follows a rule of thumb foraerators of one horsepower per surface acre. Anyÿsystem that breaks up a water streaminto small droplets falling into the pond should oxygenate well.It’simpossible to aerate a pond too much, he said. The oxygen dissolves in the water. When thewater is holding as much as it can, no more will dissolve into it.”Not all ponds will need aeration during the summer,” Lewis said. “Butif a pond needs oxygen, it needs it quickly.”
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- Precautions in the Sun