The Effects of Turbidity in a Pond
Low water turbidity makes bug catching easier.
Ponds come in all shapes and sizes and are generally distinguished from lakes by a shallow depth that allows sunlight to reach the bottom. As the sunlight penetrates the water it provides life-giving energy for aquatic plants and animals. When the sunlight is intercepted by turbid water the pond appears dirty to people, but to aquatic organisms an increase in turbidity can decrease the pond's ability to provide the elements required to live.
1. What Is Turbidity?
o When you look into a pond you may be able to see all the way to the bottom or only part way because the water appears murky, dirty or cloudy. The water's color is from sunlight reflecting off of tiny particles of algae and sediment floating in the water.Turbidity is a measurement of how far sunlight penetrates into the water before reflecting off of these particles. Ponds with a higher amount of algae and sediment are more turbid and more difficult to see through, while less turbid ponds are more clear. How far sunlight can penetrate into a pond is critical for the plants and animals that live in the pond.
Plants
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Pond algae are tiny plants that live in most ponds. Like all plants, algae depend upon the sun for life. And, like all plants, algae release oxygen critical for animals to survive. In ponds the oxygen provided by algae is used by fish and other aquatic organisms. But too much algae can cause an increase in turbidity and a decrease in oxygen. As the algae die they decompose. The decomposition removes oxygen from the water. Humans greatly influence the amount of algae in pond water by overfertilizing land that drains into a pond and by improper maintenance of septic sewer systems on land next to ponds. When the fertilizer and sewage enters the pond they cause excessive algal growth.
Animals
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Ponds are permanent home to fish and a variety of worms, beetles and amphibians and critical temporary habitat for migrating waterfowl. Too much turbidity in a pond, either by plants or sediment, creates a challenge for these animals. Sediment turbidity, often caused by erosion from human construction activities, can clog the gills of aquatic animals and smother the pond bottom habitat that some species depend upon. Because many aquatic animals and waterfowl are visual feeders they have to see the food they catch and eat. Turbid water reduces their ability to find food.
Measuring Turbidity
o Pond turbidity is often measured with a secchi disk. This 4 to 6-inch-diameter metal or plastic disc is painted in alternating black and white triangles radiating from the disk's center. It is lowered on a rope over the side of a boat to the point that it cannot be seen and the depth is recorded. By comparing secchi disk depths taken at different intervals scientist are able to predict changes in turbidity and recommend actions to reduce the turbidity.