Salinity

What is salinity?

Salinity is the measure of the concentration of dissolved salts in water. Salinity is measured indirectly by testing the electrical conductivity (EC) of the water. Saltwater conducts more electricity than water with no dissolved salt. Fresh water has almost no dissolved salt, whereas ocean water has a salinity in the range of around 34 to 36 parts per thousand (ppt). Brackish water is a mixture of fresh and saltwater.

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The salinity of water is an important measure of water quality because different species of animal and plant life survive in different ranges of salinity. Even a small change in salinity could cause stress, or even death, to these organisms and could have a devastating effect on the local, and wider, ecosystem.

Sources of salinity in freshwater include urban and rural runoff from industry, sewage, agriculture and stormwater. Clearing of vegetation can also cause raised levels of salinity due to a resultant rise in the water table. Areas within the tidal limit of rivers that flow into the sea will experience fluctuations in salinity between low and high tide. In estuaries there is usually a gradual alteration in salinity, as freshwater entering the estuary from tributaries meets the seawater moving in from the ocean.

Aquaread’s salinity sensors & testing equipment

Salinity is a standard parameter on both the portable Aquaprobe AP-2000 and Aquaprobe AP-5000 devices, as well as on the Aquaprobe AP-7000 which is designed for long term water quality monitoring in the field, as it has a self-cleaning facility. If you don’t need multiple parameters the AquaPlus probe just takes measurements of dissolved oxygen, EC and temperature.

AquaPlus probe with sleeve off

 

The AquaPlus doesn’t require a flow of water to take a reading, so is ideal for use in aquaculture. Readings of salinity are taken in the range of 0-70 PSU or 0-70 ppt, with an accuracy of +/-1% of the reading or 0.1 unit if that’s greater. Each Aquaprobe is used in conjunction with the handheld Aquameter that, in addition to displaying the measurements from each parameter, tracks the GPS coordinates of each sample location.

The GPS Aquameter

Why use a water salinity meter?

Using a water salinity meter is a quick and easy way to measure salinity. Aquaread’s water salinity testing equipment is specifically designed to be used in the field, and is suitable for measuring salinity in surface water, groundwater and wastewater.

There are various purposes for a water salinity tester. It could be used to indicate if water is safe for irrigation, which is important for agriculture. Salinity is a fundamental parameter for monitoring water in fish farming, and is also important for monitoring salinity in industrial discharge. Salinity testing can help to determine the extent that runoff and effluent discharges influence an aquatic system.

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How to use Aquaread’s salinity testing equipment

A water salinity tester is just one function of Aquaread’s multiparameter water quality testing equipment. Salinity can be measured at the same time as many other parameters to gain an overall understanding of the water quality. When salts dissolve in water they breakdown to create free ions in the water.

These ions are either positively or negatively charged. Examples of positively charged ions are sodium, calcium and magnesium. Examples of negatively charged ions are chloride and carbonate. When our Aquaprobes are placed in a water sample they take the measurement of EC by sending a current between electrodes. The drop in voltage measures the resistance of water, which is converted to conductivity. The higher the conductivity measurement the higher the salinity of the water.

Our salinity sensor and testing equipment uses the measurements of electrical conductivity (EC) and temperature to provide a measurement of salinity in Parts Per Thousand (ppt) or Practical Salinity Units (PSU). Aquaread’s salinity meters can be used for varying time scales, from spot monitoring to long term monitoring of salinity in water.

Get into monitoring with Aquaread

If you would like any further information regarding measuring salinity in water or water testing in general, please do not hesitate to get in touch. Click here to see our product range.

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