Methods Manual for Salt Lake Studies/Temperature

Authors: PSJ Coleman,

Overview
Water temperature is a measure of how warm or cool a body of water is. This plays an important role in the functioning of aquatic ecosystem and influences a wide range of other chemical and physical parameters. Higher water temperatures decrease the ability of water to hold oxygen, reduce the density of the water (how heavy it is) and may also have a controlling impact on events such as algae blooms. Temperature readings are also used to improve the interpretation of other measured parameters. Higher water temperatures influence the ability of water to hold oxygen, and may influence salinity readings (Methods Manual for Salt Lake Studies/Salinity).

Factors that influence water temperature include the time of day, season, depth of water and the presence of stratified salinity layers. In some saline lakes the denser underlying layers of brine may trap heat, resulting in a higher water temperature in the deeper layers than in layers of water closer to the surface. Where such 'thermoclines' are recorded, they can indicate the presence of previously unsuspected salinity layers (haloclines).

Equipment types
There are several types of equipment used to measure water temperature. The most common are glass thermometers or electronic temperature meters. A glass thermometer is the cheapest method. An accurate electronic temperature meter is quite expensive in comparison. Accurate electronic temperature sensors are also commonly found in multi-sensor CTP meters, where conductivity, temperature and pH are measured together.

Sampling temperature
Red spirit thermometer or temperature meter

Sampling dipper or collection bottle attached to a pole for sampling

Record form and pencil

To ensure good results
The thermometer or meter should be calibrated yearly against a certified thermometer.

Glass spirit thermometers should be checked prior to every use for bubbles in the red spirit or cracks in the glass housing.

If bubbles or gaps are found in the red spirit, the thermometer should be ‘shaken down’ until the bubbles or gaps disappear. If cracks are found in the glass housing the thermometer should be replaced.

When you collect the water sample, make sure it is at least a metre out from the shore (preferably further out) and from at least 20 cm below the surface.

Place the thermometer or the meter's probes into the water sample as soon as it is collected and leave in the water until the reading stabilises (this may take up to 2 minutes).

Record the reading

If the water is deep, you may like to take several samples from different depths to construct a graph of the temperature variation with depth.