# Assessment of Ecosystem Services across the Land-Sea Interface in Baltic Case Studies
## 2 Materials and Methods
### Case Study Sites  
Three Baltic CSS were assessed in this study. Their location in the Baltic Sea Region and main CLC types are shown in Figure 1.  
The Schlei is located in northern Germany and represents the land-dominated CSS. It comprises the 43 km long water inlet Schlei with a surface area of 54 km\({}^{2}\) and its adjacent municipalities with a total population of 60,000 inhabitants which are concentrated mainly in the cities Schleswig and Kappeln (2018). The landscape was formed during the Weichselian glaciation and is characterized by a gently hilly landscape ([PERSON], 2018). The Schlei is a brackish and shallow water body with a strong salinity variation range between a few to 20 PSU ([PERSON], 2018) and an average depth of 2.5 to 3 m ([PERSON], 2018). The CSS Schlei has total area of 398 km\({}^{2}\), which is dominated by agricultural areas (61%). Other land-cover types include artificial surfaces  
Figure 1: Location of the three case study sites (CSS) Schlei (land-dominated system), Greifswald Bay (balanced system) and Curonian Lagoon (sea-dominated system) (from west to east) in the Baltic Sea. CSS maps show the dominating land cover types. (9%), and forests and semi-natural areas make up 7%. 23% of the area is covered by water, which includes the water bodies of the Schlei and adjacent water bodies of the Baltic Sea. The Schlei region is a popular tourist destination with around 82,700 overnight stays in 2019 [43] and many additional day visitors. Popular tourism activities in the area include hiking, cycling, sailing, canoeing, and angling. Another tourist attraction is the Viking Age trading site Haithabu close to Schleswig, which was included in the World Heritage list in May 2018. The CSS Greifswald Bay is located in the north east of Germany and represents the balanced system. The CCS has a total area of 1139 km\({}^{2}\), of which 66% (748 km\({}^{2}\)) are water bodies. The marine area includes Greifswald Bay with a total surface area of 514 km\({}^{2}\) and adjacent water bodies. Greifswald Bay is shallow with a mean depth of 5.8 m and a salinity range between 5 and 7 PSU [44]. The terrestrial area is dominated by agricultural land (22% of the total CCS area). Artificial areas make up 4% of the area and include the Hanseatic city of Greifswald and several smaller towns and seaside resorts. The northern part of the CSS is situated on the island of Rugen and characterized by rolling hills and heathland. In contrast, the southern part of the CSS is characterized by lowlands and includes long sandy beaches, but also wetland areas. Forests and semi natural areas make up 6% of the total CSS area and wetlands 2%. The CSS has a total population of around 84,000 inhabitants, which are mainly concentrated in Greifswald (ca. 59,000) and Putbus (ca. 4400) [45]. Tourism is the main economic driver in the area, with around 460,000 tourists and 2.5 mio. overnight stays, which are mostly concentrated in the municipalities at the outer coast, such as Baabe, Gohren, and Monchgut (ca. 240,000 tourists and 1,4 mio. overnight stays). Popular tourism activities include water sports like sailing and (kite-) surfing. As the main spawning ground for Baltic Herring, Greifswald Bay [46] is also a popular destination for angling tourists, as well as an important catch area for inland and coastal fisheries. The CSS Curonian Lagoon represents the sea-dominated system in this study and is located in the most western part of Lithuania. It comprises Neringa municipality on the Curonian Spit (a narrow peninsula) and adjacent water bodies, that is the Curonian lagoon on the eastern side and the Baltic Sea on the western side. It has a total area of 1590 km\({}^{2}\), of which 93% is water bodies. The terrestrial part of the CCS is dominated by forest and semi natural areas (mostly sea dunes and coniferous forest) which comprise 6% of the total CSS area. Artificial areas (0.5%), agricultural land, and wetlands can also be found in the study area, but are spatially negligible.