Water Framework Directive Marine Plants Task Team Tools Paper ...

The final metric system works on a sliding scale to enable an accurate EQR value to
be calculated for each of the different parameters, an average of these values is then
used to establish the final classification status. For the calculation of the EQR value
for each of the parameters this requires two slightly different calculations. For species
richness, proportion of red species and the ESG ratio, all of which increase in value
with increasing EQR, use the following equation:
Class Range = CR Class Width = CW
EQR Band Range = BR EQR Band width = BW
EQR = {(value – lower CR)/(CW) x EQR BW} + lower EQR BR
Example using a value for species richness: 34 – this lies between 20­35 and with an
EQR between 0.4­0.6) therefore:
Score = {(34 – 20)/15 x 0.2} + 0.4
Score = 0.186 + 0.4 = 0.587
For the proportion of green species, proportion of opportunist species and shore
description, all of which decrease in value with increasing EQR, use the following
equation:
Class Range = CR Class Width = CW
EQR Band Range = BR EQR Band width = BW
EQR = Upper EQR BR ­ {(value – lower CR)/(CW) x EQR BW}
Example using a value for the proportion of greens: 29.4 – this lies between 25­30 and
with an EQR between 0.6­0.8)
Score = 0.8 ­ {(29.4 – 25)/5 x 0.2}
Score = 0.8 – 0.176 = 0.624
This scoring system was then applied to the full data set to ensure the calculated
quality status matched the predicted quality status. This is necessary to ensure a level
of confidence in the metric.