Methods Manual for Salt Lake Studies/Salinity

Authors: PSJ Coleman,

Overview

Salinity is the result of the dissolved ions present in water. Measuring salinity is complicated by the fact that the species of dissolved ions are not the same in every salt lake. The ionic composition and concentration of seawater is fairly constant around the globe, however salt lakes vary considerably, with some being chloride dominated, while others are carbonate dominated.

Methods typically used to measure salinity

The main approaches to estimating the salinity of salt lake brine include:

• measuring brine density
• measuring electrical conductivity
• measuring refractive index
• measuring chloride concentration
• evaporating brine and weighing the residue (gravimetry)

Each approach has its strengths and weaknesses, discussed on the respective method pages.

Relationships between different salinity measures

Conversion table This table is based on information collated by Prof. Bill (WD) Williams of Adelaide University. He presented the information at the 6th International Symposium on Saline Lake Research, Beijing, 1994, and argued strongly for the use of a standardised approach to measuring salinity. He felt that the use of direct, mass-derived measures such as density (either w/w or w/v) would enable scientists to more simply discuss and compare the properties of their lakes. Some indirect measures, such as electrical conductivity are well understood in the range 0-60mS/cm, but the relationship in non-linear in very hypersaline situations (Williams & Sherwood 1994, Williams 1986). Note that the C-TDS relationship shown in the table presented here is based on aqueous solutions of sodium chloride.

The table presented here allows comparisons of various brine salinity measures between 22 ^oC and 25 ^oC.

As the different approaches to measuring salinity all actually measure different properties of salinity (its mass, its conductivity, its effect on the density of water, its effect on how water bends light, etc), the various measures do not all have a linear relationship with each other. In the References section of this manual there are details of several papers that provide an excellent understanding of the various salinity measures and their relationships to each other (Williams & Sherwood 1994, Williams 1986, Baseggio 1974)