Entropy production indices for waterbodies

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The quantities necessary to estimate entropy production (see Aoki, 1989, 1990) can be obtained from experimentally observed data. Entropy production plotted against adsorbed solar radiation energy for Lake Biwa and Lake Mendota are shown in Figures 9.1 and 9.2, respectively. The monthly entropy production per unit of volume (Sp) of the Trasimeno Lake was calculated by simple division of entropy production per surface units (Sprod) by monthly mean values of water depth; the annual values were calculated as the sum of monthly values and are given in Table 9.1.

Entropy production is expressed in MJm 2 month1 K_1, while solar radiation in MJ m2 month1. According to Aoki, entropy production in month j (denoted as (A,. S)) is a linear function of the absorbed solar radiation energy in month j (denoted as Q):

According to Ludovisi (2003) the definition of the b index as a ratio of Sp (in units MJm"3 year^K"1) and the solar energy absorbed by the lake surface (Qs) (MJm"2peryear K"1) in a year is not proper, because entropy and energy flows do not refer to the same

Lake Biwa (northern basin)

Lake Biwa (northern basin)

200 400

Absorbed solar energy/[MJ m-2 month-1]

Figure 9.1 Monthly entropy production (Sprod) in the northern basin of Lake Biwa per m2 of the lake surface plotted against monthly solar radiation energy absorbed by 1 m2 of the lake surface (Qs). The circles represent, from left to right, the months: December, January, November, February, October, September, March, April, June, July, August, May.

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