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Lake Mendota

Lake Mendota

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

Figure 9.2 Monthly entropy production (Sprod) in Lake Mendota 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: January, February, December, November, March, October, September, April, August, May, June, July.

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

Figure 9.2 Monthly entropy production (Sprod) in Lake Mendota 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: January, February, December, November, March, October, September, April, August, May, June, July.

spatial unit. This fact introduces an artificial dependence on the water depth. Partially following Aoki's indices, a set of new ones (c, d, d') analogous to the a, b, and b' were proposed by Ludovisi (2003) on the basis of the relationship between the 6"prod and Qs. The index d' does not demonstrate any significant trend during the years 1988-1996 (Table 9.1).

A good linear correlation between the monthly entropy production (^prod) per surface unit of Lake Trasimeno and the monthly Qs has been found on a monthly time scale (Figure 9.3) and the regression coefficients of the curve (c, intercept and d, slope) can be compared with the analogous Aoki's indices a, b (Table 9.2).

The comparison of c, d (regression coefficients of the curve Figure 9.3 intercept and slope), d' (the ratio between the annual £ d and Qs) values (Table 9.2) calculated for Lake Mendota and the northern basin of Lake Biwa significantly distinguishes the eutrophic Lake Mendota from the oligotrophic Lake Biwa, and attributes to Lake Trasimeno higher values of d and d' than both other lakes.

Regarding Equation 9.1, the second term on the right-hand side is the entropy production dependent on solar radiation energy, which is caused by the conversion into heat of the solar energy absorbed by water, by dissolved organic matter, and by SS (negligible are the contributions from photosynthesis and light respiration of phytoplankton). The first term on the right-hand side of Equation 9.1 is the entropy production independent of solar radiation energy and it is caused by respiration of organisms in the lake.

For Lake Biwa and Lake Mendota total and solar energy-dependent entropy productions (per year, per MJ of absorbed solar radiation energy per m3 of the lake water), and

Year |

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