Measuring natural capital value and ecological complexity of lake ecosystems

Abstract

Healthy ecosystems are capable of maintaining their structures and functions, ensuring the generation and maintenance of natural capital stocks delivering ecosystem services flows vital for human well-being. The development of ecosystems can be investigated by using different ecological goal functions. Among them, emergy and eco-exergy can be used to unfold the role of matter and energy flow exchanges in the functioning of ecological systems. In this paper, the emergy and eco-exergy accounting methods were integrated to investigate three forest lake ecosystems characterized by a different trophism (oligotrophic, mesotrophic, and eutrophic) and located in the Tuchola Forest UNESCO-MAB Biosphere Reserve (Northern Poland). In particular, emergy was used to account for the work of nature invested to generate natural capital stocks, while eco-exergy was used to characterize the development stage of lake ecosystems reflecting their trophic and health state. The eutrophic lake showed the highest emergy investment (4.36∙1012 sej m−2) for the generation of natural capital stocks, mainly due to the high convergence of nutrient flows. The eutrophic lake also showed the highest value of eco-exergy density (1.38∙106 KJ m−2) mainly due to the high ß value of macrophyte and aquatic birds. Finally, the eco-exergy / emergy ratio was calculated to assess the efficiency of the three lake ecosystems. The mesotrophic lake showed the highest value of the ratio (1.43∙10−3 J sej-1), highlighting a better efficiency in maintaining and developing ecosystem structure and organization. Overall, the outcomes of this study were consistent with the different trophism of the investigated lakes, confirming how external driving forces can orient the development and complexity of lake ecosystems. In conclusion, integrated assessments adopting an ecosystem and holistic perspective can result in a promising approach to investigate lake ecosystems worldwide, providing useful scientific information to policy makers committed to ensure the sustainable management of surface water ecosystems.