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2c. Key questions and general approach

Within TIDE, an approach was developed to tackle a number of key questions concerning ecosystem services in estuaries.

• What are the most important ecosystem services for these estuaries?
• What is the demand for services in each estuary?
• How does this demand vary over time and along the salinity gradient?
• How do habitats differ in supply of ecosystem services?
• What is the spatial variation in that supply?
• How did morphological changes affect ES supply?
• What are potential trade-offs or synergies in supply of ES?
• How can ES be used in habitat conservation/restoration/development?
• How can ES be used to assess estuarine management measures?

Tackling these key questions requires a broad ecosystem service assessment, taking into account the four estuaries entirely and including a broad bundle of services.

Particularly in estuaries, ecosystem functioning is inherently complex, there are many data gaps and management decisions affect a multitude of societal groups, (Granek et al 2010). Also, as pointed out by Barbier et al (2011), many of the important estuarine benefits have not been estimated reliably, and even for those services that have been valued, only a few dependable studies have been conducted.
A service is supplied by an intertwined web of structures and processes, finally supported/insured by the resilience of the entire ecosystem. Quantifying the supply of all services requires delineation of the all processes and structures involved and linking all these to measured or measurable units per service, which was impossible within the scope of TIDE.
Therefore, the ecosystem service assessment in TIDE aimed at providing a broad overview for inter-estuarine comparison and general conclusions on NW European estuaries in general, this meant that the ecological complexity and biophysical supply had to be captured and evaluated in a more generally applicable way. Rather than focusing on functional description and quantifications of detailed fragments of this whole picture, the choice was made to involve about 30 professional estuarine experts in obtaining a more general, but complete semi-qualitative overview to tackle the research questions.

Involving professionals in the ecosystem service assessment allows to increase the awareness of ecosystem services in estuaries, and is in line with the development of an ecosystem based estuarine management (e.g. Granek et al 2010). Ideally, technical information from natural and social scientists, experiential knowledge of people familiar with the ecosystem, and information on the benefits that different individuals and groups receive from goods and services provided by the ecosystem would flow to policy makers and managers to help guide policy formulation and implementation (Granek et al 2010).

The approach of this study:

• Focuses on comparing a broad bundle of services rather than on the detailed assessment of a few single services, well-known supply functions or case studies.
• Is based on experiential knowledge of people familiar with the system to provide a broad assessment in semi-quantitative units rather than quantitative data using diverse units and suffering from knowledge gaps.
• Involves professional experts from the TIDE regional working groups, conveying the importance and potential of ecosystem service based management to professionals active in estuarine management.

The work within the TIDE project provides a broad overview of ecosystem service demand and supply in the four TIDE estuaries, but it is only the first step towards capturing the value of ecosystem services (TEEB 2010). This capturing can be obtained by seeking solutions to overcome the current undervaluation of many ES, using economically informed policy instruments, which are based on local quantifications and assessments. These should take into account biophysical and ecological underpinning as well as social and economic values of the specific local context.

The approach for this study was as follows:
Firstly, the important ecosystem services for TIDE estuaries are distinguished from a “longlist” of estuarine services, and the variation in demand (“societal importance”) is assessed along estuaries, salinity zones and for historical, present and future time steps.
Secondly, the “ecosystem service supply” results are presented. ES supply is compared for the different along the estuaries and basic underlying processes and structures are pointed out. A historical ES supply evolution through habitat change is estimated. An indicator for trade-off risk generated by differential supply of ES by habitats is discussed. In the Measures report, (see report “Management measure analysis and comparison”), the expected effect of estuarine management measures on ES supply was estimated. In our report, the synergies in ES supplies (which ES supplies are increasing together) occurring from these measures are discussed.
Finally, key questions are answered and recommendations for research, policy and practice are provided in the conclusion section.

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