## 4 Discussion  
Ecosystem service assessment approaches that compare different ecosystems spatially or compare different ecosystem states in time within one area have several advantages: they are flexible with respect to the participants and can be carried out by single experts, expert groups or stakeholder groups, they require only limited knowledge about the background and technical aspects of ecosystem service assessments, and they can be carried out within a relatively short time of days to weeks [19; 20; 21; 32]. However, they require a sound preparation, an experienced moderator and well-developed scenarios. Scenarios in this respect refer to a detailed description and visualization of what shall be compared. These ecosystem service assessments increase the awareness of the consequences of ecosystem changes from an anthropocentric perspective and provide insight into the complexity and interrelationships of ecosystem processes, structures and functions. However, they do not provide reliable crisp data that can be expressed in monetary values. They only reflect perceived qualitative changes largely based on opinions. Further, they are case-specific and hardly allow generalizations or a transfer to other regions or topics. During our post-assessment discussions with the participants, several weaknesses were pointed out, namely that the given scores for ecosystem service changes are subjective and influenced by the scenario visualizations, the scenario presentations, the moderator and, of course, by the composition, background and knowledge of the involved participants. Theses weaknesses bear the risk of manipulation. This limits the value of these ecosystem service assessments for applications within spatial planning and climate change adaptation processes, because both require reliable data. The assessment of future scenarios, compared to the present situation, is a special challenge because the visualizations of future states are based on projections and expected changes. The uncertainties increase the further the scenario is located in the future. Further, our visualizations represent only one possible future state. Possible future management measures that could modify the environment and cause a different state of the environment are not taken into account. The German proactive planning system adds uncertainty to future projections. For example, it can be expected that settlement areas with high touristic values, such as Ahrenshoop, will continue to be protected from flooding because of societal pressure. As a consequence, the situation in 2070 will, very likely, look differently than shown in our scenario 2070, which assumes flooding of the lowlands. As a consequence, our future scenarios may lead to wrong expectations and perceptions among participants. With respect to the Ahrenshoop scenario 2070, the hypothetical and awareness-rising character and the limited value for concrete spatial planning is obvious. With respect to Huttelmoor 2040, this is different, as the future scenario is only 20 years ahead. Model projections for the morphometric development of the Huttelmoor and the coastline carried out around the year 2000 suggested a dune breach and partial moor flooding even before 2020 and a strong coastline retreat for the year 2040 [38]. As of today, a lasting dune breach has not taken place and a strong coastline retreat until 2040 seems unlikely. Ecologically, the Huttelmoor itself did not, as expected in the beginning of the measure implementation, develop into a diverse habitat with a high number of species. Today, in reality, it is dominated by freshwater, large reed areas and a limited number of well-adapted species. The deviating biological development results in modified biogeochemical processes, gas emissions and peat development [39]. Our 2020 scenario reflects the real situation today. However, had the future scenarios been developed 20 years ago, they would look different, with consequences for the ecosystem service assessments.