Assessment of European streams with diatoms, macrophytes ...

1764 D. Hering et al.
streams/eutrophication; 86 sites for lowland streams/
land use; 78 sites for lowland streams/hydromorphology
(reach scale); 70 sites for lowland streams/
hydromorphology (microhabitat scale); 98 sites for
lowland streams/general degradation.
Metric calculation and selection
A large number of candidate metrics was calculated
for each of the four organism groups. Correlation
was used to reduce the number of candidate metrics
to a similar number for each organism group. If
metric pairs had a Spearman Rank Correlation
coefficient of greater than 0.8 or less than )0.8, one
of the two metrics was excluded from further
analyses (the metric with the lower average Spearman
Rank Correlation coefficient to the other candidate
metrics was kept). Removal of redundant
metrics resulted in 25 to 32 metrics per organism
group that were selected for assessing the response
of the four organism groups to the stress gradients
(Table 4).
Correlation analysis
Spearman Rank Correlation of metrics and the four
PC stressor gradients was used to evaluate the
response of the four organism groups to stress. If
the first PCA axis of a stressor gradient analysis had
an eigenvalue