Taking in-stream nitrogen retention as a proxy for water purification, the study estimates the actual value of the contribution of sustainable water bodies to human activities.
According to the findings, a total of 50 to 80 million tonnes of nitrogen entered river basins in Europe between 1985 and 2005 (mainly from the agricultural sector), about 5 million tonnes of which ended in the river network. Additional 1.1 million tonnes of nitrogen entered the river network from industries and households. For almost all European countries, with the exception of Estonia, Finland, Norway and Sweden, in-stream nitrogen retention occurs at unsustainable levels, and their river ecosystems are progressively degrading as a result of nitrogen pressure.
The authors calculate that the full potential of a sustainable water purification ecosystem service in Europe is worth up to €31 billion per year.
The study gives the first ever physical and economic evaluation of water purification by ecosystems across Europe, based on the System of Environmental Economic Accounting – Experimental Ecosystem Accounts (SEEA-EEA). SEEA-EEA is an experimental tool developed by the United Nations, the European Commission, World Bank, OECD, and FAO.
The authors define the stocks and flows for individual ecosystem services in accounting terms in order to put a value on the regulating ecosystem service of water purification in Europe over 20 years, from 1985 to 2005. For each ecosystem service they define the stock as the capacity of ecosystems to sustainably generate services, and the flow as the sustainable and actual services that are delivered.
The role of nitrogen in water pollution
Nitrogen (N) is the leading cause of global water pollution and eutrophication of rivers and lakes, characterised by lack of space, sunlight and oxygen, as a result of excessive use of fertilisers and the related booming algae growth. Nitrogen enters the water system through runoff from agriculture and livestock activities (mineral fertilisers, manure applications) and industrial and household waste. It can be naturally reduced by processes occurring in the aquatic system (aquatic plant and microorganism uptake, sedimentation and denitrification), depending on the characteristics of the water and the organisms living within it, i.e. the ecological functioning and biodiversity of the system. On the other hand, aquatic biodiversity is threatened by excessive levels of nutrients.
In order to translate the outcomes obtained by the biophysical model into monetary terms, the study uses the cost of replacing natural water purification ecosystem services with constructed wetlands, which provide ecosystem functions (including nitrogen retention) similar to those delivered by aquatic ecosystems. Accounts are presented at both European and national scales for 34 countries in year 2000 values.
Ecosystem accounting
Healthy ecosystems provide provisioning (e.g. food production), regulating (e.g. water purification) and maintenance (e.g. pollination) services that societies benefit from, seemingly free of charge. The value of these services, which has yet to be precisely defined, would greatly help to inform and monitor the design and implementation of policies to protect ecosystems and biodiversity.
Ecosystem accounting is a relatively recent concept that aims to monitor the capacity of ecosystems to sustainably deliver the multiple services they naturally supply that benefit human wellbeing, and to make this information consistently readable together with the economic accounts reported in the System of National Accounts (SNA). SNA is an international standard for the systematic compilation and presentation of economic data and provides the information needed for economic analysis and policy-making, for example Gross Domestic Product, households consumption and saving, exports and imports. This will give policymakers a more complete perspective on the conception of adequate policies.
To develop a standard framework for integrated ecosystem and economic accounting, a way of measuring the potential or sustainable flow versus the actual flow of ecosystem services needs to be devised. The authors suggest that the concepts of the SEEA-EEA be operationalised using the concepts of capacity and of potential/sustainable and actual flows in integrated ecosystem and economic accounting systems.