At the Microscope


The Pollen Sum
Pollen sums in excess of 200 must be achieved otherwise individual pollen taxon totals will not be representative. Where practicable a pollen sum of 500 pollen should be counted. However, it is also important to consider the diversity of the local vegetation. In areas with a rich flora a higher pollen sum will be necessary. In any case counting should continue until more than 50 Lycopodium spores have been encountered (see point B under Laboratory Preparation!). One reason for achieving the agreed pollen and Lycopodium sums is to ensure that when pollen influx values (grains cm-2 year-1) are compared across Europe the comparison is statistically valid.

Counting Spherical Carbonaceous Particles (SCP) and Non-Pollen Micro-Fossils
Investigators are encouraged, in the course of pollen counting, to identify and record SPC (the result of fossil fuel combustion at high temperatures) on their pollen slides (Odgaard, 1993, 1994). These can be a good indicator of heavy industry and, as a very general rule, the size of the spheres declines as distance from the source increases. They can be useful in providing an indication of wind direction and distance of pollen transport. At lower magnifications these spheres are difficult to distinguish from microbially derived metallic sulphide spherules (Wiltshire et al. 1994), which not infrequently occur in lake sediments but which should not be present in the trap samples. If an extra check on the composition of any black spheres in the pollen preparations is necessary, add hydrogen peroxide to the sample, after the pollen slides have been made up ready for counting, and boil for an hour. After this treatment any pyrite will have disappeared (along with the pollen!!!) but SPC will remain. Microfossils other than pollen - fungal spores (van Geel 1978, van Geel et al. 1982/83, 1989), should also be recorded as these often have an ecological significance.

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