Article,
The equation of state of lakes
AQUATIC GEOCHEMISTRY, 6 (1): 1--17 (2000)
Abstract
In recent years, a number of workers have studied the stability of
deep lakes such as Lake Tanganyika, Lake Baikal and Lake Malawi.
In this paper, the methods that can be used to determine the effect
that the components of lakes have on the equation of state are examined.
The PVT properties of Lakes have been determined by using apparent
molal volume data for the major ionic components of the lake. The
estimated PVT properties (densities, expansibility and compressibilities)
of the lakes are found to be in good agreement with the PVT properties
(P) of seawater diluted to the same salinity. This is similar to
earlier work that showed that the PVT properties of rivers and estuarine
waters could also be estimated from the properties of seawater. The
measured densities of Lake Tanganyika were found to be in good agreement
(+/- 2 x 10(-6) g cm(-3)) with the values estimated from partial
molal properties and the values of seawater at the same total salinity
(S-T = 0.568 parts per thousand). The increase in the densities of
Lake Tanganyika waters increased due to changes in the composition
of the waters. The measured increase in the measured density (45
x 10(-6) g cm(-3)) is in good agreement (46 x 10(-6) g cm(-3)) with
the values calculated for the increase in Na+, HCO3-, Mg2+, Ca2+
and Si(OH)(4). Methods are described that can be used to determine
the conductivity salinity of lakes using the equations developed
for seawater. By combining these relationships with apparent molal
volume data, one can relate the PVT properties of the lake to those
of seawater.
