Ecosystem Service Assessment of TIDE Estuaries

The main inter-estuarine variations are caused by lower importance scoring of all cultural and some regulating services in the Humber, and lower scoring of ‘landscape maintenance’ in the Weser. In these analysis, ‘unknown’ scores are added as zero, instead of leaving them out of the average. This assumes very low demand when demand is unknown by the regional working group. This occurred for very few services.
The lower scoring of three regulating services (biological mediation of sedimentation and erosion, water current reduction and landscape maintenance) in the Humber could reflect the exceptional features of this estuary compared to the others: extremely high turbidities, almost ‘fluid mud’ conditions on tidal flats and lack of rigid subtidal structures and marsh habitats (ref “Interestuarine comparison: hydro- geomorphology”) .

Salinity zones were defined in four zones: freshwater zone, oligohaline, mesohaline and polyhaline zone. This allowed to obtain a similar, comparable zonation over all four TIDE estuaries. However, this also reduced the detail of estuaries with more elaborate zonation schemes of the report “zonation of the TIDE estuaries” (eg the Elbe contains three freshwater zones and the Scheldt 10 zones), which were averaged within the four comparable zones. In some single cases the merge of the freshwater zones can lead to results which differ from the result obtained by the expert group; this will be indicated at the particular cases.
Variations between salinity zones are generally very low. Only about four services exert small variations in demand along the salinity gradient. In these cases, the fresh and oligohaline zones separate from the meso- and polyhaline zones. Three of these higher demands can be linked to the specific features of the upper reaches of estuaries: higher flood risk, vulnerability for high turbidities induced by tidal pumping and wave erosion of habitats and infrastructures in confined upper reaches.