Application of Eco Exergy for the Health Assessment of Ecosystems

Specific eco-exergy has been applied on line with co-exergy several times as ecosystem health indicator. A short overview of the results is presented in the following:

Specific exergy vs. nutrients (mg l 1)

Specific exergy vs. nutrients (mg l 1)

Figure 1 The results are obtained by use of a eutrophication model with 7 state variables are shown. The specific eco-exergy is plotted versus the total inputs of nutrients (nitrogen and 7.phosphorus, mg T1). The curve reflects the increase in fish biomass up to a low nutrient concentration, followed by a decreasing specific eco-exergy due to increase of the phytoplankton biomass.

Figure 1 The results are obtained by use of a eutrophication model with 7 state variables are shown. The specific eco-exergy is plotted versus the total inputs of nutrients (nitrogen and 7.phosphorus, mg T1). The curve reflects the increase in fish biomass up to a low nutrient concentration, followed by a decreasing specific eco-exergy due to increase of the phytoplankton biomass.

Figure 2 Specific eco-exergy mean annual values: present scenario (continuous line), removal of Ulva, optimal strategy from costs-benefits point of view (dotted line) and nutrients load reduction from watershed (dashed line).

1. For ecosystem health assessment of eutrophied lakes. Increasing eutrophication means increasing phytoplankton biomass. Therefore, the specific eco-exergy will generally decrease with the increasing eutrophication. On the other hand, a very oligotrophic lake may contain insufficient food to maintain a reasonable large fish population. Specific eco-exergy has therefore a maximum at a low nutrient concentration, corresponding to about 0.01 mgPT1 ifP is the limited nutrient (see Figure 1).

2. For ecosystem health of coastal zones. It was found that specific eco-exergy is strongly correlated with several of E. P. Odum's attributes.

3. For ecosystem health assessment of Mondego Estuary in Portugal. It was found that specific eco-exergy is a good holistic indicator; but it is not sufficient to apply only eco-exergy and specific eco-exergy. The indicator should be supplemented by other indicators such as biodiversity to give a more complete holistic picture of the ecosystem health.

4. For ecosystem health assessment of a series of Italian and Chinese lakes. It was found that specific eco-exergy is well correlated with many other indices such as zoo-plankton/phytoplankton ratio, zooplankton abundance, and fish abundance.

5. For ecosystem health assessment of different farming systems. It was found that the more integrated the agricultural system is, the higher the specific eco-exergy it has, although domestic animal farms, for instance, chicken farms, pig farms, and aquacultures, all have a high specific eco-exergy, while other holistic indicators for instance biodiversity are low for animal farms. The specific eco-exergy is of course maintained very high in domestic animal farms at a very high energy cost, which makes them not sustainable.

6. For ecosystem health assessment in situations where contamination by a toxic substance has taken place. It was found, not surprisingly, that toxic substance contamination means decreasing specific eco-exergy.

7. For the ecosystem health assessment for European lagoons. It was found that the presence of Ulva, that is characteristic for eutrophied lagoons, means low specific eco-exergy. Removal of Ulva implies a higher clam production and therefore higher specific eco-exergy, as shown in Figure 2. Wastewater treatment with nutrient removal means also higher specific eco-exergy due to the lower Ulva production. It is also shown in Figure 2.

From these examples, it has been possible to show that specific eco-exergy can be used as holistic indicator to assess the ecosystem health and that the application of specific eco-exergy as indicator gives important information that can be utilized in environmental management, although more indicators are needed to get a more complete holistic picture of the ecosystem health of the ecosystem.

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