Ideally pollen diagrams are derived from samples taken from peat or lake sediments. The formation of peat and lake sediments is well known. Both peat and lake sediments are formed by accumulation processes. Peat is formed by the accumulation of partially decayed vegetation matter. Organic materials can accumulate when the production of biomass is greater than its chemical breakdown. Lake sediments consist of accumulated organic and inorganic material, forming layers containing an environmental archive. In both peat and lake sediment pollen was caught in each layer. There is hardly any vertical movement of material and therefore pollen from the lower layers represents the oldest vegetation.
The anaerobic condition found in both peat and lake sediment enable good preservation of pollen grains. In this way the peat bog or the sediment in a lake becomes an archive of the vegetation history of the surroundings of the peat bog or lake. Under the right circumstances, pollen can also be preserved in mineral soils, when the soil is covered and protected from the air by for example a layer of drift sand.
Sampling of the sediment including the pollen archive can be accomplished with different methods. A common way to
sample peat or lake sediments is coring. Another way is to take samples from a clean section. Samples can directly be taken from the section by cutting out pieces of the peat or lake sediment or a monolith can be used to sample part of the section. Subsampling will then take place in the lab.
To extract pollen from the sediment a number of steps is required, including the treatment with several chemicals and sieving. This procedure takes place in a laboratory setting. After chemical preparation of the samples slides are made from the residues to be able to identity the pollen grains that are present. The pollen samples are analysed with the help of a microscope at a magnification of 400-100x.