Plants add oxygen sources for ponds

By Mike Surbrugg

Globe Farm Editor

AFTON, Okla. - Aquatic plants are often the biggest issue for a healthy farm pond, according to Mitch Fram, an Oklahoma State University area extension water quality specialist.

Fram spoke at a recent pond-management program held in Afton.

Helthy ponds require more biomass of plants than life that eats the plants, he said.

Life in a pond begins with plants and the small fish that eat plants.

Plants produce oxygen in the daytime and at night, plants and animals use the oxygen. Among largest users of oxygen in the water are dead plants, he said.

An excessive number plants will shade the bottom of the pond and disrupt the cycle, he said.

Another advantage of plants in a pond is to take up nutrients that run into the water from animals or commercial fertilizer.

An excessive number of weeds get in the way of fishing and put the pond out of balance.

The only way to know nutrient levels in a pond is to have water tested and consult a county extension center for suggestions to correct any water problems.

Weeds are not the problem, but a symptom of the problem created by what is flowing into the water from surrounding fields. "What is in your watershed will eventually get into your pond," he said.

Large plants should not cover more than 15 percent of a pond's surface. Algae is not a problem when an adult who sticks an arm into the water to elbow depth and the submerged hand is still visible.

Some plants such as bull rush help keep pond water clean, he said.

Oxygen levels are critical in water. Water has no more than 20 parts per million oxygen, compared to 200,000 parts per million in air. Fish are stressed with the oxygen in water is below three parts per million.

To see if a pond lacks oxygen, check it at daybreak to look for a lot of fish at the surface gulping for air. A small pump intake in shallow water to shoot water over the pond will mix air with water and save fish.

When this is done, then look for sources of nutrients that are getting into the pond, he said.

He said that 99 percent of fish kills in the summer are caused by low levels of dissolved oxygen in the water. Warm water dissolves less oxygen than does cold water.

Fish kills are most likely to happen in hot weather with warm, still nights, he said.

When fish die, they initially sink to the bottom to decompose and then float to the surface. "When you see a lot of dead fish at the surface, it is too late to do anything for fish killed in that event," he said.

Ponds can become too shallow because of improper construction or erosion.

Cows standing in water generate manure and that means trouble for fish, he said. It is better to pipe water from a pond to cattle than allow cattle to come to the pond to drink.

Fram said improper drainage from septic systems, manure and fertilizer must be kept out of the pond. A buffer of 50 to 100 feet is needed around the pond, he said.

Excessive fish feeding is another problem. Fram recommends feeding no more than 10 pounds of fish food per acre a day and feed no more than 10 minutes a day.

Weed control can be done with prevention, herbicides, dyes that stop plant growth but not harm fish, grass carp or mechanical removal, he said.

Herbicides are quick to act, but are selective in what they control. It is costly and only a third of the pond must be treated at a time.

There are risks of herbicides being in water flowing out of the pond. Herbicides can be costly and have short-term benefit. "You need to read and follow herbicide directions on labels," he said.

Weeds must first be identified before buying a herbicides.

"If you use a herbicide with copper get a water analysis before using the product to prevent a fish kill," he said.

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