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9a. Key question answers

• What are the key ES for the TIDE estuaries and what is the demand for these services in the estuary?
  20 key ecosystem services were determined based on a broad demand survey among regional working group experts of the TIDE estuaries. These were the subject of further investigation.
  ES demand in the four estuaries is very similar, due to the fact that these estuaries are both ecological as socio-economic very similar. A remarkable difference is the lower demand for sedimentation-erosion regulation by biological mediation, extreme water current reduction and landscape maintenance services in the Humber estuary, due to its naturally extreme turbidities and fluid mud conditions, combined with lower dredging requirements compared to the other estuaries.
  Assessing the importance of a long list of ES by performing a survey is an efficient method to determine focal ES and involve a broad range of stakeholders in applying the ES concept. However, local particularities should be addressed when implementing estuarine management projects, and surveys should be thoroughly checked for reliability.
  
  
• How does ES demand vary in time and along the salinity gradient?
  The demand survey included a spatio-temporal component that covered this aspect. Demand was only slightly variable since only ES linked to specific features of freshwater zones have a higher demand there (e.g. flood control, wave reduction), while future demand was higher for services mainly related to climate change (e.g. protection from flooding, carbon sequestration). Again, local particularities should be addressed when implementing projects, and surveys should be thoroughly checked for reliability.
  
  
• How do habitats differ in ES supply?
  An expert survey resulted in a semi-quantitative estuarine zone specific ES-supply score for estuarine habitats. Generally all habitats are important to very important, especially the marsh and intertidal mudflat habitats. Steep intertidal habitats have the lowest importance.
  The statistical reliability of the survey method is acceptable, and the matrix can be applied for the mapping of ES in similar estuaries. However, it is advisable to perform the survey method in the local context to increase validity of the data and participation of local experts. Differential supply of ES by habitats means that trade-offs between ES supplies occur when habitat surfaces change. Mechanistic and empirical research is needed to quantify these trade-offs.
  
  
• What is the spatial variation and historical changes in ES supply?
  The scores for supply of ES differ only slightly among the zones. However, habitat ratios can differ through time or among zones and this influences the estimated total supply. A rough historical image can be derived by hind-casting supply and demand functions and using historical habitat surfaces. This analysis reveals a clear decrease in service supply over time for the Scheldt, even affecting provision services related to direct use of the estuary. In the Weser, the decrease was less clear as the habitat shifts over the available time period were less pronounced.
  
  
• What are potential trade-offs or synergies in supply of ES?
  As ecosystem services are delivered by different (combinations of) habitats, trade-offs and synergies are exhibited. Provisioning services and supporting services exhibit most potential trade-offs, but many potential synergies among regulating services and with supporting services are present. On the other hand, some habitats (and combinations) deliver bundles of related services. The risk of exhibiting trade-offs or synergies can be directly derived from the supply scores. As expected, these risks coincided well with the inventory of direct use conflicts occurring in the TIDE estuaries (see report “Conflict Matrices: Comparisons For TIDE Es tuaries”).
  
  
• How can the ES approach be used in conservation / restoration / development?
  On the short term, the demonstration (by mapping, valuation etc.) of socio-economic importance of regulating and supporting services can raise awareness, increase legitimacy and improve existing conservation and development of natural habitats.
  On the long run, ES can provide more integrated visions and policies on natural resource use and protection, as described in detail in section 6.4.
  
  
• How can ES be used to assess estuarine management measures?
  In the measures work package (see report “Management measure analysis and comparison”) and the valuation study (Liekens et al 2013), first steps to include an ecosystem service assessment are taken based on the ES analysis within TIDE. These assessments aim to widen the scope of measure assessments, from strictly technical or strictly red list species approaches to a more integrative assessment directed towards socio-economic effects. It is essential to focus on tangible, concrete projects and increase data availability to perform any quantitative ES approach.
  Not only could cost-effectiveness of measures be determined, but also the ecological sustainability and social fairness could be evaluated (see 9.2.2).