Report on Harmonisation of freshwater biological methods

97. The use of range values to record individual occurrence allows the estimation oftaxa abundance. Compared to the first option, this alternative is time saving becausean exact count of individual organisms is not necessary. Different abundanceclassification schemes are in use, the most common are listed in Table 5.98. The 3-class scheme derives from the well-known publication of Pantle and Buck(1955) and is mostly used in eastern European countries applying the Saprobic Index(Bosnia-Herzegovina, Croatia, Slovenia).99. Two systems to classify abundance in a five-fold scheme exist in Europe: Theclasses of the British system are based on a logarithmic scale of organisms’abundance (Murray-Bligh, 1999). Different from this is the allocation of classes in theQuality Rating System as applied by Bulgaria. Here, the presence of more than 100individuals of a certain taxon is assigned to the highest class. Hungary specifiesrelative taxa abundance of a sample (five metres section kicked for 15 minutes). Otherschemes do not specify numerical boundary values but provide only verbaldescriptions of abundance classes (e.g. McGarrigle et al., 1992).100. In German watercourse bioassessment abundance is stated in seven classes.Established by Knöpp (1955) this classification has been included in the Germanstandard DIN 38 410 (1990, 2003): Determination of Saprobic Index of RunningWaters. Beyond its broad application in Germany, methods in Serbia-Montenegro,Slovakia and Switzerland operate on the basis of a seven-class abundance scheme.101. 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. (France, Luxembourg), IBE (Italy), BMWP-ASPT (e.g. Cyprus,Portugal, Spain, United Kingdom) or BBI (Belgium) 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.89