Calculating density of water in geochemical lake stratification models

Bertram Boehrer, Peter Herzsprung, Martin Schultze, and Frank. J. Millero

Limnol. Oceanogr. Methods 8:567-574 (2010) | DOI: 10.4319/lom.2010.8.0567

ABSTRACT: To model chemically stratified lakes numerically, chemical transformations must be reflected in the density function. In this contribution, partial molal volumes are used to calculate density from the chemical composition of lake water. Such values have been evaluated for cations and anions separately, to facilitate an easy implementation into geochemical stratification models for lakes. Coefficients for temperature dependence and variation for higher ionic strengths were evaluated from previously published data. An algorithm RHOMV to calculate density with a second order approximation for temperature dependence and ionic strength dependence is proposed. The accuracy is tested for seawater composition. We conclude that this approach delivers a representation of density based on the actual chemical composition of the lake water, which is accurate enough for most limnological purposes. The implementation of RHOMV into geochemical stratification models facilitates the numerical tackling of pressing questions, such as meromixis or double diffusive features or altered circulation patterns of lakes due to changing climate or change of use.