Interim report of the HELCOM CORESET project

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When a reference data set cannot be defi ned
If a reference data set cannot be identifi ed based on the above criteria, trends in the available data are
used to assess the environmental status. Prior to the assessment, the available data (not including the assessment
period) in combination with other relevant information, is judged by expert opinion as either
representing GES or sub-GES conditions.
Criteria for GES within the assessment period
In case of reference data set representing GES conditions
In cases when a reference data set representing GES is used, for GES the median value of the indicator during
the assessment period must be above the 5th (or within the 5th and the 95th, depending on the index)
percentile of the median distribution of the reference data set. The trend within the assessment period is
given as supplementary information.
If a reference data set cannot be identifi ed, the long term trend in the whole monitoring data set is analyzed.
For GES, the slope must not be signifi cantly negative (or positive depending on the indicator).
In case of reference data set representing Sub-GES conditions
In cases when a reference data set for sub-GES is used, for GES the median value of the indicator during the
assessment period must be above the 99th percentile of the median distribution of the reference data set.
If a reference data set cannot be identifi ed, the long-term trend in the whole monitoring data set is analyzed.
For GES, the slope must be signifi cantly positive (or negative depending on the indicator).
Proposed GES/subGES boundaries
As described in section 2, the anticipated GES/subGES boundaries are data dependent and will be different
for different monitoring areas and methods. The suggested approach for defi ning the GES boundary was
described above. In Figure 2.18, examples for GES determination in one area are provided for the indicators
described earlier in this document.
Kvädöfjärden
Species Demographic Index Community Trophic Index
16 17 18 19 20
Mean Length of Perch
1990 1995 2000 2005
SUB-
GES
SUB-
3.0 3.2 3.4 3.6 3.8 4.0
Mean Trophic Level
1990 1995 2000 2005
SUB-
GES
SUB-