Turbidity

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What is turbidity?

Turbidity is a measure of water clarity, or the clearness or cloudiness of the water. It is not the same thing as the color of the water- you may notice that the water in the marsh and the pond at IslandWood is brown, but this does not affect the clarity of the water. The unit for turbidity is an ntu, or nephelometric turbidity unit. Measuring turbidity allows us to quantify how much material is suspended (floating) in the water. Suspended materials include living things and soil particles, such as clay, silt and sand.

Why is measuring turbidity important? It is important because the more suspended materials, the more heat those particles can absorb. Surely water itself will absorb heat,, but particles in the water can absorb a lot more heat. The more heat that is absorbed into the water will increase the temperature. Warm water will also hold less dissolved oxygen than cold water. This will have an effect on living things such as plankton, macroinvertebrates, fish and frog larvae, all whom need oxygen in the water to survive.

Higher turbidity will also not allow light to penetrate the water column. Plants growing on the bottom of the pond, lake or stream will not get enough sunlight in order to photosynthesize. This will decrease the amount of oxygen gas being dissolved into the water (dissolved oxygen). Particles in the water can also clog fish gills, reduce disease resistance and lower growth rates.

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What causes turbidity?

Living things such as algae, plankton and microbes suspended in the water column will also increase the cloudiness or “murkiness” of the water. Natural disturbances such as a heavy rain storm and erosion will temporarily increase turbidity. Human-made disturbances such as dredging, run-off from developed areas and ships’ wakes will also alter the clarity of the water.