Monthly variations of entropy production in Lake Biwa

Abstract

Monthly entropy fluxes in the northern basin of Lake Biwa are calculated from the corresponding energy data of the lake. Net entropy flows into the lake are negative in all months. That is, the lake absorbs 'negative entropy' from its surroundings according to the terminology by Schrödinger: the lake is structured by its surroundings. From the net entropy flow and the change of entropy content, entropy production in the lake is estimated. Entropy production, which is positive in all months, is larger in summer and smaller in winter. The monthly entropy production (Sprod in units of MJ m-3 month-1 K-1) increases linearly with the monthly solar radiation energy absorbed by the lake (Esolar in units of MJ m-2 month-1); Sprod = a + bEsolar, a = 0.002 [MJ m-3 month-1 K-1], b = 0.60 × 10-4 [m-1 K-1]. The values (a, b) are holistic indices characterizing the lake from an entropy point of view. Another index (b′) similar to b is also introduced. Comparison of these indices in the northern basin of Lake Biwa (oligo-mesotrophic) with those in Lake Mendota (eutrophic) shows that processes of eutrophication or succession are accompanied by the increase of these entropy production indices. © 1990.