Report on Harmonisation of freshwater biological methods

70. Nearly 50 percent of macroinvertebrate methods record the abundance in numberof individuals per area. In fact, purely quantitative data require area-related samplingprocedures by means of quadrate samplers, grabs or similar devices. Since theserequirements are only met by a few schemes, abundance statements based on semiquantitativehand-net sampling are in most cases of restricted reliability but they arecheap, practical and effective.71. There are different abundance classification schemes in use, the most commonare: i) 3-class scheme, derived from Pantle and Buck (1955) applying the SaprobicIndex; ii) 5-class scheme, there two systems in Europe: one based on a logarithmicscale of organisms’ abundance (Murray-Bligh, 1999) and the Quality Rating System;iii) 7-classes scheme, established by Knöpp (1955) this classification has beenincluded in the German standard DIN 38 410 (1990, 2003): Determination ofSaprobic Index of Running Waters.72. Assessment methods operating on the basis of presence/absence data ofmacroinvertebrate taxa do not necessarily need to record taxa abundance. Many bioticindices like I.B.G.N., IBE, BMWP-ASPT or BBI are not designed to includeabundance information. Their outputs may be biased by single organisms drifting intothe sample from upstream reaches. Therefore, the individual systems prescribe toinclude only taxa that exceed a certain threshold of abundance to avoid false results.73. Seven different categories of assessment methods can be distinguished among themethods currently used according to the type and scope of measured parameters(“metrics“) (Knoben et al., 1995; Verdonschot, 2000):− Saprobic Indices (represent specific modes of biotic scores)− Diversity Indices− Predictive Assessment− Process Assessment− Rapid Bioassessment− Multimetric Assessment− Ecosystem Components Assessment18