The impact of the Laacher See Volcano (11000 yr BP) on terrestrial vegetation and diatoms

Late-glacial lake sediments containing the Laacher See Tephra (LST, 11000 yr B. R) have been analyzed for their pollen and diatom content at three sites at varying distances from the volcano and on different bedrock geologies. The aim was to test the null hypothesis that this major volcanic eruption had no effect on terrestrial pollen or aquatic diatom assemblages. The pollen spectra at all sites show a short-lived increase in grass pollen following the LST. Partial redundancy analysis and associated Monte Carlo permutation tests suggest, however, that the LST had no statistically significant effect at two sites but it had a statistically significant impact on the pollen assemblages at the site nearest (60 kin) to the volcano. The diatom assemblages at the three sites changed individualistically after the LST deposition, with increases in Achnanthes minutissima at one site, an expansion of Aulacoseira species at another, and an increase of Asterionella formosa and Fragilaria brevistriata at the third site. Partial redundancy analysis and associated permutation tests suggest a statistically significant change in diatoms in relation to the LST and associated changes in sediment lithology at the one site situated on acidic bedrock. No significant impacts were found at the sites on volcanic or calcareous rocks. Due to the interaction between tephra and sediment lithology, it is not possible to conclude if the statistically significant diatom changes were a direct result of the LST deposition or an indirect result of lithological changes following LST deposition.