A Methods Manual for the Collection, Preparation and Analysis of ...

depending on the period of exposure prior to sampling, the flora may not represent a‘climax’ community,the smooth surfaces of some artificial substrata often lead to ‘sloughing off’ of the diatomfilm.substrata are often lost, removed or vandalised if the substratum is not fixed in position.An appropriate method and apparatus needs to be devised for each site.artificial substrata need to be immersed in the river for at least four weeks beforesampling (although this period is dependent on the trophic status of the water). Thiscauses a delay in the availability of data, as well as adding to the cost of the monitoringprogram as transport costs to and from the site in question are doubled.Further information about the use and application of artificial substrata can be found inCattaneo and Amireault (1992), Gold et al (2002) and Lane et al. (2003).2. Sampling for aquatic bio-diversity studiesAll the methods mentioned in this manual can be used for sampling diatoms from differenthabitats for biodiversity studies. However, certain techniques are less suitable when samplingdiatoms to infer water quality. Phytoplankton drifts downstream and thus is not as stable orreliable as the phytobenthos if an indication of a water quality impact at a specific point isrequired.2.1 Cobbles and small boulders (rocks)See section 1.1.2.2 Phytobenthos (“Floatation method” for epipsammon and epipelon)The epipsammon and epipelon are components of the phytobenthos and yield very diverseassemblages of usually motile diatoms. However, the “floatation method” discussed belowdoes not allow for the inclusion in the analysis of non-motile diatoms. The method has theconsiderable advantage of extracting the motile living fraction of the diatom community forsubsequent analysis of the assemblage. Samples taken from the epilithon may contain manyattached and non-motile species which cannot be removed from the sample in the mannerbelow.2.3 Qualitative sampling of sedimentsThe common method, described by Round (1991) is to use 5 mm Ø glass tube about a meterlong or more attached (splinted) to a rod (e.g. a broomstick) for deeper water at the margin ofa river.13