APPLICATION OF ECOSYSTEM ENERGETIC INDICATORS FOR THE VALUATION OF ECOSYSTEM SERVICES AND HEALTH

Abstract

Ecosystems services are benefits that humans receive from ecosystem functions. Ecosystem health is a term that is commonly used in the literature to describe the state of an ecosystem. Ecologists and economists have stated that ecosystem health is important for the preservation and maintenance of ecosystem services essential to human society. Various methods and means have been proposed to assess ecosystem services and the economic values they provide to society, in relation to ecosystem health, by developing reliable holistic methods which assess health and services. Energy is a common denominator in all processes and measures of activity and if an ecosystem is distressed, it will not efficiently convert energy to work. In this study, energy indices were used to evaluate ecosystem health in relation to the ecosystem service of metals retention (iron and zinc) in wetlands. These indices included emergy (which evaluates the energy memory of the system), eco-exergy (a concept adapted to ecology to determine the efficiency of the work within the ecosystem) and ascendency (the diversity of the networks acting as an indicator of activity and organization within the system). Six wetlands, three volunteer and three treatment, which were all receiving metals contaminated water, were modeled using the STELLA dynamic simulation programming. A total system model was developed with hydrologic, ecosystem, and biogeochemical (iron and zinc retention) submodels. Field data from these systems were used to calibrate and validate each model. These models were evaluated for relationships between the indices, ecosystem service of metals retention, and to assess how the different systems (volunteer and treatment wetlands) vary between these indices. The results from this study suggest that there are relationships between ecosystem services and ecosystem health indices including iron retention and emergy, relative ascendency, specific exergy and the exergy/emergy ratio. In the case of zinc retention, there was a relationship with all indices excluding the exergy indices. Ascendency was a poor indicator of iron retention but it was also discovered that more zinc is retained in the higher ascendant systems. The systems with higher emergy had more metals retention suggesting that a system with greater emergy can provide a greater ecosystem service. This trend did not hold true with exergy and ascendency, meaning that as these indices increased, the service of metal retention decreased. Using exergy and ascendency indicators to determine a system’s potential to provide a service was less clear from the results. These six models, for both treatment and volunteer wetland systems, suggest that emergy is the only indicator that determines the potential ability of the system to provide a service.