The MARS ‘cookbook’ for assessing freshwater multiple stresses and ecosystem services
Last week we wrote about the new MARS factsheets, which are designed to give brief, accessible and engaging introductions to some of the key freshwater topics covered by the project. This week, we introduce the first factsheet (pdf), which outlines the new ‘cookbook’ methodology for understanding how multiple stressors on freshwaters affect the ecosystem services they can provide to humans.
The cascade model: quantifying the capacity, flow and benefits of ecosystem services
Building on the expertise of project partners and insights from wider scientific and economic research, the MARS cookbook uses a cascade model methodology (Figure 1) that links the structure and function of an ecosystem to its service provision. This methodology includes the capacity of an ecosystem to provide a service (assessed using biophysical data), the actual flow of the services used by humans (assessed using socio-economic data), and finally the benefits that ecosystem services provide.
By assessing both the capacity of an ecosystem to provide services, and the actual use of these services, the MARS cookbook methodology allows assessments on the sustainability of ecosystem use to be made. The unsustainable use of ecosystem services may become an additional stressor the ecosystem’s health and status.
The MARS cookbook: four steps
The MARS cookbook methodology is split into four steps. The first is scoping, the process by which the aquatic ecosystem and ecosystem services of interest are selected and mapped, and the spatial and temporal scale of analysis are defined. The second step is to develop the assessment framework, through which multiple stressors and ecosystem services are linked in a stressor-ecological status-ecosystem service series. A key step here is to check whether the ecological indicators used (e.g. biodiversity, ecological status) capture the effects of the stressors, and can be linked to the ecosystem services of interest.
The third step is assessment, where biophysical indicators are organised according to the ecosystem’s capacity to deliver a service, its actual use, and the resulting human benefits provided. Indicators are organised in three categories: capacity (e.g. biomass of commercial fish species); flow (e.g. fish catch); and sustainability (e.g. % of catch within sustainable limits). Their ability to indicate ecosystem stress and / or service provision is quantified through the computer modelling of existing ecological data.
The fourth step is valuation, to identify the benefits provided by ecosystem services and aggregate them at three scales: water body, catchment and European continent. The valuations are undertaken at appropriate scales to support decision making in Integrated River Basin Management Plans and the Water Framework Directive. In the valuation process, the ecosystem service, benefit and value are separated, because a service (e.g. water purification) can provide numerous societal benefits depending on the location (e.g. drinking water; swimming areas). The economic value of the ecosystem services provided can then be valued through revealed and stated preference methodologies, and cost-based and benefit transfer approaches.
Case study: applying the MARS cookbook to Welsh river catchments
To give an example of the methodology in action, we can apply it to water purification ecosystem services provided by rivers in Wales studied by MARS led by Steve Ormerod and Isabelle Durance at Cardiff University. The first analysis step defines the geographical area, the ecosystem service and the scale of analysis (amount of purification in the catchment per year). The second framework step links the pressures faced by the catchment (e.g nutrient pollution) to the ecosystem status and service provision.
The third biophysical assessment step analyses the ecological structure and processes (e.g. an analysis of the nutrient cycle) and selects ecosystem service indicators (e.g. nutrient retention levels). In step four, the economic benefits of the service are identified (e.g. free, clean water), and appropriately valued (e.g. unit cost of purification by alternative process). This value is then aggregated to the scale of interest (e.g. the catchment) to give an overall economic value of the water purification service provided by the ecosystem.
You can read and download all the MARS factsheets on the project website here.