Figure 6.5 Log-log plot of the ratio of nitrogen to phosphorus turnover rates, R, at maximum exergy versus the logarithm of the nitrogen/phosphorus ratio, log N/P. The plot is consistent with Vollenweider (1975).

resource is non-limiting. A modeling study (Jorgensen, 2002) indicated that free-energy storage increases when an abundant resource recycles faster. Figure 6.5 shows such results for a lake eutrophication model. The ratio, R, of nitrogen (N) to phosphorus (P) cycling which gives the highest exergy is plotted in a logarithmic scale versus log (N/P). The plot in Figure 6.5 is also consistent with empirical results (Vollenweider, 1975). Of course, one cannot "inductively test" anything with a model, but the indications and correspondence with data do tend to support in a general way the exergy storage hypothesis. The cycling ratio giving the highest ascendency is also correlated similarly to the N/P ratio (Ulanowicz, personal communication). In the light of the close relationship between exergy and ascendency this result is not surprising (see above, Jorgensen, 1995; Ulanowicz et al., 2006).

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