Ecosystems play a crucial role in providing a favourable living environment and spaces for different species to interact while providing important resources and regulating key ecological processes that are influenced by human activities, natural events and climate change. The availability of sufficient natural resources such as water, food and energy depends on the quality of the ecosystem and its current capacity to provide services. Many studies indicate that 74% of the freshwater used by humans comes from healthy soils, which can absorb and store more green water than soils in poor ecosystem conditions. The importance of protecting ecosystems for the security of water, energy and food resources has been mentioned in many international frameworks, such as the 2012 Framework of the International Center for Integrated Mountain Development (ICIMOD), the 2013 Framework of the United Nations Economic Commission for Europe (UNECE) and the 2014 Framework of the United Nations Environment Program (UNEP). 

With the support of the COST Action Network on the Water-Energy-Food Nexus, we conducted a study to identify and quantify ecosystem elements in the Water-Energy-Food Ecosystem (WEFE) Nexus. We provided a systematic review of the current literature on this topic. We held an in-depth discussion and drew a variety of conclusions regarding the identification of ecosystem elements that require further research, protection and investment in the global water-energy-food security nexus. We also discussed and proposed the Ecosystem Sustainability Index (ESI) in the water-energy-food nexus, which will serve as a tool to assess the balance between the demand for WEF ecosystem services and the sustainability of ecosystems in countries around the world.  

Many ecosystem elements have been defined, especially in the areas of water, land, food, city, energy, ecosystem services, socio-economic variables and technical ecosystem components. In quantifying the ecosystem elements, we found that it is necessary to understand all sources of water, energy and food resources used by humans, whether they come from aquatic ecosystems, terrestrial ecosystems or atmospheric sources, and to understand their interdependencies and the factors that cause their interaction and interdependence. For example, for the ecosystem component of water, the main sources of water resources include precipitation, virtual water transfers, transboundary water and the reuse of wastewater. This water can then be stored in an ecosystem, which can be rivers or basins, groundwater, glaciers, wetlands or oceans.  

In our research, we find that researchers need to communicate more to policymakers about the need to explore the possibilities of green roofs, greenhouse cultivation, agri-PV and water harvesting, especially in developing and highly urbanized and populated countries, to reduce the ecological footprint of water, energy and food production. Many other ecosystem elements from seas, oceans, aquaculture ecosystems, melting glaciers, virtual water, urban ecosystems, technology ecosystems, and industries also need to be explored. 

For our soon-to-be-published Ecosystem Sustainability Index (ESI), we find very low ESI values in almost all countries. This is an indication of the major critical challenges in WEFE production, especially in the Middle East and North Africa (MENA), Oceania and Sub-Saharan Africa. Interestingly, the greatest difficulties were observed in the management of water-related ecosystems and not in energy and food elements. 

References 

1. Karabulut, A.A., A. Udias, and O. Vigiak, Assessing the policy scenarios for the Ecosystem Water Food Energy (EWFE) nexus in the Mediterranean region. Ecosystem Services, 2019. 35: p. 231-240.
2. De Strasser, L., et al., A Methodology to Assess the Water Energy Food Ecosystems Nexus in Transboundary River Basins. Water, 2016. 8(2): p. 59.
3. Karabulut, A.A., et al., A proposal for integration of the ecosystem-water-food-land-energy (EWFLE) nexus concept into life cycle assessment: A synthesis matrix system for food security. Journal of Cleaner Production, 2018. 172: p. 3874-3889.
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6. Rodríguez, B.M., The Water-Energy-Food nexus: trends, tradeoffs and implications for strategic energies. 2016, Universidad Complutense de Madrid Espagne. p. 1-202.