Report on Harmonisation of freshwater biological methods

Table 2. Percentage of assessment methods detecting specific pressures.pressurepercentageOrganic Pollution 48General Degradation 29Morphological Degradation 9Acidification 9Toxic Substances 5Sampling techniques81. The sampling procedure of a large number of methods applied in monitoringprogrammes using benthic invertebrates is based on the International Standard ISO7828 (1985) or the adopted European Norm EN 27828 (1994): Water quality –Methods of biological sampling - Guidance on handnet sampling of aquatic benthicmacro-invertebrates. Several methods which do not directly refer to theseinternational standards carry out ‘kick and sweep’ sampling that is regulated bynational norms/methods.82. In general, this technique is the most common sampling procedure and applied in30 methods using a hand-net. The nets used differ in size of the opening and mesh.Net-openings specified by the assessment methods vary between approximately 600and 900 square centimetres. In half of the schemes, animals are retained by meshsizesof about 500 µm. Mesh-sizes of 1 mm are particularly used in British schemesoperating at family level (Biological GQA, Hungarian adaptation of the BMWPscore). Hand-nets of less than 350 µm mesh-size are used in methods focussing onselected orders (e.g. Oligochaetes: Oligochaeta Index for Sediment Bioindication). Inaddition, small mesh-sizes are in use in some Mediterranean countries (Croatia, Italy,Spain). To sample sandy or silty substrates or sites with large amount of detritushydrobiological sieves are used in Bulgaria with a mesh-size of 1.5 mm.83. The procedure of quantitative sampling is standardised by the guidance ISO 8265(1988) or EN 28265 (1994): Methods of biological sampling - Guidance on the designand use of quantitative samplers for benthic macro-invertebrates on stony substratain shallow freshwaters. Surber samplers are most commonly used for quantitative,area-related sampling. The recommendations of this standard for maximum aperture85