Report on Harmonisation of freshwater biological methods

Table 5. Common abundance classification schemes used in European watercourseassessment methods based on benthic invertebratesclass number of organisms description3-classscheme(Pantle andBuck,1955)1 1 – 10 sporadic3 10 – 100 frequent5 > 100 in massesBulgarian Standard Murray-Bligh (1999) McGarrigle (1992)5-class scheme1 1 – 5 1 – 9 usually absent2 6 – 20 10 – 99 sparse or absent3 21 – 50 100 – 999 present in small numbers4 51 – 100 1,000 – 9,999 common5 > 100 10,000 + well represented or dominant1 1 single2 2 – 20 sparse7-class schemeKnöpp (1955)3 21 – 40 sparse to medium4 41 – 80 medium5 81 – 160 medium to abundant6 161 – 320 abundant7 > 320 in massesAssessment102. The assessment of the biological quality of running waters is based on theanalysis of measurable attributes of the biotic environment. According to the type andscope of measured parameters (“metrics“) different categories of assessment methodscan be distinguished (Knoben et al., 1995; Verdonschot, 2000):103. Biotic Indices integrate taxa richness and pollution tolerance metrics. Thebasic principle of this approach is the assumption that taxa showing differentsensitivity to disturbance disappear in a certain order as the pressure increases. Inaddition, the number of taxonomic groups is reduced.104. Extended by abundance information Saprobic Indices represent specific modesof biotic scores. Based on the work of Kolkwitz and Marsson (1902; 1908; 1909)saprobic systems have been revised with regard to quality classification and90