Salinity – the awakening monster from the deep
Glossary
dryland salinity and irrigation salinity. There are two kinds of soil salinity resulting from human activities: dryland salinity (occurring on land not subject to irrigation) and irrigated-land salinity. Both occur when rising watertables dissolve natural salts in the soil and bring them to the surface.
electrical conductivity (EC) units. The measure of a solution's ability to conduct electricity. EC units are used to express salinity levels in soil and water. When salt is dissolved in water the conductivity increases, so the more salt, the higher the EC value. Another salinity measurement is the total dissolved solids (TDS). For more information see Measuring the salinity of water (Department of Primary Industries, Victoria).
electromagnetic radiation. Electromagnetic radiation is simply energy which travels through space at about 300,000 kilometres per second – the speed of light. We imagine radiation moving like a wave. The distance between two adjacent wave crests is called a wavelength. The shorter the wavelength, the more energetic the radiation is said to be. Also, the shorter the wavelength, the greater the frequency of the radiation. Other than wavelength, frequency and energy there is no difference between a radio wave, an X-ray and the colour green. They all possess the same physical nature. For more information see Back to Basics: Electromagnetic radiation (Australian Academy of Science) and Electromagnetic Spectrum (NASA Goddard Space Flight Center, USA).
gamma rays. The shortest wavelength of electromagnetic radiation. For more information see Gamma rays (NASA,USA).
groundwater. Water stored naturally below the land surface in a saturated zone of the soil. The top of this groundwater is called the watertable. For more information see What is groundwater? (Connected Waters, University of New South Wales, Australia).
parent rock. The original rock from which a soil has come. For example, sandstones are often the parent rocks for sandy soils. Except where there is extensive weathering, the composition of the mineral fraction of the soil generally indicates the nature of the parent rock underneath. Layers of soil and subsoil lie on top of the bedrock.
recharge or discharge. The recharge rate is the rate at which an aquifer is replenished or topped up with water (inflow). The other important variable for groundwater management is the discharge rate, or the rate at which water is taken out of the system (outflow). In some cases aquifers can discharge naturally to rivers and springs and so the water is not being removed from the system. The two variables determine the water balance, which is part of the larger water cycle involving the journey of water as it falls from the sky, onto land or sea or aquifer, and back again.
remote sensing. The act of obtaining information about an object from a distance. Although that distance can be small or large, remote sensing usually means gathering data from some distance above the Earth's surface (eg, aerial photography and satellite remote sensing). For more information see About remote sensing (Geoscience Australia) and An introduction to remote sensing (CSIRO Mathematical and Information Sciences, Australia).
soil profile. Where soil has been cut through vertically, such as along a roadside embankment, you may see that it has various layers of different textures and shades. This is called the soil profile. The top layer, called the A horizon, contains most of the plant roots, it is where most biological activity occurs and where organic matter accumulates. Water washes clay particles down out of this horizon.
The next layer – the B horizon – is where the clay particles and soluble substances washed down from above tend to accumulate. Below that is the C horizon, or parent rock. The type of parent rock can affect the fertility and structure of the soil that develops above it.
watertable. The top surface of the groundwater.
Page updated August 2006.