The Changes in the Composition of the Diatom Assemblages Found in the Surface Sediments of Blelham Tarn in the English Lake District During 1973

A study has been made of the accumulation of diatom frustulesin the surface layers of lake sediments, taking advantage ofthe appearance of a new diatom bloom in Blelham Tarn in theEnglish Lake District. Results from monitoring the top 5 cmof sediment and seston trap material, and comparison with phytoplanktonrecords show that there is good agreement between all threeand that sediment diatom assemblages change in response to theliving populations so that the record of large ‘blooms’can be quickly diluted. The centric diatom, Stephanodiscus astraeavar. minutula appeared to sink out of the phytoplankton quicklyand mix down into older sediments fairly readily, circumstanceswhich may be assisted by the compact shape of its frustule.