Calculation of indices. ICM-LM trophic index and Xxxxxxxxx index Taxon-specific trophic rank scores, also known as Intercalibration Metric scores and referred to in this report as ICM-LM (Intercalibration Common Metric for Lake Macrophytes) scores, were supplied by Xxxxx Xxxxxx, of the University of Stirling, UK. These scores are in use by the Water Framework Directive Intercalibration Exercise as a means of comparing lake macrophyte condition across Member States, where assessment methods are not consistent. For submerged aquatic plant taxa, scores were derived using methods similar to those used by UKTAG (2009), and Xxxx and Xxxxxx (2010). In general, scores were calculated by rescaling the median of the logarithms of the concentration of total phosphorus concentrations in lakes across Europe in which the taxon is found. These scores are available in the WISER Deliverable 3.2-3: „Report on the most suitable lake macrophyte based assessment methods for impacts of eutrophication abnd water level fluctuations” (Xxxxxx et al., 2011). Scores are combined across sites to form a metric, either as a simple mean, or by using some measure of abundance to weight the mean (see formula below). The site metric is intended to be representative of the nutrient status of the nutrient status of the water, as experienced by the macrophyte flora. The ICM-LM scores were only available for real hydrophytes, as this metric was only ever designed to be used with submerged taxa. Xxxxxxxxx’x Nitrogen values for soil fertility (scores from 1 to 9; Xxxxxxxxx et al., 1991) were compiled for all taxa in the dataset in order to test the use of a metric with and without helophytes. We supplemented the original values with British values where original values were missing (Xxxx et al., 1999). Even with these supplements, there were 13 taxa, notably charophytes, for which no score was available. Scores for the missing taxa were derived by making a regression analysis of the ICM-LM and Xxxxxxxxx values for all species with both values and used the regression line to fill in the blanks for charophytes. These Xxxxxxxxx values were then used to calculate an average Xxxxxxxxx-N metric per lake. There were 16 taxa for which neither Xxxxxxxxx nor ICM-LM scores were available, and these were excluded from further analyses. In this study, ICM-LM and Xxxxxxxxx metrics were calculated from scores both as simple averages of the scores of the taxa found (unweighted), or as weighted averages, where M is the metric, Si is the...
