Application of Eco Exergy for the Health Assessment of Ecosystems

Eco-exergy has been applied several times as an ecosystem health indicator. A short overview of the results is presented below.

1. For ecosystem health assessment of eutrophied lakes. Increasing eutrophication means increasing biomass which explains that eco-exergy also increases with increasing eutrophication (see Figure 1).

2. For ecosystem health of coastal zones. It was found that eco-exergy is strongly correlated with several of E. P. Odum's attributes, which are able to distinguish between ecosystems at an early and at a mature stage.

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

4. For ecosystem health assessment of a series of Italian and Chinese lakes. It was found that eco-exergy correlates well with many other indices such as phytoplankton indices, zooplankton/phytoplankton ratio, and fish abundance, which are all used as health indicators.

5. For ecosystem health assessment of different farming systems. It was found that the more integrated the agricultural system is, the higher eco-exergy it has, although animal farms for instance chicken farms, pig farms, and aquacultures all have a high eco-exergy, while other holistic indicators, for instance, biodiversity is low for animal farms. Biodiversity together with eco-exergy can

Exergy vs. nutrients (mg l 1)

1200 1000 800

x LU

200 0

0 10 20 Nutrients

Figure 1 The results obtained by use of a eutrophication model with seven state variables are shown. The eco-exergy is plotted against the total inputs of nutrients (nitrogen + 7 x phosphorus, mg T1). The curve reflects the increase in biomass, which is less than proportional to the nutrient concentration. The slope of the plot is decreasing.

1989 1990 1991 1992 1993 1994 1995 1996 1997 1998

Time (year)

Figure 2 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).

therefore be applied to determine how close an agriculture system is to a natural system.

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 decreased eco-exergy.

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

From these examples, it has been possible to show that eco-exergy can be used as a holistic indicator to assess ecosystem health and that the application of eco-exergy as an indicator gives important information that can be utilized in environmental management.

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