What is gypsum used for in lake management? It is used to remove what is called “turbidity”. Turbidity would be more simply described as dirty, muddy, murky, or cloudy water. Some turbidity is caused by motion disturbances of fish, livestock runoffs, or anything else physically stirring and clouding the water. Other turbidity is caused by chemical disturbances. It is this turbidity that is offset by gypsum.
There are bucket tests landowners can do to determine if the discoloration is chemical or physical. Once it is determined which it is, it is possible to map out a solution. It may be simpler to correct the chemical cause of muddy waters, rather than waters muddied by some physical element.
Gypsum is a substance used to help clear the chemical component of muddy waters. It is a mineral found in drywall, plaster, and fertilizers. It is pH neutral, which is important as pH is one of the factors that must be kept at the right level for the health of a lake. Gypsum works by clumping particles of clay together which then sink to the bottom as the clumps get heavier in weight.
Lakes can be treated with gypsum in two ways. One is with gypsum powder. While this may work faster, it may not last as long. The other is with gypsum rocks. The rocks are dumped into the water. These may take longer to clear the body of water, but the results are also more long-lasting. The amount of gypsum powder or rocks used will vary from location to location depending on the severity of the turbidity and also the size of the lake or pond.
The clay which the gypsum attracts comes from many sources. The main source is soil erosion. This can occur in rain runoff, from bare croplands, and from over-grazed pastures. A crop cover on the surface of the soil helps prevent this erosion. Livestock on a shoreline or wading in a pond can also suspend sediment, as well as add manure. Ducks, geese, and bottom-feeding fish can affect turbidity. Unusual weather conditions sometimes also stir up sediment. Shallow water allows windy conditions to keep the sediment stirred up.
Tests can be run to determine the amount of treatment necessary. Also, proactive steps can be taken. If the pond or lake is one in the planning stages, to be constructed, the watershed size should be considered in terms of the pond or lake to be constructed. In other words, the watershed is all the land that drains to the same place, and thus, the character and properties of that land needs to be considered. If it is bare ground, then planting crops or vegetation will help prevent the sloughing off of particles into the lake. It is easier to keep soil from entering the water than removing it once it is there.
Turbidity of ponds and lakes can be dealt with through the use of gypsum. However, as with many other things, prevention is the best cure.