Status evaluation is carried out against scientifically based and commonly agreed sub-basin specific threshold values, i.e. the concentration that should not be exceeded (Thresholds and Status evaluation figure 1).
Thresholds and Status evaluation figure 1. Schematic representation of the threshold value applied in the chlorophyll-a core indicator, the threshold values are assessment unit specific (see Thresholds and Status evaluation table 1).
Some of the open-sea indicator threshold values are based on the results obtained in the TARGREV project (HELCOM 2013), also taking advantage of the work carried out during the EUTRO PRO process (HELCOM 2009) and national work for EU WFD implementation. The TARGREV values were derived as geometrical means, thus bearing close resemblance to median values (J. Carstensen, pers. comm.). The final threshold values were set through an expert evaluation process done during intersessional activity to develop the core eutrophication indicators (HELCOM CORE EUTRO), and the threshold value were adopted by the HELCOM Heads of Delegations 39/2012.
Thresholds and Status evaluation table 1. Assessment unit specific threshold values for the chlorophyll-a core indicator.