Conductivity is a measure of the salinity in water.
Conductivity and salinity are measures of the salts dissolved in water. In solution, the salts dissociate into positive and negative ions which allow electricity to flow through the liquid. Salinity measures the dissolved salts in a water sample as compared to the concentration of ocean salts. Conductivity reflects how well water samples can conduct electricity. This property is directly proportional to the concentration of ions present in the solution.
Conductivity
Electrolytic conductivity (EC) is the measure of the ability of water to conduct electricity which is usually expressed in terms of microsiemens/cm. It estimates the amount of total dissolved salts (TDS), or the total amount of dissolved ions in the water such as chloride, nitrate, sulfate and phosphate anions with a negative charge or sodium, magnesium, calcium, iron and aluminum cations with a positive charge present. Organic compounds or pollutants like phenol, oil, alcohol and sugar don't conduct electric current and have a low conductivity in water. The conductivity is directly proportional to the ion concentration in solution. Conductivity is a good measure of salinity in water.
Factors That Affect Conductivity
Conductivity in rivers and streams is determined by the geology of the area. Streams flowing through granitic bedrock areas have a low conductivity because granite is composed of inert materials that don't ionize on contact with water. Water flowing through areas with clay-based soils have a higher conductivity because of the presence of materials that ionize on contact with water. The same factors affect subterranean groundwater. Pollutants will affect conductivity. A leaking sewage system raises conductivity because of the presence of phosphate, chloride and nitrate ions. A factory pollutant such as oil, phenol or alcohol will lower the conductivity.
Salinity
Salinity measures the mass of dissolved salts or ionic constituents in a given mass of solution. It is usually expressed as parts per thousand (ppt). Cations or positive ions found in water usually include calcium, magnesium, potassium and sodium. The anions are bicarbonate, carbonate, chloride, nitrate and sulfate. Conductivity is a good indicator of the measure of salinity in water. Others are water density, refractive index and sound speed.
Factors Affecting Salinity
Weather including heat patterns, evaporation, rain, river flow, freezing and melting of sea ice influences the salinity and density of water. This can lead to the formation of convection currents in a body of water in which warm water rises and cool water sinks, thus changing the salinity and density of the water mass as it rises, falls and mixes.
Other Factors Affecting Salinity and Conductivity
Urban runoff from roads, especially road salt, can shock the water with intermittent inputs of runoff from snowmelts or excessive rains. The size of the watershed with respect to the lake or holding pond facilities and the wastewater from septic systems and drainfields and on-site wastewater treatment plants and disposal systems can cause extreme variations in pollution concentrations. Also nutrients such as ammonium-nitrogen, nitrate-nitrogen and phosphate from fertilizers, pesticides such as insecticides and herbicides have a significant impact on streams and lakes. Evaporation during hot summer weather as is seen especially in the southwestern states. This explains why the Great Salt Lake in Utah, Mono Lake in California and Pyramid Lake in Nevada are extremely salty.
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